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Due to the forecast for extreme weather conditions, with strong winds and rain expected in Greece until Saturday 29th,

the Regional Administration has made the following announcement:

All necessary measures should be taken by the appropriate services in the region (Fire Service, Civil Protection, Police etc.) in readiness for possible emergency needs.

The public to be updated (by mass media) so that they can avoid the following.

Going out if not necessary (in heavy rain), torrents, parking their cars under trees etc. Hopefully, difficult situations can be avoided and the public's safety ensured.

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Greece standing by for extreme Weather conditions. What is the forecast?

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Due to the forecast for extreme weather conditions, with strong winds and rain expected in Greece until Saturday 29th, the Regional Administration has made the following announcement: All necessary measures should be taken by the appropriate services in the region (Fire Service, Civil Protection, Police etc.) in readiness for possible emergency needs.

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Flash floods caused by heavy overnight rain have killed at least 15 people and caused destruction in central Greece.

The industrial towns of Mandra, Nea Peramos and Megara, west of the capital Athens, were the most affected.

Many of the dead were elderly people whose bodies were found inside their homes, reports say. Fast-flowing torrents of red mud flooded roads.

Prime Minister Alexis Tsipras declared a period of national mourning in the wake of the tragedy.

"Everything is lost. The disaster is biblical," Mandra Mayor Yianna Krikouki told state broadcaster ERT.

At least 37 people have been taken to hospital, the broadcaster said, and some are still missing.

Grim weather warning for Europe's future

Bad weather has hit parts of Greece for about a week, but particularly heavy rain overnight caused the sudden flooding, for which locals said they were unprepared.

The force of the water moved vehicles, damaged walls and roofing, and left many homeless as their homes flooded to a life-threatening level.

By Wednesday afternoon, Greece's fire service said it had received over 600 calls for help and dispatched almost 200 firefighters in 55 vehicles to the towns, which have a combined population in the tens of thousands.

"The water came down the mountain, millions of tonnes," Stavros Fotiou, the deputy mayor of Nea Peramos, told ERT.

"Our roads are completely destroyed... 1,000 homes have been flooded, that's a third of the town," he added.

The region's deputy governor, Yiannis Vassileiou, told the broadcaster that emergency services had been prepared for poor weather, but then "the Niagara Falls came down and could not be stopped".

Prime Minister Tsipras said that declaring a period of national mourning was "the least we can do".

He also vowed to provide aid to the victims and ensure they were housed safely.

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Flash floods caused by heavy overnight rain have killed at least 15 people and caused destruction in central Greece. The industrial towns of Mandra, Nea Peramos and Megara, west of the capital Athens, were the most affected. Many of the dead were elderly people whose bodies were found inside their homes, reports say.

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Greece's National Meteorological Service (EMY) has issued a "red alert" warning of extreme weather phenomena with heavy rainfalls and powerful thunderstorms. Barometric low "Nefeli" started on Monday and is expected to move away by Friday, June 29, 2018.

The weather took a turn for the worst on Tuesday, with rainfall exceeding 50 millimetres in many parts of the country.

There was serious flooding in Mandra, the seaside town that was hard hit in last November's deadly floods.

The rain was also heavy in central Greece, where there were reports of serious flooding.

In the area of Kanalia, streams broke their banks and flooded around 30 homes while local roads were submerged.

Some 40 firefighters were on duty in the broader area and responded to scores of calls to pump out flooded basements or rescue stranded motorists, with the assistance of 17 fire engines.

There was widespread flooding in Larissa too and strong storms turned the streets of many areas of Halkidiki into rivers, while several vehicles in Nikiti drifted from the raging water and ended up in the sea and resulting in terrible traffic conditions in Cassandra and Sithonia.

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"Nefeli" causes extreme weather phenomena across Greece - Greek City Times

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Greece's National Meteorological Service (EMY) has issued a "red alert" warning of extreme weather phenomena with heavy rainfalls and powerful thunderstorms. Barometric low "Nefeli" started on Monday and is expected to move away by Friday, June 29, 2018. The weather took a turn for the worst on Tuesday, with rainfall exceeding 50 millimetres in many...

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Severe weather conditions and heavy rain that hit northern Greece over the weekend flooded Pineios river. As a result, a bridge in Diava, Kalambaka, partially collapsed, while according to locals' reports, the water level is constantly rising.

Greek police have blocked the way to the area near the bridge and stopped the traffic.

Meanwhile a man was found dead in northern Greece. The 47-year-old was found dead inside a vehicle that fell into Kroussovitis stream in Sidirokastro, Serres.

Firefighters were called when residents witnessed a car drifting into the torrent during the intense rainfall.

A police investigation is underway in the area with the help of two fire department vehicles and four EMAK divers, however, the search has not led to the discovery of another body.

The vehicle was pulled from the mud with a crane and police are currently trying to identify the deceased.

In the mountainous region of Epirus, northwestern Greece, dozens of villages including Konitsa, Zagori, Tzoumerka and Metsovo have been cut off due to the overnight snowstorm and special vehicles have been sent to clear the roads.

Further south, farmlands in the plains of Arta and Filiata have flooded, while rocks fell on the roads surrounding the region.

The forecast is rain and snow today and Monday, while a gradual improvement is expected in the evening.

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Greece Hit By Extreme Weather - 1 Dead; Bridge Collapses

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Severe weather conditions and heavy rain that hit northern Greece over the weekend flooded Pineios river. As a result, a bridge in Diava, Kalambaka, partially collapsed, while according to locals' reports, the water level is constantly rising. Greek police have blocked the way to the area near the bridge and stopped the traffic.

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On Thursday morning, December 11, Greek rescuers were able to locate the body of a man at the bed of Gallikos River in Thessaloniki, northern Greece. The search for the unlucky man started on Wednesday afternoon by the Greek Police and the fire department in the area of Nea Philadelphia.

His body was recovered from the river bed in an area were the river had overflowed and covered the road that runs next to it. The body was later transported to the morgue for an autopsy.

However, the tragedy did not end there. A few hours later, another man was found dead in Aspro village, near the town of Kilkis. The Greek man who had been driving a taxi with FYROM license plates was swept away by the water while he was still inside the vehicle.

Meanwhile, his passenger from Skopje managed to get out of the taxi and was able to alert the authorities.

Several villages in Orestiada, Didymoteicho, Soufli and Feres have been declared in a state of emergency by the General Secretariat for Civil Protection, after the request of the Coordinating Body for Civil Protection at the Evros Regional Unity. According to local authorities, at least 20,000 acres have flooded, due to dike breakage.

Turkish authorities in Kastanies are also taking emergency measures on a daily basis, since several customs offices are closed throughout the day due to flooding, thus preventing vehicles from crossing the border.

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Two Dead Due to Extreme Weather in Northern Greece

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On Thursday morning, December 11, Greek rescuers were able to locate the body of a man at the bed of Gallikos River in Thessaloniki, northern Greece. The search for the unlucky man started on Wednesday afternoon by the Greek Police and the fire department in the area of Nea Philadelphia.

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HE EXTREME WEATHER EVENTS OF 2017 IN GREECE

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HE EXTREME WEATHER EVENTS OF 2017 IN GREECE

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The meteorological service of the National Observatory of Athens announced the record of the temperature, rainfall and wind speed recorded during 2017 in Greece.

