Population genetics of the diamondback terrapin, Malaclemys terrapin, in Louisiana

Abstract

Previous population genetic studies of diamondback terrapins (Malaclemys terrapin) have typically focused on either the entire range or relatively small spatial scales. The Louisiana coastline contains vast salt marshes suitable for terrapins; however, two major freshwater inputs (Atchafalaya River and Mississippi River Deltas) break up the seemingly contiguous habitat and may isolate populations of terrapins. To determine population genetic structure and connectivity of terrapins occupying Louisiana marshes, we collected 573 individuals from 26 study sites across the Louisiana coastline. Twelve microsatellite loci were used to evaluate population structure using standard genetic and spatially explicit approaches. Patterns of gene flow were examined via model testing, including those to determine if freshwater inputs serve as barriers to movement. We also assessed levels of genetic diversity, inferred the historical demography and estimated effective population sizes across our sampling. While we did not detect significant population structure, we found that terrapins are not panmictic, and demonstrated a pattern of isolation by distance along the Louisiana coastline. Genetic diversity in this study was comparable to the Atlantic coast, but was higher than other sites within the Gulf of Mexico. Though terrapins in eastern Louisiana were historically harvested and apparently experienced a genetic bottleneck, this is not reflected in estimates of effective population sizes. Although, there was no strong genetic structuring across Louisiana, historical differences and patterns of habitat loss suggest that it may be necessary to develop separate management strategies for the western and eastern portions of the state.

Conservation genetics of the Mary River turtle (Elusor macrurus) in natural and captive populations

“…Overall estimates of genetic diversity based on microsatellite data (average Hs = 0.55) were similar to values estimated for Elseya albagula, an endangered freshwater turtle co-distributed with MRT (average Hs = 0.57; Todd et al, 2013), but lower than values observed in a range of other threatened turtle species (Davy, Bernardo, & Murphy, 2014;Escalona et al, 2009;Petre, Selman, Kreiser, Pearson, & Wiebe, 2015). The low microsatellite-based estimate of heterozygosity (Hs = 0.55) found in MRTs is close to the threshold of 0.54 identified by Willoughby et al (2015) as symptomatic of a species that merits conservation concern as Critically Endangered.…”

“…Likewise, the timescale of divergence between Tinana and Mary populations of Australian lungfish is relatively recent (less than 10,000 years) and linked to periods of lowered sea level in the late Pleistocene(Bishop et al, in press).Overall estimates of genetic diversity based on microsatellite data (average Hs = 0.55) were similar to values estimated for Elseya albagula, an endangered freshwater turtle co-distributed with MRT (average Hs = 0.57;Todd et al, 2013), but lower than values observed in a range of other threatened turtle species(Davy, Bernardo, & Murphy, 2014;Escalona et al, 2009;Petre, Selman, Kreiser, Pearson, & Wiebe, 2015). Lack of phylogeographic mtDNA divergence in MRTs indicates that the Tinana-Mary barrier is not an old one.…”

“…Likewise, the timescale of divergence between Tinana and Mary populations of Australian lungfish is relatively recent (less than 10,000 years) and linked to periods of lowered sea level in the late Pleistocene(Bishop et al, in press).Overall estimates of genetic diversity based on microsatellite data (average Hs = 0.55) were similar to values estimated for Elseya albagula, an endangered freshwater turtle co-distributed with MRT (average Hs = 0.57;Todd et al, 2013), but lower than values observed in a range of other threatened turtle species(Davy, Bernardo, & Murphy, 2014;Escalona et al, 2009;Petre, Selman, Kreiser, Pearson, & Wiebe, 2015). Effective population size estimates derived from microsatellite data in turtle species distributed across multiple drainages are also higher than those obtained for MRTs(Petre et al, 2015;Pittman, King, Faurby, & Dorcas, 2011;Spradling, Tamplin, Dow, & Meyer, 2010). A comparable study of a threatened species restricted to a single drainage in the USA (yellow-blotched sawback, Graptemys flavimaculata) found minimum N e estimates >800(Selman, Kreiser, & Qualls, 2013).…”

Genetic diversity, structure, and kinship analysis ofTrachemys venusta venustain Wildlife Management Units and wild populations in south Mexico. Implications for conservation and management

“…With the exception of some studies that present low genetic diversity (value of H e < 0.4; [68–69]), freshwater turtles exhibit high values of genetic diversity (generally H e > 0.6-0.7; see Table 4 in [69] for examples, and [70]) based on microsatellites. Our values could be considered lower ( H e < 0.6) than many other freshwater turtles or even threatened species (see Table 4 in [69] for examples, and [70–71]), and are in agreement with values for wild populations of Elusor macrurus Cann & Legler 1994 (Testudines, Chelidae) an endangered Australian freshwater turtle [72]. The sole genetic study that reports value of genetic diversity for Trachemys spp.…”

Conservation and Management of Trachemys venusta venusta in Southern Mexico: A Genetic Approach

“…With the exception of some studies that present low genetic diversity (value of H e < 0.4; Echelle et al., 2010; Vargas-Ramírez et al., 2012), freshwater turtles generally exhibit high values of genetic diversity (generally H e > 0.6–0.7; Vargas-Ramírez et al., 2012, Table 4 for examples; Davy et al., 2014) when using methodology based on microsatellites. Our values could be considered lower ( H e < 0.6) than many other freshwater turtles or even threatened species (Davy et al., 2014; Petre et al., 2015; Vargas-Ramírez et al., 2012, Table 4 for examples), and correspond with values for wild populations of Elusor macrurus Cann & Legler 1994 (Testudines, Chelidae) an endangered Australian freshwater turtle (Schmidt et al., 2018). Very few studies report values of genetic diversity for Trachemys spp.…”