North‐facing slopes and elevation shape asymmetric genetic structure in the range‐restricted salamander Plethodon shenandoah

Abstract

Species with narrow environmental tolerances are often distributed within fragmented patches of suitable habitat, and dispersal among these subpopulations can be difficult to directly observe. Genetic data can help quantify gene flow between localities, which is especially important for vulnerable species with a disjunct range. The Shenandoah salamander ( Plethodon shenandoah ) is a federally endangered species known only from three mountaintops in Virginia, USA. To reconstruct the evolutionary history and population connectivity of this species, we generated both mitochondrial and nuclear data using sequence capture from individuals collected across all three mountaintops. Applying population and landscape genetic methods, we found strong population structure that was independent of geographic distance. Both the nuclear markers and mitochondrial genomes indicated a deep split between the most southern population and the genetically similar central and northern populations. Although there was some mitochondrial haplotype‐splitting between the central and northern populations, there was admixture in nuclear markers. This is indicative of either a recent split or current male‐biased dispersal among mountain isolates. Models of landscape resistance found that dispersal across north‐facing slopes at mid‐elevation levels best explain the observed genetic structure among populations. These unexpected results highlight the importance of incorporating landscape features in understanding and predicting the movement and fragmentation of this range‐restricted salamander species across space.

Abiotic and biotic factors reduce the viability of a high‐elevation salamander in its native range

“…In this system, Griffis and Jaeger (1998) described higher colonization of range-edge habitats by P. shenandoah when P. cinereus was experimentally removed, which may result in our overestimating population viability under the biotic model. However, both north-facing aspects and elevation appear to be barriers for genetic exchange; populations are genetically distinct (Mulder et al, 2019), suggesting that dispersal (and population recovery)…”

rspatialdata: a collection of data sources and tutorials on downloading and visualising spatial data using R

“…35 As another example, researchers also have been using elevation data as a complementary source of information in the analysis of species connectivity through genetic structure. 36,37 For retrieving elevation data from many different regions, one may choose to work with the the elevatr package. 38 elevatr provides access to elevation data from several web services including the Amazon Web Services Terrain Tiles, 39 the Open Topography Global Datasets API, 40 and the USGS Elevation Point Query Service.…”

“… 35 As another example, researchers also have been using elevation data as a complementary source of information in the analysis of species connectivity through genetic structure. 36 , 37 …”

Physical and ecological isolation contribute to maintain genetic differentiation between fire salamander subspecies

“…Other environmental features, and the scale (spatial or temporal) at which they act, can also help to explain observed patterns of genetic differentiation (see for details Epps and Keyghobadi 2015;Winiarski et al 2020). Some examples include physical isolation driven by the barrier effect of mountain ridges (Sanchez-Montes et al 2018), exposure to wind, which is known to significantly constrain the movement of S. salamandra even in less exposed landscapes (Lourenço et al 2019), or less obvious factors such as the orientation of mountain slopes, that affects overall patterns of humidity and temperature (Mulder et al 2019). Also, ecological isolation driven by landscape factors rather than the climatic factors (and elevation) explored in this study could play an important role, including the type of water bodies available for breeding and development (e.g., lotic vs. lentic, persistent vs ephemeral) or vegetation cover (e.g., deciduous, coniferous, mixed and shrublands).…”