Abstract
In many animal species, females and males differ in physiology, lifespan, and immune function. The magnitude and direction of the sexual dimorphism in immune function varies greatly and the genetic and mechanistic bases for this dimorphism are often unknown. Here we show that Drosophila melanogaster females are more likely than males to die from infection with several strains of the fungal entomopathogen Beauveria bassiana. The sexual dimorphism is not exclusively due to barrier defenses and persists when flies are inoculated by injection as well as by surface exposure. Loss of function mutations of Toll pathway genes remove the dimorphism in survivorship. Surprisingly, loss of function mutation of relish, a gene in the Imd pathway, also removes the dimorphism, but the dimorphism persists in flies carrying other Imd pathway mutations. The robust sexual dimorphism in D. melanogaster survival to B. bassiana presents opportunities to further dissect its mechanistic details, with applications for biological control of insect vectors of human disease and insect crop pests.
Highlights
Physiology and lifespan differ between females and males across many animal species[1,2]
To determine whether the dimorphism was dose-dependent in two commonly used B. bassiana strains, ARSEF12460 and GHA were sprayed onto Canton-S D. melanogaster with suspensions of various dilutions
To establish whether the post-inoculation housing conditions impacted the sexual dimorphism in D. melanogaster survivorship and to determine whether the dimorphism extended to a genetically diverse population, we inoculated the D. melanogaster population PopC3 with GHA and tracked post-infection survival in both vials and population cages
Summary
Physiology and lifespan differ between females and males across many animal species[1,2]. The laboratory fruit fly, Drosophila melanogaster, can be used as a model organism to study sex differences in immune defense. Sex differences in susceptibility to infection may depend on barrier defenses such as cuticle integrity and on behavioral defenses such as grooming. Taylor and Kimbrell[20] observed lower survival in D. melanogaster females than males after B. bassiana spores were introduced to their cuticles. Taylor and Kimbrell[20] observed that mutating genes in the Toll and Imd pathways did not eliminate sexual dimorphism in defense against fungal infection. As our preliminary results opposed those prior findings, we tested the relative importance of these pathways by assessing whether mutants in different components of the signaling pathways demonstrated sexual dimorphism in their survival to fungal infection
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