Drought and Wildfire Compromise Genetic Diversity and Recovery in Gila trout

Authors: Thomas F.* Turner, Megan J. Osborne, Tyler J. Pilger, David L. Propst, James E. Brooks, Wade D. Wilson

Year: 2015 (xlvii)

Abstract

Gila trout, Oncorhynchus gilae, maintains a tenuous presence in the Upper Gila River basin. Beginning in 2011, a series of catastrophic wildfires negatively impacted nearly all remaining populations, with local effects ranging from reduced abundance to extirpation. We assessed genetic responses by assessing variation in 13 microsatellite loci and a gene critical for immune function (MHC). We show that, in addition to severe demographic losses, levels of genetic diversity changed radically over a 10-year period of extensive drought preceding the wildfires. Two distinct lineages (Spruce and Whiskey), both with behavioral characteristics that complicate large-scale hatchery rearing, experienced extensive losses of heterozygosity and allelic diversity at all loci, including MHC. Diversity did not change in lineages more amenable to hatchery rearing (Main Diamond, South Diamond). Marker-assisted crosses will likely be necessary to restore diversity and viability to the Spruce lineage. Restoration of genetic connectivity across multiple lineages in complex watersheds could also ameliorate negative demographic and genetic effects of drought, but could be complicated by climate change. Catastrophic fires and extensive drought will increase in frequency and geographic scale in coming decades, and we expect similar losses of diversity in other native trout populations. Gila trout serves as a case study in efforts to preserve other inland trout species.