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.

A unified model of Hymenopteran preadaptations that trigger the evolutionary transition to eusociality

“…Thus, multiple sources of evidence point towards bivoltinism as a predecessor a facilitating factor for retaining helpers at the nest. Multivariate statistical analysis shows that indeed the number of broods, governed by breeding season length and developmental time, is positively correlated with the level of sociality among facultative and obligately eusocial species57. Moreover, environmental factors related to season length appear to be important determinants for the expression of helping behaviour in species that can either have helpers or be solitary, depending on geographical location36375859.…”

Predicting abundances of plants and pollinators using a simple compartmental mutualistic model

“…This excess population is due to Apis mellifera (mean proboscis length of 5.95 mm), which had a disproportionate weight in the dataset, representing almost one-third of the total abundance of pollinators across the 111 species (295 of 887 individuals) [10,11]. Apis mellifera is an artificially introduced, domesticated agricultural species, bred and maintained, whose abundance depends mostly on local beekeeping practices [22,23]. The fact that the abundances of the other four plantpollinator pairs are rather well fitted by equation (3.3), containing only two parameters, K P and a AP , suggests neutrality: the effect of pollinators on plants is generally independent of size class i, that is, a…”

Habitat productivity predicts the global distribution of social spiders

“…Our understanding of these relationships are, further challenged by a complex set of interactions between life history and environment on the probability of group formation and degree of social organization (Hatchwell and Komdeur, 2000). Geographical patterns of variation in the level of sociality has been documented in a number of social lineages, suggesting a strong influence on ecology, and environment on the evolution and complexity of cooperation, e.g., in social insects (Wilson, 1975;Kaspari and Vargo, 1995;Wcislo, 1997;Schwarz et al, 2007;Gunnels et al, 2008;Kaspari and Weiser, 2011;Kocher et al, 2014), social spiders (Avilés et al, 2007;Purcell, 2011;Majer et al, 2013a), and cooperatively breeding birds (Jetz and Rubenstein, 2011). While these patterns show altitudinal or latitudinal and thereby ecological correlations with degree of sociality, nest size or other social traits, our understanding of the causal relationships between ecological factors and social traits is incomplete.…”