Offspring size at weaning affects survival to recruitment and reproductive performance of primiparous gray seals

Abstract

Offspring size affects survival and subsequent reproduction in many organisms. However, studies of offspring size in large mammals are often limited to effects on juveniles because of the difficulty of following individuals to maturity. We used data from a long-term study of individually marked gray seals (Halichoerus grypus; Fabricius, 1791) to test the hypothesis that larger offspring have higher survival to recruitment and are larger and more successful primiparous mothers than smaller offspring. Between 1998 and 2002, 1182 newly weaned female pups were branded with unique permanent marks on Sable Island, Canada. Each year through 2012, all branded females returning to the breeding colony were identified in weekly censuses and a subset were captured and measured. Females that survived were significantly longer offspring than those not sighted, indicating size-selective mortality between weaning and recruitment. The probability of female survival to recruitment varied among cohorts and increased nonlinearly with body mass at weaning. Beyond 51.5 kg (mean population weaning mass) weaning mass did not influence the probability of survival. The probability of female survival to recruitment increased monotonically with body length at weaning. Body length at primiparity was positively related to her body length and mass at weaning. Three-day postpartum mass (proxy for birth mass) of firstborn pups was also positively related to body length of females when they were weaned. However, females that were longer or heavier when they were weaned did not wean heavier firstborn offspring.

Patterns of age‐related change in reproductive effort differ in the pre‐natal and post‐natal periods in a long‐lived mammal

“…Previous work across a variety of species has demonstrated that offspring weaning mass is positively associated with both juvenile survival (Wauters, Bijnens & Dhondt ; McMahon, Burton & Bester ; Ailsa, Bernie & Barker ; Côté & Festa‐Bianchet ; Proffitt, Garrott & Rotella ) and future reproductive success (Festa‐Bianchet, Jorgenson & Réale ; Bowen et al . ). Our results imply that the pups with the highest weaning mass are born to experienced, prime‐aged and older mothers with above‐average individual effect on parturition masses and daily mass gains through the lactation period.…”

The effect of prey quality and ice conditions on the nutritional status of Baltic gray seals of different age groups

“…Blubber thickness of hunted adult females also partly explained the variation in the birth rate of gray seal females (birth rate from Kauhala et al 2016: Table 2; r 2 = 0.53, F = 8.9, df = 1, 6, p = 0.024) in recent years. Nutritional status (or body mass) of female seals may thus have an impact on reproduction (age at sexual maturity, ovulation rate, implantation of embryos, and maintenance of pregnancy) of seal females (e.g., Boyd 1984;Boyd et al 1999;Harwood et al 2000;Bowen et al 2006Bowen et al , 2015.…”

“…Average thickness of the blubber layer in a population varies between years with environmental conditions and can be used as an index of nutritional status of seals. Blubber layer and weight of pups of the year are closely correlated to their subsequent first year survival (Hall et al 2001;Harding et al 2005) but also have delayed effects influencing age at sexual maturity and size at first parturition of female seals (Boyd et al 1999;Bowen et al 2015). Blubber thickness may also affect reproductive rate of mature females through implantation of embryos and fetal mortality (e.g., Boyd 1984).…”

The presence of the diagnostic character of the genus Paraleucilla (Amphoriscidae, Calcarea, Porifera) may depend on the volume and body wall thickness of the sponges

“…All models having a ∆AIC c <2 were considered as having some support, but we preferred models with the fewest parameters and the highest weight and, therefore, highest evidence ratio (Burnham & Anderson ; Bowen et al. ). The effect size ( r‐ value) was calculated using the z ‐statistic for each predictor variable, such that the covariates were taken into account.…”