Genetic covariance in immune measures and pathogen resistance in decorated crickets (Gryllodes sigillatus) is sex and pathogen specific

Insects are important models for studying immunity in an ecological and
evolutionary 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. We use nine
highly inbred lines to thoroughly examine the genetic relationships
between a suite of commonly used immune assays (haemocyte count, implant
encapsulation, total phenoloxidase activity, antibacterial zone of
inhibition, pathogen 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. 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. cereus and M. robertsii. In addition, the clearance of S. marcescens
was genetically correlated with the resistance to all three pathogens in
both sexes. Genetic correlations 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 suggesting
that these measures could evolve independently in the sexes. Our finding
that the genetic architecture of immune function is sex and pathogen
specific suggests that the evolution of immune function in male and female
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.