According to the NOA's automatic weather station network, the temperature of 45.9 degrees Celsius recorded at Mires Heraklion on July 17, 2017, was the absolute maximum temperature of last year, but also the highest maximum temperature recorded in nearly 13 years its operation.

Also, the absolute minimum temperature in residential areas was -18.8 degrees Celsius in Florina on January 12, 2017, while the maximum wind gust was recorded in Paxi and was 133.6 km / h.

The maximum daily rainfall was in Platanias, Crete, on 26/10/2017, reaching 242mm. On an annual basis, the maximum rainfall occurred last year in Zagora Pelion, which received a total of 2,068 millimeters of rain. The minimum annual rainfall was recorded in Mykonos (242 mm throughout 2017),

The most notable finding was the temperature of 40.2 degrees Celsius recorded in Argos on 13/5/2017, which is the highest temperature ever recorded for the month of May.

Source: Meteo.gr

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The extreme weather events of 2017 in Greece

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The meteorological service of the National Observatory of Athens announced the record of the temperature, rainfall and wind speed recorded during 2017 in Greece. According to the NOA's automatic weather station network, the temperature of 45.9 degrees Celsius recorded at Mires Heraklion on July 17, 2017, was the absolute maximum temperature of last year, but also the highest maximum temperature recorded in nearly 13 years its operation.

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The caretta-caretta sea turtles in Greece 

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The caretta-caretta sea turtles in Greece 

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There are animals that survive on the planet for millions of years. One of these species is the sea turtle. Sea turtles live on earth for more than 100 million years. They spend their life in sea and they come ashore to lay their eggs on sandy beaches during the appropriate season. There are 7 species of sea turtles: caretta-caretta, the green sea turtle, the leatherback sea turtle and others.
Sea turtles in Greece

Greece hosts these strange but beautiful animals. The sea turtle caretta-caretta (known also as loggerhead sea turtle) has chosen the Greek waters to live. They swim throughout the Greek sea. The country's value is that it hosts some of the most important nesting beaches in the Mediterranean Sea: on the island of Zakynthos (Laganas Golf), on the island of Crete (Rethymnon, Chania, Messara), in Peloponnese (Kyparissia, Lakonia Golf, Koroni) and in the Ambrakikos Golf (north-west Greece). According to research, the most important nesting beach of caretta-caretta in the whole Mediterranean Sea is located on the island of Zakynthos.
Nesting beaching
The nesting beaches are of great importance. Female turtles make their nests on sandy beaches where they lay their eggs. After cracking the egg shells, the new born turtles start their life's most important journey. Relying on their DNA and their instinct, they are searching their destination towards the open sea, where they will live for the rest of their life. This first journey is the most important as a lot of enemies are around: crabs, seagulls, fish and human presence (even the city lights may disorient the young turtles). If they make it to the sea, the female ones will return to the same beach 20 years later to lay their own eggs! Those beaches are often destroyed because of tourist and settlement development but also because of climate changes. It is observed that the young turtles are disoriented by the city lights, they are entangled in plastic bags or they become prey of dogs and foxes. Consequently, only 1 out of 1000 new born turtles arrives to the sea.
Dangers
The dangers for the turtles do not stop as soon as they arrive to the sea. A sea turtle lives about 80 years. During this period the turtle has to face more enemies. The biggest enemy is human. It is to notice that the most of turtles that need treatment have injuries caused by fishing gear. Today the sea turtle is supposed to be an endangered species.

This situation has lead to the creation of a lot of associations whose aim is the protection of the sea turtles and their habitats in Greece. Archelon, Medasset, WWF are some of them. They try to protect the nesting beaches, to keep them clean and to help the new born turtles to reach the sea. Beach controls, excavation of nests to find "belated" young turtles and lead them safely to the sea are some of their duties. The action of those organizations includes the treatment of hurt turtles to eliminate their mortality rate. So there are a lot of rescue centers which provide the turtles with the first aid or host them until they are ready to swim again and survive on their own in the open sea.
Cooperation
It is also very important that these organizations co-operate with the local authorities and businesses (such as hotels). In Rethymnon for example, Archelon is an advisor to the Environmental Department of Grecotel in issues such as coastal management. The hotels implement management suggestions of Archelon relative to the reproductive habitat of sea turtles (they remove umbrellas, heavy lighting and everything that could disturb the procedure).
Volunteers have a crucial role in the rescue of sea turtles.
Next time you are in a nesting beach, get informed about the turtles and try to do everything you can to help them. The most important is to seek the least possible disturbance of the animal.
You can find more info on the website of Medasset.

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The caretta-caretta sea turtles in Greece | Omilo

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There are animals that survive on the planet for millions of years. One of these species is the sea turtle. Sea turtles live on earth for more than 100 million years. They spend their life in sea and they come ashore to lay their eggs on sandy beaches during the appropriate season.

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The Kri-Kri goat is a feral goat inhabiting the Eastern Mediterranean. It is also called by some other names such as Agrimi, Bezoar goat, Cretan goat or Cretan Ibex. The Kri-Kri goat was previously considered a subspecies of wild goats. And now the breed is found only on the island of Crete, Greece and three small islands just offshore. These three small islands are Agii Pantes, Dia and Thodorou. The breed is not thought to be indigenous to Crete. And most likely having been imported to the island during the time of the Minoan civilization. The Kri-Kri goat was once common throughout the Aegean, but the peaks of the 2400 meters White Mountains of Western Crete are their last strongholds.

This mountain range is protected as a UNESCO Biosphere Reserve and hosts another 14 endemic animal species. Their range extends to the White Mountains, the Samaria National Forest and the islets of Dia, Thodorou, and Agii Pandes in total. And some were introduced onto two more islands recently. The Kri-Kri goat was under threat by the 1960, with a population below 200. Today there are still only about 2000 animals available on the island and they are considered vulnerable. Excessive hunting for their tender meat, scarcer grazing grounds and diseases are the main reasons for decreasing their numbers. Hybridization is also a threat, because the Kri-Kri goat population has interbred with ordinary goats. Today hunting them is strictly prohibited. Read more information below.

Kri-Kri goat is a small to medium sized goat breed. It has a light brownish coat with a darker band around it's neck. Bucks are usually larger than the does, sometimes the bucks weight about double of the does. Both bucks and does have horns with annual rings and knobs. And their horns are curved backwards.

The bucks usually have beard, which rarely occurs in does. They have a black line on the back, which extends from their neck to the top of the tail. There are also black patterns on the front parts of their legs. Average body weight of the Kri-Kri bucks is about 90 kg. And the does on average weight about 26-42 kg. Photo from Wikipedia.

Uses

Kri-Kri goats are feral goats. Previously they were hunted for their tender meat.

Special Considerations

The Kri-Kri goat is usually shy animal and avoid tourists. They usually rest during the day. They are excellent climbers, and can leap some distance or climb seemingly sheer cliffs. They are very hardy and strong animals. Review full breed profile of the Kri-Kri goat in the table below.

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Kri-Kri Goat Breed Information | Modern Farming Methods

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The Kri-Kri goat is a feral goat inhabiting the Eastern Mediterranean. It is also called by some other names such as Agrimi, Bezoar goat, Cretan goat or Cretan Ibex. The Kri-Kri goat was previously considered a subspecies of wild goats. And now the breed is found only on the island of Crete, Greece and three small islands just offshore.

