Genetic tools illuminate reproductive strategies of gray mouse lemurs (Microcebus murinus) Manfred Eberle1 and Peter M. Kappeler1,2 1Department of Behavioral Ecology & Sociobiology, German Primate Center, Germany, 2Department of Sociobiology/Anthropology, University of Göttingen, Germany Abstract Performing reliable tests on causes and consequences of mating strategies necessitates an intimate knowledge of the players involved and their genetic relationships. We compiled a precise genetic database of more than 400 animals of a wild population of gray mouse lemurs in Kirindy Forest in western Madagascar. We used this detailed genetic data basis together with field observations for analyses of reproductive strategies. Gray mouse lemurs are small omnivores that spend the majority of their nocturnal activity foraging alone. During the day, they rest in hollow trees and females usually form sleeping groups while most males sleep alone. They are characterized by seasonal reproduction, large testes and a high degree of home range overlap within and between the sexes. This combination of traits suggested scramble competition polygyny and the potential for cooperatively breeding females. We captured animals on a regular basis since 1994, and determined the genetic relationships among all animals using 4 microsatellite markers from the literature and 13 newly developed markers. We performed observations with the help of radio-tracking and video techniques and determined sleeping sites and the composition of sleeping groups regularly. Our study revealed that – despite suggestive evidence for scramble competition polygyny – male reproductive success was determined by both finding ability and contest competition. Heavier males and males that mated relatively early had a higher reproductive success. However, most litters had mixed paternities, indicating a relatively low overall monopolization potential, determined by a highly male-biased operational sex ratio and female choice for multiple matings. Females raised their young cooperatively in groups of close relatives. Although they discriminate offspring, they regularly groomed and nursed young of relatives and even adopted related orphans. These results and conclusions regarding reproductive success and cooperation among close relatives were only possible due to a detailed knowledge of genetic relationships.