Assessing genetic diversity and connectivity in a tule elk (Cervus canadensis nannodes) metapopulation in Northern California

Joshua P. Bush,Benjamin N. Sacks,Thomas J. Batter

doi:10.1007/s10592-021-01371-0

Abstract

The tule elk (Cervus canadensis nannodes) is a California endemic subspecies that experienced an extreme bottleneck (potentially two individuals) in the mid-1800s. Through active management, including reintroductions, the subspecies has grown to approximately 6000 individuals spread across 22 recognized populations. The populations tend to be localized and separated by unoccupied intervening habitat, prompting targeted translocations to ensure gene flow. However, little is known about the genetic status or connectivity among adjacent populations in the absence of active translocations. We used 19 microsatellites and a sex marker to obtain baseline data on the genetic effective population sizes and functional genetic connectivity of four of these populations, three of which were established since the 1980s and one of which was established ~ 100 years ago. A Bayesian assignment approach suggested the presence of 5 discrete genetic clusters, which corresponded to the four primary populations and two subpopulations within the oldest of them. Effective population sizes ranged from 15 (95% CI 10–22) to 51 (95% CI 32–88). We detected little or no evidence of gene flow among most populations. Exceptions were a signature of unidirectional gene flow to one population founded by emigrants of the other 30 years earlier, and bidirectional gene flow between subpopulations within the oldest population. We propose that social cohesion more than landscape characteristics explained population structure, which developed over many generations corresponding to population expansion. Whether or which populations can grow and reach sufficient effective population sizes on their own or require translocations to maintain genetic diversity and population growth is unclear. In the future, we recommend pairing genetic with demographic monitoring of these and other reintroduced elk populations, including targeted monitoring following translocations to evaluate their effects and necessity.

Highlights

Fragmentation of wildlife populations as a consequence of human activity can result in inbreeding and a loss of genetic variation, leading to lower fitness levels and reduced adaptive potential (Frankham et al.2017)
Characterizing the genetic structure of populations allows wildlife managers to quantify genetic variation, infer connective corridors and barriers, and inform management activities based on predicted genetic outcomes, such as if and where humanmediated translocations should occur (Buchalski et al 2015; Frankham et al 2019)
After eliminating genotypes with < 18 of 20 loci, 1145 sample genotypes remained for analysis, from which we identified 490 unique individual elk (257 females, 233 males; Fig. 1a, b; Online resource 1)

Summary

Introduction

Fragmentation of wildlife populations as a consequence of human activity can result in inbreeding and a loss of genetic variation, leading to lower fitness levels (i.e., inbreeding depression) and reduced adaptive potential (Frankham et al.2017). Landscape connectivity is desirable for maintenance of gene flow, in small populations. In the absence of landscape connectivity, translocations have been used as a management tool to augment genetic diversity and improve fitness of recipient populations (Frankham 2015; Whiteley et al 2015). Characterizing the genetic structure of populations allows wildlife managers to quantify genetic variation, infer connective corridors and barriers, and inform management activities based on predicted genetic outcomes, such as if and where humanmediated translocations should occur (Buchalski et al 2015; Frankham et al 2019).

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Results

Discussion

Conclusion