title: Social polymorphism in the sweat beeLasioglossum(Evylaeus)calceatum.
abstract: Temperate-zone socially polymorphic sweat bees (Hymenoptera: Halictidae) are ideal model systems for elucidating the origins of eusociality, a major evolutionary transition. Bees express either social or solitary behaviour in different parts of their range, and social phenotype typically correlates with season length. Despite their obvious utility, however, socially polymorphic sweat bees have received relatively little attention with respect to understanding the origins of eusociality.Lasioglossum(Evylaeus)calceatumis a widespread sweat bee that is thought to be socially polymorphic, with important potential as an experimental model species. We first determined the social phenotype ofL. calceatumat three sites located at different latitudes within the UK. We then investigated sociality in detail across two years at the southernmost site. We found thatL. calceatumexhibits latitudinal social polymorphism within the UK; bees were solitary at our two northern sites but the majority of nests were social at our southern site. Sociality in the south was characterised by a relatively small mean of two and 3.5 workers per nest in each year, respectively, and a small to medium mean caste-size dimorphism of 6.6 %. Foundresses were smaller in our more northern and high altitude populations. Sociality is clearly less specialised than in some closely related obligately social species but probably more specialied than other polymorphic sweat bees. Our research provides a starting point for future experimental work to investigate mechanisms underlying social polymorphism inL.calceatum.
authors.affiliation: School of Life Sciences, University of Sussex, John Maynard Smith Building, Brighton, BN1 9QG UK.
authors.forename: P J
authors.initials: PJ
authors.lastname: Davison
authors.affiliation: School of Life Sciences, University of Sussex, John Maynard Smith Building, Brighton, BN1 9QG UK.
authors.forename: J
authors.initials: J
authors.lastname: Field
keywords: Caste-size dimorphism; Eusociality; Halictinae; Lasioglossum; Sweat bees; Workers