CHROMOSOMAL HOMOLOGY AND DIVERGENCE BETWEEN SIBLING SPECIES OF DEER MICE: PEROMYSCUS MANICULATUS AND P. MELANOTIS (RODENTIA, CRICETIDAE).

Abstract

From a chromosomal standpoint, speciation in the Peromyscus maniculatus complex has been accompanied by considerable change in the number of arms in the autosomal complement. This report is concerned with a determination of the chromosomal homologies and types of chromosomal rearrangements between two members of this complex, P. melanotis and P. maniculatus, as determined by Gand Cband comparisons. This study was undertaken to document the level of chromosomal evolution that is characteristic of some sibling species as well as to provide some insight into the evolutionary history of these two species. The diploid number for all species of Peromyscus thus far described is 48. Numerous authors have, however, documented extensive chromosomal variation dealing with the number of chromosome arms in Peromyscus (Hsu and Arrighi, 1966; Ohno et al., 1966; Singh and McMillan, 1966; Sparkes and Arakaki, 1966; Hsu and Arrighi, 1968; Arakaki et al., 1970; Te and Dawson, 1971; Bradshaw and Hsu, 1972; Lee et al., 1972; Bowers et al., 1973; Pathak et al., 1973; Arrighi et al., 1976; Schmidly and Schroeter, 1974; Murray and Kitchin, 1976). Hsu and Arrighi (1968) described the karyotype for 19 species of Peromyscus and reported both interand intraspecific variation of 56-96 in the total number of chromosome arms. Bradshaw and Hsu (1972) documented chromosomal variation in 15 subspecies of P. maniculatus and suggested that where dual modes were evident such as in P. m. rufinus of southeastern Arizona that these populations might be representative of another species (e.g., P. melanotis). Bowers et al. (1973) and Bowers (1974) have shown by karyotypic, electrophoretic, and breeding data that this is indeed the case. It has been most convenient and practical to describe chromosomal variation in Peromyscus in terms of the number of biarmed versus the number of acrocentric elements in the autosomal complements, although in some cases it is difficult to separate the two categories. Bradshaw and Hsu (1972) chose to describe variation in P. maniculatus in terms of the number of biarmed elements in the autosomal complement, whereas Bowers et al. (1973) chose to employ the number of autosomal acrocentrics for their descriptions. We have chosen the latter for our discussion. A summary of the current view of chromosomal variation in P. maniculatus is presented in our discussion.