The effect of mating on immunity can be masked by experimental piercing in female Drosophila melanogaster

Abstract

Mating and immunity are two major components of fitness and links between them have been demonstrated in a number of recent investigations. In Drosophila melanogaster, a seminal fluid protein, sex-peptide (SP), up-regulates a number of antimicrobial peptide (AMP) genes in females after mating but the resulting effect on pathogen resistance is unclear. In this study, we tested (1) whether SP-induced changes in gene expression affect the ability of females to kill injected non-pathogenic bacteria and (2) how the injection process per se affects the expression of AMP genes relative to SP. The ability of virgin females and females mated to SP lacking or control males to clear bacteria was assayed using an established technique in which Escherichia coli are injected directly into the fly body and the rate of clearance of the injected bacteria is determined. We found no repeatable differences in clearance rates between virgin females and females mated to SP producing or SP lacking males. However, we found that the piercing of the integument, as occurs during injection, up-regulates AMP gene expression much more strongly than SP. Thus, assays that involve piercing, which are commonly used in immunity studies, can mask more subtle and biologically relevant changes in immunity, such as those induced by mating.

In the monarch butterfly the juvenile hormone effect upon immune response depends on the immune marker and is sex dependent

“…All groups were injected with 2 µL of the corresponding solution (JHa or DMSO) with a Hamilton micro syringe (10 µL), in the membranous area anterior to the thorax, next to where the wings are inserted. Although no real immune challenges were carried out in this study, this method of injection favors the immune response activation because its injury and piercing favor immune response to combat bacterial entrance and leads wound repair [13,28,29]. In addition, studies that have used the JH or its analogues to record the phenoloxidase (PO) production with [11] or without [10,30] immune challenge reported similar results in different species.…”

Female and male genetic contributions to post-mating immune defence in female Drosophila melanogaster

“…Other studies have measured overall defence as a function of mating in the context of experimental infection (McKean & Nunney 2001Shoemaker et al 2006;Fedorka et al 2007;Wigby et al 2008). Three of the cited studies have been performed using female D. melanogaster (McKean & Nunney 2005;Fedorka et al 2007;Wigby et al 2008), but no clear consensus has emerged even from those as to whether females suffer a meaningful reduction in immune defence after mating. Two of these studies (McKean & Nunney 2005;Wigby et al 2008) show no change owing to mating in the ability of females to clear non-pathogenic bacteria, while Fedorka et al (2007) demonstrated that females infected with a pathogenic bacterium suffer higher mortality if they have mated.…”

“…Examples of post-mating immune depression include a reduction in phenoloxidase activity after mating in the beetle Tenebrio molitor (Rolff & Siva-Jothy 2002), and decreased encapsulation ability correlated with increased oviposition in damselflies (Siva-Jothy et al 1998). Additionally, mating causes decreased survival after infection with a pathogen in female D. melanogaster (Fedorka et al 2007) but see (McKean & Nunney 2005;Wigby et al 2008), and increased mating effort leads to decreased hemocyte number, lytic activity and encapsulation ability in the cricket Allonemobius socius (Fedorka et al 2004). Postmating immunosuppression may not be universal, as it was not detected in yellow dung flies Scathophaga stercoraria (Schwarzenbach et al 2005), and phenoloxidase activity and parasite resistance are even increased after mating in female A. socius and Gryllus texensis, respectively (Fedorka et al 2004;Shoemaker et al 2006).…”

Correlated evolutionary changes in Drosophila female genitalia reduce the possible infection risk caused by male copulatory wounding

“…In the future, similar works should be conducted using actual pathogenic bacteria, possibly those isolated from male genitalia of Drosophila, instead of a simulated treatment. In future studies, a b the possible masking or mitigating effects of the immune response to infection risks should be accounted for (Wigby et al 2008). All of the observed fluorescent beads in the female genital region were immobilized within the melanized wound patches.…”