Cooperative breeding favors maternal investment in size over number of eggs in spiders

Grinsted, Lena, Breuker, Casper J and Bilde, Trine (2014) Cooperative breeding favors maternal investment in size over number of eggs in spiders. Evolution, 68 (7). pp. 1961-1973. ISSN 0014-3820

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The transition to cooperative breeding may alter maternal investment strategies depending on density of breeders, extent of reproductive skew, and allo-maternal care. Change in optimal investment from solitary to cooperative breeding can be investigated by comparing social species with nonsocial congeners. We tested two hypotheses in a mainly semelparous system: that social, cooperative breeders, compared to subsocial, solitarily breeding congeners, (1) lay fewer and larger eggs because larger offspring compete better for limited resources and become reproducers; (2) induce egg size variation within clutches as a bet-hedging strategy to ensure that some offspring become reproducers. Within two spider genera, Anelosimus and Stegodyphus, we compared species from similar habitats and augmented the results with a mini-meta-analysis of egg numbers depicted in phylogenies. We found that social species indeed laid fewer, larger eggs than subsocials, while egg size variation was low overall, giving no support for bet-hedging. We propose that the transition to cooperative breeding selects for producing few, large offspring because reproductive skew and high density of breeders and young create competition for resources and reproduction. Convergent evolution has shaped maternal strategies similarly in phylogenetically distant species and directed cooperatively breeding spiders to invest in quality rather than quantity of offspring.

Item Type: Article
Schools and Departments: School of Life Sciences > Evolution, Behaviour and Environment
Subjects: Q Science > QH Natural history > QH0301 Biology > QH0359 Evolution
Q Science > QH Natural history > QH0301 Biology > QH0540 Ecology
Depositing User: Lena Grinsted
Date Deposited: 11 Aug 2014 15:24
Last Modified: 11 Aug 2014 15:24
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