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Notes on the egg parasitoids of Thaumetopoea pityocampa (Den. & Schiff.)(Insecta, Lepidoptera, Thaumetopoeidae) collected on the Greek island Hydra

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Prevalence and Risk Factors of Gastrointestinal ParasiticInfections in Small Ruminants in the Greek TemperateMediterranean Environment 

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Prevalence and Risk Factors of Gastrointestinal ParasiticInfections in Small Ruminants in the Greek TemperateMediterranean Environment 

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Predator-Prey Interactions between Shell-Boring Beetle Larvae and Rock-Dwelling Land Snails

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Predator-Prey Interactions between Shell-Boring Beetle Larvae and Rock-Dwelling Land Snails

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Els Baalbergen,

Renate Helwerda,

Rense Schelfhorst,

Ruth F. Castillo Cajas,

Coline H. M. van Moorsel,

Robin Kundrata,

Francisco W. Welter-Schultes,

Sinos Giokas,

Menno Schilthuizen

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Abstract

Drilus beetle larvae (Coleoptera: Elateridae) are specialized predators of land snails. Here, we describe various aspects of the predator-prey interactions between multiple Drilus species attacking multiple Albinaria (Gastropoda: Clausiliidae) species in Greece. We observe that Drilus species may be facultative or obligate Albinaria-specialists. We map geographically varying predation rates in Crete, where on average 24% of empty shells carry fatal Drilus bore holes. We also provide first-hand observations and video-footage of prey entry and exit strategies of the Drilus larvae, and evaluate the potential mutual evolutionary impacts. We find limited evidence for an effect of shell features and snail behavioral traits on inter- and intra-specifically differing predation rates. We also find that Drilus predators adjust their predation behavior based on specific shell traits of the prey. In conclusion, we suggest that, with these baseline data, this interesting predator-prey system will be available for further, detailed more evolutionary ecology studies.

Citation: Baalbergen E, Helwerda R, Schelfhorst R, Castillo Cajas RF, van Moorsel CHM, Kundrata R, et al. (2014) Predator-Prey Interactions between Shell-Boring Beetle Larvae and Rock-Dwelling Land Snails. PLoS ONE 9(6): e100366. https://doi.org/10.1371/journal.pone.0100366

Editor: Fabio S. Nascimento, Universidade de São Paulo, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Brazil

Received: December 10, 2013; Accepted: May 26, 2014; Published: June 25, 2014

Copyright: © 2014 Baalbergen et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: Funding for this study came from NWO-ALW (grant 819.01.012, awarded to M.S.), the Jan-Joost ter Pelkwijkfonds (awarded to E.B, R.S., and R.H.), the Uyttenboogaart-Eliasen Fonds (awarded to M.S.), the Kees Bakker award (awarded to R.H.), and a doctoral fellowship to F.W.-S. from the Evangelisches Studienwerk. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Gastropods are among the most diverse groups of animals, and the most readily observable aspect of this diversity is in their shell form and ornamentation. Gastropod shell shape is generally considered to evolve under a strong direct influence of biotic and abiotic agents, and, at least in marine gastropods, predator-prey interactions are paramount among these [1]-[2]. On land, however, the influence of predators on snail shell evolution is less clear [3].

One particularly diverse group of land snails is the clausiliid genus Albinaria, of which the >100 species occur abundantly on limestone rocks throughout Greece and surrounding regions ( fig. 1A) [4], with most species occupying small, usually non-overlapping ranges [5]-[7]. The animals actively forage on micro-flora on the rocks during the wet months (roughly October to April), but estivate, usually with their apertures firmly sealed to the rock, and often in dense clusters, during the dry part of the year. Species differentiation is most apparent in various shell traits, such as radial ribbing, apertural folds and lamellae, and the structure of the clausilium (a door-like aperture closing apparatus and a Clausiliidae synapomorphy; figs. 1B, C).

A, Albinaria hippolyti from Crete (photo: V. Wiese). B and C, the clausilium, shown in the shell aperture after removal of the left lateral shell wall (B shows a less-obstructing, N-type clausilium, C shows a more obstructing, G-type clausilium). D and E, a male and a female, respectively, of a yet undescribed Drilus species from Crete (scale: 2 mm). F, a full-grown larva of Drilus "L" from the Peloponnese (same scale as D and E). G, an estivating A. discolor from the Peloponnese, with a Drilus exit bore hole. H, a Drilus "L" exiting from its prey, an A. menelaus from the Peloponnese.

Although Albinaria snails are preyed upon by a wide range of predators, including rodents, molluscivorous snails, and carabid beetles [8], their chief enemies appear to be larvae of the elaterid beetle genus Drilus ( fig. 1D-F). These enter Albinaria snails by boring a hole through the shell wall ( fig. 1G), killing and eating the snail's soft body, and, after molting or pupating, leaving via a second bore-hole ( fig. 1H) [9]-[10]; but see below. Often, the entry and exit holes can be distinguished by their shape [8]. In many locations, more than 50% of the empty shells carry such Drilus bore-holes [11].

Given their intimate relationship with Albinaria and their shells, we expect that Drilus might be an important selective agent in Albinaria shell evolution. Indications of non-random predation by Drilus already exist, since Mesher and Welter-Schultes [11] found that on the island of Día (off Crete), Drilus attack was high in the three native Albinaria species, but low in a fourth, possibly introduced, species. To assess such possibilities further, we have investigated in more detail the interaction between Albinaria and Drilus in various regions in Greece.

Biogeography and Diversity of Drilus Predators

We first investigated the geographic variation in predation rate, by mapping the proportions, relative to the total number of empty shells, of shells with Drilus bore-holes, which have a characteristic size and shape, and are easily distinguished from other types of shell damage-see fig. S1 and [8]-throughout Crete. We did this by measuring the proportion of shells with Drilus holes in each of 1,160 museum samples. (With "sample" we mean a number of empty shells from a single location, usually taken in a 50×50 m area; see Data files S1 and S3.) These show a pattern of high, but regionally varying predation rates, with an average of 0.239±0.168 ( fig. 2). In the Peloponnese and Kephalonia, where our geographic coverage was much less complete, we found predation rates that appeared lower than in Crete, but still substantial: average  =  0.082±0.079 (n = 18 samples, 7,450 shells in total; in view of the mixed character of the samples, we refrained from testing for significance in the Crete vs. Peloponnese+Kephallonia difference). Drilus predation therefore accounts for a large proportion of total adult mortality [12].

Maps were drawn using inverse kriging distance calculation in R v.2.15.2 [23], with packages gstat [24], maptools (R v.0.8-27), rgdal (R v.0.8-12) and rgeos (R v.0.3-2).

We then used a combination of larval and adult characters, and mtDNA sequencing, to determine the number of Drilus species in the region, as well as their prey specificity (see Data file S2). We found that at least nine species can be distinguished (for the taxonomic and phylogenetic details we refer to Ref. [13], and Kundrata et al. unpublished manuscript; we provide a preliminary map of the species' distributions in fig. S2). For the four species that occur in Crete, we did not assess prey specificity, but for the remaining five, occurring in the Peloponnese, Zakynthos, and Kephalonia, we were able to do this by investigating bore holes and exuviae in shells of the entire snail fauna in 39 locations. The results ( Fig. 3A) show that Drilus includes obligate Albinaria-specialists (e.g., Drilus "L") as well as generalists that only rarely attack Albinaria (e.g., Drilus "E"). Although these results may be somewhat confounded by differences in the snail species abundance distributions, the data from two locations, Paralíon Ástros and Koutróufa, where two Drilus species ( D. "D" and D. "E") occur syntopically, confirm the differences in prey specificity between these two species ( Fig. 3B). As in other members of the genus, our Drilus species tend to have small geographic ranges (e.g., Drilus "D," "L," and "M" may have range lengths of 50 km or less), which may be explained by the fact that Drilus females are wingless ( fig. 1E) [14].

