One sperm and one egg is what it takes to fertilize mammalian embryos. But for birds, multiple sperm is needed, and it? crucial to their survival, according to a new study.
The study, called “Polyspermy in birds: sperm numbers and embryo survival,?published in the Royal Society Proceedings B.
“When just a single sperm enters the bird egg, fertilization may occur normally, but the resulting embryo will probably die at a very early stage,?explained Nicola Hemmings. post-doctoral research associate at the University of Sheffield’s Department of Animal and Plant Sciences, in a university press release. “This is surprising because when more than one sperm enters the human or mammalian egg ?a process we call polyspermy ?the egg is destroyed.”
Why this happens, is unknown.
According to the study? abstract:
“Polyspermy is a major puzzle in reproductive biology. In some taxa, multiple sperm enter the ovum as part of the normal fertilization process, whereas in others, penetration of the ovum by more than one sperm is lethal. In birds, several sperm typically enter the germinal disc, yet only one fuses with the female pronucleus. It is unclear whether supernumerary sperm play an essential role in the avian fertilization process and, if they do, how females regulate the progression of sperm through the oviduct to ensure an appropriate number reach the ovum. Here, we show that when very few sperm penetrate the avian ovum, embryos are unlikely to survive beyond the earliest stages of development. We also show that when the number of inseminated sperm is limited, a greater proportion than expected reach and penetrate the ovum, indicating that females compensate for low sperm numbers in the oviduct. Our results suggest a functional role for supernumerary sperm in the processes of fertilization and early embryogenesis, providing an exciting expansion of our understanding of sperm function in birds.?lt;/span>