Introduction
Climate represents a major selective force in the evolution of
sociality. Climatic conditions can shape developmental rates, nesting
strategies, biotic interactions, and other processes that determine the
relative costs and benefits of group formation (Blumstein et al., 2022;
Fisher et al., 2021; Menzel and Feldmeyer, 2021; Moss and While, 2021;
Wilson, 1971). Social living can give rise to emergent strategies for
coping with climatic stressors (Arnold, 1988; Fahrenholz et al., 1989;
Klok and Chown, 1999). Observed patterns in global biogeography support
hypotheses linking climate to social evolution, with distributions of
social organisms falling along gradients of temperature, precipitation,
and climatic stochasticity (Jetz and Rubenstein, 2011; Lukas and
Clutton-Brock, 2017; Purcell, 2011). These interactions between climate
and sociality raise important questions about the fate of social
organisms and social phenotypes under changing climate.
Climate change is predicted to have major consequences for the survival,
health, and distributions of organisms globally, including ecologically
and economically important animals like pollinators (da Silva et al.,
2023; Forrest, 2016; Potts et al., 2010). Bees (Hymenoptera: Apoidea:
Anthophila) are the primary animal pollinators of terrestrial ecosystems
(Ollerton et al., 2011). Bees possess some of the richest diversity of
social behaviors of any animal taxon, with multiple independent origins
of eusociality and a broad range of non-eusocial forms (Michener, 1974;
Wcislo and Fewell, 2017). Within the past decade, researchers have
increasingly investigated species-level social traits as possible
predictors of bee responses to environmental change (Forrest et al.,
2015; Hall et al., 2019; Harrison et al., 2018). Social organization in
bees correlates with other behavioral and life history traits, like
foraging strategy and phenology, that can influence susceptibility to
climate change stressors. However, a unifying pattern linking sociality
to climate change vulnerability has remained elusive.
Climate change is also likely to shift the expression and geographic
distribution of social behaviors across animal populations. Expected
consequences of climate change include not only increasing average
temperatures, but also increasing climate variability and increasing
frequency and severity of extreme events like drought, flooding, and
wildfire (IPCC, 2022). For bees, many of which can flexibly express
sociality in response to environmental conditions (Wcislo and Fewell,
2017), the social impacts of these shifts could be particularly
profound. Nevertheless, very few studies have directly assessed the
impacts of climate change on bee social organization. Still, these
effects may be extrapolated from known relationships between bee
sociality and local environmental conditions. Drawing from this
literature, we make predictions about the consequences of climate change
for bee sociality and identify promising directions for future research.
Box 1: Notes on bee social biology and terminology
The ancestor of bees was solitary, as are the vast majority of extant
bee species (Debevec et al., 2012). Nevertheless, diverse forms of
social living are known to be found in all currently recognized bee
families except the Stenotritidae (Michener, 1974; Wcislo and Fewell,
2017). The extent of and capacity for social living among bees is likely
to be vastly underestimated, given that social strategies may be present
at low levels in otherwise solitary populations (Wcislo, 1997, 1993;
Yagi and Hasegawa, 2012). Social organization in bees takes a diversity
of forms, and includes several independent origins of (and reversals
from) eusociality (Danforth et al., 2003; Kocher and Paxton, 2014).
Among and within taxa, bee societies vary considerably in group size, in
the degree of reproductive skew and morphological specialization, and in
the genetic relatedness of group members (Michener, 1974; Ostwald et
al., 2022b; Wcislo and Fewell, 2017). Particularly instructive for
social evolutionary studies are the many lineages in which social living
is a facultative state, which may be determined by environmental
conditions.
The studies we review here vary considerably in their categorizations of
social states. For the purposes of this review, we will define sociality
as multi-female group living within a nesting context, with or without
reproductive division of labor (sensu Wcislo & Fewell, 2017). We
consider communal living as a social category because it entails
behaviors and characteristics distinct from solitary living that are
relevant to environmental tolerance, for example, by enhancing nest
defense from predators and parasites, by generating advantages in nest
excavation and initiation, and by enabling social thermoregulatory
behaviors. In general, we will broadly compare social groups to solitary
individuals, but emphasize that sociality represents a broad spectrum of
behaviors with corresponding diversity in their responses to climate
conditions.