Variation and Evolution of Gulf Coast Populations of Beach Mice, Peromyscus polionotus

Abstract

Inadequate taxonomic research has resulted in misinterpretation of the course of evolution in these beach mice. Five new subspecies are here described. Pelage patterns are described and in the case of the three primary hair-tip rump patterns, preliminary results of laboratory breeding experiments are given, along with a model based on four postulated genes. Basal-hair melanin patterns appear to be under separate control from the hair-tip xanthophyll pigment patterns. Disharmonious interactions between two presumed phylogenetic lines with different hair-base patterns are described and discussed. Zonal variance in width of dorsal body pigment in certain specimens is attributed to epigenetic interaction during molt and an approximate molt sequence is given. Variations in color, relative paleness, and body dimensions are also discussed. Polymorphism occurs in some subspecies. Several of the pelage pattern traits that characterize different beach mouse populations have been discovered also in occasional specimens of P. maniculatus, and it is believed that many, if not all of the genes responsible for pigment reduction in intensity and extensity in the beach mice, were already present before the species came in contact with the beach dune habitat. Evolutionary sequences are discussed and certain partial reproductive barriers are noted. The species appears to be in process of splitting into two species along a line initiated by a topographical barrier during the Yarmouth interglacial stage of the Pleistocene. The two ends of a circular overlap appear to be sympatric, and a partial break in the middle of the chain of subspecies is also manifest.