Temperature-mediated inhibition of a bumble bee parasite by an intestinal symbiont

Abstract

Competition between organisms is often mediated by environmental factors including temperature. In animal intestines, nonpathogenic symbionts compete physically and chemically against pathogens, with consequences for host infection. We used metabolic theory-based models to characterize differential responses to temperature of a bacterial symbiont and a co-occurring trypanosomatid parasite of bumble bees, which regulate body temperature during flight and incubation. We hypothesized that inhibition of parasites by bacterial symbionts would increase with temperature, due to symbionts having higher optimal growth temperatures than parasites.We found that a temperature increase over the range measured in bumble bee colonies would favor symbionts over parasites. As predicted by our hypothesis, symbionts reduced the optimal growth temperature for parasites, both in direct competition and when parasites were exposed to symbiont spent medium. Inhibitory effects of the symbiont increased with temperature, reflecting accelerated growth and acid production by symbionts. Our results indicate that high temperatures, whether due to host endothermy or environmental factors, can enhance the inhibitory effects of symbionts on parasites. Temperature-modulated manipulation of microbiota could be one explanation for fever- and heat-induced reductions of infection in animals, with consequences for diseases of medical and conservation concern.

Drivers of inter-population variation in the gut microbiomes of sister species ofPhanaeusdung beetles

“…Temperature variation across the range of the host may also select for distinct gut microbiomes across host populations. First, varying temperatures can alter competitive dynamics among microbes in the gut, changing the relative abundances of microbial community members (Palmer-Young, Raffel, & McFrederick, 2018). Second, gut-specialized microorganisms often have narrower thermal tolerances than their hosts (Corbin, Heyworth, Ferrari, & Hurst, 2017; Kikuchi et al, 2016; Zhang et al, 2019) or may confer different selective advantages to the host depending on the temperature (Russell & Moran, 2006).…”