Repeatability in lactation performance and the consequences for maternal reproductive success in gray seals
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Date
2009-09Author
Lang, S. L. C.
Iverson, Sara J.
Bowen, W. D.
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In mammals, the most significant maternal effect on offspring growth during lactation is the
ability of females to efficiently transfer milk energy to their neonates. However, despite the
importance of the transfer of milk energy to both maternal and offspring fitness, nothing is known
about the extent to which variation among females may be attributed to differences in individual
quality or environmental variation in natural populations. We measured repeatability over multiple
lactation periods in components of lactation performance in free-ranging, multiparous gray seal
(Halichoerus grypus) females to examine to what extent variation among females in pup weaning mass
may be attributed to inherent differences in their physiological capacity to deliver milk energy.
Levels of repeatability were high for milk composition (r = 0.38-0.50), daily milk output (r =
0.46), and the duration of lactation (r = 0.57), demonstrating that there are consistent differences
among females in these characters across lactations and that the overall capacity of gray seal
females to deliver milk energy to their pups is characteristic of individuals. The repeatability in
pup weaning mass (r = 0.48) was consistent with the values for the components of total milk energy
output and suggests that, over a large proportion of their reproductive life, individual gray seal
females will consistently wean pups with greater or lesser probabilities of survival. Our results
suggest that inherent differences among females in their physiological capacity to deliver milk
energy may be an important component of variation in individual quality and, thus, lifetime
reproductive success in mammals. High levels of repeatability also suggest that components of milk
energy transfer may have a significant heritable genetic basis.
Citation
Lang, S. L. C., S. J. Iverson, and W. D. Bowen. 2009. "Repeatability in lactation performance and the consequences for maternal reproductive success in
gray seals." Ecology 90(9): 2513-2523. Copyright by the Ecological Society of America.