Phylogenetic Implications of mtDNA Sequence Variation in a Species of Peromyscus (Deer Mouse) Endemic to Islands in the Sea of Cortez  

     Sequence variation of a 1,439 base pair region (ND3/ND4L/ND4) of the mitochondrial genome of Peromyscus sejugis, a species of deer mouse endemic to two islands in the Sea of Cortez, was analyzed and compared to sequences of Peromyscus maniculatus coolidgei from Baja California and to Peromyscus keeni from the Pacific Northwest.  These sequences were compared in order to: test the genetic relatedness of P. sejugis and P. m. coolidgei, resolve the geographic origin of P. sejugis, and verify the apparent sister-group relationship between P. sejugis and P. keeni.   Three haplotypes were obtained for P. m. coolidgei with an overall sequence variation of 0.3%.  Two haplotypes were obtained for P. sejugis with an overall sequence variation of 0.7%.  Genetic distance between P. sejugis and P. m. coolidgei was 1.7%.  Phylogenetic and pairwise distance analyses place P. sejugis and P. m. coolidgei in a group that associates more closely to P. keeni than to central (WA. and CO.) P. maniculatus.  These data support the conclusion that P. sejugis is conspecific with, and is an island isolate of, what is currently recognized as P. m. coolidgei.  Additionally, the data support the geographically improbable sister-group relationship between P. sejugis/P. m. coolidgei and P. keeni and suggest that the deer mice from Baja California are specifically distinct from northern and centrally distributed populations of P. maniculatus.

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