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Sex-specific effects of antagonistic coevolution: Insights from an insect host and a bacterial pathogen coevolution system

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Mar 24, 2025 version files 284.55 KB

Abstract

Experimental host-pathogen coevolution provides an opportunity to understand the long-term consequences of adaptive interactions between hosts and pathogens. Studies using prokaryotic and eukaryotic hosts and their pathogens have explored the changing dynamics of antagonistic interactions with time, evolution of generalists or specialists, and potential costs associated with coevolution. However, the dependence of host-pathogen coevolutionary responses on sex of the host remains unexplored.

To address this, we chose a host species which allow us to compare coevolved traits between male and female hosts with their native pathogens. Towards this end, we conducted a laboratory experiment where we coevolved insect host Drosophila melanogaster with its bacterial pathogen Pseudomonas entomophila. Apart from the host-pathogen coevolution regimen, the experimental design included three other selection regimes - host adaptation to a non-evolving ancestral pathogen, and two control regimes. To study coevolved traits in hosts in pathogens across time and sex, we measured host survivorship post infection against pathogens from three evolutionary time points – ancestor, pathogen from the past, and present coevolution cycle. Our results showed that the coevolved hosts exhibited higher survivorship when exposed to pathogens, relative to the hosts adapted to non-evolved pathogen and control hosts. These results are true against pathogenic exposure from all three time points. Coevolved pathogens from the present time exhibited the highest virulence, which was variable across the replicate pathogen populations. We also observed that despite comparable mortality, the two sexes differ in the onset of mortality in the control regimes, a response not observed in the coevolved hosts.

Taken together, our results showed that pathogens and hosts had the greatest success against each other as they coevolved together, but the susceptibility of naïve hosts was sex-specific. These results provide important insights into the process of host-pathogen coevolution.