No evidence for ovarian synchrony or asynchrony in hamadryas baboons

Abstract

The tendency for females to have synchronous or asynchronous ovarian cycles has been reported in several species, including hamadryas baboons, Papio h. hamadryas. Both fitness benefits and costs have been postulated for each condition; however, these remain to be demonstrated. Moreover, uncertainty remains about whether these ovarian cycle patterns are ‘real’ or an artefact of sampling and statistical design. We used a null model incorporating a bootstrap randomization procedure to examine whether ovarian cycles were more synchronous or asynchronous than expected by chance in a large captive hamadryas colony. Male contraception meant that all female colony members underwent repeated ovarian cycling throughout the 1-year study. No pairing or group of females had synchronous or asynchronous ovarian cycles. Rather, females oscillated between pseudosynchronous and pseudoasynchronous states, because ovarian cycle length varied between and within females. We outline why the absence of synchrony and asynchrony and variation in cycle length in this and other studies are explicable when one considers (1) the brief ovarian cycle bouts typical of natural fertility populations and (2) the type of synchrony or asynchrony measures that were employed. Furthermore, we demonstrate that while variation in ovarian cycle length appears to be ubiquitous among animals with these cycles, this does not rule out the possibility of synchrony and asynchrony occurring in natural fertility populations. Further research on this phenomenon in hamadryas and other species is justified, therefore, albeit with a focus on natural fertility populations and employing null-model techniques similar to that used here.