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Marine Ecology Progress Series

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MEPS 720:175-189 (2023)  -  DOI:

Lactation performance in polar bears is associated with fasting time and energetic state

L. C. Archer1,*, S. N. Atkinson2, A. M. Pagano3, S. R. Penk1,4, P. K. Molnár1,4

1Laboratory of Quantitative Global Change Ecology, Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, M1C 1A4, Canada
226104 Melrose Road, Cooks Creek, Manitoba, R5M 0B9, Canada
3US Geological Survey, Alaska Science Center, Anchorage, Alaska, 99508 USA
4Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, M5T 3B2 Canada
*Corresponding author:

ABSTRACT: Females must continually make resource allocation decisions because of fitness trade-offs between self-maintenance and investment in current offspring, yet factors underpinning these decisions are unresolved. Polar bears Ursus maritimus face considerable allocation challenges when seasonal sea-ice melt precludes access to prey for several months, and females rely solely on energy stores to cover their own energetic needs and provision offspring. We tested how female polar bears regulate lactation during onshore fasting (i.e. capital breeding) and determined the consequences of moderated lactation for females and cubs. Overall, milk energy declined, and lactation was more likely to cease with longer time fasting. Lactation was partially mediated by maternal energetic state and depended on litter characteristics. Milk energy declined more sharply with fasting time (~2.6 times more strongly) in females with 2 offspring compared to those with 1. Females with cubs-of-the-year produced higher energy milk than those with yearlings, and their milk energy also increased more strongly with maternal energy density. Milk energy declines benefited females via reduced depletion of maternal energy reserves, but cub growth decreased. Altered lactation investment likely has consequences for both female survival and the fate of offspring, which could scale up to influence population dynamics. Given that Arctic warming means polar bears across much of their range will experience longer periods without access to primary prey, our results underscore how lactation will likely become increasingly compromised.

KEY WORDS: Ursus maritimus · Sea ice · Arctic · Climate change · Life-history tactics · Capital breeding

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Cite this article as: Archer LC, Atkinson SN, Pagano AM, Penk SR, Molnár PK (2023) Lactation performance in polar bears is associated with fasting time and energetic state. Mar Ecol Prog Ser 720:175-189.

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