Abstract
For mammalian males, copulating with females during ovulation is critical to
reproductive success. However male knowledge of ovulation may not always be
advantageous for females, as it could hinder mate choice or promote
harassment. White-faced saki monkeys live in variably monogamous and
polygamous social groups and hence females may have multiple motivations to
conceal ovulatory timing. White-faced sakis further show no obvious physical
or behavioral signs of ovulation, although they do use scent in a variety of
contexts, including sexual behavior. We collected data on three wild groups
of white-faced sakis at Brownsberg Naturepark, Suriname in order to assess
whether male copulations are coordinated with female ovulatory timing. We
recorded all occurrences of copulations and genital inspections, and
collected fecal samples from females which were radioimmunoassayed to obtain
estradiol and progesterone levels. We found that males copulated throughout
the female reproductive cycle, although the association between copulation
and reproductive state varied between dyads. Only one male–female dyad
showed significantly more copulations than expected during ovulation.
However four of five dyads copulated less than expected with pregnant
females, suggesting that males may be able to differentiate cycling from
non-cycling females. While genital inspections were distributed randomly
with regard to female reproductive state, the decision to copulate was not:
males were more likely to mate with both ovulating and cycling females than
with non-cycling females after genital inspection. Regardless, males were
not more likely to copulate with an ovulating vs. a cycling (non-ovulating)
female. These data indicate that while males may receive olfactory
information on female hormonal status, they do not make entirely accurate
decisions with regard to copulation timing. This inaccuracy may be due to
males' inability to detect ovulation, or alternately a lack of motivation to
limit copulations solely to conceptive periods. Pair familiarity and sexual
experience may also play a role in copulation accuracy.