![]() intermedius comprises 10 subspecies ( Benson, 1933 Dice and Blossom, 1937 Weckerly, 1983). intermedius habitat is largely discontinuous through most of its range. intermedius lives exclusively in rocky habitat across the southwestern deserts, and thus C. In particular, we have been interested in the evolution of color differences in response to local environmental conditions. The rock pocket mouse, Chaetodipus intermedius, provides an excellent system to study geographic variation in phenotype within a single species, and allows us to explore this variation in light of the underlying genetic structure of this species. Here, we focus on the extent to which phenotypic variation is correlated with local environmental conditions versus phylogenetic history. In other cases, pleiotropic effects of otherwise beneficial mutations may limit their spread. For example, young populations in new environments may not have had time to adapt to local conditions. On the other hand, populations may sometimes be constrained by their evolutionary history. It has long been appreciated that strong selection can lead to local adaptation, provided that it is not swamped by gene flow ( Haldane, 1948 Slatkin, 1985 Lenormand, 2002). One ongoing debate concerns the relative roles of deterministic evolutionary processes and historical contingency in shaping the outcome of evolution ( Travisano et al, 1995). As differences among species must initially occur as intraspecific polymorphism, understanding the causes of intraspecific variation can provide information about the origin of species-level differences. Together, the results suggest that color variation can evolve very rapidly over small geographic scales and that gene flow can both hinder and promote local adaptation.Ī central goal of developmental and evolutionary biology is to explain the morphological diversity observed across species. Finally, we raise the possibility that, in some cases, migration between populations of pocket mice inhabiting different lava flows may be responsible for similar melanic phenotypes in different populations. At a finer geographical scale, high levels of gene flow between neighboring melanic and light populations suggest the selection acting on color must be quite strong to maintain habitat-specific phenotypic distributions. Using Mantel tests, we show that there is no correlation between color variation and mtDNA phylogeny, suggesting that pelage coloration has evolved rapidly. Analyses of mtDNA sequences from these same individuals revealed strong population structure in this species across its range, where most variation (63%) was partitioned between five geographic regions. First, we quantified variation in pelage color ( n=107 mice) and habitat color ( n=51 rocks) using a spectrophotometer, and showed that there was a correlation between pelage color and habitat color across 14 sampled populations ( R 2=0.43). Here, we investigate whether phenotypic variation in color is correlated with local environmental conditions or with phylogenetic history. Rock pocket mice, Chaeotdipus intermedius, are an ideal system in which to study intraspecific phenotypic divergence because of the extensive color variation observed within this species. The Google Drive folder is set as “View Only” to save a copy of a document in this folder to your Google Drive, open that document, then select File → “Make a copy.” These documents can be copied, modified, and distributed online following the Terms of Use listed in the “Details” section below, including crediting BioInteractive.Elucidating the causes of population divergence is a central goal of evolutionary biology. Not all downloadable documents for the resource may be available in this format. ![]() The “Resource Google Folder” link directs to a Google Drive folder of resource documents in the Google Docs format. In an extension activity, students can use the accompanying spreadsheet to explore how the selection coefficient(s) influences the coat color phenotype of future generations. They then apply Hardy-Weinberg to data collected by Michael Nachman and his colleagues on the coat color of rock pocket mouse populations in Arizona and New Mexico. ![]() Students begin by watching the film and reviewing the basic principles of the Hardy-Weinberg theorem. Students apply the Hardy-Weinberg equation to real data collected on rock pocket mouse populations. This activity reinforces concepts of variation and natural selection covered in the short film Natural Selection and Adaptation.
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