Toni Lyn Morelli

The rules of disengagement: takeovers, infanticide, and dispersal in a rainforest lemur, Propithecus edwardsi

Summary Dispersal is a critical issue for understanding various aspects of animal biology and for conserving endangered species. We investigated the conditions that determine dispersal in four groups of sifakas inhabiting Ranomafana National Park, Madagascar. Following this population for 22 years, we collected and analyzed data on birth, relatedness, immigration, dispersal and death of 77 sifakas. We predicted that dispersal would function to prevent inbreeding and occur seasonally to aid establishment in a group before the breeding season. We further predicted that immigrants would evict same-sex residents and immigrant males would commit infanticide to shorten interbirth intervals. Although most dispersal theories predict male-biased dispersal in mammals, both male and female sifakas dispersed at equal rates from their natal and breeding groups. Behaviourally and genetically, there was no evidence for inbreeding within this population; individuals never produced offspring with close relatives. Dispersal matched the strong seasonal pattern of reproduction. Immigration events were always associated with the disappearance of the group infant(s). As a result of infanticide by male immigrants, mothers came into estrus sooner; infanticide by female immigrants caused mothers to disperse from their groups. This study reveals a clear pattern of dispersal that is condition, not sex, dependent.

Morphometrics and pattern of growth in wild sifakas (Propithecus edwardsi) at ranomafana national park, madagascar

We summarize morphometric data collected over a period of 22 years from a natural population of rainforest sifakas (Propithecus edwardsi) at Ranomafana National Park, Madagascar, and we use those data to document patterns of growth and development. Individually identified, known‐age sifakas were successfully captured, measured, and released. We found that body segment lengths increased faster during growth than did body mass, with individuals attaining adult lengths earlier than adult mass. Females can begin reproducing before they are fully grown, but this may not be common. With the exception of hand length, we found no significant sex difference in any adult metric including body mass, chest, and limb circumferences, body segment lengths, and canine tooth height; however, body masses of individual females fluctuated more, independently of pregnancy, than did those of males. We found considerable interannual fluctuation in body mass with single individuals differing more within the same season in different years than from season to season in the same year. Such body mass fluctuation may be a consequence of eastern Madagascars variable and unpredictable environment in which rainfall during any selected month varies from year to year. Am. J. Primatol. 73:155–172, 2011.