Strain filtering and transmission of a mixed infection in a social insect

Proc. Natl. Acad. Sci. U.S.A.

2011

693

702

Populations of important pollinators, such as bumble bees and honey bees, are declining at alarming rates worldwide. Parasites are likely contributing to this phenomenon. A distinct resident community of bacteria has recently been identified in bumble bees and honey bees that is not shared with related solitary bee species. We now show that the presence of these microbiota protects bee hosts against a widespread and highly virulent natural parasite ( Crithidia bombi ) in an experimental setting. We add further support to this antagonistic relationship from patterns found in field data. For the successful establishment of these microbiota and a protective effect, exposure to feces from nest mates was needed after pupal eclosion. Transmission of beneficial gut bacteria could therefore represent an important benefit of sociality. Our results stress the importance of considering the host microbiota as an “extended immune phenotype” in addition to the host immune system itself and provide a unique perspective to understanding bees in health and disease.

Section: Resultsmentioning

confidence: 99%

Socially transmitted gut microbiota protect bumble bees against an intestinal parasite

Koch

Proc. Natl. Acad. Sci. U.S.A.

2011

693

702

“…The frequency of multiple infections is of importance for pathogen evolution because it is thought to select for more virulent strains [6,32 -35]. In the Bombus -Crithidia system, the multiplicity of infection in workers is associated with the probability of transmission to queens, and therefore linked to host fitness [13].…”

Section: Discussionmentioning

confidence: 99%

“…DNA was extracted from these individual gut preparations using a Qiagen DNeasy 96 tissue kit. The gut extracts were then genotyped at the C. bombi microsatellite markers Cri 4, Cri 1B6, Cri 4G9 and Cri 2F10 following Ulrich et al [13] to identify the strains present in each infected individual. Previous work shows that the method is sensitive enough to detect very low concentrations of different C. bombi strains in mixed infections [21].…”

mentioning

confidence: 99%

See 1 more Smart Citation

Host modulation of parasite competition in multiple infections

Ulrich

2012

Proc. R. Soc. B.

Parasite diversity is a constant challenge to host immune systems and has important clinical implications, but factors underpinning its emergence and maintenance are still poorly understood. Hosts typically harbour multiple parasite genotypes that share both host resources and immune responses. Parasite diversity is thus shaped not only by resource competition between co-infecting parasites but also by host-driven immune-mediated competition. We investigated these effects in an insect-trypanosome system, combining in vivo and in vitro single and double inoculations. In vivo, a non-pathogenic, general immune challenge was used to manipulate host immune condition and resulted in a reduced ability of hosts to defend against a subsequent exposure to the trypanosome parasites, illustrating the costs of immune activation. The associated increase in available host space benefited the weaker parasite strains of each pair as much as the otherwise more competitive strains, resulting in more frequent multiple infections in immune-challenged hosts. In vitro assays showed that in the absence of a host, overall parasite diversity was minimal because the outcome of competition was virtually fixed and resulted in strain extinction. Altogether, this shows that parasite competition is largely host-mediated and suggests a role for host immune condition in the maintenance of parasite diversity.

“…Moreover, we predict that a decrease in residence time of infection and more frequent transmissions reduce the genotypic diversity of the parasite by eliminating slowly replicating and non-suitable strains (see [21]). A reduction in parasite diversity at the time of colony reproduction is important, because high strain diversity increases the likelihood of daughter queens becoming infected [22]. Eventually, at the end of a colony cycle, fastpaced colonies may thus have fewer infected workers with fewer persisting strains, which may result in fewer daughter queens being infected and a higher colony founding success in the next generation.…”

Section: Introductionmentioning

confidence: 99%

Colony pace: a life-history trait affecting social insect epidemiology

Buechel

2016

Proc. R. Soc. B.

Among colonies of social insects, the worker turnover rate (colony 'pace') typically shows considerable variation. This has epidemiological consequences for parasites, because in 'fast-paced' colonies, with short-lived workers, the time of parasite residence in a given host will be reduced, and further transmission may thus get less likely. Here, we test this idea and ask whether pace is a life-history strategy against infectious parasites. We infected bumblebees (Bombus terrestris) with the infectious gut parasite Crithidia bombi, and experimentally manipulated birth and death rates to mimic slow and fast pace. We found that fewer workers and, importantly, fewer last-generation workers that are responsible for rearing sexuals were infected in colonies with faster pace. This translates into increased fitness in fast-paced colonies, as daughter queens exposed to fewer infected workers in the nest are less likely to become infected themselves, and have a higher chance of founding their own colonies in the next year. High worker turnover rate can thus act as a strategy of defence against a spreading infection in social insect colonies.