Antifungal activity in thrips soldiers suggests a dual role for this caste

Abstract

The social insect soldier is perhaps the most widely known caste, because it often exhibits spectacular weapons, such as highly enlarged jaws or reinforced appendages, which are used to defend the colony against enemies ranging in size from wasps to anteaters. We examined the function of the enlarged forelimbs of soldiers (both male and female) of the eusocial, gall-inhabiting insect Kladothrips intermedius , and discovered that they have little impact on their ability to repel the specialized invading thrips Koptothrips species. While the efficacy of the enlarged forelimb appears equivocal, we show that soldiers secrete strong antifungal compounds capable of controlling the specialized insect fungal pathogen, Cordyceps bassiana . Our data suggest that these thrips soldiers have evolved in response to selection by both macro- and micro-organisms. While it is unknown whether specialized fungal pathogens have been major selective agents in the evolution of the soldier caste in general, they were probably present when sociality first evolved and may have been the primordial enemies of social insects.

Save your host, save yourself? Caste‐ratio adjustment in a parasite with division of labor and snail host survival following shell damage

“…It is thus possible that these nonreproductive morphs fulfill additional roles in the colony. For example, parasite colonies as well as their molluscan hosts are likely to face repeated bacterial or fungal infections (Bayne, 1983;Ducklow, Boyle, Maugel, Strong, & Mitchell, 1979;van der Knaap & Loker, 1990;Morley, 2010); soldier rediae might play a "cleaning" role in the defense against such microorganisms, as documented in social insects (Lloyd & Poulin, 2012, 2014aMouritsen & Andersen, 2017;Turnbull et al, 2012). Since trematode infection can suppress host immune defenses, the risk of secondary infection by pathogens should be increased (Bayne, 1983;Iakovleva, Shaposhnikova, & Gorbushin, 2006;Loker & Adema, 1995;Walker, 1979Walker, , 2006.…”

Quality and quantity: transitions in antimicrobial gland use for parasite defense

“…; Turnbull et al. ), which can mitigate or even outweigh the fitness cost from parasites for group‐living animals (Rosengaus et al. ; Hughes et al.…”

“…However, in addition to individual-level immune defenses, social organisms are able to employ social defenses that have been termed "social immunity" in the broad sense (Dunbar 1991;Cremer et al 2007;Wisenden et al 2009;Otti et al 2014). This can include behavioral defenses such as grooming, and the production and transfer of antimicrobial compounds (Rosengaus et al 1998(Rosengaus et al , 2004Fern andez-Mar ın et al 2006;Yanagawa et al 2008;Hamilton et al 2011;Baracchi et al 2012;Turnbull et al 2012), which can mitigate or even outweigh the fitness cost from parasites for group-living animals (Rosengaus et al 1998;Hughes et al 2002;Ugelvig and Cremer 2007;.…”

Termite soldiers contribute to social immunity by synthesizing potent oral secretions

“…GNBP2 is evolutionarily conserved across Isoptera and has been shown to be a key regulator of social immunity in termites (Bulmer & Crozier, ; Bulmer et al ., ). If this hypothesis is correct, it would be consistent with other soldier‐first insect societies, such as the thrips, where a dual defensive/immune role for soldiers, via the synthesis of potent antifungal compounds, has been shown (Turnbull et al ., ). Taken together, these findings raise the interesting hypothesis that soldier involvement in colony‐level immunity may be required for the evolution of soldier‐first societies (Tian & Zhou, ).…”