Maternal effects on offspring growth rate and weaning mass in harbour seals

Abstract

We studied maternal effects on offspring traits during lactation in harbour seals (Phoca vitulina) on Sable Island, Nova Scotia, from 1988 to 1996. Duration of lactation was correlated with rate of pup mass gain (r = -0.34, n = 116) and weaning mass (r = 0.29, n = 154). Pups that grew faster had shorter nursing periods, whereas those that attained higher weaning masses nursed for a greater number of days. Pup sex did not affect patterns of maternal effects. The pups of young females (4-6 years old) gained mass at a constant but lower rate (0.56 kg/d) than the pups of older females through midlactation (0.74-0.78 kg/d; n = 75). In older females, rates of pup mass gain decelerated between mid and late lactation. Although maternal age did not directly affect weaning mass of pups, path analysis showed that maternal age acted on weaning mass through intermediary traits. Lighter females gave birth to smaller and slower growing pups, but invested relatively more than heavier females (n = 153). Effects of maternal postpartum mass on weaning mass (n = 100) were weaker in harbour seals than in phocids that fast during lactation, but apparently stronger than in otariids that forage during lactation, suggesting that the strength of maternal effects is influenced by lactation strategy.Résumé : Nous avons étudié les effets maternels sur les caractéristiques de la progéniture durant l'allaitement chez le Phoque commun (Phoca vitulina), à l'île des Sables, au large de la Nouvelle-Écosse, de 1988 à 1996. La durée de la période d'allaitement est reliée au taux de gain de masse des petits (r = -0,34, n = 116) et à la masse des petits au moment du sevrage (r = 0,29, n = 154). Les petits qui grossissent plus rapidement ont des périodes d'allaitement plus courtes, alors que ceux qui atteignent une masse importante au sevrage sont allaités pendant une longue période. Le sexe des petits n'affecte pas l'Influence maternelle. Chez les petits nés de mères jeunes (4-6 ans), les gains de masse sont constants, mais moins rapides (0,56 kg/jour) que chez les petits nés de mères plus âgées jusqu'au milieu de la période d'allaitement (0,74-0,78 kg/jour; n = 75). Chez ces derniers, les taux de croissance en masse diminuent entre le milieu et la fin de la période d'allaitement. Bien que l'âge de la mère n'affecte pas directement la masse des petits au moment du sevrage, une analyse des pistes causales démontre que l'âge de la mère influence la masse au sevrage via des caractères intermédiaires. Les femelles moins lourdes donnent naissance à des petits moins gros, à croissance plus lente, mais elles investissent relativement plus que les femelles plus lourdes (n = 153). Les effets de la masse de la mère après la mise bas sur la masse des petits au moment du sevrage (n = 100) sont plus faibles chez ce phoque que chez les phocidés qui jeûnent pendant l'allaitement, mais, semble-t-il, plus importants que ceux des otariidés qui continuent de chercher leur nourriture durant l'allaitement, ce qui indique que l'impact des effets maternels est influencé par...

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