Decline of heterozygosity in a large but isolated population: a 45-year examination of moose genetic diversity on Isle Royale

Renae L Sattler,Janna R Willoughby,Bradley J Swanson

doi:10.7717/peerj.3584

Renae L Sattler, Janna R Willoughby + Show 1 more

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https://doi.org/10.7717/peerj.3584

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Abstract

Wildlife conservation and management approaches typically focus on demographic measurements to assess population viability over both short and long periods. However, genetic diversity is an important predictor of long term population vitality. We investigated the pattern of change in genetic diversity in a large and likely isolated moose (Alces alces) population on Isle Royale (Lake Superior) from 1960–2005. We characterized samples, partitioned into five different 5-year periods, using nine microsatellite loci and a portion of the mtDNA control region. We also simulated the moose population to generate a theoretical backdrop of genetic diversity change. In the empirical data, we found that the number of alleles was consistently low and that observed heterozygosity notably declined from 1960 to 2005 (p = 0.08, R2 = 0.70). Furthermore, inbreeding coefficients approximately doubled from 0.08 in 1960–65 to 0.16 in 2000–05. Finally, we found that the empirical rate of observed heterozygosity decline was faster than the rate of observed heterozygosity loss in our simulations. Combined, these data suggest that genetic drift and inbreeding occurred in the Isle Royale moose populations over the study period, leading to significant losses in heterozygosity. Although inbreeding can be mitigated by migration, we found no evidence to support the occurrence of recent migrants into the population using analysis of our mtDNA haplotypes nor microsatellite data. Therefore, the Isle Royale moose population illustrates that even large populations are subjected to inbreeding in the absence of migration.

Highlights

Though wildlife conservation and management approaches typically focus on demographic measurements to assess population viability over both short and long periods, increased attention is being placed on including an assessment of genetic diversity as a measurement of population health and vitality
All nine microsatellite loci in all sample periods were in Hardy Weinberg Equilibrium (HWE; all P > 0.0055) and no loci were linked after Bonferroni corrections
Our main objectives were to quantify the changes in genetic variation over forty-five years in a naturally isolated moose population, investigate the occurrence of recent migrants into the population, to use simulations to establish a baseline of heterozygosity loss for comparison to empirical values, and to determine the factors that may have influenced the observed changes

Summary

Introduction

Though wildlife conservation and management approaches typically focus on demographic measurements to assess population viability over both short and long periods, increased attention is being placed on including an assessment of genetic diversity as a measurement of population health and vitality. This cycle is problematic in isolated populations, as without input of novel genetic diversity into the population, the population does not typically recover (Frankham, 2015; Akesson et al, 2016)

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