Is diversity in worker body size important for the performance of bumble bee colonies?

Abstract

16Specialization and plasticity are important for many forms of collective behavior, but the 17 interplay between these factors is little understood. In insect societies, workers are often 18 predisposed to specialize in different tasks, sometimes with morphological or physiological 19 adaptations, facilitating a division of labor. Workers may also plastically switch between tasks 20 or vary their effort. The degree to which predisposed specialization limits plasticity is not clear 21and has not been systematically tested in ecologically relevant contexts. We addressed this 22 question in 20 freely-foraging bumble bee (Bombus terrestris) colonies by continually 23 manipulating colonies to contain either a typically diverse or reduced ("homogeneous") worker 24 body size distribution, over two trials. Pooling both trials, diverse colonies did better in several 25indices of colony performance. The importance of body size was further demonstrated by the 26 finding that foragers were larger than nurses even in homogeneous colonies with a very 27 narrow body size range. However, the overall effect of size diversity stemmed mostly from one 28 trial. In the other trial, homogeneous and diverse colonies showed comparable performance. 29By comparing behavioral profiles based on several thousand observations, we found evidence 30 that workers in homogeneous colonies in this trial rescued colony performance by plastically 31 increasing behavioral specialization and/or individual effort, compared to same-sized 32 individuals in diverse colonies. Our results are consistent with a benefit to colonies of 33 predisposed (size-diverse) specialists under certain conditions, but also suggest that plasticity 34 or effort, can compensate for reduced (size-related) specialization. Thus, we suggest that an 35 intricate interplay between specialization and plasticity is functionally adaptive in bumble bee 36 colonies. 37 Keywords: bumble bee, division of labor, task specialization, behavioral plasticity, collective 38 behavior 39 Short title: Bumble bee size diversity 40 41

Thermal flight performance reveals impact of warming on bumblebee foraging potential

“…Ultimately, our controlled laboratory findings imply that larger individuals are able to reach flowering resources more quickly and over a greater distance than their smaller counterparts, supporting field observations of foraging scope and efficiency increasing with body size (Goulson et al., 2002; Greenleaf et al., 2007; Spaethe & Weidenmuller, 2002; Willmer & Finlayson, 2014) and providing a further mechanistic explanation for observed alloethism in bumblebees (Herrmann et al., 2018; Holland et al., 2020). Interestingly, agricultural intensification and associated declines in habitat quality and quantity appear to be leading to shrinkages in bee body size, not just in Bombus terrestris but also across other social and solitary species (Oliveira et al., 2016; Renauld et al., 2016).…”

Stop and go: exploring alternative mechanisms for task allocation in social insects - response and satisfaction thresholds trade off cost, accuracy, and speed differently

“…each cue-threshold type combination, was capable of producing some level of division of labor (Fig. 1A), in the range of what is empirically seen in social insects (Gorelick et al, 2004;Dornhaus et al, 2009;Jandt et 9 al., 2009;Holbrook et al, 2011;Holland et al, 2020;Sharma & Gadagkar, 2023), although those using 'completion cues' tended to be on the lower end of this range. 'Random choice', as expected, produced essentially no division of labor (Fig 1A).…”