No major cost of evolved survivorship in Drosophila melanogaster populations coevolving with Pseudomonas entomophila

Abstract

Rapid exaggeration of host and pathogen traits via arms race dynamics is one possible outcome of host–pathogen coevolution. However, the exaggerated traits are expected to incur costs in terms of resource investment in other life-history traits. The current study investigated the costs associated with evolved traits in a host–pathogen coevolution system. We used the Drosophila melanogaster (host) –Pseudomonas entomophila (pathogen) system to experimentally derive two selection regimes, one where the host and pathogen both coevolved, and the other, where only the host evolved against a non-evolving pathogen. After 17 generations of selection, we found that hosts from both selected populations had better post-infection survivorship than controls. Even though the coevolving populations tended to have better survivorship post-infection, we found no clear evidence that the two selection regimes were significantly different from each other. There was weak evidence for the coevolving pathogens being more virulent than the ancestral pathogen. We found no major cost of increased post-infection survivorship. The costs were not different between the coevolving hosts and the hosts evolving against a non-evolving pathogen. We found no evolved costs in the coevolving pathogens. Thus, our results suggest that increased host immunity and pathogen virulence may not be costly.

Correlated responses to experimental evolution of increased post-infection survival in Drosophila melanogaster: Life-history trade-offs and reaction to novel stressors

“…Selected populations also did not exhibit an increased susceptibility to abiotic stress. Put together with previous studies that have experimentally evolved fly populations for increased immunity against bacterial population (Ye et al 2009, Faria et al 2015, Gupta et al 2016, Ahlawat et al 2022), we propose that whether evolving increased defense comes at the cost of other organismal function depend on the bacterial pathogen used for selection. The cost of mounting an immune defense was specific to the trait under focus but did not differ across different selection histories.…”

“…On the other hand, no life-history costs were reported in two separate experimental evolution studies where flies were selected for increased defense against the bacteria Pseudomonas entomophila (Faria et al 2015, Gupta et al 2016). Flies experimentally co-evolved with P. entomophila also do not incur any life-history costs (Ahlawat et al 2022). There may be a few possible reasons for the inconsistency in results obtained in these studies, such as the pathogen/parasite used for selection, genetic architecture of the host population, specific life- history trait tested, and the amount of resource available to the host for allocation into different traits.…”

Experimental evolution for improved post-infection survival selects for increased disease resistance inDrosophila melanogaster

“…By design in most, if not all, experimental evolution studies the reproduction window comes after the first wave of infection-induced mortality (the acute phase of infection) has passed (viz. Ye et al, 2009, Martins et al, 2013, Faria et al, 2015, Gupta et al, 2015, Ahlawat et al, 2022). The same is true for our populations.…”

Despite COVID: showcasing new research in evolutionary biology from academic care-givers in the middle of a pandemic

“…Considering life-history evolution, Matesanz et al [18] show how inherited negative effects of parental stress may override adaptive responses to drought in a wild lupin, questioning the adaptive value of transgenerational plasticity. Ahlawat et al's experimental evolution experiment [19] comparing host-parasite coevolution to host-only evolution in a fruit fly-bacterial pathogen situation revealed no evidence for different costs of post-infection survivorship between coevolving and non-coevolving hosts, hinting that the increased host immunity and pathogen virulence that can result from host-parasite coevolution might not confer major costs. Reviewing the current state of the field of the mechanisms underlying male-killing mediated by bacterial endosymbionts, Hornett et al [20] provide a novel argument that selection imposed by male-killing and favouring host nuclear suppressors will often involve the evolution of host sex determination pathways.…”

“…Ahlawat et al . 's experimental evolution experiment [19] comparing host–parasite coevolution to host-only evolution in a fruit fly-bacterial pathogen situation revealed no evidence for different costs of post-infection survivorship between coevolving and non-coevolving hosts, hinting that the increased host immunity and pathogen virulence that can result from host–parasite coevolution might not confer major costs. Reviewing the current state of the field of the mechanisms underlying male-killing mediated by bacterial endosymbionts, Hornett et al .…”