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

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 colouration. Nevertheless, we suggest that lysozyme-associated antibacterial activity in ejaculates may be the target of natural and sexual selection and that these enzymes likely function to defend avian sperm from bacterial-induced damage.科研人员已在多种动物的精液中鉴定出大量抗菌物质，这类物质被认为可在雌雄生殖道内保护精子免受细菌诱导的损伤。溶菌酶（Lysozyme）是一类可通过裂解细菌细胞壁发挥杀菌活性的酶类，因其属于组成型固有免疫系统的组分，能够即刻发挥作用抵御细菌侵袭，因此在精子防御过程中可能发挥尤为关键的作用。由于鸟类泄殖腔兼具排泄废物与转运精子的双重功能，鸟类成为研究精液抗菌防御机制的理想模型。但目前学界对鸟类精液的抗菌活性仍知之甚少，仅在家养火鸡（Meleagris gallopavo）中报道过精液溶菌酶水平的相关数据。此外，尚无针对野生动物精液溶菌酶水平的相关报道，而众多学者认为，这类数据对于全面解析免疫应答的功能与动态变化至关重要。本研究证实，野生雀形目鸟类华丽细尾鹩莺（Malurus cyaneus）的精液中存在溶菌酶，且不同雄性个体的精液溶菌酶浓度存在显著差异。但这种浓度差异与雄性个体健康状况、精子质量以及羽色均无关联。尽管如此，我们认为精液中溶菌酶介导的抗菌活性可能是自然选择与性选择的作用靶点，且这类酶类大概率可保护鸟类精子免受细菌诱导的损伤。