Age‐Specific Weaning Success of Northern Elephant Seals in Relation to Previous Breeding Experience

Abstract

We studied the effect of age and previous breeding experience on the probability of successful reproduction in female northern elephant seals (Mirounga angustirostris). Reproductive data, collected over a 12—yr period, were analyzed by multiple logistic regression to describe the functional relationships among the variables. We also examined the relationships among age, experience, date of breeding, and reproductive success to determine if differences in timing explain age—specific productivity. Finally, we investigated the relationship among age, experience, and maternal behavior to determine if correlates of reproductive effort could be related to age— and experience—specific patterns of reproductive success. Reproductive success increased between the maternal ages of 3 and 7 yr and then levelled off, demonstrating an asymptotic relationship. However, the relationship between reproductive success and age, after statistically controlling for previous experience, showed instead that success increased linearly throughout an animal's lifetime. In contrast, after statistically controlling for age, reproductive success was related to experience in a parabolic fashion; success increased with experience for the first few breeding attempts, but declined later in an animal's reproductive lifetime. The effects of experience depended on age: among young animals experience was apparently beneficial, but among old animals greater experience was deleterious. These results suggest experience—related senescence. Timing of breeding was related to experience, rather than age, in a curvilinear fashion; arrival and parturition dates were later for inexperienced and very experienced females, and were earliest for moderately experienced animals. Young animals that gave birth later in the season experienced reduced reproductive success; we observed no such decline in older animals. Thus, among young females, arriving and giving birth earlier each year was adaptive. Aggressiveness and dominance increased with age and experience, but we were unable to separate the effects of age and experience. We contend that the experience—related drop in reproductive success reflects the cost of reproduction. Breeding at a young age and/or continuously appears to result in lower reproductive success later in life. Furthermore, curvature in age—specific reproductive success can be explained by experience—related senescence. This result has general applicability, suggesting that age—related senescence instead may be due to reproductive "burn—out". These results indicate that previous breeding experience and differences in individual quality do not explain the pattern of increasing reproductive success with age in northern elephant seals, and provide indirect support for the hypothesis that animals increase reproductive effort as they age to offset a concomitant decrease in residual reproductive value.

Maternal Traits and Reproductive Effort in Northern Elephant Seals

“…This pattern is not consistent with a fecundity trade-off based on energy costs of reproduction, which the present study suggests would be most likely found in young individuals. This pattern is more consistent with an increase in weaning success with maternal experience in young animals that appears to plateau and then decline for very experienced females (Sydeman et al 1991). This increase in reproductive performance with experience may be an important selective force for high levels of expenditure in young females, despite potential fitness costs.…”

The impact of maternal experience on post-weaning survival in an endangered arctic fox population

“…In a broad range of species, first-time breeding females not only give birth to fewer offspring than experienced females, but the survival of their offspring is lower (e.g. Sydeman et al 1991;Daunt et al 2007). The increase in offspring survival for experienced females has mainly been attributed to improved experience in food provisioning (Daunt et al 2007).…”

Annual and seasonal variation of survival rates in the garden dormouse (Eliomys quercinus)

“…Reasons for a higher juvenile mortality might be a greater predation risk because young animals are often less experienced and less able to escape, or they may be more sensitive to diseases or parasite infections. The decrease in survival probability with age (senescence) might arise from increased tooth wear (Gaillard et al, 1993), from cumulative effects of reproductive activities (Sydeman et al, 1991) or from deleterious mutations that have their effects later in life (Rose, 1991). Survival rates are typically different for the sexes if males have different life cycles than females.…”