COS 305-3 - CANCELLED - Using an Interdisciplinary Approach for the Rangewide Conservation of the Mojave Desert Tortoise

Abstract: Climate change and urban development in the southwestern United States are projected to rapidly impact the region. The effects of these stressors on ecosystems, such as the Mojave Desert, are of concern due to projected warmer and drier conditions and increased habitat fragmentation. The federally-listed Mojave desert tortoise (Gopherus agassizii) has suffered population declines yet continues to persist in this fragmented landscape. These stressors have been increasing across the species’ range for decades, but have recently accelerated, occurring on a shorter time scale than one tortoise generation. While adaptation and acclimatization may help species like the desert tortoise persist under environmental disturbances, adaptive intraspecific genetic variation in combination with landscape level connectivity is not often considered in studies examining extinction risk under forecast models of climate change. The spatial distribution of adaptive genetic variation is a function of historical interactions between genetic drift, natural selection, habitat connectivity, and demography; therefore, adequately characterizing adaptive genetic variation for sensitive species, such as the tortoise, would benefit from pairing high-resolution genomic datasets with current and future habitat modeling efforts that includes functional connectivity. We used genome-wide single-nucleotide polymorphisms (SNPs) as well as outlier detection and Genotype-Environment Association (GEA) approaches to identify loci associated with environmental gradients between various regions across the species range. We pooled the identified loci into a dataset of potentially adaptive SNPs. These GEA analyses were then compared to regional and range-wide current and forecasted habitat suitability models built using an ensemble approach. Forecasted habitat suitability models were built across four Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathway (RCP) climate scenarios (RCP 2.6, 4.5, 6.0, and 8.5) and were also compared to connectivity analyses. Results indicate that there may be greater adaptive genetic variation along edge regions compared to core habitat. We also found that there was extensive habitat loss along both edge and core regions as well as a loss of habitat connectivity within these areas, both currently and across all forecasted climate scenarios. While the tortoise shows range-wide isolation-by-distance, we documented variable magnitudes of genetic divergence and migration rates between some genetic clusters across the range. Overall, this integrated, interdisciplinary approach helps us better understand the evolutionary rescue potential of this threatened species and may aid in improving management plans for it.