Phytochemicals and reproductive function in wild female Phayre's leaf monkeys (Trachypithecus phayrei crepusculus)

Female reproduction is known to be influenced by food availability and its impact on energetic status. However, emerging evidence suggests that the phytochemical content of food may also be an important factor. Here, we investigated this hypothesis, presenting 20 months of data on fecal progestin (fP) patterns in wild female Phayre's leaf monkeys (Trachypithecus phayrei crepusculus). We examined whether (a) the availability of Vitex (a plant known to contain phytochemicals) might be linked to seasonal fP levels, (b) fP levels were associated with female reproductive performance, and (c) reproductive performance might also be linked with energetic status (as measured by physical condition). We collected fecal samples (N=2077) from 10 adult females to analyze estrogen (fE) and progestin (fP) metabolites, behavioral data from 7 cycling females to determine receptivity, and monthly data on Vitex availability and female physical condition. Seasonally elevated fP levels were found in all females, with higher levels when Vitex leaves and fruits were abundant. During the period of high progestins, females had longer cycle lengths and follicular phases, while receptive periods did not change. Nevertheless, when ovulations occurred, females were more likely to conceive. On the other hand, conceptions were also more likely when physical condition was improving, suggesting that the effects of phytochemicals and energetic status on reproduction may be difficult to separate. Although our results support the predicted effects of Vitex on endocrine and reproductive function, future studies with detailed feeding data and chemical analyses of plants are needed to confirm this finding.