Cranial morphology of the California vole (Microtus californicus, Cricetidae) in a contact zone

Abstract

Zones of contact between divergent biological forms within or between species are critical to the study of speciation. How characters flow across contact zones can be informative of the speciation process. To better understand this phenomenon in a mammal, we investigated cranial shape change in a contact zone between northern and southern phylogeographical groups of California voles (Microtus californicus). We took 12 linear measurements of skulls, one measurement of the mandible, and coded the presence and absence of two skull foramina for 427 specimens. In multivariate analyses, skulls within parental regions were correctly assigned more than 90% of the time. In the contact zone, 49% were classified as northern and 51% as southern, with a bimodal distribution of posterior probability values. Foraminal patterns in the contact zone were intermediate between northern and southern regions. A cline analysis for coastal populations suggested a similar centre for mitochondrial and nuclear markers, although a centre for the morphological data was offset. Cranial morphology indicates an intermediate area with overlap between the two regions, as suggested by the molecular data, with a pattern distinct from mitochondrial DNA or nuclear DNA markers.

Mito‐nuclear discordance across a recent contact zone for California voles

“…Collection of tissue samples for M. californicus was conducted along a transect in California that extended from Monterey Bay (Monterey County) in the north to Irvine (Orange County) in the south. This transect consisted of 10 collecting localities that included the northern and southern lineages of this species as well as populations from the putative contact zone in Santa Barbara County (Conroy & Gupta, ; Conroy & Neuwald, ; Table and Figure ). Ten to 15 individuals were collected from each locality.…”

Robust discrimination ofReithrodontomys megalotisandR. montanus(Mammalia: Rodentia) from Colorado, using cranial morphology and external characteristics within age classes

“…Institution abbreviation: CMM ¼ University of Colorado Museum of Natural History. species (Ruedi 1995, Hoofer et al 1999, D'Anatro & Lessa 2006, Jansa et al 2008, Bachanek & Postawa 2010, Conroy & Gupta 2011, Shahabi et al 2011, and using this method, we were able to robustly differentiate between Colorado specimens of Reithrodontomys megalotis and R. montanus (Fig. 1).…”

Linking patterns of intraspecific morphology to changing climates

“…We address these questions by examining the California vole, Microtus californicus (Rodentia: Arvicolinae; Peale, 1848), an excellent study species because its teeth are abundant in the Quaternary fossil record and are identifiable to the species level using discriminant shape analyses (McGuire, 2011; McGuire & Davis, 2013). M. californicus is abundant in present‐day ecosystems of western North America (Conroy et al., 2016), where it influences the structure of ecological communities by differentially consuming plant species (Borchert & Jain, 1978; Conroy & Gupta, 2011) and serves as food for predators (Huntly, 1991). Prior research has found that precipitation is important for determining this species’ range (Church, 1966; McGuire & Davis, 2013), and this species generally lives in the drier regions of the west coast of North America.…”