Geology topics

R.S. Wagner

Publications and source records attributed to R.S. Wagner.

4 recordsLinked to original sources

USGS2006

Phylogeography and spatial genetic structure of the southern torrent salamander: Implications for conservation and management

The Southern torrent salamander ( Rhyacotriton variegatus ) was recently found not warranted for listing under the US Endangered Species Act due to lack of information regarding population fragmentation and gene flow. Found in small-order streams associated with late-successional coniferous forests of the US Pacific Northwest, threats to their persistence include disturbance related to timber harvest activities. We conducted a study of genetic diversity throughout this species' range to 1) identify major phylogenetic lineages and phylogeographic barriers and 2) elucidate regional patterns of population genetic and spatial phylogeographic structure. Cytochrome b sequence variation was examined for 189 individuals from 72 localities. We identified 3 major lineages corresponding to nonoverlapping geographic regions: a northern California clade, a central Oregon clade, and a northern Oregon clade. The Yaquina River may be a phylogeographic barrier between the northern Oregon and central Oregon clades, whereas the Smith River in northern California appears to correspond to the discontinuity between the central Oregon and northern California clades. Spatial analyses of genetic variation within regions encompassing major clades indicated that the extent of genetic structure is comparable among regions. We discuss our results in the context of conservation efforts for Southern torrent salamanders.

Oregon, Washington↗

USGS2006

Phylogeography and genetic identification of the newly-discovered populations of torrent salamanders (Rhyacotriton cascade and R. variegatus) in the central Cascades (USA)

Newly discovered populations of Rhyacotritonidae were investigated for taxonomic identity, hybridization, and sympatry. Species in the genus Rhyacotriton have been historically difficult to identify using morphological characters. Mitochondrial (mtDNA) 16S ribosomal RNA sequences (491 bp) and allozymes (6 loci) were used to identify the distribution of populations occurring intermediate between the previously described ranges of R. variegatus and R. cascadae in the central Cascade Mountain region of Oregon. Allozyme and mitochondrial sequence data both indicated the presence of two distinct evolutionary lineages, with each lineage corresponding to the allopatric distribution of R. cascadae and R. variegatus . Results suggest the Willamette River acts as a phylogeographic barrier limiting the distribution of both species, although we cannot exclude the possibility that reproductive isolation also exists that reinforces species' distributions. This study extends the previously described geographical ranges of both R. cascadae and R. variegatus and defines an eastern range limit for R. variegatus conservation efforts.

Washington↗

USGS2005

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

Endemic to Oregon in the northwestern US, the Oregon slender salamander ( Batrachoseps wrighti ) 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.

Conservation Genetics↗

USGS2001

Geographic variation and genetic structure in Spotted Owls

We examined genetic variation, population structure, and definition of conservation units in Spotted Owls ( Strix occidentalis ). Spotted Owls are mostly non-migratory, long-lived, socially monogamous birds that have decreased population viability due to their occupation of highly-fragmented late successional forests in western North America. To investigate potential effects of habitat fragmentation on population structure, we used random amplified polymorphic DNA (RAPD) to examine genetic variation hierarchically among local breeding areas , subregional groups , regional groups , and subspecies via sampling of 21 breeding areas (276individuals) among the three subspecies of Spotted Owls. Data from 11 variable bands suggest a significant relationship between geographic distance among local breeding groups and genetic distance (Mantel r = 0.53, P < 0.02) although multi-dimensional scaling of three significant axes did not identify significant grouping at any hierarchical level. Similarly, neighbor-joining clustering of Manhattan distances indicated geographic structure at all levels and identified Mexican Spotted Owls as a distinct clade. RAPD analyses did not clearly differentiate Northern Spotted Owls from California Spotted Owls. Among Northern Spotted Owls, estimates of population differentiation (F ST ) ranged from 0.27 among breeding areas to 0.11 among regions. Concordantly, within-group agreement values estimated via multi-response permutation procedures of Jaccard's distances ranged from0.22 among local sites to 0.11 among regions. Pairwise comparisons of F ST and geographic distance within regions suggested only the Klamath region was in equilibrium with respect to gene flow and genetic drift. Merging nuclear data with recent mitochondrial data provides support for designation of an Evolutionary Significant Unit for Mexican Spotted Owls and two overlapping Management Units for Northern and California Spotted Owls.

Conservation Genetics↗