Birds require multiple sperm to penetrate eggs to ensure normal embryo development

  • One sperm is not enough to ensure normal embryo development in birds
  • Female birds can control the number of sperm that make it to the egg

Unlike humans, birds require multiple sperm to penetrate an egg to enable their chicks to develop normally.

A new study by scientists at the University of Sheffield revealed there is a functional role for ‘extra’ sperm in the early stages of embryo development.

hungry baby birds in nestThis is very different to humans and other mammals where the entry of more than one sperm into an egg is lethal.

Researchers also discovered female birds are able to regulate the number of sperm that make it to the egg, ensuring that sufficient sperm are available for fertilisation – particularly when the numbers of inseminated sperm are limited.

The study, led by Dr Nicola Hemming from the University’s Department of Animal and Plant Sciences, gives an insight into the biological significance of polyspermy which is a major puzzle in reproductive biology.

It has been a long-standing question in the natural world whether the extra sperm that enter a bird’s egg have any role to play in fertilisation or early embryo development.

The pioneering research shows that when very few sperm penetrate a bird’s egg, the embryo is unlikely to survive.

Dr Hemmings explained: “Our research shows that, in contrast to humans and other mammals, one sperm is not enough to ensure normal embryo development in birds.

“When just a single sperm enters the bird egg, fertilisation may occur normally, but the resulting embryo will probably die at a very early stage. This is surprising because when more than one sperm enters the human or mammalian egg – a process we call polyspermy – the egg is destroyed.

“Polyspermy has generally been considered to be bad for reproduction, but our results suggest that, in certain animal groups, polyspermy may in fact be necessary.”

The research is published today (Wednesday 28 October 2015) in the journal Proceedings of the Royal Society B.

Dr Hemmings added: “These findings provide an exciting expansion of our view of the sperm’s role in fertilisation. It is fascinating to speculate how the ‘extra’ sperm contribute to the early stages of embryo formation and development.”

Notes to Editors

To view the full paper please visit http://rspb.royalsocietypublishing.org/lookup/doi/10.1098/rspb.2015.1682

University of Sheffield
With almost 26,000 of the brightest students from around 120 countries, learning alongside over 1,200 of the best academics from across the globe, the University of Sheffield is one of the world’s leading universities. A member of the UK’s prestigious Russell Group of leading research-led institutions, Sheffield offers world-class teaching and research excellence across a wide range of disciplines. Unified by the power of discovery and understanding, staff and students at the university are committed to finding new ways to transform the world we live in. In 2014 it was voted the number one university in the UK for Student Experience by Times Higher Education and in the last decade has won four Queen’s Anniversary Prizes in recognition of the outstanding contribution to the United Kingdom’s intellectual, economic, cultural and social life. Sheffield has five Nobel Prize winners among former staff and students and its alumni go on to hold positions of great responsibility and influence all over the world, making significant contributions in their chosen fields. Global research partners and clients include Boeing, Rolls-Royce, Unilever, AstraZeneca, Glaxo SmithKline, Siemens and Airbus, as well as many UK and overseas government agencies and charitable foundations.

Contact

For further information please contact:

Amy Pullan
Media Relations Officer
University of Sheffield
0114 222 9859
a.l.pullan@sheffield.ac.uk