Genetic Variation and Systematics of Four Species of Mice of the Peromyscus Boylii Species Group

Kilpatrick, C. William, and Earl G. Zimmerman (Department of Zoology, University of Vermont, Burlington, Vermont 05401 and Department of Biological Sciences, North Texas State University, Denton, Texas 76203) 1975. Genetic variation and systematics of four species of mice of the Peromyscus boylii species group. Syst. Zool. 24:143-162.The genetic structure of 52 natural populations of four species (P. attwateri, P. boylii, P. pectoralis, and P. polius) of the Peromyscus boylii species group was analyzed through application of chromosomal and electrophoretic techniques. Only slight or no chromosomal variation was observed in three species (attwateri, pectoralis, and polius), but considerable chromosomal variation occurred among populations of P. boylii. Chromosomal evidence indicated that gene flow occurred between two of the chromosomal forms of P. boylii (spicilegus and rowleyi). Analysis of electrophoretic variation in proteins encoded by 17 structural loci of populations of P. boylii, consisting of eight chromosomal forms, indicated that these forms of P. boylii form a conspecific unit. Populations of P. attwateri were genetically distinct from other members of this group, thus supporting the specific status of this form. Examination of specific loci for allelic homology indicated that P. attwateri probably arose from P. boylii. A sample of P. polius suggested that the affinities of this species are with the boylii group. Populations of P. pectoralis demonstrated very low levels of genetic similarity with other members of this species group suggesting that the affinities of P. pectoralis may lie with other forms of Peromyscus. [Genetic variation; Peromyscus. ] The Peromyscus boylii species group is comprised of nine species ranging from Honduras northward to Oregon and Utah and eastward to the Ozark Mountains in Missouri and Arkansas. Although the species of the boylii group are morphologically distinct, they constitute a reasonably compact group which probably stemmed from a single ancestral stock (Hooper, 1968). Peromyscus boylii has the largest geographic distribution, with twelve geographic races being currently recognized. Data have accumulated indicating that some of these forms occur sympatrically without losing their respective identities (Hooper, 1968), suggesting P. boylii is not a conspecific unit. Recent studies of chromosomal variation in the boylii species group have revealed markedly different karyotypes in allopatric populations of P. boylii (Lee et al., 1972; Schmidly and Schroeter, 1974), adding support that all populations currently recognized as P. boylii are not conspecific. The evolutionary significance of these chromosomal patterns in P. boylii is not presently known, but in one case (attwateri) there is evidence for elevation to specific status (Lee et al., 1972). Schmidly and Schroeter (1974) present chromosomal data to indicate that gene flow may occur between certain chromosomal forms of P. boylii. This study was concerned with populations of four species of the boylii species group which occur in northern and central Mexico and parts of the southern United States (New Mexico, Utah, Texas, Oklahoma, and Kansas). Populations of P. polius, P. attwateri, all the recognized subspecies of P. pectoralis, and six subspecies of P. boylii (rowleyi, utahensis, levipes, ambiguus, spicilegus, and beatae) were examined utilizing karyological and electrophoretic techniques. Working on the assumption that the sample of loci controlling the proteins examined electrophoretically was representative of the genome (Hubby and Throckmorton, 1968) it was possible to