B, difference ( P<0.05, Fisher's exact test) in prey specificity between Drilus "D" (more Albinaria-specific) and "E" (less Albinaria specific) in two localities where both species occur syntopically (these data are not included in fig. 3A). C, differences in Drilus predation rate (dark portion of the bar) between solitarily ("sol") and group-wise ("agg") estivating snails of A. caerulea in four 5 m ² plots in the islands of Paros, Naxos, and Thira (voucher numbers RMNH.MOL.84354-84363, RMNH.MOL.85192, and RMNH.MOL.85193). An aggregate was defined as a cluster of >20 snails, with distances of <2 cm separating them. A snail was considered solitary if it was >20 cm distance from a conspecific (significance tested with Chi-square test). D, positions of entrance holes in shells of species with an N-type clausilium compared with those in shells of species with a G-type clausilium, shown for the entire eastern Peloponnese as well as for the site Monemvasia, where both clausilium types occur microsympatrically. ( P-values are derived from Fisher's exact test.)

Behavior of Drilus preying on Albinaria

Unexpectedly, we found that Drilus may successfully attack Albinaria without leaving any bore-holes in the shell. We opened 645 dead Albinaria shells from the Peloponnese, and out of 169 shells that had been preyed by Drilus (judged by the presence of exuviae or a live larva), 60 contained exuviae but showed no trace of a bore-hole. This means not only that predation rates calculated from bore-hole frequencies are underestimates, but also that Drilus employs more than one attack strategy.

To understand better the predatory behavior of Drilus, we obtained three live pseudopupae (an immobile resting stage) from field-collected Albinaria shells, as well as live Albinaria, and used these for observations in the laboratory. Of these three, one remained in pseudopupal state. The other two (both Drilus "L") molted into active larvae. One (obtained from an A. edmundi) entered an Albinaria edmundi via the aperture and killed it. It remained inside for 28 days, bored a hole in the shell wall to exit, but then died while emerging. However, the third one (obtained from an A. discolor) stayed alive and active for almost two years, and during that time consumed eight adult prey individuals. In all eight predation events (which took place under dark conditions in a box with several loose Albinaria individuals, i.e., not adhering to any substrate), the larva entered the snail via the aperture (after having inspected several potential prey), never boring a hole in the shell wall nor into the clausilium ( Video S2). After entering a snail, it apparently attacked and ate (part of) the snail immediately, because it moved fragments of dried, undigested snail tissue outside of the aperture within three days. In total, it would remain in a shell for 22-32 days, except for one very lengthy stay inside a prey shell that lasted from September 19 th until May 1 st, and possibly indicated hibernation. Each time the larva exited from an empty prey shell, it left behind an exuvia, meaning that the number of larval stages may be much larger than the three to four that had been suspected previously [15]-[16]. In all cases except one, the larva did bore a hole from within the prey shell to exit. Boring was done with the jaws and a copious amount of (possibly acidic) saliva and, based on the one occasion when it was observed from start to finish ( Video S1; fig. 4) took seven hours.

These observations confirm that a Drilus may enter an Albinaria prey either by apertural-entry or by shell-boring (see also Video S2 for these behaviors in Cretan species). Similarly, it may also exit the (empty) prey shell either via the aperture or via a new bore-hole. As in other snail-predator interactions [16]-[18], each of these entry and exit strategies have their advantages and disadvantages. For example, apertural entry as well as exit may be hindered by the clausilium and/or by apertural folds that project into the lumen of the whorl. On the other hand, it may be less costly than boring in terms of time, energy, and saliva (if the saliva indeed helps dissolve the shell). Entering and perhaps also exiting the shell by boring may be hindered by the presence of dense and/or tall radial ribs on the shell surface, but is more costly. Finally, it should be noted that shell features that impede predator entry will primarily impose a selection pressure on the prey (by ensuring its survival), whereas those that impede predator exit will primarily select for predator traits (by causing the predator to die within the prey shell).

Potential Evolutionary Impact of Predator-Prey Interaction on the Prey

We may predict that more heavily-ribbed Albinaria species [19] are better protected against boring (and therefore show a lower proportion of bored shells and/or more bore-hole failures) and that Albinaria species with a more completely obstructed aperture [20] are better protected against apertural-entry (and therefore show more bored shells). As a preliminary test of these predictions, we scored numbers of bored and intact shells in pairs of syntopic Albinaria species, exposed to the same Drilus species, but differing in either radial rib height or apertural obstructions. Our results ( Table S1) do not provide consistent support for the predictions. At Argínia, the strongly ribbed A. adrianae has, as predicted, a lower proportion of bored shells than the smooth A. contaminata, but at Póros, no difference was found. Bore-hole failures do not differ among the four populations. At one of the three sites where a species with a partly-obstructed aperture (an N-type clausilium) co-occurs with a species with a completely obstructed (G-type) aperture, the latter has fewer bored shells, while at the other two locations, no difference was found. Obviously, these results are inconclusive since they are based on small numbers of populations and should be repeated with a larger-scale study, including more species and more locations.

We also obtained some data that suggest that predation by Drilus may be non-random within a single Albinaria population and hence may cause natural selection on variable traits. In a population of A. krueperi, preyed upon by Drilus "G", we found that predation (derived from exuviae in the shells) was predominantly towards the smaller individuals; however, such a response was not found in a population of A. adriani, preyed upon by Drilus "D" and "E" ( Table S2). In addition, in a population of A. caerulea from the Cyclades, we found that predation risk (derived from bore-hole data) was greater in snails estivating in isolation than in snails estivating in clusters ( fig. 3C), which may be one way in which such clustered estivation (a conspicuous behavioral pattern in most Albinaria species) evolved.

Potential Evolutionary Impact of Predator-Prey Interaction on the Predator

In contrast to the evolutionary impact that the predator may have on the prey, the reverse may also be the case. Albinaria snails are, at least during the dry months of the year, often firmly sealed against the substrate, whereas most of the other species that we recorded as Drilus prey tend to estivate in the soil. We may therefore expect that Drilus species that are more specialized in feeding on Albinaria, have a greater tendency to bore holes for entering, and, probably more importantly, for exiting the shell (an inability to do the latter would mean death for the Drilus larva). Indeed, we find a positive correlation between Albinaria-specificity and hole-boring tendency among the five Drilus species from the Peloponnese and Kephalonia ( fig. 3A).

