title: Transitions in social complexity along elevational gradients reveal a combined impact of season length and development time on social evolution.
abstract: Eusociality is taxonomically rare, yet associated with great ecological success. Surprisingly, studies of environmental conditions favouring eusociality are often contradictory. Harsh conditions associated with increasing altitude and latitude seem to favour increased sociality in bumblebees and ants, but the reverse pattern is found in halictid bees and polistine wasps. Here, we compare the life histories and distributions of populations of 176 species of Hymenoptera from the Swiss Alps. We show that differences in altitudinal distributions and development times among social forms can explain these contrasting patterns: highly social taxa develop more quickly than intermediate social taxa, and are thus able to complete the reproductive cycle in shorter seasons at higher elevations. This dual impact of altitude and development time on sociality illustrates that ecological constraints can elicit dynamic shifts in behaviour, and helps explain the complex distribution of sociality across ecological gradients.
authors.affiliation: Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138, USA skocher@fas.harvard.edu.
authors.forename: Sarah D
authors.initials: SD
authors.lastname: Kocher
authors.affiliation: Arctic Research Centre, Department of Bioscience, Aarhus University, 4000 Roskilde, Denmark Department of Biology, Ecology and Evolution, University of Fribourg, CH-1700 Fribourg, Switzerland.
authors.forename: Loïc
authors.initials: L
authors.lastname: Pellissier
authors.affiliation: Program for Evolutionary Dynamics, Harvard University, Cambridge, MA 02138, USA Department of Economics, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Carl
authors.initials: C
authors.lastname: Veller
authors.affiliation: Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.
authors.forename: Jessica
authors.initials: J
authors.lastname: Purcell
authors.affiliation: Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138, USA Program for Evolutionary Dynamics, Harvard University, Cambridge, MA 02138, USA Department of Mathematics, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Nowak
authors.affiliation: Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.
authors.forename: Michel
authors.initials: M
authors.lastname: Chapuisat
authors.affiliation: Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Naomi E
authors.initials: NE
authors.lastname: Pierce
mesh_terms: D000531:Altitude; D000818:Animals; D001516:Bees / Q000502:physiology*; D005075:Biological Evolution; D004777:Environment; D012098:Reproduction; D012621:Seasons; D012919:Social Behavior; D013557:Switzerland
keywords: altitude; development time; hymenoptera; social behaviour; species distributions