Cytosystematics of the Peromyscus boylii species group with phylogenetic implications for the subgenus Peromyscus (Rodentia : Cricetidae)

Abstract

A description and analysis of differentially stained (G- and C-banded) chromosomes is provided for 12 described taxa in the Peromyscus boylii species group. Consistent with other species of Peromyscus, all boylii group taxa examined in this study have a diploid number of 48. Variation in the autosomal complement appears to be limited to the number of chromosomal arms (FN) and ranges from 47 to 78 for the specimens examined. Although small short arm additions of heterochromatin were observed in some taxa, chromosomal rearrangements in the boylii group primarily involved terminally positioned pericentric inversions. Karyotypic descriptions are, also provided for two apparently undescribed taxa related to the boylii group. One of these taxa was collected in Oaxaca and is karyotypically similar to examples of P. spicilegus. The other undescribed taxon was collected from Hidalgo and is karyotypically characterized by two pericentric inversion polymorphisms and an unusually large Y chromosome. Homology of chromosomal rearrangements, inferred from the G- and C-banded karyotypes, are used to construct systematic hypotheses within the boylii group. Whereas the cladistic analysis of the chromosomal data does not unequivocally support or refute Carleton's (1979) hypothesis that the group comprises two lineages, a hiatus represented by several chromosomal rearrangements delineates two species assemblages within the boylii group: one assemblage includes species allied with P. boylii, and the other includes species allied with P. aztecus. This chromosomal hiatus corroborates the cranial and phallic differences between the two assemblages reported by other authors (Carleton, 1979; Bradley and Schmidly, in press), and in conjunction suggest that the boylii group is probably polyphyletic. A cladistic analysis of the subgenus Peromyscus, which assumes the boylii group is polyphyletic, indicates that the boylii assemblage is phylogenetically allied with P. crinitus and P. hooperi, and that the aztecus assemblage is related to the leucopus species group. Based on biochemical and other evidence, a hypothesized relationship between the boylii assemblage of species and P. truei, P. gratus and P. difficilis (truei group) suggests that two major radiations occurred within the subgenus Peromyscus. One radiation appears to have included P. hooperi, P. crinitus and the boylii assemblage, and the other included the aztecus assemblage, and the leucopus, maniculatus, mexicanus, and melanophrys species groups.