Finally, another indication that the prey shell morphology affects the predator was obtained when we compared the positions of entrance holes in shells of species with an N-type clausilium ( A. argynnis, A. discolor, and A. solicola; all from the Eastern Peloponnese) with those in shells of species with a G-type clausilium ( A. adriani, A. edmundi, and A. campylauchen, all roughly sympatric with the previous three). We found that in the N-type group, more shells had a bore-hole in the outer shell wall between the aperture and the clausilium than in the G-type group ( fig. 3D). Since the N-type species have a clausilium that does not completely close off the aperture, whereas the G-type clausilium does, these data may indicate that predator populations faced with G-type prey have evolved a shell entry strategy by which the hole is bored at a position beyond the obstruction. However, the same difference is seen in Monemvasia, where the N-type A. discolor lives syntopically with the G-type A. campylauchen. This suggests that, rather than an evolved behavioral difference between predator populations, the predator may also be able to detect the clausilium type before boring a hole and that the difference in strategy is due to a behavioral response, rather than an evolved, fixed behavior ( fig. 3D).

Conclusion

Given the complexity of this predator-prey system, with multiple predator species, multiple prey species, varying prey specificity, and complex small-scale biogeographic patterns, we will not hazard a conclusion on the impact of these interactions on shell evolution in Albinaria. However, we think we have shown that detailed study of the natural history of these ecological interactions reveal a potential for such evolutionary responses. Elements from our study may provide starting points for further work, specifically targeted at understanding the possible predator-prey arms races or patterns of escalation in this system, an approach that has proved successful in a similar terrestrial system consisting of tropical micro-snails and shell-boring slugs [21]-[22].

Additional Methods Details

Sampling of live specimens was done at the locations with the following coordinates: 37°09.694′ N, 22°48.745′ E and 37°20.132′ N, 22°45.769′ E. No specific permissions were required for the accomplished field sampling activities by the University of Patras. The field studies were conducted exclusively in public and not protected land areas. The field studies did not involve any endangered or protected species. Sampling was conducted according to the main legal texts in the field of biodiversity (UN Convention on Biodiversity), which became part of the Greek legislation in 1994 (law 2204), and the EU Directive 2004/35 regulating environmental liability. Animal capturing, handling and killing was designed to avoid distress and unnecessary suffering to the animals as laid down in the Council Directive 86/609/EEC, art. 7.4 and the Council of Europe (CoE) European Convention for the protection of vertebrate animals used for experimental and other scientific purposes (1986, ETS 123). All relevant information was also given to the Bioethics Committee of the University of Patras".

Supporting Information

Fig. S1. Drilus bore hole proportions (both entry and exit holes), based on measurements taken from shells of A. discolor and A. adriani from Agios Andreas and in A. discolor, A. campylauchen and A. discolor x A. campylauchen hybrids from Monemvasia.
https://doi.org/10.1371/journal.pone.0100366.s001
(PDF)

Distribution map for Drilus morphospecies in the Peloponnese and surrounding area. In addition to morphospecies "D," "E," "G," "L," and "M," mentioned in the text, a location for a sixth species, "U," is also shown. Each dot represents one or more specimens. Bicolor dots indicate syntopic occurrence of multiple species. Scale bar  =  100 km.
https://doi.org/10.1371/journal.pone.0100366.s002
(PDF)

Five shell traits in Albinaria krueperi and A. adriani populations, with indications for selection by Drilus predation. Shell height and width were measured with hand-held calipers, the other traits with a graded ocular. Drilus attack was ascertained by the presence of a bore hole and/or an exuvia in the shell. Significance was tested with 2-sample t-test in R.
https://doi.org/10.1371/journal.pone.0100366.s007
(DOCX)

Series of three clips (footage sped up 64x), taken in the lab: First, Drilus longulus larva entering an Albinaria ( cretensis complex) shell via an entry bore-hole, followed by footage in which entry is made by a Drilus sp. via the aperture of an Albinaria ( cretensis complex) snail. Finally, a Drilus "L" larva selecting and entering an A. menelaus snail via the aperture.
https://doi.org/10.1371/journal.pone.0100366.s009
(WMV)

Acknowledgments

We thank Edmund Gittenberger and Robert Cameron for help with the identification of certain species of Greek snails, and Bertie-Joan van Heuven and Marcel Eurlings for lab assistance. Paulien de Jong, Heike Kappes, Theo Kemperman, Thor-Seng Liew, Aydin Örstan, Ton de Winter, and Nikita van Zeijl served as valuable discussion partners during various parts of the study. Material from the Natural History Museum, Budapest, was kindly provided by P. Subai and L. Pintér, from Naturalis Biodiversity Center by Jeroen Goud and Bram van der Bijl, and from the Haus der Natur by Vollrath Wiese, who also supplied the photo of Albinaria hippolyti. In Patras, Evi Thanou provided logistical support.

Author Contributions

Conceived and designed the experiments: EB RH RS RC CvM RK MS SG FWS. Performed the experiments: EB RH RS RC CvM RK MS SG FWS. Analyzed the data: EB RH RS RC CvM RK MS SG FWS. Contributed reagents/materials/analysis tools: MS SG FWS. Wrote the paper: MS.

References

1. 1. Vermeij GJ (1987) Evolution and Escalation: An Ecological History of Life. Princeton: Princeton University Press. 544 p.

2. 7. Welter-Schultes FW (2012) European non-marine molluscs, a guide for species identification. Göttingen: Planet Poster Editions. 760 p.

3. 13. Baalbergen E (2013) Larvae of Drilini (Coleoptera: Elateridae) beetles preying on snails. M.Sc. thesis, Leiden University. 65 p.

4. 15. Schilthuizen M (1994) Differentiation and Hybridisation in a Polytypic Snail. Ph. D. thesis, Leiden University. 178 p.

5. 22. Liew TS, Schilthuizen M (2014) Association between shell morphology of micro-land snails (genus Plectostoma) and their predator's predatory behaviour. PeerJ 2: e329 Available: https://peerj.com/articles/329/. Accessed 1 June 2014.

6. 23. R Core Team (2012) R: A language and environment for statistical computing. Vienna: R Foundation for Statistical Computing.

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Predator-Prey Interactions between Shell-Boring Beetle Larvae and Rock-Dwelling Land Snails

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Drilus beetle larvae (Coleoptera: Elateridae) are specialized predators of land snails. Here, we describe various aspects of the predator-prey interactions between multiple Drilus species attacking multiple Albinaria (Gastropoda: Clausiliidae) species in Greece. We observe that Drilus species may be facultative or obligate Albinaria-specialists.

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Predation on Greek Albinaria (Pulmonata: Clausiliidae) by Poiretia (Pulmonata: Oleacinidae) and by an unknown organism making circular holes: possible drivers of shell evolution

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Predation on Greek Albinaria (Pulmonata: Clausiliidae) by Poiretia (Pulmonata: Oleacinidae) and by an unknown organism making circular holes: possible drivers of shell evolution

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Abstract

Albinaria is an extremely species-rich genus of land snails, with about a hundred species occurring in limestone habitats in Greece. Among their predators are other terrestrial snails, namely Poiretia dilatata peloponnesica on the Peloponnese and P. compressa on the Ionian Islands. The elongated holes Poiretia make in shells were investigated in samples of empty Albinaria shells, in order to compare predation rates in different Albinaria populations. Another type of predation mark, frequently found on Albinaria shells, is a small, circular or nearly circular hole, made by an unknown organism. Poiretia predation rates reached up to 21% in the Albinaria populations studied and they were significantly higher in species with high rib prominence vs low rib prominence, as well as in sinistral species vs dextral species. Circular-hole predation reached up to 36%, but did not seem to be consistently connected with conchological traits. Marks made by P. compressa occurred most frequently on the abapertural side of Albinaria shells, whereas marks made by P. dilatata peloponnesica occurred most frequently on the apertural side. Circular-hole predation marks were located most often on the apertural side of Albinaria shells. Hybrids between Albinaria species generally seemed to suffer the same level of predation as one or both of their parent species. Predation pressure is substantial in the investigated populations and shows significant differences, but assessing its contribution to shell evolution requires more study.

