Central American Trachemys revisited: New sampling questions current understanding of taxonomy and distribution (Testudines: Emydidae)

Using 3226-bp-long mtDNA sequences and five nuclear loci (Cmos, ODC, R35, Rag1, Rag2, together 3409 bp), we examine genetic differentiation and relationships of Central American slider turtles (Trachemys grayi, T. venusta). Our investigation also included samples from taxa endemic to North America (T. gaigeae, T. scripta), the Antilles (T. decorata, T. decussata, T. stejnegeri, T. ter-rapen), and South America (T. dorbigni, T. medemi plus the two T. venusta subspecies endemic to northern South America). Our mitochondrial phylogeny retrieves all studied species as distinct, with three well-supported clades in a polytomy: (1) the Central and South American species (T. grayi + T. venusta) + (T. dorbigni + T. medemi), (2) the Antillean species, and (3) T. gaigeae + T. scripta. Our nuclear DNA analyses also suggest three distinct but conflicting clusters: (1) T. scripta plus the Antillean species, (2) T. gaigeae, and (3) the Central and South American species T. dorbigni, T. grayi, T. medemi, and T. venusta. However, in the mitochondrial phylogeny, T. gaigeae is the little divergent sister taxon of T. scripta. This conflicting placement of T. gaigeae suggests a distinct evolutionary trajectory and old hybridization with T. scripta and mitochondrial capture. Despite prominent color pattern differences, genetic divergences within T. grayi and T. venusta are shallow and the taxonomic diversity of each species with several currently recognized subspecies could be overestimated. Finally, we provide for the first time evidence for the occurrence of T. grayi along the Caribbean versant of Costa Rica.

Automated summary

By analyzing mtDNA sequences and nuclear loci, this study examines the genetic differentiation and relationships of Central American slider turtles. The results show distinct genetic clusters among different species, but conflicting placements in certain cases. The study also suggests that the taxonomic diversity of certain species may be overestimated. Additionally, evidence of the occurrence of a specific species in a new location is provided for the first time.