Genetic diversity of the Khorat snail-eating turtle (Malayemys khoratensis) in Thailand.

Introduction: Malayemys khoratensis is a freshwater turtle species endemic to northeastern Thailand and Lao PDR. While M. khoratensis is relatively common and widespread in Thailand, its population size and demographic trends remain largely unknown, as direct population estimates are lacking. This species faces significant threats from consumption, exploitation, and trade. Therefore, this study aims to investigate the genetic diversity, population structure, and demographic trends of M. khoratensis in northeastern Thailand, using two mitochondrial DNA genes, Cyt b and ND4.

Method: We grouped the turtles based on three major river basins in northeastern Thailand: Mun, Chi, and Northeast Mekong to assess population structure and test the isolation-by-basin hypothesis. The Cyt b and ND4 genes of 49 M. khoratensis individuals across 15 provinces in Thailand were sequenced, and 15 sequences from a previous study of Ihlow et al. (2016) were included into the analyses. We constructed a haplotype network from the concatenated sequences and analyzed the population structure with the analysis of molecular variance (AMOVA). Additionally, we used a Bayesian Skyline plot (BSP) analysis to estimate the effective female population size and explore the demographic history of this species.

Results: Our analysis identified 13 unique haplotypes defined by 26 polymorphic sites from 64 samples. The total haplotype diversity for M. khoratensis was 0.819, while nucleotide diversity was 0.0031. The haplotype network and AMOVA revealed no distinct population structure among the river basins, suggesting gene flow across these regions. The BSP estimated a stable effective female population size of approximately 130,000 individuals since around 100,000 years ago (late Pleistocene).

Conclusion: Our findings indicated no significant population structure by river basin, which may be due to natural movement between basins or potential human-mediated translocations linked to the turtle trade. The demographic trend of M. khoratensis appears to have been stable over time. However, given the ongoing exploitation of this species, we recommend regular monitoring of population trends to support its long-term survival.