The population genetics of urban and rural amphibians in North America

Human land transformation is one of the leading causes of vertebrate
population declines. These declines are thought to be partly due to
decreased connectivity and habitat loss reducing animal population sizes
in disturbed habitats. With time, this can lead to declines in effective
population size and genetic diversity which restricts the ability of
wildlife to efficiently cope with environmental change through genetic
adaptation. However, it is not well understood whether these effects
generally hold across taxa. We address this question by repurposing and
synthesizing raw microsatellite data from online repositories for 19
amphibian species sampled at 554 georeferenced sites in North America. For
each site, we estimated gene diversity, allelic richness, effective
population size, and population differentiation. Using binary urban-rural
census designations, and continuous measures of human population density,
the Human Footprint Index, and impervious surface cover, we tested for
generalizable effects of human land use on amphibian genetic diversity. We
found minimal evidence, either positive or negative, for relationships
between genetic metrics and urbanization in our repurposed data. Together
with previous work on focal species that also found varying effects of
urbanization on genetic composition, it seems likely that the consequences
of urbanization are not easily generalizable within or across amphibian
species. Questions about the genetic consequences of urbanization for
amphibians should be addressed on a case-by-case basis. This contrasts
with general negative effects of urbanization in mammals and consistent,
but species-specific, positive and negative effects in birds.