Patterns of Contemporary Genetic Variation and Effective Population Size in Blanding’s Turtle Populations

Mark A. Jordan^1,*, Brendan N. Reid^2,3, Daniel J. Guinto¹, Whitney J.B. Anthonysamy⁴,Christina M. Davy⁵, Judith Rhymer⁶, Michael Marchand⁷, Matthew Cross⁸, Gregory Lipps Jr.⁹, Yu Man Lee¹⁰, Bruce Kingsbury¹, Lisabeth Willey¹¹, Michael Jones¹², Jonathan Mays⁶, Glenn Johnson¹³, and Lori Erb¹⁴

¹Department of Biological Sciences, Purdue University Fort Wayne, 2101 E. Coliseum Boulevard, Fort Wayne, IN 46805. ²University of California Santa Cruz, Department of Ecology and Evolutionary Biology, 130 McAllister Way, Santa Cruz, CA 95060. ³Rutgers University, Department of Ecology, Evolution, and Natural Resources, 14 College Farm Road, New Brunswick, NJ 08901. ⁴University of Health Sciences and Pharmacy, St. Louis, MO 63110. ⁵Department of Biology, Carleton University, Ottawa, ON K1S 5B6, Canada. ⁶Department of Wildlife, Fisheries, and Conservation Biology, University of Maine, Orono, ME 04469. ⁷New Hampshire Fish and Game Department, 11 Hazen Drive, Concord, NH 03301. ⁸Toledo Zoo Conservation Department, 2 Hippo Way, Toledo, OH 43609. ⁹Department of Evolution, Ecology, Organismal Biology, Ohio State University, 318 W. 12th Avenue, 300 Aronoff Laboratory, Columbus, OH 43210. ¹⁰Michigan Natural Features Inventory, Michigan State University Extensions, 1st Floor Constitution Hall, 525 W. Allegan St., Lansing, MI 48933. ¹¹Massachusetts Cooperative Fish and Wildlife Research Unit, University of Massachusetts Amherst, 160 Holdsworth Way, Amherst, MA 01003. ¹²Natural Heritage and Endangered Species Program, Massachusetts Division of Fisheries and Wildlife, 1 Rabbit Hill Road, Westborough, MA 01355. ¹³Department of Biology, SUNY College at Potsdam, Potsdam, NY 13676. ¹⁴Mid-Atlantic Center for Herpetology and Conservation, PO Box 620, Oley, PA 19547. *Corresponding author.

Northeastern Naturalist, Volume 31, Special Issue 12: E131–E150

First published early online: 31 August 2024

Abstract
Adequate genetic variation in a population is fundamental to reducing the risk of inbreeding depression in the short term and maintaining its ability to respond to evolutionary forces over the long term. There are now several studies that use microsatellite loci to assess genetic variation within populations across the geographic range of Emydoidea blandingii (Blanding’s Turtle), but direct comparisons among studies have not been conducted. We present estimates of allelic richness (A) and expected heterozygosity (H_E) from 59 localities across much of the species’geographic range and compare them using a resampling method that calibrates values relative to a reference population to account for different sample sizes and microsatellite panels. We further compared these measures between 2 datasets, from the midwestern US and from the northeastern US, that were made compatible using a sample of re-genotyped individuals. In both cases, we found lower A and H_E in the northeastern localities. We also developed a sensitivity analysis of effective population size (N_e) estimation with the linkage disequilibrium method (N_eLD) that used a well-sampled population modelled in the program ‘NeOGen’ to explore the effects of adult population size (N_C), sample size, and locus number while accounting for overlapping generations, life history, and demography. We find that it is possible to estimate Ne with accuracy and precision in populations with N_C < 400 when sample size is ~25% of adult population size and ≥11 microsatellite loci are used. With this benchmark, we then estimated N_eLD in 7 localities using single-sample linkage disequilibrium in NeEstimator, a method that does not account for overlapping generations, demography, and life history but is more accessible for users. This approach overestimated N_eLD by ~37%. Collectively, our analyses of genetic variation within populations facilitate assessment of population status and resiliency in Blanding’s Turtles by demonstrating the range of genetic variation across a large number of populations and developing a baseline for the estimation of effective population size in natural populations.

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