Sperm-pathogen interactions and the evolution of ejaculate antimicrobial defences in passerine birds
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 mating 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 consequences 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 bacteria 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) test 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 between 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.
Research Council of Norway, FRIPRO, 2014-2018 (project number 230434 / F20)