Microbes in tree swallow semen

A frequently hypothesized but poorly studied cost of multiple mating in bir ds is that exposure to pathogenic sexually transmitted microbes (STM's) can lower reproductive success. Conversely, female birds may benefit from high frequencies of copulation and multiple copulation partners If they receive cloacal inoculations of beneficial STM's that can either protect them agai nst future encounters with pathogens and/or serve as therapy against presen t infection. We examined the semen of 30 male tree swallows (Tachycineta bi color) in 1998 to determine the presence and prevalence of potential pathog enic and beneficial STM's. Semen was collected directly from males after ap plying gentle pressure to the cloaca and we used standard microbiological t echniques to identify microbes. We found that 19 of 30 samples contained on e or more types of microbes. In these 19 positive samples, we isolated both pathogenic and beneficial microbes from 11, only pathogenic microbes from seven, and only beneficial microbes from one. This variation among males su ggests that females would benefit from considering a particular male's pote ntial as a donor of either pathogenic or beneficial STM's as a criterion fo r mate choice. There were few significant differences between males with pa thogen-infected semen and those without pathogens in their semen in measure s of size, morphology, and ectoparasite score and feather damage. Likewise, there were few significant differences between males with beneficial Lacto bacilli spp. in their semen and those without Lactobacilli spp. in their se men in measures of sizer morphology, and ectoparasite score and feather dam age. We were unable to determine if there was a relationship between microb e presence and prevalence on reproductive performance.