The influence of landscape on gene flow in the eastern massasauga rattlesnake (Sistrurus c. catenatus): insight from computer simulations

Abstract

Understanding how gene flow shapes contemporary population structure requires the explicit consideration of landscape composition and configuration. New landscape genetic approaches allow us to link such heterogeneity to gene flow within and among populations. However, the attribution of cause is difficult when landscape features are spatially correlated, or when genetic patterns reflect past events. We use spatial Bayesian clustering and landscape resistance analysis to identify the landscape features that influence gene flow across two regional populations of the eastern massasauga rattlesnake, Sistrurus c. catenatus. Based on spatially explicit simulations, we inferred how habitat distribution modulates gene flow and attempted to disentangle the effects of spatially confounded landscape features. We found genetic clustering across one regional landscape but not the other, and also local differences in the effect of landscape on gene flow. Beyond the effects of isolation-by-distance, water bodies appear to underlie genetic differentiation among individuals in one regional population. Significant effects of roads were additionally detected locally, but these effects are possibly confounded with the signal of water bodies. In contrast, we found no signal of isolation-by-distance or landscape effects on genetic structure in the other regional population. Our simulations imply that these local differences have arisen as a result of differences in population density or tendencies for juvenile rather than adult dispersal. Importantly, our simulations also demonstrate that the ability to detect the consequences of contemporary anthropogenic landscape features (e.g. roads) on gene flow may be compromised when long-standing natural features (e.g. water bodies) co-exist on the landscape.

Lack of detectable genetic differentiation between den populations of the Prairie Rattlesnake (Crotalusviridis) in a fragmented landscape

“…The lack of road fragmentation observed in the present study of the Prairie Rattlesnake differs from the pattern reported for the Timber Rattlesnake by Clark et al (2010) and other rattlesnake studies (e.g., DiLeo et al 2013) that showed significant subdivision associated with roads over a similar time frame. Despite using many of the same analyses as these previous studies, we found no clear evidence that roads (or any other obvious geographic features, e.g., cultivation) were restricting gene flow.…”

“…Reptiles, such as snakes, are known to suffer high mortality on roads (Rosen and Lowe 1994;Andrews and Gibbons 2005;Row et al 2007), but have received limited attention in the conservation genetic literature (Holderegger and Di Giulio 2010) until recently (Clark et al 2010(Clark et al , 2011DiLeo et al 2010DiLeo et al , 2013. Emerging information suggests that snakes may also be susceptible to genetic fragmentation by road networks, but the evolutionary consequences of fragmentation and its detectability with genetic markers may vary from species to species depending on key demographic and evolutionary parameters, such as effective population size (DiLeo et al 2010).…”

Applying landscape genetics to evaluate threats affecting endangered Atlantic salmon populations

“…proportions, counts, or densities) can be directly compared, with the caveat that relationships between genetic distance and environmental distance are assumed to be linear. Although landscape genetics would not be an appropriate method in situations where population decline was extremely rapid (given that there would not be adequate time for evolutionary effects to become detectable; Landguth et al 2010;Dileo et al 2013), it would be appropriate in the majority of situations where declines are observed for many years prior to their identification as a conservation concern, provided the same suite of threats are influencing populations over the entire time period. Although these analyses only provide a way to compare the influence and magnitude of threats relative to each-other among a group of watersheds (rather than developing predictive relationships between specific populations and a suite of threats), they appear to be a powerful basis from which to develop future research priorities and remediation strategies to address population declines.…”

“…Gene * Model|IBE). Here we used the IBE model only in order to avoid overestimating the effect of land use on gene flow, given that spatially correlated landscape features can mask or confound the independent contribution of contemporary land use effects on genetic distance (Dileo et al 2013). However, we recognize that essentially equivalent results could have been obtained in this study by controlling for IBD.…”

“…Such population-level responses to contemporary threats are expected to be relatively rapid. Simulation studies have found that contemporary landscape changes leading to reduced population connectivity are detectable from microsatellite variation in as little as 1-5 generations (longer if dispersal rates are extremely low), provided dispersal distances are sufficiently large (Landguth et al 2010) or population size is low (Dileo et al 2013). This suggests that the influence of recent threats on populations would be detectable even if the threats had been acting for a relatively short period of time.…”