Abstract
When females mate promiscuously, female sperm storage provides scope to bias the fertilization success towards particular males via the non-random acceptance and utilization of sperm. The difficulties observing post-copulatory processes within the female reproductive tract mean that the mechanisms underlying cryptic female choice remain poorly understood. Here, we use zebra finches Taeniopygia guttata, selected for divergent sperm lengths, combined with a novel technique for isolating and extracting sperm from avian sperm storage tubules (SSTs), to test the hypothesis that sperm from separate ejaculates are stored differentially by female birds. We show that sperm from different inseminations enter different SSTs in the female reproductive tract, resulting in almost complete segregation of the sperm of competing males. We propose that non-random acceptance of sperm into SSTs, reflected in this case by sperm phenotype, provides a mechanism by which long sperm enjoy enhanced fertilization success in zebra finches.
Highlights
Darwin’s classic view of sexual selection saw males competing for access to females, and females choosing males based on traits expressed prior to copulation [1]
The single tubule where sperm from both males were found was branched, and sperm from the long-sperm producing male were located in a separate branch of the tubule to sperm from the short-sperm producing male, maintaining a degree of inter-male segregation
We have shown that, following sequential inseminations, sperm from different males, with different sperm lengths, do not mix in in the sperm storage tubules (SSTs) of female zebra finches, but instead enter different tubules
Summary
Darwin’s classic view of sexual selection saw males competing for access to females, and females choosing males based on traits expressed prior to copulation [1]. Our understanding of reproductive behaviour in internal fertilizers has been revolutionized by the realization that females often copulate with more than one male, providing the scope for sexual selection to continue after copulation [2]. The inevitable delay between insemination and fertilization, often prolonged by a period of female sperm storage in specialized regions of the oviduct, creates the conditions under which sperm from different males can interact and compete [2]. Avian SSTs are tubular invaginations in the oviduct epithelial tissue. They vary in size within and between individuals and species [10,11], and may or may not be branched [12]. Undoubtedly specialized for sperm storage, the role of the SSTs in post-copulatory sexual selection remains unknown
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
