Molecular evidence for historical and recent population size reductions of tiger salamanders (Ambystoma tigrinum) in Yellowstone National Park

Abstract

Population declines caused by natural and anthropogenic factors can quickly erode genetic diversity in natural populations. In this study, we examined genetic variation within 10 tiger salamander populations across northern Yellowstone National Park in Wyoming and Montana, USA using eight microsatellite loci. We tested for the genetic signature of population decline using heterozygosity excess, shifts in allele frequencies, and low ratios of allelic number to allelic size range (M-ratios). We found different results among the three tests. All 10 populations had low M-ratios, five had shifts in allele frequencies and only two had significant heterozygosity excesses. These results support theoretical expectations of different temporal signatures among bottleneck tests and suggest that both historical fish stocking, recent, sustained drought, and possibly an emerging amphibian disease have contributed to declines in effective population size.

Climatic change and wetland desiccation cause amphibian decline in Yellowstone National Park

“…2-4), which may have damaged amphibian populations even before the baseline measurement. Additionally, multiple studies have documented amphibian decline in this area (37)(38)(39)47), corroborating our results.…”

Evidence for recent population bottlenecks in northern spotted owls (Strix occidentalis caurina)

“…No significant reductions were observed in H e or R S between these sampling periods which is not particularly surprising given the short time interval (*10 years) relative to the life span of northern spotted owls (at least 16-17 years in the wild; Gutiérrez et al 1995). Additionally, as mentioned above, previous work (Cornuet and Luikart 1996;Beebee and Rowe 2001;Garza and Williamson 2001;Williamson-Natesan 2005;Goossens et al 2006;Spear et al 2006) demonstrates that the Cornuet and Luikart method is most effective at detecting recent changes in N e . Previous mitochondrial DNA (mtDNA) studies of northern spotted owls also provide some corroborating evidence for recent declines.…”

“…It uses a single population sample to test whether there has been a recent reduction in allelic variation. Simulations (Cornuet and Luikart 1996;Williamson-Natesan 2005), theory (Garza and Williamson 2001), and case studies (Cornuet and Luikart 1996;Beebee and Rowe 2001;Goossens et al 2006;Spear et al 2006) all show that this is the best method available for detecting recent, low-magnitude declines in N e . Simulation studies (Cornuet and Luikart 1996;Williamson-Natesan 2005) also demonstrate that this method has low type I error rates (i.e., falsely detecting a bottleneck when there is not one).…”

Extremely low genetic diversity and weak population differentiation in the endangered Colombian river turtle Podocnemis lewyana (Testudines: Podocnemididae)

“…The parallel application of all three methods allows exploration of bottleneck effects at a relative timescale (Spear et al 2006). This concept is based on the fact that the M-ratio recovers much more slowly than heterozygosity excess and rare allele distribution (Garza and Williamson 2001).…”