Unexpectedly Low Rangewide Population Genetic Structure of the Imperiled Eastern Box Turtle Terrapene c. carolina

Abstract

Rangewide studies of genetic parameters can elucidate patterns and processes that operate only over large geographic scales. Herein, we present a rangewide population genetic assessment of the eastern box turtle Terrapene c. carolina, a species that is in steep decline across its range. To inform conservation planning for this species, we address the hypothesis that disruptions to demographic and movement parameters associated with the decline of the eastern box turtle has resulted in distinctive genetic signatures in the form of low genetic diversity, high population structuring, and decreased gene flow. We used microsatellite genotype data from (n = 799) individuals from across the species range to perform two Bayesian population assignment approaches, two methods for comparing historical and contemporary migration among populations, an evaluation of isolation by distance, and a method for detecting barriers to gene flow. Both Bayesian methods of population assignment indicated that there are two populations rangewide, both of which have maintained high levels of genetic diversity (HO = 0.756). Evidence of isolation by distance was detected in this species at a spatial scale of 300 – 500 km, and the Appalachian Mountains were identified as the primary barrier to gene flow across the species range. We also found evidence for historical but not contemporary migration between populations. Our prediction of many, highly structured populations across the range was not supported. This may point to cryptic contemporary gene flow, which might in turn be explained by the presence of rare transients in populations. However these data may be influenced by historical signatures of genetic connectivity because individuals of this species can be long-lived.

Nest-Site Fidelity and Sex-Biased Dispersal Affect Spatial Genetic Structure of Eastern Box Turtles (Terrapene carolina carolina) at Their Northern Range Edge

“…Eight loci showed significant deviations from HWE following Bonferroni correction, and the average frequency of null alleles was 0.076. In spite of the high proportion of loci that showed significant deviations from HWE, we attributed these deviations to either undetected genetic structuring (i.e., Wahlund effect; Sinnock, 1975) or the high allelic richness present in these microsatellite loci relative to our sample size (also noted by Kimble et al, 2011Kimble et al, , 2014aKimble et al, , 2014b. Therefore, we retained all loci for further analyses.…”

“…Because range-edge populations are subject to environmental extremes and are more isolated, they tend to be characterized by greater genetic differentiation and lower genetic diversity than populations closer to the core of the geographic range (Sexton et al, 2009). Eastern Box Turtles generally lack genetic population structure at broad scales (Kimble et al, 2014a); however, local spatial genetic structure could be present particularly in geographic range-edge populations where migration may be limited and individuals are faced with limiting environmental conditions. Our objectives were to examine patterns of fine-scale spatial genetic structure in a range-edge population, from which we will be able to infer the underlying ecological processes responsible for generating patterns.…”

The reduction of genetic diversity in threatened vertebrates and new recommendations regarding IUCN conservation rankings

“…Additionally, some reductions in demographic population size do not result in reductions in genetic diversity due to life history traits that limit the effects of inbreeding and drift (e.g. long generation time; Kimble et al, 2014;Marsack and Swanson, 2009). Alternatively, the lack of difference between Least Concern and threatened species could be due to the use of insufficiently sensitive criteria to effectively identify species with reduced N e .…”

Comparative landscape genetics of two river frog species occurring at different elevations on Mount Kilimanjaro

“…; Richardson ; Kimble et al . ), or on species with wide altitudinal distributions (e.g. Funk et al .…”

“…Despite tropical and montane biotas being expected to experience the highest biodiversity losses in the near future (Ricketts et al 2005), most landscape genetic studies have been conducted in temperate regions Manel & Holderegger 2013), either on relatively widespread low-elevation species (e.g. Coulon et al 2006;Stevens et al 2006;Richardson 2012;Kimble et al 2014), or on species with wide altitudinal distributions (e.g. Funk et al 2005;Giordano et al 2007;Spear & Storfer 2008;Murphy et al 2010;Savage et al 2010).…”