Discovery of a New, Disjunct Population of a Narrowly Distributed Salamander (Taricha rivularis) in California Presents Conservation Challenges
A newly discovered population of Red-bellied Newts (Taricha rivularis) in the Stevens Creek watershed in Santa Clara County, California, represents a significant southerly range extension of this species, by approximately 130 km from the nearest records in Sonoma County, California. To investigate the origin of this population we sequenced two mitochondrial genes (ND1, cytochrome b) and one nuclear exon (POMC) from the Santa Clara County population and from the main portion of the range including Sonoma, Mendocino, and Humboldt Counties. Phylogenetic relationships, historical demography, and genetic diversity were used to infer the origin of the newly discovered population and to elucidate the evolutionary history of the species. This species exhibits the lowest genetic diversity of any salamander in coastal California, and we infer unique signatures of population expansion not found in sympatrically occurring salamander species. The newly discovered population, characterized by a ubiquitous mtDNA haplotype found throughout the main range, is not genetically divergent. Although we were unable to determine whether the Santa Clara population is natural or introduced, we consider it to be of potential conservation significance and to warrant management protection. Although it may be unconventional to protect a population that is possibly introduced, this newly discovered population might be a critical assurance colony that will aid in the long-term persistence of this declining species. Because T. rivularis lacks genetic variation, has a small geographic range, and has experienced high levels of habitat disturbance, we recommend that it receive protection throughout its range.Abstract
Map of Taricha rivularis occurrence and sampling localities. Yellow = vouchered records (from CAS and MVZ); Red = newly discovered population; Black triangles = location of genetic samples. The base map includes expert opinion range map of T. rivularis in orange (IUCN 2010) and the extent of coast redwood (Sequoia sempervirens) in dark green.
(A) A Taricha rivularis from the Stevens Creek watershed, Santa Clara County, (B) the characteristic black band across the vent; (C) a T. rivularis egg mass found in Stevens Creek; and (D) the portion of Stevens Creek where egg masses were found. (All photos: D. Portnik.)
A maximum-likelihood mitochondrial phylogram and haplotype network of the ND1 and cytb genes. Numbers above branches are Bayesian posterior probabilities, whereas numbers below are maximum-likelihood bootstrap percentages. Scale bar is representative of substitutions/site for the phylogram. Main range localities are depicted by grey circles and the Santa Clara County specimens by white circles. The mitochondrial allele network was constructed with statistical parsimony with a 95% connection significance. Unique haplotypes are separated by one mutational step, and black circles along connecting lines represent additional mutational steps. Shades of haplotypes correspond to the main range (grey) and Santa Clara County population (white).
The nucleotide diversity (π) and average number of within-population pairwise differences (K) of mtDNA data across four species in the genus Taricha. Error bars represent confidence intervals for each parameter. Calculations are based on a 773 bp fragment of cyt b for Taricha granulosa, Taricha sierrae, and Taricha torosa, whereas calculations for T. rivularis are based on 1347 bp of ND1 and 422 bp of cyt b.
Contributor Notes