INTRODUCTION

All organisms are shaped by evolution. Their morphology is under selection pressure by abiotic conditions of the environment and biotic interactions with other organisms. In particular, predators and prey exert selective pressure on each other. This may lead to various defensive adaptations in prey species, including behavioural, morphological and physiological defences. Predators in turn possess adaptations for catching and killing prey ( Campbell & Reece, 2005). Pairs of predator and prey species may co-evolve when the prey is under sufficient selective pressure to evolve defensive adaptations against the predator and also exerts sufficient pressure on the predator to overcome its defence by evolving counter-adaptations ( Vermeij, 1987). These conditions are usually only met when the predator is highly prey-specific.

The land snail genus Albinaria (Clausiliidae: Alopiinae) is extremely species-rich, including more than 100 species ( Nordsieck, 2007; Welter-Schultes, 2012). The family is characterized by the presence of a door-like structure in the aperture, the clausilium. Albinaria originated about 10 Ma ( Uit de Weerd & Gittenberger, 2013). Their shells are high-spired and usually sinistrally coiled. The clausilial apparatus (CA) is either of the G-type, which seals off the aperture entirely, or of the N-type, which leaves a bypass canal within the aperture. Some species have very prominently ribbed shells, whereas others have smooth shells. The snails occur in arid limestone habitats in Greece, southern Albania, Cyprus and western and southern coastal Turkey, where they feed on microflora and algae. They aestivate during the hot summers, either by adhering to open rock faces or by hiding in crevices or on the ground. During aestivation, they usually form a thick epiphragm to seal off the aperture. The species usually have narrow distributions. The genus displays an impressive diversity in conchological and anatomical characters among species, but also among populations. In contrast, the morphological variation within populations is usually surprisingly small ( Gittenberger, 1991). Intraspecific COX1 sequence divergence in Albinaria is also quite low, compared with that of other pulmonate genera ( Parmakelis, Kotsakiozi & Rand, 2013).

The existence of such a large number of species within the genus Albinaria, having originated in a geologically short period of time, could justly be described as an evolutionary radiation. This radiation, however, does not conform to the concept of adaptive radiation, because all Albinaria species apparently occupy the same ecological niche or a very narrow range of niches. In any case, the small amount of niche differentiation within Albinaria does not parallel the range of morphological differentiation. Hence, Gittenberger (1991) proposed the term 'non-adaptive radiation' for this pattern. Albinaria species usually occur allopatrically, with no more than two species occurring syntopically. Neighbouring species may differ in morphology while occupying apparently identical niches. While these differences might reflect cryptic differences in the abiotic environment, it is possible that differences are affected by sexual selection, genetic drift or biotic interactions. In particular, the effects of locally significant predator pressure might influence morphology.

This study aimed to gain more insight into the interactions between Albinaria snails and their predators in order to assess the contribution of predation to speciation and morphological differentiation within the genus. Predators other than vertebrates usually have to make holes in the shells of Albinaria to gain access to the snails' tissues, as the snails will retract and close off their apertures with their clausilium when they are under attack. These holes are distinctive for each type of predator ( Schilthuizen, Kemperman & Gittenberger, 1994), which enables us to estimate predation rates in Albinaria populations by collecting empty shells.

Drilus beetle larvae are important predators of Albinaria, but this interaction has already been considered elsewhere ( Schilthuizen et al., 1994; Baalbergen et al., in press). Here, we consider predation by Poiretia snails and an unknown organism making circular holes ( Schilthuizen et al., 1994). An initial investigation of the circular holes was published by Örstan (1999), who suggested that these holes were made by a predator or a parasite.

If predation pressure has acted as a selective agent for shell features in Albinaria, then co-occurring Albinaria populations that differ in conchological characters should show differences in predation rates. To find out if predation rates were correlated with specific shell characters, species pairs were selected that differed in rib prominence, chirality or CA type and also co-occurred at rare zones of overlap or hybridization between the two species. For each of these three shell characters, we attempted to sample at least two replicates of species pairs. If species with a specific shell character consistently showed higher predation rates, then this shell character might be maladaptive in the face of predation.

MATERIAL AND METHODS

Sample collecting

Locations on the Peloponnese and Kephallinia, Greece, were explored and small samples were collected by MS and Sinos Giokas in July and August 2011. Suitable locations were selected for the presence of multiple syntopic species of Albinaria, differing in conchological characters and preferably hybridizing, to investigate the presence of hybrid inferiority or superiority. Locations with high densities of Albinaria shells and high predation rates were also preferred. Large samples of empty Albinaria shells were collected at selected locations during fieldwork in Greece, from 5 to 21 September 2011, by Els Baalbergen, Rense Schelfhorst and RAH. These samples and the small samples collected at these locations during the exploratory fieldwork were all used in this study and are listed in Table 1. Samples from the same approximate location, with the same location name in Table 1, were combined. Authorities for all Albinaria species used, along with the combined samples in which they are present, are given in Table 2. The distance between the most distant sampling points within combined samples ranged from 10 m in Nemea and Astros wetland, to 600 m in Lagia and averaged 215 m. During the exploratory sampling, broken specimens were not collected but, during the collection of large samples, broken specimens were collected unless the aperture was broken off. Only one species of Albinaria was present in the sample from Astros wetland (M4 and 130903), so this combined sample was not used in species comparisons. In the sample from Nemea (MNemea and 120901) a species of the closely related clausiliid genus Idyla, namely I. bicristata (Rossmässler, 1839) co-occurred with a species of Albinaria, so the Idyla species was treated similarly to an Albinaria species.

Sample number

Location

Area

Latitude (MinDec)

Longitude (MinDec)

Elevation (m)

Side of rock face, habitat

Sample treatment

Albinaria specimens were separated from non- Albinaria specimens, which were not processed further in this study, except for Idyla in the Nemea sample. Juveniles were separated from adults and the juveniles were not processed further, because species assignment is more difficult, especially in samples from hybrid zones, and because predation on juveniles did not necessarily involve production of a hole in the shell, the juveniles being more easily attacked through the aperture. Broken specimens were processed, as long as most of the aperture and the body whorl were present. Specimens with their shell covered in dirt were cleaned by soaking them in water and brushing them with a toothbrush. Specimens of different species were separated. Samples from locations within hybrid zones were separated into the two parent species and hybrids, by assigning hybrid scores to all specimens. Hybrid scores were assigned by examining the shell characters in which the two parent species differed and deciding if the characters were the same as in one or the other parent species, or intermediate (see Supplementary Material for description of method of assigning hybrid scores).

All shells were examined for the presence of predation marks other than the oval holes made by Drilus larvae. Poiretia predation marks are recognizable as an elongated hole on one side of the shell, where two to three whorls appear to be eroded away, while the rest of the shell showed no sign of erosion (Fig. 1A). A failed or incomplete Poiretia predation mark differs from the normal mark in that the shell is not eroded all the way through, so that there is no hole present, only an elongated abrasion on the shell surface.

