Genetic covariance in immune measures and pathogen resistance in decorated crickets is sex and pathogen specific

Authors: LETENDRE, CORINNE - Western Sydney University; Duffield, Kristin; SADD, BEN - Illinois State University; SAKALUK, SCOTT - Illinois State University; HOUSE, CLARISSA - Western Sydney University; HUNT, JOHN - Western Sydney University

Submitted to: Journal of Animal Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2022
Publication Date: 4/26/2022
Citation: Letendre, C., Duffield, K.R., Sadd, B.M., Sakaluk, S.K., House, C.M., Hunt, J. 2022. Genetic covariance in immune measures and pathogen resistance in decorated crickets is sex and pathogen specific. Journal of Animal Ecology. 00:1-18. https://doi.org/10.1111/1365-2656.13709.
DOI: https://doi.org/10.1111/1365-2656.13709

Interpretive Summary: Insects are important study organisms across many fields of research, including pest management. Researchers working with insects are often interested in studying their immunity (or, their ability to resist disease) and they do so by using various assay techniques. However, we know very little about how reliable or meaningful these immune assays are because they are often not related to the insect's ability to fight and resist disease. Here, we measured immunity in crickets (a model insect in these assessments) using several commonly used immune assays. We then measured resistance to infection from three pathogens (two bacteria and one fungus), allowing us to determine how these assays relate to fight infection. We found support for the assumption that immune assays accurately measure disease resistance. We also provide a framework for measuring and interpreting assays of immune function in insects for future research, which will be a very valuable resource for researchers studying insects. This foundational research will have impacts on biological control as it provides a better understanding of measuring insect immunity, assisting the development of pesticides that effectively target and kill agricultural insect pests.

Technical Abstract: 1. Insects are important models for studying immunity in an ecological and evo-lutionary context. Yet, most empirical work on the insect immune system has come from phenotypic studies meaning we have a limited understanding of the genetic architecture of immune function in the sexes. 2. We use nine highly inbred lines to thoroughly examine the genetic relationships between a suite of commonly used immune assays (haemocyte count, implant en-capsulation, total phenoloxidase activity, antibacterial zone of inhibition and path-ogen clearance) and resistance to infection by three generalist insect pathogens (the gram- negative bacterium Serratia marcescens, the gram-positive bacterium Bacillus cereus and the fungus Metarhizium robertsii) in male and female Gryllodes sigillatus. 3. There were consistent positive genetic correlations between haemocyte count, antibacterial and phenoloxidase activity and resistance to S. marcescens in both sexes, but these relationships were less consistent for resistance to B. cereusand M. robertsii. In addition, the clearance of S. marcescens was genetically cor-related with the resistance to all three pathogens in both sexes. Genetic correla-tions between resistances to the different pathogen species were inconsistent, indicating that resistance to one pathogen does not necessarily mean resistance to another. Finally, while there is ample genetic (co)variance in immune assays and pathogen resistance, these genetic estimates differed across the sexes and many of these measures were not genetically correlated across the sexes, sug-gesting that these measures could evolve independently in the sexes. 4. Our finding that the genetic architecture of immune function is sex and patho-gen specific suggests that the evolution of immune function in male and fe-male G. sigillatus is likely to be complex. Similar quantitative genetic studies that measure a large number of assays and resistance to multiple pathogens in both sexes are needed to ascertain if this complexity extends to other species.