Kyliana Schipper

Bree Stemplewski

Why we chose it: We chose to research this topic in part because the phrasing of it sounded quite interesting when listed on the guidelines document. We also wanted to see the difference between that and kin selection. From there, we found that the potential to link new information we learn to things we've covered in class sounded really interesting.

Knowing just how complex this all is, for out group our focus could shift to analyzing a specific animal species and how the many factors affect pay-to-stay behavior in that species.

They studied a color-marked population at the Hastings Reservation in California, between 1979 and 2010. During this time the population was monitored continuously. when testing the skills hypothesis they examined the age related feeding rates of the helpers, the dependent variable being the feeding rate per hour. When testing the pay-to-stay hypothesis they expected more useful helpers to stay in the native populations longer than less useful helpers. However, there was a potential confound, the birds that remained as helpers were more likely to inherit the territory, not because of their behavior but for being around for longer.

The findings are consistent with the two key pay-to-stay predictions, the more useful helpers remain as helpers for longer and by doing so they gained fitness benefits. However, the pay-to-stay hypothesis assumes helpers that are not preforming at the expected rate are potentially evicted from the group. The acorn woodpecker population did not show this behavior, helpers maintain access to resources despite their provisioning rate of the groups young. Some of the helpers that feed less have more time to look for reproductive opportunities.

The pay-to-stay behavior may not have been the only one seen but there are aspects of it along with kin selection and environmental factors that lead to these behaviors. As discussed in class there are many benefits to these Acorn Woodpeckers behaviors, from increased awareness and learning, having supply for slow seasons, increasing relative fitness of other young and access to resources.

They focused on a series of populations located in an agricultural region of northern Spain. In these groups, there was often a dominant breeding pair, female offspring, male offspring, and immigrant males present. A clear social hierarchy is also displayed through their prioritized access to food: the dominant breeding male is at the top, followed by male immigrants, male offspring, the dominant breeding female, and the female offspring in that order.

This social hierarchy was found to be a factor in the degree to which they intentionally displayed caretaking behaviors for new offspring in the nest. Researchers observed instances in which non-breeding individuals visited the nests of breeding individuals specifically while the dominant individuals were present. The relevance of this in regards to the study being conducted lies in the idea that, in a pay-to-stay society, the more an individual has been observed helping the breeding pair, the less likely they are to be kicked out of the group.

The results of this study did indeed support this idea: non-breeding individuals of lower social standing were more likely to visit the nests of the breeding pair while they were present, likely due to an increased risk of being kicked from the group.

Kin selection theory proposes that an organism will more readily help a relative at their own expense due to the close genetic relatedness between them.

Signals of prestige are displays of a dominant individual that indicate and help solidify their rank to subordinate individuals. Prestige itself is just the social standing of an animal which can provide benefits if their rank is high enough.

Group augmentation is the building of group size in order to gain benefits. These benefits often come from collective help in resource gathering, defense, and sometimes care of young.

Because these four factors tend to be closely related at times. It has proven difficult for researchers to tease apart pay-to-stay's direct effect compared to other mechanisms.

If subordinates stay to help breeders, are they benefited in return?

Is the pay-to-stay hypothesis seen in different species, what are the different functions and behaviors?

Is pay-to-stay more prominent in cichlids compared to other mechanisms?

The Neolamprologus pulcher was the species being focused on, found in Lake Tanganyika. The breeding male is usually the largest male in the group, with be breeding female being the next largest. Both the breeding pair and helpers defend and maintain the territory, as well as caring for the young. It was found that the helping females would produce eggs, leading to believe they might be helping in order to breed within the group. These results represented a step towards linking immediate reproductive benefits and helping behavior.

When looking at the benefits to the breeders, it was found that a breeding pair with helpers had higher rate of absolute breeding success than a breeding pair without helpers. Under natural conditions there was positive correlation between fry emerging and and the number of helpers. Fry had lower survival rates in groups where the helpers were removed. It was noted that territory size is a driving factor for breeding fitness, also that helpers being removed experimentally can disrupt the hierarchy of the social group, mothers may adjust their levels of investment due to amount of helpers present, and it is unsure which aspect of the helpers behavior leads to the proposed benefits.

Four possible hypotheses of why helpers help; Kin selection, pay-to-stay hypothesis, signals of prestige, or group augmentation hypothesis. In order to find which explanation could be responsible for helping, there are further evaluations of predictions and long term investigations that need to be conducted. There are many factors making it difficult to determine if the pay-to-stay hypothesis has the biggest impact on helpers.

There are three other proposed mechanisms to explain this which benefit direct fitness. The first of them is group augmentation. Simply by the members of a group collectively helping out, the survival rate of the group is exponentially higher. This also leads to more reproductive opportunity as they get to live longer than otherwise, but also may get additional benefits. This can include territory inheritance or learned skills that allow for more successful mating attempts.

The second proposed mechanism is social prestige. By helping out dominants, their own rank can potentially rise. Eventually this may lead to them becoming dominant or gaining access to mates.

The last of these mechanisms is pay-to-stay. If the cost of a subordinate being in a group is too high, then they can offset this by helping out, so they remain needed. High costs that force helpers into these scenarios include resource and reproduction competition. On the other hand, helpful tasks to offset this include territory defense and brood care.

Control: The focal helper was placed in a plastic cylinder which was relocated nearby it's home and territory. This fish was only held for five minutes before being released. The researchers left and returned 24 hours later to observe them for 10 minutes. When possible, this was done alongside the prevented help treatment. This was mainly done just to see how the fish react to the manipulations of the researchers.

Prevented help treatment: The focal helper was placed in a plastic cylinder that was attached to a custom shelter. This was also placed nearby the fish's home and territory. When in the custom shelter they seemed to swim around not under any stress. One of the cichlids returned to the shelter after being released. The purpose of this treatment was to have the fish present, but unable to participate in help. Researchers returned 24 hours later, released the cichlid, and then observed for 10 minutes.

Helper removal treatment: The focal helper was trapped in a mesh cage and removed from the colony. It was reintroduced 24 hours later where the researchers then observed behaviors for 10 minutes. The researchers would return an additional 24 hours later to see if the reintroduced fish was accepted back into the family.

After release, all treatment groups (not including control) were less defensive. Helpers were much less defensive in large groups, while breeders were much less defensive in small groups. In these small groups breeders were also the primary aggressors. In large groups the aggressors tended to be other helpers of similar size.

While there were families that existed within the groups, they were not all closely related like in certain other social animals. The helpers often helped out more than their own family showing that kin selection wasn't nearly as strong as pay-to-stay. The main motivation for the fish to help out seemed to be the avoidance of ostracization of when they don't help out. This lines up with the pay-to-stay hypothesis where if they don't contribute enough for their cost of living, then they get put in their place.

Broadly pay-to-stay is now understood, but knowing this we can maybe more easily tease apart different components of it. It may also be much easier now to develop research opportunities where the other mechanisms can be compared in species alongside it.