Life on the edge: a changing genetic landscape within an iconic American pika metapopulation over the last half century

Declines and extirpations of American pika (Ochotona princeps) populations
at historically occupied sites started being documented in the literature
during the early 2000s. Commensurate with global climate change, many of
these losses at peripheral and lower elevation sites have been associated
with changes in ambient air temperature and precipitation regimes. Here,
we report on a decline in available genetic resources for an iconic
American pika metapopulation, located at the southwestern edge of the
species distribution in the Bodie Hills of eastern California, USA.
Composed of a highly fragmented habitat created by hard rock mining, the
ore dumps at this site were likely colonized by pikas at the end of the
19th century from nearby natural talus outcrops. Genetic data extracted
from both contemporary samples and archived natural history collections
allowed us to track population and patch-level genetic diversity for Bodie
pikas across three distinct sampling points during the last half-century
(1948, 1988-1991, 2013-2015). In addition to declines in within-population
allelic diversity and expected heterozygosity, we observed an increase in
population structure and a reduction in effective population size from
more extensive sampling of extant patches during 1988-1991 and 2013-2015,
respectively. Furthermore, census records from the last 50 years as well
as archived museum samples collected in 1947 from a nearby pika population
in the Wassuk range (NV, USA) provide further support for the increasing
isolation and genetic coalescence occurring in this region. This study
highlights the importance of museum samples and long-term monitoring in
contextualizing our understanding of population viability.