Demographic and descriptive studies at La Parguera, Puerto Rico.

The La Parguera facility was established in part to contrast the social behavior of free-ranging groups with that in enclosures, as well as to compare the seasonal events linked to reproduction with those at Cayo Santiago. Onset of breeding was correlated with onset of the rainy season at both sites. Male rank in new social groups was correlated with seniority, and males often joined groups containing older brothers. Dominant males had little influence on group movements or group rank. Maternal rank influenced the likelihood that male offspring would survive and reproduce: sons of dominant females had higher survival. High-ranking females and high-ranking groups produced more sons than daughters at birth. Observational techniques employed at La Parguera demonstrated the biases of using ad lib. field notes and the need to correct for observability of individuals as a function of their age, sex, and social rank. Although social behavior was qualitatively similar in enclosed and free-ranging groups, significant quantitative differences existed. During its 18 years of existence the La Parguera colony proved to be a fertile site for both descriptive and experimental studies. In this paper we briefly review behavioral and ecological findings from the free-ranging population, review the demographic analysis of a cohort of monkeys born early in the colony's history and followed until death, and, finally, focus on methodology in the study of free-ranging primates.

Effects of geographic transfer on the timing of seasonal breeding of rhesus monkeys.

This is a study of the effects of geographic transfer on the timing of seasonal breeding of free-living rhesus monkeys on Cayo Santiago and La Parguera islands in Puerto Rico. The results demonstrated a progressive shift in the breeding season of the transferred group. The full shift required a period of 2 years. Change from one environment to another produced shifts in onset of estrous. The explanation for this phenomenon proposes an interaction between the specific reproductive state of the female, which may or may not be sensitive to a particular environmental change, and the environmental variation which is correlated with onset of breeding.

Phenotypic differences in the GnRH neuronal system of deer mice Peromyscus maniculatus under a natural short photoperiod.

The neural mechanisms by which short photoperiod induces gonadal regression among seasonally breeding mammals are not well understood. One hypothesis suggests that the proximate cause of seasonal gonadal regression is a photoperiod-induced modification in GnRH secretion. This hypothesis is indirectly supported by our recent findings using immunocytochemistry which identified specific photoperiod-induced adjustments in the number and morphology of GnRH containing neurones between reproductively competent and reproductively regressed laboratory housed male deer mice. Herein, we report that the GnRH neuronal system is similarly affected in reproductively responsive and nonresponsive wild male deer mice Peromyscus maniculatus exposed to a natural short photoperiod. The distribution of immunoreactive (IR)-GnRH neurones was nearly identical in field caught animals and those housed under artificial photoperiod in the laboratory. Compared with reproductively nonresponsive males, reproductively responsive mice from the field population possessed a greater total number of IR-GnRH neurones, a greater number of IR-GnRH neurones within the lateral hypothalamus, and a greater proportion of bipolar IR-GnRH neurones. Each of these distributional and morphological characters was consistent with our findings in laboratory housed male deer mice exposed to an artificial short photoperiod. Taken together, these data underscore the validity of using an artificial photoperiod to evaluate seasonal adjustments in reproductive function in the laboratory.