Antimicrobial defences increase with sociality in bees

Abstract

Evidence for the antiquity and importance of microbial pathogens as selective agents is found in the proliferation of antimicrobial defences throughout the animal kingdom. Social insects, typified by crowding and often by low genetic variation, have high probabilities of disease transmission and eusocial Hymenoptera may be particularly vulnerable because of haplodiploidy. Mechanisms they employ to reduce the risk of disease include antimicrobial secretions which are particularly important primary barriers to infection. However, until now, whether or not there is selection for stronger antimicrobial secretions when the risk of disease increases because of sociality has not been tested. Here, we present evidence that the production of progressively stronger antimicrobial compounds was critical to the evolution of sociality in bees. We found that increases in group size and genetic relatedness were strongly correlated with increasing antimicrobial strength. The antimicrobials of even the most primitive semi-social species were an order of magnitude stronger that those of solitary species, suggesting a point of no return, beyond which disease control was essential. Our results suggest that selection by microbial pathogens was critical to the evolution of sociality and required the production of strong, front-line antimicrobial defences.

Reduced cellular immune response in social insect lineages

“…Lett. 12: 20150984 of external antimicrobial secretions between solitary, semisocial and social bees found evidence of progressively stronger antimicrobial activity in species with higher levels of sociality [25]. Stronger antimicrobial activity is a form of heightened immune response [26], as expected under SGH, and suggests that selection is strongly acting on external immune defences in social insects.…”

Adult honeybees (Apis mellifera L.) abandon hemocytic, but not phenoloxidase-based immunity

“…With respect to these hypotheses, we note that the closely related eusocial bumble bees, which differ from honeybees in their hygienic behavior and the antibacterial conditions in nests, do not show a reduction in hemocyte number with age (Doums et al, 2002;König and Schmid-Hempel, 1995). Returning to our comment that the evolutionary forces driving hemocyte loss are complex, we suggest the evolution of more complex hygienic behaviors and nest conditions (Stow et al, 2007) enabled honeybees, but not bumble bees, to trade off individual hemocytic-based defense while retaining an effective, albeit less expensive, PO-based defense system.…”

Reduced biological control and enhanced chemical pest management in the evolution of fungus farming in ants

“…The evolution of larger colony sizes places greater demands on 'public health' adaptations (e.g. Fefferman et al 2007;Stow et al 2007), but tradeoffs associated with different disease management strategies are not well understood.…”

“…Disease agents are important selective forces on social evolution (Hamilton 1982;Schmid-Hempel 1998;Fefferman et al 2007;Stow et al 2007). Pathogens can determine upper limits of host group size, because increasing density of individuals results in elevated contact rates that facilitate high rates of pathogen transmission (Hamilton 1982;Schmid-Hempel 1998;Boomsma et al 2005), potentially leading to epidemics within genetically homogeneous groups (Schmid-Hempel 1998;Hughes et al 2002).…”