Unraveling the Complex Population History and Intergradation of Pond Sliders (Trachemys scripta) through Approximate Bayesian Computation Analysis of the Mitochondrial Control Region

Trachemys scripta (Pond Sliders), a North American freshwater turtle species, includes three subspecies, T. s. scripta, T. s. elegans, and T. s. troostii, whose relationships and status remain enigmatic. Particularly intriguing is T. s. troostii, which exhibits weak genetic distinctiveness from the other two subspecies. Rather than viewing their evolution as a simple bifurcating process, our study delves into the complex demographic history of T. s. troostii. We leveraged mitochondrial control region DNA sequences to investigate the subspecies’ demographic history and intraspecific systematics, with special emphasis on T. s. troostii. Haplotype network and phylogenetic analyses using Maximum Likelihood and Bayesian Inference consistently revealed that T. s. troostii is incompletely differentiated genetically from T. s. elegans. To investigate the demographic history of the three subspecies, we conducted the model-testing-based approximate Bayesian computation (ABC) analysis. Our findings support the hypothesis that T. s. troostii originated through admixture between T. s. scripta and T. s. elegans, with later secondary contact with the latter shaping the genetic makeup of present-day T. s. troostii populations.