Therefore, there should be other processes capable of maintaining this pattern of geographic and genetic differentiation. A similar pattern is observed in the western slope of the Andes (OCA), but with no vicarious events reported. Generally, the cause to explain this pattern (geographic and genetic) has been the existence of a geographic barrier located at the center of the peninsula in the form of a trans-peninsular marine channel, although its empirical evidence has been questioned. In the Baja California Peninsula (PBC), there is a pattern of intraspecific genetic differentiation that separates the geographic distribution of different species into two lineages, one in the northern half and the other in the southern half. POCKET MOUSE IN DESERT DRIVERSSeveral causes have been proposed as drivers of speciation, from the presence of physical barriers to the emergence of ecological barriers that limit genetic exchange between populations. Intraspecific genetic differentiation, including its causes, geographic expression, and relationship with the emergence of new species, is a central topic in ecology. Furthermore, the ENM for the Mojave clade in particular indicates retention of suitable habitat during the LGM in small isolated patches within northern areas, consistent with the haplotype network that supports the perspective that some populations from the Mojave clade were isolated within northern refugia during the last glacial period. Models for the LGM indicate broad retention of potential habitat within the area of contact among the major clades. The ENMs for each clade indicate differences in predicted current geographic distributions as well as distributions during the LGM. penicillatus, and project these models onto reconstructions of climatic conditions during the latest glacial maximum (LGM 18,000–21,000 years ago). We develop ecological niche models (EMNs) for the major lineages of C. The secondary contact among the major clades appears to have some longevity, with little evidence of recent, postglacial range expansion. Based on rough estimates for rates of sequence evolution, divergence among the major clades appears to have occurred during the Pleistocene, but well before the latest glacial maximum. stephensi and in populations from the western Mojave Desert in the northern range of C. Northern clade haplotypes occur in populations within the ranges of C. pricei and extend to the northwestern edge of the Sonoran Desert within the southern range of C. Outside this zone of mtDNA clade overlap, Sonoran clade haplotypes occur in populations from across the range of C. These clades broadly overlap along the Lower Colorado River valley and adjacent desert regions across most of the range of C. We identify 2 major monophyletic mtDNA lineages (clades) roughly centered in the Mojave and Sonoran deserts. penicillatus by sequencing regions of mtDNA for 220 individuals from 51 locations representing all continental subspecies. We investigated phylogeographic structure in C. Subsequent genetic assessments using chromosomal, allozymic, and mitochondrial DNA (mtDNA) sequence data detected a general east–west divergence centered on the Colorado River, but few locations were included in these assessments. The most thorough morphological assessment within the species noted variable levels of distinctiveness, leading to uncertainty regarding the geographic distributions of subspecies. The desert pocket mouse (Chaetodipus penicillatus) comprises 6 nominate subspecies that occupy warm, sandy desert-scrub habitats across the Mojave and Sonoran deserts.
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