Sperm-pathogen interactions and the evolution of ejaculate antimicrobial defences in passerine birds

Kliniske studier på mennesker har dokumentert en sammenheng mellom bakterielle infeksjoner og mannlig infertilitet. De potensielle implikasjonene av bakterier for infertilitet hos ville dyr er imidlertid i stor grad neglisjert. Dette prosjektet fant at en vanlig bakterie, E. coli, kan i betydelig grad redusere spermienes svømmeevne hos gråspurv. Ved bruk av avanserte genetiske metoder fant vi videre at ejakulater hos gråspurv har komplekse og varierte bakteriesamfunn, som inkluderer en rekke potensielt patogene bakterier. Arbeid som ble utført i dette prosjektet bekreftet også at sæd hos ville fugler har antibakteriell aktivitet, og at hanner med høyere antibakteriell aktivitet har høyere sædkvalitet. Arbeidet gir dermed støtte til ideen om at hannfugler har utviklet et antibakterielt forsvar i sædvæsken for å beskytte sædcellene fra bakterieindusert skade og redusert motilitet, og dermed sikre god fertilitet. I tillegg avdekket prosjektet det molekylære grunnlaget for antibakteriell aktivitet i fuglers sæd, og fant et antall proteiner med en funksjonell rolle i antibakterielt forsvar og immunitet i både spermier og sædvæsken. Videre har dette arbeidet vist at disse proteinene kan ha en avgjørende betydning for fertiliseringsprosessen og kan bidra til reproduktive barrierer mellom nært beslektede arter, og dermed ha betydning for artsdannelsesprosesser.

The project has generated new knowledge of the effects of bacteria on sperm quality and the implications of these effects for male reproductive health and fertility. Additionally, the project has provided new information on the molecular basis of immune defenses in male semen. The potential impacts of these findings are diverse. Most notably, knowledge generated by this research will likely be of interest to those studying evolutionary medicine and reproductive microbiomes and male infertility in humans. The knowledge generated from this research may provide conceptual and methodological advances to the researchers. Thus, there is significant potential for cross-fertilization of research ideas and methods among research fields. This project has also contributed to the training and education of a number of researchers, including 3 undergraduate researchers, a masters student (who is now pursuing a PhD in the Netherlands), a PhD student, and a research technician.

Organisms are constantly exposed to pathogens, and the ability of individuals to combat microbial attack is an important component of fitness. Sperm cells are not immune to microbial exposure; sperm encounter bacteria in the testes and ejaculate, during m ating and in the female reproductive tract. Bacteria can cause reductions in sperm quality and compromise male fertility. Moreover, ejaculate-borne bacteria can be transferred during mating (i.e. sexually transmitted diseases; STDs), with negative consequ ences for female fertility. Ejaculate-borne bacteria are thus predicted to generate intense selection for the evolution of antibacterial substances in seminal fluid that minimise bacterial-induced sperm defects and limit the transmission of STDs. However, little is known about the evolutionary consequences of ejaculate-borne bacteria and STDs in non-human taxa. This project brings together expertise in avian ecology, sperm biology, microbiology, immunology and proteomics to investigate the role of bacteri a in the evolution of avian seminal fluid and examine the consequences of STDs for the evolution of male secondary sexual traits. Our aims are to: 1) determine the consequences of ejaculate-borne bacteria for male sperm quality and paternity success, 2) t est the hypothesis that male traits reflect a male's current ejaculate bacterial load or antibacterial capacity, 3) characterise the immunity proteome of seminal fluid and test the functionality of antimicrobial substances, 4) examine the relationship bet ween ejaculate and general immunity, 5) quantify the impact of positive selection on immunity components of the seminal fluid proteome, and 6) examine the role of bacteria-driven ejaculate evolution in ejaculate-female interactions. As such, the proposed study will offer novel insight into pathogen-mediated selection and ejaculate evolution, as well as bacterial-induced fertility problems in domestic species and endangered species in conservation programs.