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Comparative Study
. 2007 May 7;274(1614):1211-7.
doi: 10.1098/rspb.2006.0394.

Post-mating Disparity Between Potential and Realized Immune Response in Drosophila Melanogaster

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Free PMC article
Comparative Study

Post-mating Disparity Between Potential and Realized Immune Response in Drosophila Melanogaster

Kenneth M Fedorka et al. Proc Biol Sci. .
Free PMC article

Abstract

Reproductive costs are an essential component of evolutionary theory. For instance, an increase in reproduction is generally coupled with a decrease in immunocompetence shortly after mating. However, recent work in Drosophila melanogaster suggests that the potential to mount an immune response, as measured by the levels of immune gene expression, increases after mating. These data are in contrast to previous studies, which suggest that mating can reduce a fly's ability to survive an actual bacterial challenge (realized immunity). This pattern may be driven by some aspect of mating, independent of resource limitation, which reduces immune function by inhibiting the effective deployment of immune gene products. Though several studies have examined both the potential and the realized immunity after mating, none have examined these immune measures simultaneously. Here, we examined the link between the potential and the realized immunity in a sterile mutant of D. melanogaster. Shortly after mating, we found that female immune gene expression was high, but survival against infection was low. Surprisingly, this pattern was reversed within 24 h. Thus, estimates of immunity based on gene expression do not appear to reflect an actual ability to defend against pathogens in the hours following copulation. We discuss the possible mechanisms that may account for this pattern.

Figures

Figure 1
Figure 1
The effect of mating on the female immune system. Mated females exhibited a significant reduction in relative survival compared with the virgins (dotted line) when infected 3 h after mating (p=0.0148) and when infected 9 h after mating (p=0.0133).
Figure 2
Figure 2
Re-examination of the effect of mating on female immunity. As in figure 1, mated females showed a reduction in relative fitness compared with virgin females (dotted line; p=0.0083). Thus, survival appears to be independent of the incomplete penetrance of the sterile phenotype found previously in some females.
Figure 3
Figure 3
Expression levels of immune genes in mated females. The genes associated with the Imd pathway, attacin (att) and cecropin A and B (cecA and cecB, respectively), were either unchanged or upregulated 3 h after mating compared with those in virgin females. At this time, mated females also exhibited a lower survival to bacterial infection (figures 1 and 2). Twenty-four hours later, these same genes were downregulated, at which time mated and virgin females exhibited similar survival rates. Metchnikowin (mtk), a gene in the Toll pathway, was upregulated at both times. Actin served as our internal PCR control and vittelogenin (vit) provided an estimate of reproductive investment. All gene expression levels are relative to virgins. Error bars represent 95% CI.

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