How many cubs can a mum nurse? Maternal age and size influence litter size in polar bears

Life-history theory predicts that females' age and size affect the level of maternal investment in current reproduction, balanced against the future reproductive effort, maintenance and survival. Using long-term (30 years) individual data on 193 female polar bears ( Ursus maritimus), we assesse...

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Bibliographic Details
Published in:Biology letters (2005) 2019-05, Vol.15 (5), p.20190070-20190070
Main Authors: Folio, Dorinda Marie, Aars, Jon, Gimenez, Olivier, Derocher, Andrew E, Wiig, Øystein, Cubaynes, Sarah
Format: Article
Language:English
Subjects:
Animals
Biodiversity and Ecology
Body Size
Environmental Sciences
Evolutionary Biology
Female
Litter Size
Maternal Age
Pregnancy
Reproduction
Ursidae
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Summary:Life-history theory predicts that females' age and size affect the level of maternal investment in current reproduction, balanced against the future reproductive effort, maintenance and survival. Using long-term (30 years) individual data on 193 female polar bears ( Ursus maritimus), we assessed age- and size-specific variation on litter size. Litter size varied with maternal age, younger females had higher chances of losing a cub during their first months of life. Results suggest an improvement in reproductive abilities early in life due to experience with subsequent reproductive senescence. Litter size increased with maternal size, indicating that size may reflect individual quality. We also found an optimum in the probability of having twins, suggesting stabilizing selection on female body size. Heterogeneity was observed among the largest females, suggesting that large size comes at a cost.
ISSN:1744-9561
1744-957X
DOI:10.1098/rsbl.2019.0070