High rates of extra-pair young in the pair-living fat-tailed dwarf lemur, Cheirogaleus medius

Cheirogaleids are one of the most primitive extant primate taxa in the worl d. Their lifestyle and mating system, therefore, have been considered to be representative for social systems in primate ancestors. Accepted models of social evolution in primates state that pair-bonding has evolved secondari ly from diurnal group-living taxa and should therefore be constrained prima rily to diurnal species. In contrast to these assumptions, the nocturnal fa t-tailed dwarf lemur (Cheirogaleus medius) lives in permanent pairs, with o bligate paternal care probably representing the evolutionary basis of pair- living. In this sociobiological field study, we analyzed the reproduction s trategy of C. medius in the tropical forest of western Madagascar. In the r ainy seasons from 1995 to 1999, 173 individuals of C. medius were captured and individually marked and 131 were genetically characterized through seve n microsatellite loci. Additionally, 36 of these individuals were radio-tra cked and observed. For 53 genotyped individuals, including 16 offspring, in formation about pair-bonding and family structure was known from field obse rvations. Genetic analyses revealed that yearlings and infants living with an adult pair were in all cases sibs of the social mother. However, C. medi us does not restrain from extra-pair copulations (EPCs) and a high rate of extra-pair paternity (44%) was detected. Males sired offspring with their f emale partners as well as with extra-pair females within the same year, ind icating that males may increase their reproductive success by EPCs without necessarily running the risk of cuckoldry. Females on the other hand do not seem to run the risk of reduced paternal care, either because males cannot detect relatedness of young, or because they might even increase their inc lusive fitness by raising offspring of closely related males. Since females reproduce preferentially with territory holders and no paternity could be assigned to floating males, superior genetic quality of the males might be crucial for female choice.