THE EFFECT OF REPRODUCTIVE PERFORMANCE ON THE DOMESTICATION OF THE PRAIRIE DEERMOUSE, PEROMYSCUS MANICULATUS BAIRDII.

The use of wild animals in captivity presents a serious problem in regard to the adequacy of the sample of the species studied. A first generation captive-born stock that is representative of the species as it exists in nature must meet the following assumptions: 1) That the wild-caught parents of the first generation stock are representative of the species studied; that all individuals are equally susceptible to the capture technique and capable of being maintained under captive conditions. 2) That reproductive success among these wild-caught individuals in captivity does not differ systematically; that all normal individuals are equally as likely to bear and rear offspring in the new environment as in nature. Although assumption one has been studied by Young et al. (1952) and Wiegert and Mayenschein (1966), the following study is concerned with the second assumption. It is unlikely that the fitness-determining factors in captivity are the same as those in nature. Although fitness in captivity is to some extent determined by artificial selection, the number of descendants left by captive wild-caught individuals is often determined by factors not under man's control. Lerner (1958) has called this latter phenomenon "natural selection'' in captivity. Survival to sexual maturity is more certain in captivity than in nature. Hence, in regard to captivity the question is more often, "Will a wild-caught individual successfully bear and rear offspring?"rather than-"Will it live long enough to bear and rear offspring?" If either all or none of a given sample of wild-caught individuals produce offspring, assumption two is not violated. But if some of the individuals produce offspring and some do not, the offspring obtained may not be representative of the species, particularly in regard to the trait measured. These offspring may represent only a certain segment of the genetic variability present in nature if the parents possess some character(s) or trait(s) common to each other but not shared with the nonbreeders and vice versa. When brought into captivity the wildcaught animal is suddenly confronted with a host of new environmental stimuli foreign to its existence in nature. On one hand, provision for food, water, and shelter are no longer important to survival, but on the other hand, many potentially stressful circumstances are encountered. The reaction to handling and confinement to relatively small living quarters may, to a great extent, determine adjustment to captivity. Spatial confinement and the inability to avoid aggressive interactions with conspecifics can result in a basic reorganization of the social structure common to a given species in nature (Anderson, 1961; Davis, 1958; Crowcroft, 1955). No longer is the animal free to choose mates and, in many cases, attain the solitude necessary for the 1 This investigation was supported by Public Health Service Research Grant M-5643 from the National Institutes of Mental Health, Public Health Service. The author acknowledges the critical reading of the manuscript by John A. King. 2 Present address: Department of Forest Zoology, State University College of Forestry at Syracuse Universitv_ Syracuse. New York 13210.