Patterns of genetic diversity in the critically endangered Central American river turtle: human influence since the Mayan age?

Abstract

We conducted a phylogeographic analysis of the strictly aquatic and critically endangered Central American river turtle, Dermatemys mawii, as part of a conservation management program for the species. We sampled 238 individuals from 15 different localities throughout the species range. Using sequence fragments from the mtDNA Cyt b and ND4 genes, we identified 16 different haplotypes. Overall, our results reveal a signal of phylogeographic structure throughout the range, which appears to have been secondarily blurred by extensive gene flow. Notably, this also applies to genetic structuring across three major hydrological basins that pose biogeographic breaks in other aquatic taxa. Divergence times of mtDNA haplotypes in D. mawii suggest that the main lineages split in the Pliocene-Pleistocene (3.73-0.227 MA) and demographic tests indicate that the species has undergone drastic demographic size fluctuations since this time period. One ancient haplotype (1D) was found to exhibit sequence divergence of up to 2% from other haplogroups. Divergence of this magnitude is indicative of species level differentiation in other turtle genera. Haplotype 1D was found in only two localities, Sarstun and Salinas, but specimens with other haplotypes were also found in those localities. It is not known whether the individuals with the 1D haplotype interbreed with non-1D individuals. Our results suggest that human activity, such as harvesting and long distance transport of animals, may have influenced the current patterns of genetic diversity. For more than 2000 years, D. mawii has been consumed by people from Middle American cultures, and the archeological record contains strong evidence that the Mayans transported animals between villages and far away from their natural distribution range. Therefore, the large-scale pattern of haplotype sharing even across hydrological barriers, the observed low haplotype diversity in some populations and the contemporary absence of a pronounced phylogeographic pattern is likely due to a combination of population expansions, gene flow, extensive human-mediated-movements and recent bottlenecks resulting from over-harvesting.

Cryptic Population Structuring and the Role of the Isthmus of Tehuantepec as a Gene Flow Barrier in the Critically Endangered Central American River Turtle

“…We test to what extent the results from the nuclear genome show concordance with previously published mtDNA structuring [16]. Assessing and maintaining genetic diversity is pivotal for conservation management plans that aim to protect the evolutionary potential of the species.…”

“…Recently, a study that characterized mtDNA variation in the species found signatures of phylogeographic structuring and phylogenetic splits among lineages up to a divergence of 2% [16]. A divergence of 2% at mtDNA loci in turtles can warrant species-level distinction [17].…”

Distribution and Abundance of the Central American River Turtle, Dermatemys Mawii, in Southern Quintana Roo, Mexico: Implications for a Regional Conservation Strategy

“…During interviews with some fishermen, adult size was mentioned to be smaller in our study area, than those fishermen have seen in other States as Tabasco [16]. The genetic differences found in this population by Gonzalez-Porter et al [37], may be associated with adult size. This issue needs further investigation, and results may contribute to exercise conservation measures focus in this population due to its differentiation.…”

“…This suggests that despite its prolonged use as a source of food for centuries [37,38], this species has been understudied. Notwithstanding the geographic proximity of the studies done in Belize up to date and as a result of the present work [16], Rio Hondo has started to be considered as a priority site for the conservation of the species [8].…”

“…Information related to archeological sites, indicates the presence of the species in areas in the center and north of the Yucatan Peninsula [41,42]. In these places the turtle was used as food resource, and because of this, it is possible that it was transported as a tribute; as it is documented that the villages offered the species as offerings at ancient cities [37]. Another possibility is that its distribution was wider in the past, and has been reduced or that the turtle still might be present in water bodies not considered as part of its current distribution, as occurred in the high and inaccessible parts of the Rio Hondo and lake systems as San Felipe and Laguna Negra, where the species was not previously recorded.…”