The typical circular holes made by an unknown organism termed Circular Hole Organism (CHO) are rather small, about 0.3 mm in diameter (Fig. 1B, C). They either narrow inwardly or have straight edges. Failed circular holes are tiny pits in the shell surface, with inwardly narrowing, concave edges.

Other predation marks were also observed, in which the spire was broken in a spiralling pattern, with the columella still intact. This damage was probably caused by mice or other rodents, or by large carabid beetles (Schilthuizen et al., 1994). As this kind of predation mark was only observed in a few shells, it was not treated further. Shells with this kind of damage were counted as broken specimens.

Predation rates were assessed by counting the number of specimens affected by each predation type, out of the total number of specimens of one species in the sample. For different species within the same samples, as well as hybrids, these numbers were tested pairwise against each other using Fisher's exact test in R. In samples with hybrids, a sequential Bonferroni correction was applied for each set of three tests.

The locations of predation marks on the shells of Albinaria were investigated to gain insight into the predator's behaviour. As done by Schilthuizen et al. (2006) and Liew & Schilthuizen (2014), the surfaces of prey shells were divided into sectors, in this case four: apertural, right, abapertural and left. When comparing the locations of Poiretia predation marks, samples from Poros and Arginia were analysed separately from samples from Monemvasia, Gerolimenas and Lagia, because Poiretia compressa (Mousson, 1859) was present in Poros and Arginia, whereas P. dilatata peloponnesica (Subai, 1980) was present in the other samples. The chi-squared test of goodness of fit in R was used to test whether the predation marks were equally distributed over the four shell sectors. Fisher's exact test in R was used to test the distribution of the marks made by P. compressa against the distribution of the marks made by P. dilatata peloponnesica.

Successful and failed CHO predation marks were measured in A. discolor and A. adriani in sample 160901 and in A. discolor, A. campylauchen and A. discolor × A. campylauchen hybrids in sample 180901. All undamaged CHO predation marks in these samples were measured with an ocular micrometer at a magnification of 64×. Shells were held so that the measured hole was in a horizontal plane. The hole was measured at the shell surface, by its outward edges. As the holes were usually not perfectly circular, the length of the hole was measured at the major axis, where the edges of the hole were furthest apart, then the width was measured at the minor axis, perpendicular to the major axis.

RESULTS

The elongated holes with eroded edges on Albinaria shells were consistent with Poiretia predation marks. There were also shells with small, circular holes, described as CHO predation marks.

Shells of Poiretia compressa were found in samples from Poros and Arginia, whereas shells of P. dilatata peloponnesica were found in samples from Gerolimenas and Lagia. Poiretia predation occurred in the samples from Poros, Arginia, Monemvasia, Gerolimenas and Lagia and was highest in Albinaria schuchii from Gerolimenas, reaching 21% (Fig. 2 and Supplementary Material). In all these samples except that from Monemvasia, there was a significant difference in the predation rates between the two Albinaria species. In samples from Poros and Arginia, A. adrianae suffered a higher predation rate than A. contaminata and in those from Gerolimenas and Lagia, A. schuchii suffered a higher predation rate than A. gerolimena and A. voithii, respectively. Albinaria gerolimena showed a higher proportion of broken specimens than A. schuchii ( Supplementary Material), so that a higher proportion of predation marks may have been missed, but it is unlikely that a significant number of Poiretia predation marks were missed, because of their large, elongated shape and recognizable edges. Failed Poiretia predation marks occurred very rarely ( Supplementary Material). The highest rate was only 1.3% of shells, in A. adrianae from Arginia.

CHO predation occurred in all samples, ranging from 0.15% in Idyla bicristata from Nemea to 45% in A. gerolimena from Gerolimenas (Fig. 3). There were significant differences between syntopic prey species in samples from Monemvasia and Gerolimenas, where A. campylauchen had a higher rate than A. discolor and A. gerolimena had a higher rate than A. schuchii, respectively. Failed CHO predation also occurred in all samples, but it did not occur in I. bicristata from Nemea ( Supplementary Material). The highest rate was 31% in A. contaminata from Poros. Albinaria grisea had a significantly higher rate than I. bicristata from Nemea, but this result was based on only two specimens. In the sample from Monemvasia, A. campylauchen again had a higher rate than A. discolor. In that from Lagia, A. schuchii had a higher rate than A. voithii.

The success rate of CHO predation differed significantly among the species pairs from Poros, Arginia and Gerolimenas ( Supplementary Material). In Poros, the success rate was higher in A. contaminata, yet in Arginia, it was higher in A. adrianae. In Gerolimenas, the success rate was higher in A. gerolimena than in A. schuchii. The predation rate in hybrids was either not significantly different from one or both of the parent species, or it was intermediate between the two parent species. It was never significantly higher or lower than in either of the parent species.

Marks made by P. compressa occurred more frequently on the abapertural side of Albinaria shells in Arginia and Poros (Fig. 4A). Marks made by P. dilatata peloponnesica occurred more frequently on the apertural side of Albinaria shells in samples from Monemvasia, Gerolimenas and Lagia combined (Fig. 4B). The distributions of marks made by P. compressa and P. dilatata peloponnesica differed significantly from each other ( P = 0.0000063). In all samples combined, CHO predation marks were located more often on the apertural side (Fig. 4C). Successful and failed CHO predation marks were on average quite small (Fig. 5). Their average length/width ratio was 1.10, so they were nearly perfectly circular. Failed marks were on average smaller than successful marks.

DISCUSSION

Poiretia snails

We interpret some of the predation marks found in Albinaria shells as made by Poiretia snails. Poiretia is the only extant European genus within the Oleacinidae, of which the other members are found in Central America and the Caribbean. As far as is known, all Oleacinidae are carnivorous, feeding on other snails ( Barker & Efford, 2004). Poiretia snails possess several morphological traits that have been linked to carnivory in Pulmonata: elongation of the radular teeth, enlargement of the buccal mass, reduction in the jaw, simplification of the digestive tract, elongation and posterior placement of the shell and enlargement of the suprapedal gland ( Barker & Efford, 2004). Although Barker & Efford (2004) suggested that these traits may not be true adaptations to carnivory, since they could result from phylogenetic constraints and selective processes not involving diet, it nevertheless seems justified to characterize the morphology of Poiretia as that of a typical carnivorous snail.

In Greece, Poiretia is represented by P. compressa in Kephallinia and the northwestern Peloponnese and by P. dilatata (Philippi, 1863) in the southern Peloponnese and western Crete ( Welter-Schultes, 2012). Poiretia dilatata in the Peloponnese is classified as the subspecies P. dilatata peloponnesica.

In Kephallinia, Ithaca and the western part of Crete, Schilthuizen et al. (1994) reported observations of P. compressa attacking Albinaria contaminata as well as the occurrence of Albinaria shells that had been scraped along one side, which was inferred to have been caused by Poiretia snails. It was thought that Poiretia made these holes by scraping with its radula. However, in 2007 an observation by Fabio Liberto was posted on the online forum naturamediterraneo.com ( http://www.naturamediterraneo.com/forum/topic.asp?TOPIC_ID=33867, last accessed 6 May 2014), of a Poiretia dilatata attacking Pomatias elegans by sitting on its shell for 2 d and dissolving it by an acid secretion from its pedal gland, instead of scraping it with its radula.

