Sexes in sync: phenotypic plasticity, sexual selection and phenological synchrony between the sexes in a wild hibernator

Abstract

Desynchrony of phenological responses to climate change is a major concern for ecological communities. Potential uncoupling between one of the most fundamental divisions within populations, males and females, has not been well studied. To address this gap, we examined sex-specific plasticity in hibernation phenology in two populations of Columbian ground squirrels ( Urocitellus columbianus ). We find that both sexes display similar phenological plasticity to spring snowmelt dates in their timing of torpor termination and behavioural emergence from hibernation. As a result of this plasticity, the degree of protandry (i.e. males' emergences from hibernation preceding those of females) did not change significantly over the 27-year study. Earlier male behavioural emergence, relative to females, improved the likelihood of securing a breeding territory and increased annual reproductive success. Sexual selection favouring earlier male emergence from hibernation may maintain protandry in this population, but did not contribute to further advances in male phenology. Together, our results provide evidence that the sexes should remain synchronized, at least in response to the weather variation investigated here, and further support the role of sexual selection in the evolution of protandry in sexually reproducing organisms.

Evolutionary trade-offs in dormancy phenology

“…Females, on the contrary, are not subject to intraspecific competition for reproduction and may have sufficient time before (generally one week after emergence) and during the breeding period to improve their body condition. Protandry may also allow the maturation of the reproductive system or monopolization of territories (Barnes et al 1988, Millesi et al 2008b, Thompson et al 2023). In addition, protandry decreases in species living in cold environments and in species with lower male body mass in accordance with the physiological contraints hypothesis.…”

“…Cricetus cricetus , protandry: 20 day, Siutz et al, 2016). Early emerging males may benefit from consuming higher quality food or in competition with other males (e.g., dominance assertion or territory establishment, Manno and Dobson 2008, Thompson et al 2023).…”