Environmental barriers to sociality in an obligate eusocial sweat bee

Abstract

Understanding the ecological and environmental contexts in which eusociality can evolve is fundamental to elucidating its evolutionary origins. A sufficiently long active season is postulated to have been a key factor facilitating the transition to eusociality. Many primitively eusocial species exhibit an annual life cycle, which is thought to preclude the expression of eusociality where the active season is too short to produce successive worker and reproductive broods. However, few studies have attempted to test this idea experimentally. We investigated environmental constraints on the expression of eusociality in the obligate primitively eusocial sweat bee Lasioglossum malachurum, by transplanting nest foundresses from the south to the far north of the United Kingdom, far beyond the natural range of L. malachurum. We show that transplanted bees can exhibit eusociality, but that the short length of the season and harsher environmental conditions could preclude its successful expression. In one year, when foundresses were transplanted only after provisioning first brood (B1) offspring, workers emerged in the north and provisioned a second brood (B2) of reproductives. In another year, when foundresses were transplanted prior to B1 being provisioned, they were just as likely to initiate nesting and provisioned just as many B1 cells as foundresses in the south. However, the life cycle was delayed by approximately 7 weeks and nests suffered 100% B1 mortality. Our results suggest that short season length together with poor weather conditions represent an environmental barrier to the evolution and expression of eusociality in sweat bees.Electronic supplementary materialThe online version of this article (10.1007/s00040-018-0642-7) contains supplementary material, which is available to authorized users.

Long‐term persistence of experimental populations beyond a species' natural range

“…However, most beyond-range transplants only monitor populations for ≤1 generation, and so risk missing critical but infrequent range-limiting events. Of the 133 published beyond-range transplant studies (Hargreaves et al 2014 plus Appendix S1: Table S1), seven repeated singlegeneration experiments in multiple years (almost all involving annual plants) and documented substantial year-to-year variation in beyond-range fitness, presumably due to environmental variation (Nagy and Rice 1997, Geber and Eckhart 2005, Norton et al 2005, Davison and Field 2018, Benning and Moeller 2019, Hargreaves and Eckert 2019. The effects of environmental fluctuations on demography may compound across generations, ultimately driving experimental populations to extinction.…”

Pollen diet diversity across bee lineages varies with lifestyle rather than colony size

“…Therefore, bee taxa that can exhibit facultative eusociality, such as certain sweat and orchid bees, have been classified as noneusocial. This classification is based on the fact that eusociality is not obligatory in these taxa and is primarily associated with specific ecological traits, such as the number and temporal sequence of individuals emerging within nests and availability of nesting space ( Soro et al 2010 , Andrade-Silva and Nascimento 2012 , Boff et al 2015 , Davison and Field 2018 , Shell and Rehan 2018 ).…”

Native Bee Habitat Restoration- Key Ecological Considerations from Recent Literature

“…By providing nesting sites that attract bees and lead to high-quality nests, and protecting existing nests, conservation efforts can contribute to the preservation of bee populations. Conserving existing nesting sites, however, is not the only option; occupied nests can be transplanted (Davison and Field, 2018), although the risks associated with transplanting native bee nests are unknown.…”