Should mothers provision their offspring equally? A manipulative field test

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Within-brood variation in offspring size is universal, but its causes are unclear. Theoretical explanations for within-brood variation commonly invoke bet-hedging, although alternatives consider the role of sibling competition. Despite abundant theory, empirical manipulations of within-brood variation in offspring size are rare. Using a field experiment, we investigate the consequences of unequal maternal provisioning for both maternal and offspring fitness in a marine invertebrate. We create experimental broods of siblings with identical mean, but different variance, in offspring size, and different sibling densities. Overall, more-variable broods had higher mean performance than less-variable broods, suggesting benefits of unequal provisioning that arise independently of bet-hedging. Complementarity effects drove these benefits, apparently because offspring-size variation promotes resource partitioning. We suggest that when siblings compete for the same resources, and offspring size affects niche usage, the production of more-variable broods can provide greater fitness returns given the same maternal investment; a process unanticipated by the current theory.

Original languageEnglish
Pages (from-to)1025-1033
Number of pages9
JournalEcology Letters
Issue number8
Publication statusPublished - 1 Aug 2017


  • bet-hedging
  • complementarity
  • fitness
  • life-history theory
  • maternal provisioning
  • niche partitioning
  • offspring size
  • sibling interactions
  • within-brood variation

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