Consequences of a warming climate for social organisation in sweat bees

Abstract

The progression from solitary living to caste-based sociality is commonly regarded as a major evolutionary transition. However, it has recently been shown that in some taxa, sociality may be plastic and dependent on local conditions. If sociality can be environmentally driven, the question arises as to how projected climate change will influence features of social organisation that were previously thought to be of macroevolutionary proportions. Depending on the time available in spring during which a foundress can produce worker offspring, the sweat bee Halictus rubicundus is either social or solitary. We analysed detailed foraging data in relation to climate change predictions for Great Britain to assess when and where switches from a solitary to social lifestyle may be expected. We demonstrate that worker numbers should increase throughout Great Britain under predicted climate change scenarios, and importantly, that sociality should appear in northern areas where it has never before been observed. This dramatic shift in social organisation due to climate change should lead to a bigger workforce being available for summer pollination and may contribute towards mitigating the current pollinator crisis.Significance StatementThe sweat bee Halictus rubicundus is socially polymorphic, expressing both solitary and social forms, and is socially plastic, capable of transitioning from solitary to social forms, depending on local environmental conditions. Here, we analyse detailed foraging data in relation to climate change predictions for Great Britain to show that worker numbers and sociality both increase under predicted climate change scenarios. Especially dramatic will be the appearance of social H. rubicundus nests in the north of Britain, where previously only solitary forms are found. Particularly, if more taxa are found to be socially plastic, environmentally driven shifts in social organisation may help to mitigate future pollinator crises by providing more individuals for pollination.Electronic supplementary materialThe online version of this article (doi:10.1007/s00265-016-2118-y) contains supplementary material, which is available to authorized users.

Field boundary features can stabilise bee populations and the pollination of mass‐flowering crops in rotational systems

“…Our simulations focused entirely on pollinator population variability induced through crop rotation. However, pollinators show large population fluctuations in response to weather patterns, which are expected to become less consistent under climate change (Kerr et al., 2015; Schürch et al., 2016). Maintaining complex boundary features, which include variation in aspect and vegetation structure and so provide a variety of stable microclimatic conditions, may help buffer populations against weather extremes and so potentially help to mitigate both weather‐induced variability and variability generated via spatially/temporally unpredictable crop flowering.…”

Environmental barriers to sociality in an obligate eusocial sweat bee

“…Although our transplant was limited to a single location, our results provide the first experimental support for the idea that primitive eusociality is absent from high altitude or latitude communities because the season is too short to rear consecutive broods (Soucy and Danforth 2002 ; Fucini et al 2009 ; Kocher et al 2014 ; Davison and Field 2016 ). Activity levels in small bees such as L. malachurum are positively correlated with ambient temperature (Bishop and Armbruster 1999 ; Schürch et al 2016 ), which at Cromarty lagged far behind the long-term average for the southeast UK. For example, temperatures at Cromarty as late as June and July did not exceed those recorded much earlier, in May, at Sussex (Fig.…”

“…Most intraspecific variation in development time is apparently driven by temperature, such that development is prolonged at lower temperatures (Weissel et al 2006 ; Field et al 2012 ); moreover, sweat bees can exert only limited control over temperatures experienced by developing brood, such as by locating nests in exposed, south-facing ground (Potts and Wilmer 1997 ; Hirata and Higashi 2008 ). Thus, future climate warming is predicted to increase the northerly range of obligate eusocial sweat bees (Schürch et al 2016 ): indeed, within the last 25 years L. malachurum has rapidly expanded its range northwards within the UK and become much commoner (Falk 1991 , 2015 ).…”

Orchid bees (Hymenoptera, Apidae, Euglossini) are seasonal in Seasonal Semideciduous Forest fragments, southern Brazil

“…The plasticity of individuals' time of development is regarded as an important response of euglossine bees to environmental fluctuation, with the production of several generations of short development in favorable contexts and delaying hatching, with increasing time as pupae, during unfavorable circumstances (Knoll, 2016). It is even possible to expect variation in the social organization itself, as sociality is dependent on local conditions and a single species may be either social or solitary (Schürch et al, 2016).…”