The American pika (Ochotona princeps) is a small, winter-active mammal inhabiting alpine environments. For alpine mammals, metabolic heat production and cellular mechanisms to cope with hypoxia are critical for survival and reproduction. Thus, because of the pikas' long association with alpine environments, they may have genetically adapted to alpine conditions. Here, we present evidence for positive selection acting at 2 loci within the Ochotona genome. These loci were identified by first assembling a list of 50 candidate genes and collecting sequence data from 2 O. princeps draft genomes available from public databases. We then tested the possibility that positive selection acted on the Ochotona lineage, relative to other mammalian species, using the CODEML program in the PAML package. These analyses indicated positive selection at 4 loci—insulin-like growth factor 1 gene (IGF-1), enoyl-CoA hydratase/3-hydroxyacyl CoA dehydrogenase (EHHADH), inducible nitric oxide synthase 2 (NOS2), and transforming growth factor beta 1 gene (TGF-β1). To test this assumption further, we collected DNA sequence data from the 4 genes of interest from multiple O. princeps individuals across a broad geographic range, as well as individuals from the congeneric collared pika (O. collaris). We used multiple interspecific and intraspecific polymorphism-based tests to test the resulting sequence data for patterns of non-neutral evolution. These tests provide additional support for positive selection acting on the IGF-1 and EHHADH loci.
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Vol. 98 • No. 4