Sperm size isn't everything

Nov 25, 2008

Contrary to common scientific belief, the length of a sperm's tail does not always determine how fast it can swim. Research published in the open access journal BMC Evolutionary Biology has shown that in the counter-intuitive microscopic world in which sperm operate, streamlining and longer tails don't always provide a speed advantage.

Stuart Humphries, from the University of Sheffield, and collaborators from the University of Western Australia have critically evaluated the evidence linking sperm shape to swimming speed. He said, "It seems clear that some assumptions regarding the physics of sperm locomotion have hampered our progress in understanding the processes mediating sperm competition. It is commonly believed that selection for increased sperm performance will favor the evolution of longer, and therefore faster swimming, sperm. In fact, the relative lengths of a sperm's constituent parts, rather than their absolute lengths, are likely to be the target of selection."

Small size and low swimming speeds mean that, in hydrodynamic terms, sperm operate in a very different regime from the one that we are used to. At this microscopic scale, although a longer tail does allow a sperm to generate more thrust, the drag created by a sperm's head is often enough to counteract any such gains. According to Humphries, "We suggest that, irrespective of whether tail length, total length or head length is used, any attempts to correlate a single measure of length to speed are likely to be futile. We argue that accounting for the balance between drag from the head and thrust from the tail will allow us to extend our understanding of the link between sperm form and function."

These findings imply that, contrary to current thinking, one cannot attribute the evolution of longer sperm to any competitive advantage that length alone gives them.

Citation: Sperm competition: linking form to function, Stuart Humphries, Jonathan P Evans and Leigh W Simmons, BMC Evolutionary Biology (in press) www.biomedcentral.com/bmcevolbiol/

Source: BioMed Central

Explore further: Revealing camouflaged bacteria

add to favorites email to friend print save as pdf

Related Stories

Cellular tail length tells disease tale

Oct 31, 2013

Simon Fraser University molecular biologist Lynne Quarmby's adventures in pond scum have led her and four student researchers to discover a mutation that can make cilia, the microscopic antennae on our cells, ...

The long and short of sperm tails

Aug 05, 2011

A team of biologists in Japan has uncovered an unexpected role for mitochondria1, the power houses of cells, in the development of sperm in the fruit fly Drosophila melanogaster.

Focusing on one cell

Jan 31, 2011

Most people don’t think highly of pond scum, but for Susan Dutcher, PhD, the single-celled green algae Chlamydomonas are incredible creatures worthy of her life’s work.

Recommended for you

Chimpanzees prefer firm, stable beds

1 hour ago

Chimpanzees may select a certain type of wood, Ugandan Ironwood, over other options for its firm, stable, and resilient properties to make their bed, according to a study published April 16, 2014 in the open-access ...

For cells, internal stress leads to unique shapes

2 hours ago

From far away, the top of a leaf looks like one seamless surface; however, up close, that smooth exterior is actually made up of a patchwork of cells in a variety of shapes and sizes. Interested in how these ...

Adventurous bacteria

3 hours ago

To reproduce or to conquer the world? Surprisingly, bacteria also face this problem. Theoretical biophysicists at Ludwig-Maximilians-Universitaet (LMU) in Munich have now shown how these organisms should ...

User comments : 0

More news stories

Chimpanzees prefer firm, stable beds

Chimpanzees may select a certain type of wood, Ugandan Ironwood, over other options for its firm, stable, and resilient properties to make their bed, according to a study published April 16, 2014 in the open-access ...

For cells, internal stress leads to unique shapes

From far away, the top of a leaf looks like one seamless surface; however, up close, that smooth exterior is actually made up of a patchwork of cells in a variety of shapes and sizes. Interested in how these ...

Down's chromosome cause genome-wide disruption

The extra copy of Chromosome 21 that causes Down's syndrome throws a spanner into the workings of all the other chromosomes as well, said a study published Wednesday that surprised its authors.

Ebola virus in Africa outbreak is a new strain

The Ebola virus that has killed scores of people in Guinea this year is a new strain—evidence that the disease did not spread there from outbreaks in some other African nations, scientists report.