Population genetic structure at the northern range limit of the threatened eastern hog-nosed snake (Heterodon platirhinos)

Abstract

Habitat loss and fragmentation have important consequences for population persistence by reducing dispersal, connectivity, and population size. Characterizing patterns of population genetic structure and gene flow, and testing for the genetic signature of population declines and inbreeding can provide key insights into conservation for at-risk species. We use 12 microsatellite DNA markers to quantify the spatial structuring across two regional populations of the threatened eastern hog-nosed snake (Heterodon platirhinos) in Ontario, Canada. We further test for inbreeding and recent, rapid population declines, for the latter using both a 'heterozygosity excess' approach and Approximate Bayesian computation. Spatial Bayesian assignment tests revealed four distinct genetic clusters that were not apparent from species occurrence data, suggesting that the current designation of a single management unit for this species is invalid. We found some evidence for inbreeding in all studied locales. However, heterozygosity excess tests provided only weak evidence for recent bottlenecks and varied according to mutational model specified. In contrast, ABC provided strong support for a recent and rapid reduction in population size within one sample locale (Wasaga Beach), where individuals are largely confined to a small area circumscribed by expanding urban areas. For three other locales investigated, we found equal support for either recent rapid or gradual population declines. Immediate action is required for Wasaga Beach if this population is to persist.

Conservation genetics of the eastern yellow-bellied racer (Coluber constrictor flaviventris) and bullsnake (Pituophis catenifer sayi): River valleys are critical features for snakes at northern range limits

“…However, the level of connectivity to larger contiguous populations in the USA is unknown and requires further research. Similar to the situation with other northern snake populations (e.g., [ 14 , 15 ]), our findings suggest that population subdivision on a regional scale is an important consideration for conservation planning.…”

“…It is important to know whether this species needs to be managed as a single entity or multiple designatable units (DUs). Other recent studies have revealed critical mismatches between the number and extent of snake populations based on genetic markers, and the scale of conservation plans or management units (e.g., [ 15 , 52 ]). According to guidelines from the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), the advisory body to the federal Minister of the Environment, populations warrant separate DU status if they are both ‘discrete’ and ‘significant’ [ 53 , 54 ].…”

“…[ 12 ]). It is only recently that snake populations at range peripheries (e.g., [ 13 – 15 ]) or in extreme environments (e.g., [ 16 ]) have become the focus of conservation genetics studies. Conservation challenges may be exacerbated for populations at range peripheries, where extreme environments and naturally sparse distributions interact with anthropogenic activities to generate additional risk factors.…”