Demographic and genetic status of an isolated population of bog turtles (Glyptemys muhlenbergii): implications for managing small populations of long-lived animals

Abstract

In this study, we sought to determine the population stability and genetic diversity of one isolated population of the federally-threatened bog turtle (Glyptemys muhlenbergii) in North Carolina. Using capture-recapture data, we estimated adult survival and population growth rate from 1992 to 2007. We found that the population decreased from an estimated 36 adult turtles in 1994 to approximately 11 adult turtles in 2007. We found a constant adult survival of 0.893 (SE = 0.018, 95% confidence interval, 0.853-0.924) between 1992 and 2007. Using 18 microsatellite markers, we compared the genetic status of this population with five other bog turtle populations. The target population displayed allelic richness (4.8 ± 0.5) and observed heterozygosity (0.619 ± 0.064) within the range of the other bog turtle populations. Coalescent analysis of population growth rate, effective population size, and timing of population structuring event also indicated the genetics of the target population were comparable to the other populations studied. Estimates of effective population size were a proportion of the census size in all populations except the target population, in which the effective population size was larger than the census size (30 turtles vs. 11 turtles). We attribute the high genetic diversity in the target population to the presence of multiple generations of old turtles. This study illustrates that the demographic status of populations of long-lived species may not be reflected genetically if a decline occurred recently. Consequently, the genetic integrity of populations of long-lived animals experiencing rapid demographic bottlenecks may be preserved through conservation efforts effective in addressing demographic problems.

Effects of Habitat Alterations on Bog Turtles (Glyptemys muhlenbergii): A Comparison of Two Populations

“…At Site 2, survival rates and population sizes declined over the 16-yr study period, consistent with an increase in low-quality habitat. Survival rate estimates of Bog Turtle at these sites were similar to survival rates and population sizes of other northern Bog Turtle populations (Pittman et al, 2011; and other long-lived, northern turtle species (Congdon et al, 1993(Congdon et al, , 1994Litzgus, 2006). However, survival rates at Site 2 in 2009 were lower than any other Bog Turtle studies reported.…”

Conservation genetics of the endangered Spotted Turtle (Clemmys guttata) illustrate the risks of “bottleneck tests”

“…In all three cases, bottlenecked populations are still vulnerable and incorrect conclusions about the genetic health of threatened populations can slow recovery efforts. We recommend caution when considering previous conclusions that populations of long-lived organisms such as turtles are not genetically impacted by bottlenecks (e.g., Kuo and Janzen, 2004;Mockford et al 2005;Marsack and Swanson 2009;Spradling et al 2010;Pittman et al 2011). These conclusions should be re-evaluated as more appropriate tests become available.…”

“…The expected genetic effects of recent, anthropogenic habitat and population fragmentation have not been detected in several turtle species, despite empirical and anecdotal evidence of significant population declines and fragmentation (Rubin et al 2001;Kuo and Janzen 2004;Marsack and Swanson 2009;Pittman et al 2011). Isolated subpopulations remain genetically identical over many years even when dispersal is severely restricted (Rubin et al 2001;Bennett et al 2010), apparently owing to their long generation times.…”

“…Isolated subpopulations remain genetically identical over many years even when dispersal is severely restricted (Rubin et al 2001;Bennett et al 2010), apparently owing to their long generation times. Severe demographic bottlenecks are expected to leave a genetic signature (Wright 1931;Frankham 1996;Piry et al 1999, Garza andWilliamson 2001), but small populations of turtles that have declined significantly in recent years often show no evidence of genetic bottlenecks (Kuo and Janzen 2004;Mockford et al 2005;Marsack and Swanson 2009;Spradling et al 2010;Pittman et al 2011). One potential explanation is that the long life span of turtles buffers small populations against the genetic effects of habitat fragmentation and bottlenecks (Kuo and Janzen 2004;Marsack and Swanson 2009;Bennett et al 2010) and the potential associated loss of allelic diversity.…”

“…IAM, infinite allele model; TPM, two-phase model. *Pittman et al (2011) present mean sample size per locus. † Tests of seven sites were not significant; when sites were grouped into three populations, two of these demonstrated a significant mode shift.…”