| Summary: | Non-genetic influences of females on offspring phenotype are known as maternal effects. Maternal effects can influence offspring traits such as mass at birth and weaning, which can in turn affect offspring survival. Since survival ultimately affects fitness of parents and offspring, maternal effects on such traits are of particular interest. I examined maternal effects on offspring traits from birth through weaning in harbour seals (Phoca vitulina) on Sable Island, 1987--1996. I explored relationships between maternal mass at parturition, age, and pupping date on birth mass, growth rate, and weaning mass of offspring. Pupping date did not significantly affect pup traits. Maternal age and mass had significant effects, but their relative influence changed between birth and weaning. At birth, a female's age significantly affected birth mass, while maternal mass did not. Age effects on birth mass were significant only among young females. Reproductive experience of young females may have affected birth mass more than did age per se. During lactation, maternal mass at parturition had stronger effects on pup traits than did maternal age. Pups of large females had high growth rate and high weaning mass. Harbour seal females make brief foraging trips during lactation, thus their pattern of maternal care is intermediate between those of otariids and fasting phocids. As predicted, effects of mass at parturition on pup growth rate and weaning mass were weaker than in fasting phocids, and stronger than in otariids. Small females appeared to begin foraging earlier in lactation than did large females, and postnatal investment of energy was lower for small females. Thus maternal body mass in species that forage during lactation may affect maternal behaviour and limit maternal investment generally. Sexual selection theory predicts that in polygynous, sexually dimorphic species small, young females will bear fewer males than females, and that mothers will invest more energy in male offspring. In this study, sex ratio at birth did not vary with maternal age or mass. Birth mass was higher for males than females. Weaning mass was also higher for males, but this resulted from differences in birth mass, rather than differential maternal investment during lactation. At weaning, sex ratio did not differ from unity. Thesis (Ph.D.)--Dalhousie University (Canada), 1998.
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