Abstract:
Population-level shifts in reproductive phenology in response to environmental
change are common, but whether individual-level responses are
modified by demographic and genetic factors remains less well understood.
We used mixed models to quantify how reproductive timing varied across
1772 female southern elephant seals (Mirounga leonina) breeding at Marion
Island in the Southern Ocean (1989–2019), and to identify the factors
that correlate with phenological shifts within and between individuals. We
found strong support for covariation in the timing of breeding arrival dates
and the timing of the preceding moult. Breeding arrival dates were more
repeatable at the individual level, as compared with the population level,
even after accounting for individual traits (wean date as a pup, age and breeding
experience) associated with phenological variability. Mother–daughter
similarities in breeding phenology were also evident, indicating that additive
genetic effects may contribute to between-individual variation in breeding
phenology. Over 30 years, elephant seal phenology did not change towards
earlier or later dates, and we found no correlation between annual fluctuations
in phenology and indices of environmental variation. Our results show how
maternal genetic (or non-genetic) effects, individual traits and linkages
between cyclical life-history events can drive within- and between-individual
variation in reproductive phenology.
