Sensory plasticity in a socially plastic bee

Abstract

The social Hymenoptera have contributed much to our understanding of the evolution of sensory systems. Attention has focussed chiefly on how sociality and sensory systems have evolved together. In the Hymenoptera, the antennal sensilla are important for optimizing the perception of olfactory social information. Social species have denser antennal sensilla than solitary species, which is thought to enhance social cohesion through nestmate recognition. In the current study, we test whether sensilla numbers vary between populations of the socially plastic sweat bee Halictus rubicundus from regions that vary in climate and the degree to which sociality is expressed. We found population differences in both olfactory and hygro/thermoreceptive sensilla numbers. We also found evidence that olfactory sensilla density is developmentally plastic: when we transplanted bees from Scotland to the south‐east of England, their offspring (which developed in the south) had more olfactory hairs than the transplanted individuals themselves (which developed in Scotland). The transplanted bees displayed a mix of social (a queen plus workers) and solitary nesting, but neither individual nor nest phenotype was related to sensilla density. We suggest that this general, rather than caste‐specific sensory plasticity provides a flexible means to optimize sensory perception according to the most pressing demands of the environment. Sensory plasticity may support social plasticity in H. rubicundus but does not appear to be causally related to it.

Genetic differentiation at extreme latitudes in the socially plastic sweat bee Halictus rubicundus

“…In the south of its geographical range, bivoltinism and a second, social, 'worker' generation are typical while in the north (and at higher altitudes), H. rubicundus populations tend to be univoltine with one solitary generation per year [4][5][6]. This is the pattern we see in North America and the UK; populations are solitary in cooler climates and social where it is warmer [4][5][6][7]. Additionally in the UK, sociality has been shown to be plastic; when solitary northern bees are transplanted to the south, they express bivoltinism and sociality [4,6,7].…”

“…rubicundus populations tend to be univoltine with one solitary generation per year [ 4 – 6 ]. This is the pattern we see in North America and the UK; populations are solitary in cooler climates and social where it is warmer [ 4 – 7 ]. Additionally in the UK, sociality has been shown to be plastic; when solitary northern bees are transplanted to the south, they express bivoltinism and sociality [ 4 , 6 , 7 ].…”

“…There is some evidence for local adaptation to the climate in H . rubicundus ; bees from the Belfast and Migdale populations in the north have denser sense organs on their antennae that detect humidity, temperature and CO 2 than bees from south-western populations in the UK [ 7 ]. In future, longitudinal studies using next-generation sequencing to assess allele frequencies across multiple populations of H .…”

“… This image was reproduced from [ 7 ] under the terms of the Creative Commons Attribution licence (CC BY). …”

Evolution of the neuronal substrate for kin recognition in social Hymenoptera

“…Accordingly, the transition to higher social complexity may be associated with expansions of brain regions supporting olfactory communication, as has been observed between ant species with different colony sizes (Riveros, Seid & Wcislo, 2012; Godfrey et al ., 2021). This idea is also supported by observations made in Halictidae (sweat bees), in which a higher investment in chemosensory structures on the antennae has been observed in social bees compared to solitary ones, at both species and population levels (Wittwer et al ., 2017; Wenseleers & van Zweden, 2017; Boulton & Field, 2022). It should be noted that beyond kinship recognition, many aspects of eusocial organisation, such as coordinated division of labour, concerted actions and reproductive dominance, also require highly efficient communication systems (Leonhardt et al ., 2016).…”