Parental care and sexual size dimorphism in wasps and bees |
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Authors: | Gavin Shreeves Jeremy Field |
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Institution: | (1) Department of Medical Oncology, Mount Vernon Hospital, Rickmansworth Road, Northwood, Middlesex, HA6 2RN, UK;(2) Department of Biology and Environmental Science, School of Life Sciences, John Maynard Smith Building, University of Sussex, Brighton, BN1 9QG, UK |
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Abstract: | Sexual size dimorphism, in which one sex is larger than the other, occurs when body size has differential effects on the fitness
of males and females. Mammals and birds usually have male-biased size dimorphism, probably because of strong sexual competition
among males. Invertebrates usually have female-biased size dimorphism, perhaps because their inflexible exoskeletons limit
ovary size, leading to a strong correlation between female body size and fecundity. In this paper, we test whether an additional
factor, the type of parental care provided, affects the degree of sexual size dimorphism. Among wasps and bees, there is a
contrast between provisioning taxa, in which females must gather and transport heavy loads of provisions to nests they have
constructed, and non-provisioning taxa, in which females lay eggs but do not construct nests or transport provisions. Males
have no role in parental care in either case. An analysis of British wasps and bees shows that provisioning taxa have significantly
more female-biased size dimorphism than non-provisioning taxa. This is true for simple cross‑species comparisons and after
controlling for phylogeny. Our data imply that the demands of carrying provision loads are at least part of the explanation
for this pattern. Thus, sexual size dimorphism is greatest in pompilid wasps, which carry the heaviest prey items. Bees, which
transport minute pollen grains, exhibit the least dimorphism. We also find that cavity‑nesting species, in which nest construction
costs may be minimized, exhibit reduced dimorphism, but this was not significant after controlling for phylogeny. |
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Keywords: | Sexual dimorphism Parental care Hymenoptera Wasps Bees |
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