Turtle soup, Prohibition, and the population genetic structure of Diamondback Terrapins (Malaclemys terrapin)

Abstract

Diamondback terrapins (Malaclemys terrapin) were a popular food item in early twentieth century America, and were consumed in soup with sherry. Intense market demand for terrapin meat resulted in population declines, notably along the Atlantic seaboard. Efforts to supply terrapins to markets resulted in translocation events, as individuals were moved about to stock terrapin farms. However, in 1920 the market for turtle soup buckled with the enactment of the eighteenth amendment to the United States’ Constitution—which initiated the prohibition of alcoholic drinks—and many terrapin fisheries dumped their stocks into local waters. We used microsatellite data to show that patterns of genetic diversity along the terrapin’s coastal range are consistent with historical accounts of translocation and cultivation activities. We identified possible instances of human-mediated dispersal by estimating gene flow over historical and contemporary timescales, Bayesian model testing, and bottleneck tests. We recovered six genotypic clusters along the Gulf and Atlantic coasts with varying degrees of admixture, including increased contemporary gene flow from Texas to South Carolina, from North Carolina to Maryland, and from North Carolina to New York. In addition, Bayesian models incorporating translocation events outperformed stepping-stone models. Finally, we were unable to detect population bottlenecks, possibly due to translocation reintroducing genetic diversity into bottlenecked populations. Our data suggest that current patterns of genetic diversity in the terrapin were altered by the demand for turtle soup followed by the enactment of alcohol prohibition. In addition, our study shows that population genetic tools can elucidate metapopulation dynamics in taxa with complex genetic histories impacted by anthropogenic activities.

Turtles and Tortoises Are in Trouble

“…In the United States, Diamondback Terrapins (Malaclemys terrapin) were harvested to make turtle soup in the late 19 th and early 20 th centuries [81,82]. The extirpation of European Pond Turtles (Emys orbicularis) from most of Central Europe was caused by overharvesting [83].…”

Genetic Analysis of a Cryptic Contact Zone between Mitochondrial Clades of the Eastern Red-Backed Salamander, Plethodon cinereus

“…We conducted 10 independent runs for K = 1 to K = 16, each with randomly generated seeds, and assessed convergence by comparing results across runs. We ran 700,000 iterations for each Markov chain Monte Carlo (MCMC) and discarded the first 350,000 iterations as burn-in (Converse et al, 2017). We used Structure Harvester web v.0.6.94 (Earl and von Holdt, 2012) to calculate DK using the Evanno method (Evanno et al, 2005); then we visualized results with the use of CLUMPP v.1.1.2 (Jakobsson and Rosenberg, 2007) and Distruct v.1.1 (Rosenberg, 2004).…”

“…We used Structure Harvester web v.0.6.94 (Earl and von Holdt, 2012) to calculate DK using the Evanno method (Evanno et al, 2005); then we visualized results with the use of CLUMPP v.1.1.2 (Jakobsson and Rosenberg, 2007) and Distruct v.1.1 (Rosenberg, 2004). Because DK detects the basal level of structure (Evanno et al, 2005), we ran STRUCTURE hierarchically to test for substructure within clusters (Converse et al, 2017;Janes et al, 2017). Finally, we used a spatially explicit Bayesian model in TESS v.2.3.1 (Durand et al, 2009) to estimate the number of clusters and admixture proportions.…”

Revisiting the comparative phylogeography of unglaciated eastern North America: 15 years of patterns and progress

“…Whereas early studies generally employed limited genetic data, such as sequences of one or a few mtDNA loci or data from a few allozyme loci (Avise et al, 1984), many newer studies now have the ability to employ genetic technologies that are more high-throughput and provide greater resolution of genetic groups and phylogenetic relationships. Currently, technology has developed to the point where studies may employ dozens of microsatellites (Converse et al, 2017;Hodel, Segovia-Salcedo, et al, 2016;Schrey et al, 2011;Williams et al, 2008), whole organellar genomes (Farrington et al, 2017), thousands of genomewide nuclear markers (Duvernell et al, 2019;Grabowski et al, 2014;…”

“…Whereas early studies generally employed limited genetic data, such as sequences of one or a few mtDNA loci or data from a few allozyme loci (Avise et al, 1984 ), many newer studies now have the ability to employ genetic technologies that are more high‐throughput and provide greater resolution of genetic groups and phylogenetic relationships. Currently, technology has developed to the point where studies may employ dozens of microsatellites (Converse et al, 2017 ; Hodel, Segovia‐Salcedo, et al, 2016 ; Schrey et al, 2011 ; Williams et al, 2008 ), whole organellar genomes (Farrington et al, 2017 ), thousands of genome‐wide nuclear markers (Duvernell et al, 2019 ; Grabowski et al, 2014 ; Hamlin & Arnold, 2014 ; Martin et al, 2016 ; Zhou et al, 2018 ), or whole‐genome resequencing (Bourgeois et al, 2019 ). However, although many advancements have been made in genotyping technologies over the past 15 years, it is unclear the extent to which phylogeographical studies have begun to employ these technologies (but see Morris & Shaw, 2018 ), whether these approaches have improved the resolution of phylogeographic discontinuities in phylogeographical studies, and whether the potential increased resolution of genetic groups and phylogeographical discontinuities has changed our overall understanding of the relative importance of phylogeographic discontinuities in eastern North America.…”