Lysozyme-associated bactericidal activity in the ejaculate of a wild passerine

Abstract

Numerous antibacterial substances have been identified in the ejaculates of animals and are suggested to protect sperm from bacterial‐induced damage in both the male and female reproductive tracts. Lysozymes, enzymes that exhibit bactericidal activity through their ability to break down bacterial cell walls, are likely to be particularly important for sperm defence as they are part of the constitutive innate immune system and are thus immediately available to protect sperm from bacterial attack. Birds are an ideal model for studies of ejaculate antimicrobial defences because of the dual function of the avian cloaca (i.e. waste excretion and sperm transfer), yet the antibacterial activity of avian ejaculates remains largely unexplored, and data on ejaculate lysozyme levels are only available for the domestic turkey (Meleagris gallopavo). Moreover, ejaculate lysozyme levels have not been reported for any species in the wild; which many argue is necessary to gain a comprehensive understanding of the function and dynamics of immune responses. Here, we show that lysozyme is present in the ejaculate of a wild passerine, the superb fairy‐wren (Malurus cyaneus), and that the concentration of lysozyme in ejaculates varies substantially among males. This variation, however, is not associated with male condition, sperm quality or plumage coloration. Nevertheless, we suggest that lysozyme‐associated antibacterial activity in ejaculates may be the target of natural and sexual selection and that these enzymes are likely to function in defending avian sperm from bacterial‐induced damage. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 92–100.

The Reproductive Microbiome: An Emerging Driver of Sexual Selection, Sexual Conflict, Mating Systems, and Reproductive Isolation

“…For example, the evolution of faster swimming sperm may allow sperm to more rapidly reach ova or female sperm storage organs, thus reducing the impact of the female reproductive microbiome and/or immunity [62], although faster sperm may have evolved because of the competitive advantage gained in sperm competition, independently of microbial effects. More convincing is the evidence for antimicrobial activity in ejaculates [44,63,64] and the presence of antimicrobial and immunity-related proteins in seminal fluid in a range of taxa (e.g., red junglefowl, Gallus gallus [65], Passer sparrows [66], Drosophila [67], and honeybee, Apis mellifera [68]). Interestingly, male junglefowl may preferentially invest in seminal fluid proteins involved in immunity over successive matings, possibly to defend depleting numbers of sperm from female antimicrobial and immune responses [69].…”

The Seminal fluid proteome of the polyandrous Red junglefowl offers insights into the molecular basis of fertility, reproductive ageing and domestication

“…Immunity proteins are widespread in both male and female reproductive systems38 and some SFPs are known to target microbes that pose a threat to sperm viability and clear pathogens introduced during copulation, thus protecting the egg from potential infections4849505152. Evidence suggests that avian semen can harbour bacteria5354 and that the SF of some birds may have antibacterial properties61852. Our results confirm that antimicrobial proteins gallinacin 9 and 10, of the defensin protein family, are amongst the most abundant proteins in the RJF SF proteome, a finding consistent with SF analysis in domestic chickens24 and of particular relevance for promiscuous populations of RJF, where ejaculates host diverse bacterial communities (R. Eccleston & T. Pizzari, unpublished).…”

Effect of nutritional interventions with quercetin, oat hulls, β-glucans, lysozyme and fish oil on performance and health status related parameters of broilers chickens

“…Plasma lysozyme may be involved in non-specific immune processes such as opsonisation, leading to phagocytosis of Gram-negative bacterial invaders that are less responsive to lysozyme (Callewaert et al 2008). In addition, lysozyme plays an essential role as a general defence molecule in the innate immune system of many vertebrates due to its continuous presence in various body fluids (Millet et al 2007;Rowe et al 2013). In most vertebrates, including birds, both plasma lysozyme concentration and activity increases along with pathogen exposure or inflammation processes (Millet et al 2007;Maraghi et al 2012), accompanied by increased blood leukocyte levels.…”