Poiretia predation rates reached up to 21% in the Albinaria populations studied. Predation rates were consistently different in Albinaria populations with different shell characters. They were significantly higher in species with high vs low rib prominence, as well as in sinistral vs dextral species. Perhaps a strongly ribbed shell is easier for a Poiretia to hold on to when its prey tries to escape, but it might also be that there are differences in the microhabitat preferences of A. adrianae and A. contaminata and that the microhabitat preference of P. compressa has more overlap with that of A. adrianae than that of A. contaminata.

The greater predation rate of Poiretia in sinistral prey may indicate that Poiretia snails are better adapted to handling sinistrally coiled Albinaria snails, because this is the common coiling direction for Albinaria species. Prey preference based on chirality has been shown before, for instance in pareatid snakes predating Satsuma snails ( Hoso et al., 2010). However, P. dilatata peloponnesica also predates other snail species, such as Lindholmiola lens and Pomatias elegans, which are dextral and also have very different shell shapes. Therefore, its preference for A. schuchii over A. gerolimena and A. voithii might be unconnected with chirality, and instead result from size or microhabitat preference.

Marks made by P. compressa occur most frequently on the abapertural side of Albinaria shells. In contrast, marks made by P. dilatata peloponnesica occur most frequently on the apertural side of Albinaria shells and the difference between these two distributions is strongly significant. This might reflect a difference in predation behaviour between the two predator species, because the apertural side of the shell usually rests on the substratum, whereas the adapertural side is exposed.

Circular hole organism

The circular perforations ascribed to the CHO were also described by Schilthuizen et al. (1994) and are most likely the result of predation or parasitism, because multiple holes can sometimes be found in one shell, but repaired holes are hardly ever found. Nematodes, perhaps of the family Mermithidae, or other worms were suggested as candidates ( Schilthuizen et al., 1994). Carnivorous snails of the families Oxychilidae and Gastrodontidae should also be considered, as some species have been observed to make holes ( Barker & Efford, 2004). The oxychilid snail Eopolita protensa was observed to attack juvenile Albinaria in Greece ( Schilthuizen et al., 1994) so, although it is not known to make holes, it should also be considered as a candidate.

CHO predation reached up to 36% in the Albinaria populations studied. There are many significant differences in predation rates between syntopic populations, but they do not seem to be consistently connected with conchological traits. CHO predation marks are located most often on the apertural side of Albinaria shells. Because the apertural side usually rests on the substratum in live snails, this result might suggest that the CHO is small, able to crawl between the shell and the substratum to make a hole. Örstan (1999) investigated the distribution of the circular holes per whorl and found that the majority were located on the penultimate and antepenultimate whorl, so that the CHO attacks the snail directly instead of having to pass the clausilium.

Successful and failed CHO predation marks are on average smaller than holes made by Drilus. Data on Drilus holes were given by Baalbergen et al. (in press). Drilus holes have a higher length/width ratio than CHO holes, but it is still higher than 1 in CHO holes, so they are not perfectly circular. There is some overlap in size between small Drilus holes and CHO marks, so when assigning small holes to hole types, special attention should be paid to the qualitative characteristics of the holes. The CHO holes either narrow inwardly or have straight edges. Drilus holes are oval, the entrance holes narrow inwardly and the exit holes narrow outwardly, but this is sometimes only true for one side of the holes. The size range of circular holes, 0.11-0.44 mm, is slightly larger than the range found by Örstan (1999), which was 0.114-0.342 mm.

Hybrids

Hybrids could be expected to suffer higher predation rates than their parent species, if the shells of each parent species were optimized against predation by their own specific set of defensive characters and if a mixture of these characters were less optimal. This is referred to as hybrid inferiority ( Harrison, 1993). Giokas, Mylonas & Sotiropoulos (2000) found indirect evidence of hybrid inferiority in the hybrid zone at Monemvasia, where alleged hybrids showed a (non-significantly) higher mortality during aestivation. A mixture of characters could also be more successful, a case of hybrid superiority, and the fitness of hybrids predicts the evolutionary fate of a hybrid zone ( Harrison, 1993). Here, the predation rates in hybrids were never significantly higher or lower than in both of the parent species. Instead, they were similar to the predation rates on one or both of the parent species or intermediate between them. No evidence for hybrid inferiority or superiority was found.

Conclusions

The results obtained in this study, although inconclusive in some respects, bring us one step further in assessing the role of predation in the evolution of shell characters and speciation in Albinaria. Predation pressure is substantial in the investigated populations, but it is difficult to demonstrate that specific shell characters are anti-predator adaptations by assessing predator preferences. Hybrids between Albinaria species generally seem to suffer the same level of predation as one or both of their parent species. The predation rate is never significantly higher than in either parent species, which indicates that the shell shapes of the parent species may not represent two alternative optimizations against predation. This outcome, however, could be influenced by the small sample sizes of hybrids. Shell characters may also be under strong selection by abiotic conditions. The different aestivation behaviour observed among Albinaria species exposes them to different conditions and may consequently contribute to the diversity in shell morphology. The predators themselves seem to be well able to overcome the defences of Albinaria by making holes in their shells.

Future work

This study provides preliminary insights into the evolutionary interactions between Albinaria snails and their predators, which can be used as a basis for further investigations. Prey preference in Poiretia could be investigated further by sampling more populations of Albinaria and by setting up choice experiments. Its predation behaviour should be observed to clarify the method by which it creates holes in shells. The identity of the CHO remains unknown. In order to catch this organism in the act, attention should be paid during fieldwork to all other organisms present in the habitat of Albinaria snails. The fact that it has not been found to date, suggests that it is probably a small organism, or only active during specific periods of time, e.g. during rainfall, at night or in the middle of winter. It may well be a snail or a slug, so all species of snails and slugs co-occurring with Albinaria, with special attention to small, carnivorous species, could be tested for predation on Albinaria by keeping them in a laboratory. More research on the complex interactions between Albinaria and its main predators will hopefully enable us to assess the contribution of predation as a selective force in Albinaria speciation.

SUPPLEMENTARY MATERIAL

Supplementary material is available at Journal of Molluscan Studies online.

ACKNOWLEDGEMENTS

Special thanks go to Els Baalbergen and Rense Schelfhorst, for being the first author's collaborators in this study and to Sinos Giokas, for his vital contributions to this study. Also many thanks to Bertie Joan van Heuven of Naturalis for helping with SEM and light microscopy and supplying the first author with research materials, to Evi Thanou of University of Patras for lending her car during fieldwork, to Edi Gittenberger of Naturalis for aiding with species identifications and to Heike Kappes of Naturalis for advising on statistics. We also thank the Associate Editor Robert Cameron and the anonymous reviewers for their valuable feedback to improve the manuscript. We gratefully acknowledge the Kees Bakker Prijs, Jan-Joost ter Pelkwijkfonds, and Uyttenboogaart-Eliasen Stichting for funding this study.

REFERENCES

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Predation on Greek Albinaria (Pulmonata: Clausiliidae) by Poiretia (Pulmonata: Oleacinidae) and by an unknown organism making circular holes: possible drivers of shell evolution

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Albinaria is an extremely species-rich genus of land snails, with about a hundred species occurring in limestone habitats in Greece. Among their predators are other terrestrial snails, namely Poiretia dilatata peloponnesica on the Peloponnese and P. compressa on the Ionian Islands.