Abstract 202 – Genetic diversity, gene flow, and effective population size of the Selkirk and Cabinet-Yaak grizzly bear populations

Megan Turnock, Lisette Waits, Justin Teisberg, Wayne Kasworm, Matthew Falcy,
Michael Proctor

Genetic monitoring is important in fragmented populations, particularly in small populations
that rely on gene flow to maintain genetic diversity. Grizzly bear (Ursus arctos) populations in
the Selkirk (SE) and Cabinet-Yaak (CYE) ecosystems are the smallest in North America and are
near the southernmost extent of the species’ range. Both populations were isolated for
generations but have recently experienced gene flow through natural migration and a
population augmentation program. A long-term dataset of grizzly bear microsatellite genotypes
from 1973-2021 presented a unique opportunity to examine genetic trends in the SE and CYE
over time. We used this dataset of 464 bears to evaluate if gene flow affected observed
heterozygosity, expected heterozygosity, allelic richness, and average pairwise relatedness in
each of these populations. We also estimated effective population size using the temporal and
linkage disequilibrium methods. Post gene flow, allelic richness increased in the Selkirk and
Cabinet populations and r decreased in all three populations. We did not observe any changes
in expected or observed heterozygosity, but expected heterozygosity values in our populations
were significantly higher than those estimated in a model without gene flow. Our effective
population size estimates were consistent between the temporal and linkage disequilibrium
methods and ranged from 15.15-15.8, 15.35-19.3, and 5.6-8.7 for the Selkirk, Yaak, and Cabinet
populations, respectively. Overall, our findings indicate that gene flow is increasing or
maintaining genetic diversity in the SE and CYE. However, effective population size remains low
and additional connectivity or augmentation may be needed, particularly in the Cabinet
population.