The largest relative testis size among primates and aseasonal reproduction in a nocturnal lemur, Mirza zaza.

OBJECTIVES Testis size is an indirect indicator of a species' mating system, along with sexual size and canine dimorphism, existence and usage of mating and advertisement calls as well as the spatial distribution of males and females ready to mate in solitary species. Upon its recent discovery, the northern giant mouse lemur Mirza zaza was suggested to have a polygynandrous mating system and to exhibit seasonal breeding. We tested these predictions in a field study in Sahamalaza National Park, NW Madagascar. MATERIALS AND METHODS We caught 12 M. zaza, before and during the suggested mating period and obtained standard field morphometric measurements, including testes size. RESULTS We show that M. zaza has the highest relative testis volume among primates, indicating strong sperm competition and polygynandrous mating. In addition, based on inferred age of captured animals, observed mating behavior, a female caught in met-estrus and data from captivity, we suggest M. zaza to be one of the few lemurs that breed aseasonally. DISCUSSION Future field work on this endangered species is required to illuminate the causes and consequences of intense promiscuity and aseasonal breeding despite strong habitat seasonality, which distinguish M. zaza from most other nocturnal lemurs.