Sex-specific immune response against bacterial infection. David Duneau, Brian Lazzaro. Entomology, Cornell university, Ithaca, NY.

   Host allocations of resources into immunity are of a prime importance for parasites. Variations in resource allocation strategies among hosts are expected to influence parasite success and therefore influence parasite evolution. Males and females are often strikingly dimorphic for many traits. We hypothesize that sex differences in immune allocation could effectively make males and females into distinct types of hosts, offering different challenges and opportunities to their parasites. We therefore are examining differences in immune responses of male and female Drosophila melanogaster facing a bacterial infection. We infected both sexes of Drosophila melanogaster with its natural Gram-negative bacteria Providencia rettgeri. We determined that bacterial load is higher in males than females at 24h after infection, despite their smaller body size. We used qPCR to measure the constitutive and dynamic post-infection expression of five immune-related genes (antimicrobial peptides; AMPs). The constitutive expression of these AMP is very low in both sexes but female hosts show faster induction after infection. This and other measures of immunological performance indicate a true difference between the sexes in immunological capacity, which can influence host-pathogen coevolution and the epidemiology of disease. Such sex differences will be particularly important to the epidemiology of infection in populations of animals with sex-biased social structures.