Manipulation of sex ratio at birth and maternal investment in female mouse lemurs (Microcebus murinus, Primates)

The lesser mouse lemur, a polygynous prosimian primate, demonstrates significant bias of sex ratio at birth in agreement with the predictions of the Local Competition Resource model for adaptive adjustment of sex ratios. When isolated prior to conception, females overproduced daughters while grouped females demonstrated a significant inverse tendency. Biased sex ratios were dependent neither on mother's body condition nor on litter size, suggesting that bias occurred at conception. The maternal investment allocated to offspring in terms of foetal growth, infant growth and survival until weaning did not differ according to the sex of newborn. Nevertheless, male newborn promoted maternal behaviour during early infancy (from birth to day 15) since in litters without males, survival and growth of neonate females significantly decreased. In mouse lemurs, social communication primarily relies on olfactory cues and significant biased sex ratios can be obtained by exposing isolated females to urinary cues from other females. Urinary stimulation was delivered from the beginning of sexual activity until oestrus. The direction of bias depended upon the temporal occurrence of chemical signal exposure, while female fecundity depended upon its duration. Possible mechanisms involved in sex biased conception are discussed. (C) 1997 Elsevier Science B.V.