Summary:

The relevance of symbiotic microbial communities in the gut is increasingly being studied in a large number of animal species, from sponges to primates. Although the red flour beetle Tribolium castaneum represents a well-established experimental model organism for studying ecological, evolutionary and developmental topics, to the best of our knowledge, there are no studies on the composition of the gut microbiota of this insect. We examined the bacterial composition of the digestive tract of T. castaneum. For this, two approaches were combined: a culture-independent metagenomic analysis based on 16S rRNA sequences and a classical bacterial cultivation method. The comparison of bacterial 16S rRNA sequences between guts of larval and adult beetles revealed a generally lower diversity of bacterial genera, compared to other insect species. Moreover, the diversity of bacterial genera was higher in guts of adults than in larvae. As expected, cultivation of gut contents on different growth media confirmed only a minor part of the genera found in the metagenomic analysis. The information on bacterial communities in the gut of T. castaneum will be useful for future studies testing interactions between T. castaneum and its microbiota, potential symbionts and pathogens.

Summary:

Social immunity has evolved as an additional level of defense in social insects. Since they live in densely populated colonies of related individuals their risk of infection is high. Social immunity therefore is an upgrade in protection against parasitic attack, on top of individual immunity. Of special interest is the horizontal transfer of immunological protection between individuals as a relevant component of social immunity. Since group-living insects, especially when aggregated in high numbers, share similar risks of infection as social insects, we hypothesize, that horizontal transfer of immunity may also be found in group-living, but non-social insects. To test this, we used the Red Flour Beetle Tribolium castaneum. The beetles live in highly populated densities and have been shown to alter their environment by secreting quinones into the flour as a form of cooperative defense against microbes. Moreover, vertical transfer of immunity (i.e. from parents to offspring) has previously been demonstrated in this species. We cohabitated naive beetles with conspecifics that were either wounded (to activate their immune system) or left naïve. By comparing several immune traits, we found that an activated immune status was transferred to conspecifics. The transfer of an activated immune status among individuals might be an important component of the defense level of a population.

Summary:

One prediction of host-parasite coevolution is that the virulence of the pathogen may change as it adapts to its host in a way that maximises its reproductive success and transmission potential. This has indeed been demonstrated in several controlled laboratory coevolution experiments, with both reductions and increases in virulence being seen. The majority of coevolution experiments, however, use discrete host generations taking only a limited number of usually uninfected hosts to start the next generation. Parasite generations are also often, to some extent, discrete, often being extracted from dead or infected hosts to start the next generation, discarding any spores or longer lasting parasite stages that made their way into the environment. For spore forming parasites, however, this is quite different from the likely natural scenario, where spores can survive for long periods of time in the environment and therefore may obtain the greatest evolutionary benefit by getting as many spores into the environment as possible. If under experimental conditions only spores from dead individuals are taken to the next generation, this benefit is not realised, potentially resulting in an outcome, substantially different to what might be seen in nature. I carried out a coevolution experiment using the red flour beetle, Tribolium castaneum, and its natural microsporidian pathogen, Paranosema whitei, with an overlap in host generations. Flour from the beetles’ environment, including any spores which made their way into it, was also transferred from generation to generation. Three treatments with different starting pathogen concentrations and a pathogen free control were used. In all cases coevolution resulted in extinction of the host population, with a pronounced increase in virulence being seen.