Perspectives on the evolutionary ecology of arthropod antimicrobial peptides

Abstract

One contribution of 13 to a theme issue 'Evolutionary ecology of arthropod antimicrobial peptides'. Antimicrobial peptides (AMPs) are important elements of the innate immune defence in multicellular organisms that target and kill microbes. Here, we reflect on the various points that are raised by the authors of the 11 contributions to a special issue of Philosophical Transactions on the 'evolutionary ecology of arthropod antimicrobial peptides'. We see five interesting topics emerging. (i) AMP genes in insects, and perhaps in arthropods more generally, evolve much slower than most other immune genes. One explanation refers to the constraints set by AMPs being part of a finely tuned defence system. A new view argues that AMPs are under strong stabilizing selection. Regardless, this striking observation still invites many more questions than have been answered so far. (ii) AMPs almost always are expressed in combinations and sometimes show expression patterns that are dependent on the infectious agent. While it is often assumed that this can be explained by synergistic interactions, such interactions have rarely been demonstrated and need to be studied further. Moreover, how to define synergy in the first place remains difficult and needs to be addressed. (iii) AMPs play a very important role in mediating the interaction between a host and its mutualistic or commensal microbes. This has only been studied in a very small number of (insect) species. It has become clear that the very same AMPs play different roles in different situations and hence are under concurrent selection. (iv) Different environments shape the physiology of organisms; especially the host-associated microbial communities should impact on the evolution host AMPs. Studies in social insects and some organisms from extreme environments seem to support this notion, but, overall, the evidence for adaptation of AMPs to a given environment is scant. (v) AMPs are considered or already developed as new drugs in medicine. However, bacteria can evolve resistance to AMPs. Therefore, in the light of our limited understanding of AMP evolution in the natural context, and also the very limited understanding of the evolution of resistance against AMPs in bacteria in particular, caution is recommended. What is clear though is that study of the ecology and evolution of AMPs in natural systems could inform many of these outstanding questions, including those related to medical applications and pathogen control.This article is part of the themed issue 'Evolutionary ecology of arthropod antimicrobial peptides'.

Eicosanoid mediation of immune responses at early bacterial infection stage and its inhibition by Photorhabdus temperata subsp. temperata, an entomopathogenic bacterium

“…Currently, it is unclear why these two homologous AMPs showed opposite response to the same bacterial infection. Rolff and Schmid‐Hempel () have raised a synergistic hypothesis of multiple AMPs because insects usually express AMPs in combinations. For example, one AMP in bumblebee ( Bombus terrestris ) targets the cell membrane of pathogen while another enters the bacterial cell to interact with chaperone DnaK (Rahnamaeian et al, ).…”

“…The recognition signal is then propagated by immune mediators such as cytokines, biogenic monoamines, nitric oxide (NO), and eicosanoids (Gillespie, Kanost, & Trenczek, ). These immune mediators activate hemocytes to express potent cellular immune responses or induce expression of genes encoding antimicrobial peptides (AMPs) mostly from fat body (Lavine & Strand, ; Rolff & Schmid‐Hempel, ). There must be cross talks between extracellular immune mediators and intracellular immune signals to modulate hemocyte shape change (Marmaras & Lampropoulou, ).…”

Cross-Species Interferon Signaling Boosts Microbicidal Activity within the Tick Vector

“…Many arthropods combat microbial infections through processes mediated by immune cells, including hemocytes (Smith et al, 2014). Arthropods can also rapidly synthesize a suite of AMPs that may persist for weeks (Rolff and Schmid-Hempel, 2016). Here, we unveil how the I. scapularis tick, the vector for the Lyme disease pathogen, B. burgdorferi , takes advantage of host-derived IFNγ to restrict spirochete proliferation within the gut.…”

Colistin Resistance ㏌ Enterobacteriaceae Isolated from Arthropods in Gifu City, Japan

“…Arthropods produce antimicrobial peptides to perform various functions including prevention of bacterial infections and mediating symbiotic relationships between the host and bene cial bacteria [6]. It could therefore be expected that the symbiotic bacteria of arthropods have developed resistance to antimicrobial peptides.…”