Abstract
Birds are model organisms in sperm biology. Previous work in zebra finches, suggested that sperm sampled from males' faeces and ejaculates do not differ in size. Here, we tested this assumption in a captive population of house sparrows, Passer domesticus. We compared sperm length in samples from three collection techniques: female dummy, faecal and abdominal massage samples. We found that sperm were significantly shorter in faecal than abdominal massage samples, which was explained by shorter heads and midpieces, but not flagella. This result might indicate that faecal sampled sperm could be less mature than sperm collected by abdominal massage. The female dummy method resulted in an insufficient number of experimental ejaculates because most males ignored it. In light of these results, we recommend using abdominal massage as a preferred method for avian sperm sampling. Where avian sperm cannot be collected by abdominal massage alone, we advise controlling for sperm sampling protocol statistically.
Highlights
Male competition over access to females, and sperm competition over fertilisation of eggs, are two sides of the same coin − both determine male reproductive success and fitness [1,2]
Of 52 males tested on two days, only three males copulated with the female dummy, and for only two of these males could we collect experimental ejaculates
Because of the limited sample size, the sperm length measures from the female dummy samples were only used for descriptive summary statistics (Table 1) but omitted from further statistical analyses
Summary
Male competition over access to females, and sperm competition over fertilisation of eggs, are two sides of the same coin − both determine male reproductive success and fitness [1,2]. Males compete with each other for access to mates, and when a male fails to secure exclusive copulation rights, his sperm need to outcompete rivals’. Sperm in fertilising eggs [3]. Sperm competition is ubiquitous across taxa and an important part of sexual selection [2,4]. One eminent interest of evolutionary biologists is to understand which traits predict the competitiveness of sperm and the likeliness to win the sperm race. In sperm evolutionary ecology research, sperm size and shape matters. Sperm length commonly correlates positively with sperm swimming speed [5,6,7], but see [8], comparative sperm morphometry (i.e. measured dimensions of different sperm components) is used to reveal
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
