DOES THE CHITTY EFFECT OCCUR IN PEROMYSCUS

I tested for the ''Chitty Effect'' in white-footed mice, Peromyscus leucopus, by looking for the presence of a large-bodied, dominant, genetic morph in peak populations. Large-sized animals were present primarily during high, but not low, densities. However, large-sized males nested with females less often than did small males and they were not dominant to small males. Body mass of offspring was not correlated with that of their mothers, and thus, large size was not a unique genetic morph. Large-sized animals were older than small animals having survived through two breeding seasons under conditions of high availability of food. The occurrence of large-sized animals in this fluctuating population of Peromyscus was similar to that proposed by Chitty (1958, Cold Springs Harbor Symposium on Quantitative Biology, 22:99-113) for microtines, but whether it was analogous or not may be conjectural until comparable studies are conducted on Microtus.