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Johora Singaporensis is a critically endangered species of freshwater crab endemic to Singapore. It inhabits a extremely small area within Singapore which is limited to about 0.01km². This habitat consists of a tragic 5 total freshwater streams on a hill in Bukit Batok. Johora Singaporensis a stenotopic species, meaning they are only able to survive in very specific habitats with almost perfect environmental conditions - in the case of singaporenis, pristine fast-flowing and well-oxygenated streams. This makes it a wonder that they managed to survive the mass deforestation of the past 200 years but have landed themselves on the top 100 most endangered species in the world.

Based on a study conducted on the genetics of Johora Singaporensis, using the heterozygosity excess method, there is significant evident to suggest that Johora Singaporensis has recently undergone a bottleneck event which reduced the total population drastically and which may have led to the current state of the gene pool.

There is not enough information to determine the type of selection but due to the extremely small population and habitat specificity, it is likely stabilising selection, with any individuals that have different mutations not being able to survive on their own.

Conservation genetics is currently being conducted on Johora singaporensis on a regular basis in order to ensure it's continuation as a staple of Singapore's great biodiversity. The species is a great example of how conservation genetics can be used to observe population trends more of which can be read in the publication in our references.

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Importance of genetic variation (batrisyia)

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Importance of genetic variation (batrisyia)

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Genetic variation is the natural differences in a DNA sequence in individuals of the same species. The variations vary, ranging from subtle to obvious differences. Essentially, genetic variation is what makes different individuals unique.

Genetic variation allows populations to adapt to the changing environments which increases their chances of survival. Additionally, genetic variation contributes to diversity in all forms of life from the smallest of microorganisms to the largest mammals.

Why is genetic variation important for the Johora singaporensis?

The Johora singaporensis is a critically endangered species with its population size being relatively small. This only further emphasizes the importance and need for genetic variation.

A lack of genetic diversity in a population teeter on the risk of extinction.

Genetic variation is crucial for these freshwater crab for many reasons and those reasons are:

Adaptability to the ever-changing environment.

Genetic variation allows for a wider range of traits within the Johora singaporensis. These variations increase the chances that some of these freshwater crabs will obtain/possess traits that are advantageous in a changing environmental condition. For example, change in water temperature, food availability or pollution levels. The adaptability will surely aid the species in persisting through the environmental challenges.

Enhanced reproductive success rates.

Seeing as the Johora singaporensis is a critically endangered species with a small population, genetic variation is crucial in their reproduction. Individuals with genetic diversity are less prone to the possibility of inbreeding depression which can lead to problems such as reduced fertility, decrease in gene pool and offspring viability. Genetic variation will also aid in preventing the bottleneck effect from occurring.

Resistance to diseases.

A small gene pool, as is the case of the Johora singaporensis, is more likely to be wiped out in a single disease outbreak. Thus, if some individuals of the population carry a genetic resistance to the pathogen related to the outbreak, they are more likely to survive and pass on that beneficial genetic variation to the next generation of offspring.

Lastly, long-term survival.

Genetic variation and diversity are generally essential for the long-term survival of a species. It provides the foundation for natural selection to act upon. This allows the population to constantly evolve and adapt to changes in conditions and environment over the generations.

In conclusion, for the Johora singaporensis crab, genetic variation is crucial for them. They are a critically endangered species with a small population size, after all. The lack of genetic diversity can and will increases the risks of extinction because of inbreeding, susceptibility to diseases and reduced adaptability.

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Defined as the differences between organisms caused by alternate forms of DNA.

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In context of Johora Singaporensis (timothy)

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In context of Johora Singaporensis (timothy)

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Generally low genetic diversity and gene variation

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Tay YC; Ng DJJ; Loo JB; D Huang; Y Cai; DCJ Yeo; R Meier*, “Roads to isolation: Similar genomic history patterns in two species of freshwater crabs with contrasting environmental tolerances and range sizes” ECOLOGY AND EVOLUTION DOI:doi.org/10.1002/ece3.4017 Published: 2018.

Shaw, A. (n.d.). What are the effects of inbreeding? BBC Earth. https://www.bbcearth.com/news/what-are-the-effects-of-inbreeding

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Uniquely from Singapore

Only a few hundred mature individuals exist in isolated populations

Findings from research:

The crabs are physically isolated and unlikely to move and breed between populations --> leads to low gene flow and inbreeding

Dispersal of individuals hampered by urbanization

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Genetic conservation of the Johora Singaporensis

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Genetic conservation of the Johora Singaporensis

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Genetic monitoring and assessment:

Genetic diversity analysis can be done through molecular techniques like DNA barcoding or genome sequencing to examine the genetic variability within the population. Such studies can help identify whether the species has a low genetic diversity, which could increase its vulnerability to diseases, environmental changes, or inbreeding.

