Season length, body size, and social polymorphism: size clines but not saw tooth clines in sweat bees
© 2017 The Authors. Ecological Entomology published by John Wiley & Sons Ltd on behalf of Royal Entomological Society. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
1. Annual insects are predicted to grow larger where the growing season is longer. However, transitions from one to two generations per year can occur when the season becomes sufficiently long, and are predicted to result in a sharp decrease in body size because available development time is halved. The potential for resulting saw-tooth clines has been investigated only in solitary taxa with free-living larvae. 2. Size clines were investigated in two socially polymorphic sweat bees (Halictidae): transitions between solitary and social nesting occur along gradients of increasing season length, characterised by the absence or presence of workers and offspring that are individually mass provisioned by adults. How the body size changes with season length was examined, and whether transitions in social phenotype generate saw-tooth size clines. We measured Lasioglossum calceatum and Halictus rubicundus nest foundresses originating from more than 1000 km of latitude, encompassing the transition between social and solitary nesting. 3. Using satellite-collected temperature data to estimate season length, it was shown that both species were largest where the season was longest. Body size increased linearly with season length in L. calceatum and non-linearly in H. rubicundus but the existence of saw-tooth clines was not supported. 4. The present results suggest that because the amount of food consumed by offspring during development is determined by adults, environmental and social influences on the provisioning strategies of adult bees may be more important factors than available feeding time in determining offspring body size in socially polymorphic sweat bees.
Natural Environment Research Council and the University of Sussex studentship. Grant Number: 1119965
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First published: 3 August 2017