Influence of maternal mass and condition on energy transfer in Weddell seals

Abstract

Summary1. Environmental variation influences food abundance and availability, which is reflected in the reproductive success of top predators. We examined maternal expenditure, offspring mass and condition for Weddell seals in 2 years when individuals exhibited marked differences in these traits. 2. For females weighing ≥ 355 kg there was a positive relationship between maternal post-partum mass (MPPM) and lactation length, but below this there was no relationship, suggesting that heavier females were able to increase lactation length but lighter females were restricted to a minimum lactation period of 33 days. 3. Overall, females were heavier in 2002, but in 2003 shorter females were lighter than similar-sized females in 2002 suggesting that the effects of environmental variability on foraging success and condition are more pronounced in smaller individuals. 4. There was no relationship between MPPM and pup birth mass, indicating prepartum investment did not differ between years. However, there was a positive relationship between MPPM and pup mass gain. Mass and energy transfer efficiency were 10·2 and 5·4% higher in 2002 than 2003, which suggests costs associated with a putatively poorresource year were delayed until lactation. 5. Heavier females lost a higher proportion of mass during lactation in both years, so smaller females may not have been able to provide more to their offspring to wean a pup of similar size to larger females. 6. MPPM had only a small influence on total body lipid; therefore, regardless of mass, females had the same relative body composition. Females with male pups lost a higher percentage of lipid than those with female pups, but by the end of lactation female pups had 4·5% higher lipid content than males. 7. It appears that for Weddell seals the consequences of environmentally induced variation in food availability are manifested in differences in maternal mass and expenditure during lactation. These differences translate to changes in pup mass and condition at weaning with potential consequences for future survival and recruitment.

Annual reproductive rates of Weddell seals in eastern Antarctica from 1973 to 2000

“…Phocid seals derive the majority of energy for lactation from maternal body stores (see Wheatley et al 2006). Thus there is potential to physiologically assess the probability of achieving viable weaning mass for each pup, during pregnancy, on the basis of maternal nutritional state (Trites & Donnelly 2003).…”

“…However, we suggest that Weddell seal investment is more prudent than simply randomly sampling a variable environment. Based on temporal variability in reproductive rate, combined with lack of evidence for costs of reproduction, we infer that Weddell seals prudently select years for reproduction, pre-empting challenging reproductive attempts.Phocid seals derive the majority of energy for lactation from maternal body stores (see Wheatley et al 2006). Thus there is potential to physiologically assess the probability of achieving viable weaning mass for each pup, during pregnancy, on the basis of maternal nutritional state (Trites & Donnelly 2003).…”

Scaling matters: incorporating body composition into Weddell seal seasonal oxygen store comparisons reveals maintenance of aerobic capacities

“…This study shows that despite the seasonal changes in Weddell seal activity budgets (Kooyman 1975;Castellini et al 1992a;Schreer and Testa 1996;Forcada et al 2012) and body condition (Wheatley et al 2006;Shero et al 2015), their ability to sustain aerobic metabolism while underwater as indicated by TBO 2 stores is conserved across the winter. Variation in O 2 stores was most strongly correlated with animal mass, and not season.…”

“…This comparison accounting for animal body composition is most physiologically relevant, as it tests whether there are differences in O 2 -storage capacities in the lean body compartment. Weddell seals exhibited a relatively small over winter increase in body condition (lipid increased by 6 %TBM) as compared to other marine mammal species and at different times of the year (i.e., lipid may decrease by 15 %TBM across lactation; Costa et al 1986;Beck et al 2003;Wheatley et al 2006;Crocker et al 2014). Still, these small changes in lipid stores were enough to bias interpretations of seasonal differences in TBO 2 stores, before including body composition in statistical models.…”

“…Because TBO 2 stores generally exhibit a linear relationship with body mass (Mass 1.0 ), whereas O 2 is depleted as an allometric function of Mass 0.75 (Kleiber 1947(Kleiber , 1975Kooyman 1989), larger animals tend to have disproportionately longer ADL times (Schreer and Kovacs 1997;Halsey et al 2006a, b). Further, O 2 is only stored in the lean body compartment, and therefore, the relationship of physiological parameters with animal size is complicated by extreme seasonal fluctuations in lipid stores (Costa et al 1986;Wheatley et al 2006;McDonald et al 2008;Crocker et al 2014).…”