Temporal changes in geographic range and population size of the Santa Cruz Black Salamander

Abstract

The Santa Cruz Black Salamander Aneides niger is a priority 3 California species of special concern with a restricted geographic range confined to the Santa Cruz Mountains. Anecdotal observations suggest that the species was relatively abundant in the early 1900’s, but it has become more difficult to find in the past few decades. To better understand if the species has undergone population size fluctuations, we analyzed mitochondrial and nuclear sequence data to examine levels of genetic variation, phylogeographic structure, and test for signatures of population size change. We then reconstructed the climatic suitability for the species to A) determine if past climate fluctuations could have influenced range size and genetic diversity, and B) to estimate the effects of future climate change on geographic range suitability as a proxy for possible future population size change. Genetic analyses detected low levels of genetic variation and a general lack of genetic structuring, suggesting a recent genetic bottleneck. While neutrality tests of individual loci were non-significant, skyline plot and isolation-with-migration analyses detected a relatively recent reduction in population size. These genetic results should be interpreted with consideration of the limited number of localities and individuals that have been sampled for this species. Climatic suitability for Santa Cruz Black Salamanders was much lower during the last glacial maximum, which could be the cause of the detected historical change in population size. Future projections of climatic suitability under a high emission scenario suggest a dramatic geographic range restriction to coastal areas. These projections highlight the need for the protection of coastal habitat patches to preserve existing coastal populations, and to maintain connectivity between coastal and inland habitats to allow the westward movement of populations and genes in response to climate change.