Abstract:
The relationship among many closely related rodent species is not completely
understood because it is primarily based upon morphological characters, which vary only
slightly among species. The accepted phylogenetic relationship between Sigmodon
hispidus, Peromyscus maniculatus, and Mus musculus indicates that S. hispidus and P.
maniculatus are more closely related to each other than either are to M. musculus. The purpose of my research was to study the developmental patterns of the three species of mice; S. hispidus, P. maniculatus, and M musculus and attempt to distinguish any similarities in ontogenic patterns that could be used to support or reject the known phylogenetic relationships. Laboratory-born neonates were collected from day 1 through day 21 after birth for each species. The neonates' tissues were cleared and the bones stained with an Alizarin Red S bone staining technique. The range of days of first appearance of calcification in the epiphyses, complete fusion between the epiphyses and the diaphysis, and complete calcification of the diaphysis of the long bones of the limbs were earlier in S. hispidus and P.maniculatus than in M musculus. The rates of decrease in the lengths of the epiphyseal plates and the rates of calcification of the diaphysis were faster in S. hispidus and P. maniculatus than in M musculus. On the other hand, the rates
of growth of the cranial bones and the rates of increase in the overall length of the long bones were fastest in M musculus, with P. maniculatus being the slowest. The similarity in the rates and timing of developmental events between S. hispidus and P. maniculatus, compared to M. musculus, supports the known phylogenetic relationship.
