Comparative phylogeography of woodland reptiles in California: repeated patterns of cladogenesis and population expansion

Abstract

The ultimate goal of comparative phylogeographical analyses is to infer processes of diversification from contemporary geographical patterns of genetic diversity. When such studies are employed across diverse groups in an array of communities, it may be difficult to discover common evolutionary and ecological processes associated with diversification. In order to identify taxa that have responded in a similar fashion to historical events, we conducted comparative phylogeographical analyses on a phylogenetically and ecologically limited set of taxa. Here, we focus on a group of squamate reptiles (snakes and lizards) that share similar ecological requirements and generally occupy the same communities in the western USA. At a gross level, deep genetic division in Contia tenuis, Diadophis punctatus, Elgaria multicarinata, the Charina bottae complex, and Lampropeltis zonata are often concordant in the Transverse Ranges, the Monterey Bay and Sacramento-San Joaquin Delta region, and the southern Sierra Nevada in California. Molecular clock estimates suggest that major phyletic breaks within many of these taxa roughly coincide temporally, and may correspond to important geological events. Furthermore, significant congruence between the phylogeographies of E. multicarinata and L. zonata suggests that the succession of vicariance and dispersal events in these species progressed in concert. Such congruence suggests that E. multicarinata and L. zonata have occupied the same communities through time. However, across our entire multi-taxon data set, the sequence of branching events rarely match between sympatric taxa, indicating the importance of subtle differences in life history features as well as random processes in creating unique genetic patterns. Lastly, coalescent and noncoalescent estimates of population expansion suggest that populations in the more southerly distributed clades of C. tenuis, D. punctatus, E. multicarinata, and L. zonata have been stable, while populations in more northerly clades appear to have recently expanded. This concerted demographic response is consistent with palaeontological data and previous phylogeographical work that suggests that woodland habitat has become more restricted in southern California, but more widespread in the North during Holocene warming. Future phylogeographical work focusing on allied and ecologically associated taxa may add insight into the ecological and evolutionary processes that yield current patterns of genetic diversity.

Cryptic diversity and biogeographical patterns within the black salamander (Aneides flavipunctatus) complex

“…Many phylogeographic studies of species in California have found high levels of cryptic genetic structure, similar to what we found in A. lugubris [2,3,9,15]. Below we compare the geographic distribution of our mtDNA clades in relation to vicariance events, as well as to physical/climatic barriers to dispersal in other species.…”

“…California has been the focus of a large number of phylogeographic studies, largely because of the great diversity of species inhabiting the state and the complex geological processes active in the region [2][3][4]. The California floristic province has been designated as one of the world's top 25 hotspots of biodiversity and the state of California encompasses 70 % of this province [4,5].…”

High genetic diversity among fossorial lizard populations (Anniella pulchra) in a rapidly developing landscape (Central California)

“…Somewhat separate from the marine embayment, another historically important isolating barrier for small vertebrates in Central California is the Kern River (Jockusch et al 1998;Jockusch and Wake 2002;Feldman and Spicer 2006). The Kern River is one of the biggest rivers in the southern Sierra Nevada and used to empty into the San Joaquin embayment and, after the Pliocene, into the Buena Vista Lake.…”

“…A few reptile and amphibian species have genetic lineages endemic to Central California, e.g., Pacific pond turtles (Spinks and Shaffer 2005), alligator lizards (Feldman and Spicer 2006), and slender salamanders (Wake 2006), but it is not as common a pattern as the north-south break. Moreover, as far as we know, the presence of deep genetic lineages within the San Joaquin Valley and Carrizo Plain (lineages B and C) is a pattern unique to Anniella.…”

“…The purpose of the latter study was not a range-wide genetic survey, but rather to test the genetic distinctiveness and relationships of melanic populations such as the morphologically diagnostic subspecies A. p. nigra Fischer 1885. They did not examine samples from either side of the Transverse Ranges, a consistent species-level barrier for much of California's herpetofauna (Feldman and Spicer 2006;Rissler et al 2006).…”