Ecological immunology

Infections and parasite loads vary among hosts. Variation results from ecological, genetic, and immunological factors. Immune defences provide benefits as well as costs and are, therefore, a compromise. Costs result from trade-offs with other needs and can be genetically encoded or plastic (i.e. can change depending on circumstances). Costs are physiological (e.g. energy consumption) or based on evolved genetic covariance. Self-damage (immunopathology) is a further, important cost. Natural selection should optimize the costs and benefits of defences and thus leads to various outcomes in terms of specificity, response delay and strength, or the formation of memory. Moreover, hosts can either resist an infection by eventual clearance, or tolerate the consequences of parasitism.

Antimicrobial peptides play a functional role in bumblebee anti-trypanosome defense

Bumblebees, amongst the most important of pollinators, are under enormous population pressures. One of these is disease. The bumblebee and its gut trypanosome Crithidia bombi are one of the fundamental models of ecological immunology. Although there is previous evidence of increased immune gene expression upon Crithidia infection, recent work has focussed on the bumblebee's gut microbiota. Here, by knocking down gene expression using RNAi, we show for the first time that antimicrobial peptides (AMPs) have a functional role in anti-Crithidia defense.