The thermal consequences of primate birth hour and its evolutionary implications

Abstract

Most primates, including humans, give birth during the inactive phase of the daily cycle. Practical constraints therefore limit our knowledge of the precise timing of nocturnal birth in wild diurnal primates and so limit our understanding of selective pressures and consequences. We measured maternal core body temperature ( T b ) across 24 births in a population of wild vervet monkeys using biologgers. We identified distinct perturbations in T b during the birth period, including declining T b during labour and the rapid recovery of T b post-parturition. Vervet monkeys typically gave birth during their inactive phase in synchrony with the nadir of the maternal nychthemeral T b rhythm but also showed remarkable inter-individual variability in their absolute T b during birth. Our findings support the view that selection may have favoured a nocturnal timing of primate birth to coincide with lower night-time T b and environmental temperatures, which improve thermal efficiency during birth.

Mother–offspring conflict and body temperature regulation during gestation and lactation in a wild primate

“…Indeed, it has been published elsewhere that vervet monkey core body temperature patterns are influenced by a range of microclimate variables (Lubbe et al., 2014; Mathewson et al., 2020; McFarland et al., 2020), individual differences in activity and microclimate selection (e.g. resting, shade use, huddling, swimming: McFarland et al., 2015, 2020; Henzi et al., 2017), prevalence of fevers (McFarland et al., 2021) and patterns of parturition (McFarland et al., 2022).…”

“…Some of these changes might be underpinned by reduced reproductive outputs when current bet‐hedging trade‐offs between offspring survival and self‐maintenance fail. Such failure may not only result in terminated pregnancies or compromised parturition events (McFarland et al., 2022), but may also culminate in compromised maternal condition that may have more long‐term costs to individual‐ and population‐level reproductive success.…”

“…We used direct observations and distinct perturbations of T b to identify the dates of parturition (McFarland et al., 2022) and used these dates to define the gestation (i.e. date of parturition – 165 days) and lactation (i.e.…”

“…Such failure may not only result in terminated pregnancies or compromised parturition events (McFarland et al, 2022), but may also culminate in compromised maternal condition that may have more long-term costs to individual-and population-level reproductive success.…”

“…Given that the regulation of body temperature reflects not only the response of an individual to its external environment (Hetem et al, 2016;McFarland et al, 2015McFarland et al, , 2020, but also the maintenance of an internal environment that supports reproduction (Kozak, 1997), there is the additional possibility that patterns of body temperature regulation might provide useful information on a mother's ability to invest in her offspring. To date, maternal thermal homeostasis during gestation and lactation has been unexplored in wild primates (but see McFarland et al, 2022 for details of maternal body temperature during birth).…”