Comments: The taxonomic and geographic relationships among P. maniculatus, P. oreas, and P. sitkensis on islands and the adjacent mainland in the Pacific Northwest have been poorly understood (Carleton 1989). Hogan et al. (1993) analyzed chromosomes, allozymes, and mtDNA of Pacific Northwest Peromyscus and concluded that P. oreas, P. sitkensis, P. maniculatus algidus, P. m. hylaeus, P. m. keeni, P. m. macrorhinus, and P. m. prevostensis should be recognized as members of the newly constituted species Peromyscus keeni; further, they suspected that P. m. carli, P. m. doylei, and P. m. triangularis also are members of Peromyscus keeni. Musser and Carleton (in Wilson and Reeder 2005) adopted this revision and assigned P. m. carli, P. m. doylei, and P. m. triangularis to P. keeni. Even with this split, P. maniculatus exhibits much morphological, biochemical, and chromosomal variation suggestive that more than one species is represented (Musser and Carleton, in Wilson and Reeder 2005).
Hogan et al. (1997) examined mtDNA variation in the P. maniculatus species group (P. maniculatus, P. keeni, P. polionotus, P. sejugis, and P. melanotis) and concluded that the group as currently recognized is polyphyletic, unless P. slevini is removed. Additionally, the phylogenetic analysis revealed that P. m. coolidgei is closer to P. sejugis than to the other examined subspecies of P. maniculatus. "The systematic integrity of P. maniculatus is further complicated by the sister-species relationship between keeni and P. sejugis-P. m. coolidgei. These relationships suggest either a high degree of lineage sorting within P. maniculatus or that some of the currently recognized subspecies may be distinct species." Further taxonomic study is needed (Baker et al. 2003; Musser and Carleton, in Wilson and Reeder 2005).
Rapid phenotypic change can occur in long-established island populations, and temporal stability of morphological characters in such populations, even over short time periods (< 100 years) cannot be assumed (Pergams and Ashley 1999).