The impact of alpha male replacements on reproductive seasonality and synchrony in white‐faced capuchins (Cebus imitator)

Abstract

Objectives Reproductive seasonality is typically associated with ecological factors, but it can also be related to social factors, such as alpha male replacements (AMR). Such events can produce distinct birth peaks outside of the ecological peak, potentially increasing hardship for mother and infant and ultimately reducing fitness. We examined the impact of AMRs on birth seasonality, birth synchrony, and infant survival in the Santa Rosa population of white‐faced capuchins (Cebus imitator). Materials and Methods We analyzed 33 years of data on seven capuchin groups to test whether AMRs and births occur seasonally and whether birth seasonality changes following AMRs. Using sliding window analysis, we tested whether ecological conditions predict births in future months. We also tested whether birth period affects infant survival and likelihood of infanticide. Results AMRs shift birth seasonality from the ecological birth peak in the early wet season (late May–July) to a social birth peak during the late dry season (March–May), but they do not affect synchrony. In addition, we found that being born in the social peak significantly decreases infant survival relative to individuals born in the ecological and nonpeak periods. Discussion These findings suggest that Santa Rosa's predictable seasons can provide conception cues for female capuchins, but AMRs disrupt this ecological timing of conceptions. We suggest the increased infant mortality associated with the social birth peak is related to seasonal factors, including water scarcity and varying resource availability, and increased risk of infanticide, as the social birth peak overlaps with the AMR peak.

Costs of male infanticide for female capuchins: When does an adaptive male reproductive strategy become costly for females and detrimental to population viability?

“…Why have more extreme counter‐strategies, such as spontaneous abortion (the “Bruce Effect”) or accelerated weaning, not evolved? Brasington (2020) concludes that accelerated weaning is likely not an effective strategy due to the capuchin female's long period of postpartum infertility (estimated to be 5–6 months in tufted capuchins; Recabarren et al, 2000). And while capuchins do appear to be likely candidates for evolving the Bruce effect (Zipple, 2019), a demographic inference approach to our study population undertaken by Brasington (2020) did not find evidence of reduced birth rates in the months following AMR, which would be an indicator of spontaneous abortions.…”

“…Brasington (2020) concludes that accelerated weaning is likely not an effective strategy due to the capuchin female's long period of postpartum infertility (estimated to be 5–6 months in tufted capuchins; Recabarren et al, 2000). And while capuchins do appear to be likely candidates for evolving the Bruce effect (Zipple, 2019), a demographic inference approach to our study population undertaken by Brasington (2020) did not find evidence of reduced birth rates in the months following AMR, which would be an indicator of spontaneous abortions. Similarly, during a recent period of extreme drought (2015–2016), capuchin females continued to produce offspring, nearly all (8/9) of which did not survive, whereas the sympatric spider monkey population did not produce a single infant during the same timespan (Campos et al, 2020).…”