Identifying distinct populations can help as well via fieldwork as there are multiple populations of Johora singaporensis in different regions of, genetic analysis helps to identify isolated groups that may require distinct management strategies. Ensuring gene flow between these isolated populations is crucial for maintaining genetic diversity and hence identifying distinct populations will help with the genetic conservation of the Johora Singaporensis.

Habitat preservation and captive breeding programs:

In situ conservation:

Protecting and restoring habitats the Johora singaporensis lives in to ensure species continuity and help it to maintain its habitat and genetic diversity.

Ex situ conservation

This should be last ditch effort should the population of Johora sinfaporensis go too low.

Ex situ conservation allows for the careful management of genetic diversity in a controlled setting, reducing the risk of inbreeding and genetic bottlenecks.

They can be bred in zoos or controlled environments and released back into the wild after.

Monitoring and management of genetic health

Regular Genetic Monitoring: Continuous monitoring of the genetic health of the population is essential to identify early signs of inbreeding or genetic drift. This can involve both field sampling and laboratory analysis to track any changes in the genetic makeup of the species over time.

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Only a few hundred mature individuals exist within a few isolated populations in areas less than 0.01 km²

Reduces the genetic pool available

Higher chance of inbreeding

Genetic drift

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Urbanisation --> habitat fragmentation

Prevents individuals from migrating and reduces gene flow

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Inbreeding due to low population and geographic isolation

Lower genetic variation

Could develop hereditary diseases

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Effects of genetic variation in Johora singaporensis (surong)

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Effects of genetic variation in Johora singaporensis (surong)

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1. Adaptability and resilience. Genetic diversity allows a species to adapt to environmental changes. For Johora singaporensis, the ability to adapt to changes in water quality, temperature, or habitat structure would depend on its genetic variability. Higher genetic variation would enable the species to withstand environmental stresses like pollution or climate change by selecting for individuals with traits that confer survival advantages. But being endemic to Singapore and living in restricted areas means that the species likely has limited genetic diversity which reduces the potential for adaptation to new environmental conditions or diseases.

2. Inbreeding depression. Johora singaporensis may be susceptible to inbreeding depression due to its small population size and limited distribution. Inbreeding can result in the expression of harmful recessive traits, leading to a decrease in overall fitness, lower reproductive success, and increased vulnerability to diseases and it also reduces genetic pool, which makes the species less resilient to environmental changes weakening its survival prospects.

3. Loss of genetic diversity. If the population size of Johora singaporensis shrinks due to habitat loss or other factors, it may undergo a genetic bottleneck, where only a small number of individuals contribute to future generations. This reduces genetic variation even further, making the population more prone to the negative effects of inbreeding, diseases, and lack of adaptability to environmental stressors.

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Threats to Johora singaporensis and Their Impact on Extinction Risk (surong)

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Threats to Johora singaporensis and Their Impact on Extinction Risk (surong)

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1. Habitat destruction and fragmentation. Urbanization and development in Singapore pose the greatest threats to Johora singaporensis as freshwater ecosystems are drained, polluted or altered, these crabs lose their natural habitats. Habitat fragmentation also reduces the population size and isolates subpopulations, preventing genetic flow between them. This isolation can exacerbate inbreeding and loss of genetic diversity.

2. Pollution. Freshwater pollution from chemical, waste and runoff can drastically affect the water quality in the streams where the crabs resides. Polluted water can reduce the oxygen levels and increase toxicity, directly threatening the survival of this species.

Pollutants can also disrupt the species' reproductive cycles, health, and overall population viability. For an already small and vulnerable population, such changes can be devastating.

3. Invasive species. Invasive species that outcompete native species or introduce new diseases could threaten Johora singaporensis. For example, invasive plants might alter the habitat, or predatory species might target the freshwater crab. Additionally, invasive species might hybridize with Johora singaporensis (if genetically similar), leading to the dilution of the native gene pool and the potential loss of distinct genetic traits.

Due to these genetic and environmental factors, Johora singaporensis is at high risk of extinction if current threats are not mitigated. the species' small population size and limited distribution make it highly vulnerable to loss of genetic diversity due to inbreeding and genetic drift, population decline from habitat destruction and pollution and difficulty adapting to environmental changes brought about by climate change.