Conservation genetics of a freshwater turtle (Trachemys hartwegi) in a threatened riverine ecosystem.

Abstract

Background: Freshwater ecosystems face unprecedented degradation due to habitat destruction, pollution, and climate change, necessitating urgent conservation actions to protect vulnerable freshwater species. Freshwater turtles are among the most threatened vertebrates globally, with their survival constrained by thermal sensitivity and aquatic habitat requirements. The Mexican Plateau Slider (Trachemys hartwegi) is a vulnerable freshwater turtle restricted to riverine areas in the arid regions of northern Mexico, which faces critical threats from habitat loss, fragmentation, and illegal pet trade collection, compromising population viability across its limited range.

Methods and results: Using 13 microsatellite loci, we genotyped 148 T. hartwegi individuals from 10 sampling sites spanning three dam-divided sections of Durango Nazas River to examine genetic diversity, structure, and estimate demographic parameters, as well as to identify suitable habitats under current and future climatic scenarios. Our results showed low levels of genetic diversity compared to other Mexican Trachemys species. Despite the presence of two dams along the Nazas River, we found no significant genetic structure. The estimated effective population size was relatively low (Ne = 307), a finding that cannot be attributed to contemporary population declines, as no evidence of recent bottlenecks was detected. Our models under climate change scenarios for 2040 and 2060 projected a decline of 73 to 76% in available habitats, with dam sites representing future refugia in the Nazas River.

Conclusions: Our findings reveal critical conservation challenges for T. hartwegi. A low effective population size may not be sufficient to ensure long-term population viability, while ENMs predicted dramatic habitat loss under current climate trends. This study highlights the critical need for adaptive management balancing competing demands for human water resources, while preserving the riverine habitat connectivity, which influences ecosystem integrity.