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Evolutionary relationships among Peromyscus from the Georgia Strait, Gordon, Goletas, and Scott Islands of British Columbia, Canada Thomas, Barry

Abstract

My study is directed towards understanding the pattern of evolution taking place among populations of Peromyscus inhabiting the islands of British Columbia. A standard morphological approach, as veil as karyotype and reproductive isolation analyses, have shown that a taxonomic revision of this faunal group is desirable. I have proposed such a revision. A discriminant analysis utilizing morphological measurements reveals the existence of two distinctive phenotypes within the islands surveyed. Breeding studies, involving 78 pairs of insular Peromyscus, indicate that reproductive isolation exists between the two morph groups. Furthermore, when given the choice the large and small morph groups prefer the company of their own type. Extensive phallic variation occurs among island populations but no suggestion of taxonomic relationships are discernible. Karyotype analysis reveals that there are two distinct karyotypic patterns. The karyotype correlates with the two morphotype classifications. The large morph has a high number of metacentric chromosomes and the small morph has a low number. The high metacentric number karyotype is identical to that possessed by the morphologically similar Peromyscus sitkehsis known to inhabit the islands to the north of the.study group. Karyotype variation within each of the tvo major divisions is minimal. I have proposed that the karyotypic differences between these two morphs is significant at the species level. The large morph should be considered as P. sitkensis and the small phenotype should remain as P. maniculatus. The degree and rapidity of evolution within these Peromyscus populations requires a broadening in the scope of some subspecific taxa. Change in subspecific nomenclature has been indicated. Additional studies of Peromyscus upon the adjacent mainland and Vancouver Island are required before meaningful relationships can be expressed between insular and mainland groups at the subspecific level.

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