Conflicting patterns of genetic structure produced by nuclear and mitochondrial markers in the Oregon slender salamander (Batrachoseps wrighti): Implications for conservation efforts and species management

Abstract

Endemic to Oregon in the northwestern US, the Oregon slender salamander (Batrachoseps wrighti= B. wrightorum) is a terrestrial plethodontid found associated with late successional mesic forests. Consequently, forest management practices such as timber harvesting may impact their persistence. Therefore, to infer possible future effects of these practices on population structure and differentiation, we used mitochondrial DNA sequences (cytochrome b) and RAPD markers to analyze 22 populations across their range. Phylogenetic analyses of sequence data (774 bp) revealed two historical lineages corresponding to northern and southern-distributed populations. Relationships among haplotypes and haplotype diversity within lineages suggested that the northern region may have more recently been colonized compared to the southern region. In contrast to the mitochondrial data, analyses of 46 RAPD loci suggested an overall pattern of isolation-by-distance in the set of populations examined and no particularly strong clustering of populations based on genetic distances. We propose two non-exclusive hypotheses to account for discrepancies between mitochondrial and nuclear data sets. First, our data may reflect an overall ancestral pattern of isolation-by-distance that has subsequently been influenced by vicariance. Alternately, our analyses may suggest that male-mediated gene flow and female philopatry are important contributors to the pattern of genetic diversity. We discuss the importance of distinguishing between these two hypotheses for the purposes of identifying conservation units and note that, regardless of the relative contribution of each mechanism towards the observed pattern of diversity, protection of habitat will likely prove critical for the long-term persistence of this species.

Geographic variation, genetic structure, and conservation unit designation in the Larch Mountain salamander (Plethodon larselli)

“…Clearly, by extension, the probability of observing 11 location-specific haplotypes (Table 1) becomes exceedingly small. Overall, this pattern is consistent with other genetic analyses of salamanders from the northwestern United States (e.g., Jockusch and Wake 2002;Mahoney 2004;Miller et al 2005) and suggests little contemporary gene flow among populations.…”

“…Amphibians often have specific ecological requirements and low dispersal rates that make them susceptible to fragmentation by historical and current processes (Blaustein et al 1994). Indeed, genetic studies of amphibians frequently reveal substantial cryptic genetic diversity attributable to the influence of vicariant events (Good and Wake 1992;Highton 1995;Jockusch 1996;Tilley and Mahoney 1996;Miller et al 2005). Therefore, to aid amphibian conservation efforts, it is important to understand the role of fragmentation in population differentiation and implement management plans that preserve within-species genetic diversity.…”

Range-wide phylogeographic analysis of the spotted frog complex (Rana luteiventris and Rana pretiosa) in northwestern North America

“…Although these two clades were well-supported, mean sequence divergence between them was only 0.74%, suggesting relatively recent divergence. These clades formed north-south phylogeographic breaks (albeit shallow breaks) as seen in many other species in the Cascade Range (Miller et al, 2005(Miller et al, , 2006aNielson et al, 2006;Steele and Storfer, 2006), although exact locations of these breaks vary. Interestingly, the Columbia River does not act as a barrier in R. pretiosa.…”

Mitochondrial DNA evolution in the Anaxyrus boreas species group

“…4). Other refugia in the Pacific Northwest have been proposed (e.g., Columbia River, McCusker et al, 2000 (fish); Miller et al, 2005;Wagner et al, 2005) and these too may have resulted in distinct northern and southern lineages of multiple species of plants, salamanders and newts (Soltis et al, 1997;Brunsfield et al, 2001;Steele and Storfer, 2006;Kuchta and Tan, 2005) and the distinct minor groups seen in A. boreas. A similar pattern of species with northern and southern populations is seen in the Sierra Nevada in frogs (Macey et al, 2001), salamanders (Moritz et al, 1992;Tan and Wake, 1995), and snakes (Rodrgíuez-Robles et al, 1999) as well as A. canorus (Shaffer et al, 2000;Stephens, 2001) which occurs in both the NW and SW clades.…”