Saving the Rare Three-Striped Turtle Through Genetic Study

Jim Crocker
13th March, 2024

Saving the Rare Three-Striped Turtle Through Genetic Study

Image Source: Natural Science News, 2024

Key Findings

  • Researchers found the three-striped roofed turtle has low genetic variation, which may affect its survival
  • The turtle's population was stable, then grew, but started declining about 2,000 years ago
  • Despite this, a moderate level of genetic diversity still exists, offering hope for conservation
The three-striped roofed turtle, Batagur dhongoka, is a species in crisis. Once thriving in the riverine ecosystems of South Asia, this turtle has seen its numbers plummet by over 80% in the last half-century. Classified as 'Critically Endangered', the survival of B. dhongoka hinges on our ability to understand its genetic makeup and implement effective conservation strategies. Researchers from the Wildlife Institute of India have taken on this challenge, aiming to unravel the genetic diversity and structure of this imperiled species[1]. The study focused on B. dhongoka individuals from two Turtle Rescue and Rehabilitation Centres located near the Ganga river. By analyzing both mitochondrial DNA (mtDNA) and nuclear DNA, the researchers sought to paint a comprehensive picture of the genetic health of the species. Mitochondrial DNA, passed down from mother to offspring, can reveal insights into the maternal lineage and historical population trends, while nuclear DNA, inherited from both parents, provides a broader view of genetic diversity within a population. The mitochondrial DNA analysis involved two regions: the cytochrome b (Cyt b) and the control region (CR). The results indicated a low level of nucleotide diversity, which is a measure of the genetic variation present within a species. This finding suggests that B. dhongoka has a limited genetic repertoire to cope with environmental changes or disease outbreaks. To understand the population's past fluctuations, the researchers employed a method known as Bayesian skyline plot (BSP) analysis. This technique uses genetic data to infer historical changes in a species' effective population size — the number of individuals contributing genetically to future generations. The BSP analysis for B. dhongoka revealed a period of stability followed by population growth, but with a concerning decline starting around 2,000 years ago. Turning to nuclear DNA, the study examined ten microsatellite loci. Microsatellites are repetitive stretches of DNA that are highly variable among individuals, making them useful markers for assessing genetic diversity. The observed heterozygosity, a measure of genetic variation within a population, was found to be moderate (Ho: 0.49). This level of genetic diversity is encouraging, as it indicates a potential for resilience within the species. Bayesian-based clustering analysis was used to detect genetic structures within the population. This method can identify distinct genetic groups and assess the degree of intermixing between them. The analysis revealed weak genetic structures and signs of admixed assignations, suggesting that individuals from different lineages are breeding with each other, maintaining a flow of genetic diversity. The findings from this study are crucial for the conservation of B. dhongoka. They indicate that despite a historical decline, there is still a moderate level of genetic diversity that conservation efforts can build upon. This is particularly relevant when considering the plight of other endangered turtle species, such as the southern river terrapin[2] and the Burmese roofed turtle[3]. These species have also faced severe population declines, but conservation efforts, including genetic analysis and captive breeding, have been instrumental in their management. For instance, in the case of the southern river terrapin, the discovery of only four kinship groups in Cambodia[2] has highlighted the need for careful genetic management to avoid inbreeding. Similarly, the genetic study of the Burmese roofed turtle[3] led to targeted reintroductions of genetically diverse individuals, boosting the wild population's fertility. These precedents underscore the importance of genetic studies in informing conservation strategies. However, as noted in a review of genetic bottleneck tests[4], it is crucial to interpret genetic data with caution. The study on B. dhongoka, while revealing a moderate level of genetic diversity, also serves as a reminder that small sample sizes and assumptions about genetic mutation rates can impact the conclusions drawn from such research. In response to the findings, the Government of India has taken decisive action by including B. dhongoka in Schedule I of the Wildlife (Protection) Act, 1972. This legal protection reflects a commitment to the species' conservation, emphasizing the need for continued monitoring and habitat preservation. In conclusion, the study by the Wildlife Institute of India offers hope for B. dhongoka. By shedding light on the genetic status of this critically endangered turtle, it provides a foundation for informed conservation actions. The challenge now is to translate this knowledge into effective management strategies that will secure a future for the three-striped roofed turtle.

WildlifeGenetics

References

Main Study

1) Population genetics of the critically endangered three-striped turtle, Batagur dhongoka, from the Ganga river system using mitochondrial DNA and microsatellite analysis.

Published 11th March, 2024

https://doi.org/10.1038/s41598-024-54816-0

Related Studies

2) Last exit before the brink: Conservation genomics of the Cambodian population of the critically endangered southern river terrapin.

https://doi.org/10.1002/ece3.5434

3) Conservation genomics of the endangered Burmese roofed turtle.

https://doi.org/10.1111/cobi.12921

4) Reliability of genetic bottleneck tests for detecting recent population declines.

https://doi.org/10.1111/j.1365-294X.2012.05635.x


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