Navigation Links
When cooperation counts
Date:7/30/2014

Everybody knows the shortest distance between two points is a straight line, and now Harvard researchers have evidence that sperm have been taking the familiar axiom to heart.

Though competition among individual sperm is usually thought to be intense, with each racing for the chance to fertilize the egg, Harvard scientists say in some species, sperm form cooperative groups that allow them to take a straighter path to potential fertilization.

A new study, conducted by Heidi Fisher, a post-doctoral student working in the lab of Hopi Hoekstra, Howard Hughes Investigator and Professor of Organismic and Evolutionary Biology and Molecular and Cellular Biology and the Alexander Agassiz Professor of Zoology in the Museum of Comparative Zoology and post-doctoral student Luca Giomi working with L Mahadevan, the Lola England de Valpine Professor of Applied Mathematics, of Organismic and Evolutionary Biology, and of Physics shows that in Peromyscus maniculatus, a species of deer mouse known to be promiscuous sperm clump together to swim in a more linear fashion. The study is described in a July 23 paper in Proceedings of the Royal Society B.

"We generally think that each individual sperm cell swims its little heart out to get to the egg," Hoekstra said. "But it had been discovered that, in at least a handful of organisms, sperm will cooperate and swim as a group."

Exactly why sperm clump together, however, had remained a mystery until now.

"We had some hints that cooperation was enhancing their swimming performance, but what we didn't understand was how it was helping," Fisher said. "With this study, we combined a mathematical model with much finer-scale measurements that looked at groups that ranged from single sperm cells to groups of as many as 30 cells. What we realized was that that while their overall speed wasn't increasing at all, but that the time it took them to go from point A to point B was decreasing -- they swim in a straighter line."

The study, also found that sperm from promiscuous mice were more likely to form clumps of the optimum size, and that, when compared with sperm from Peromyscus polionotus a closely-related, but monogamous, species of mouse the trait is likely driven by sexual selection.

The new paper builds on a 2010 study conducted in Hoekstra's lab which found that sperm cells preferentially clump with those produced by the same male. Spurred by that earlier paper, Mahadevan approached Hoekstra with the idea of creating a mathematical model to understand whether and how sperm received an advantage by forming groups.

"I read the paper and thought we could make a quantitative theory of the observations they had made," he said. "But of course, the only way to know whether any model was capable of anything predictive was to make it testable.

"In this contextthe question was: Is it possible to make the aggregate do better than then individual?" he continued. "One way to do that is to get all the tails to synchronize, but that doesn't happen. The other way is to cancel out the random motion of the individuals in an aggregate because the sperm adhere to each other. Eventually, for large aggregates, the sperm point towards each other and thus cannot swim at all. This mechanism when quantified in a model that Luca and I developed and this led to testable predictions., When Heidi did the experiment, we found that this was essentially correct."

In addition to finding that sperm which group together to swim in a more linear fashion, researchers were able to identify at what clump size sperm reaped the largest reward for grouping together. Groups with too few cells, Hoekstra said, continued to swim along more meandering paths, while much larger groups often resulted with sperm swimming against each other.

"What we found is that both species have an optimum at around eight, which was what the model predicted, but there were many fewer groups that were too big or too small in the promiscuous species," she said. "That is consistent with the idea that sexual selection is driving this trait in the promiscuous species, whereas in the monogamous species, where there's not as much competitive pressure, things are a bit more relaxed, so we see more variance in the clump sizes."

In the end, Mahadevan said, the study represented an ideal collaboration between the theoretical and the empirical.

"If you talk to evolutionary biologists, their approaches are often genetic, because they're trying to understand what the genetic bases are for natural selection pressures," he said. "From a theoretical point of view, the focus is on reproductive capacity. What's interesting in this particular situation is we can take a question of reproductive capacity and add a physiological twist to it that's associated with sperm motility, and then we can take that apart in the context of what happens when you change the shape of the sperm, or their ability to adhere to each other, or their ability to move."

"In my view we haven't so much answered the question as we've sharpened it," he continued. "And we've done by that couching a conceptual notion of competition and cooperation in terms of physical and physiological variables that can be measured and lead to testable predictions."


'/>"/>

Contact: Peter Reuell
preuell@fas.harvard.edu
617-496-8070
Harvard University
Source:Eurekalert

Related biology news :

1. Sibling cooperation in earwig families gives clues to early evolution of social behavior
2. What cooperation and conflict in an insects society can teach us about social acceptance
3. Rewards facilitate human cooperation under natural selection
4. Delayed gratification hurts climate change cooperation
5. Leopoldina signs cooperation agreement with the Academy of Science of South Africa
6. Southerners are less trusting, but trust is a factor in environmental cooperation, study shows
7. Study: MicroRNA cooperation mutes breast cancer oncogenes
8. Leopoldina strengthens cooperation with French national academy
9. JRC and US NOAA enhance cooperation on climate, weather, oceans and coasts
10. BGI, University of Helsinki and Wuhan University sign a MOU concerning cooperation on genomics
11. Suburban sprawl accounts for 50 percent of US household carbon footprint
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:6/22/2016)... , June 22, 2016   Acuant ... and verification solutions, has partnered with RightCrowd ... solutions for Visitor Management, Self-Service Kiosks and ... products that add functional enhancements to existing ... corporations and venues with an automated ID ...
(Date:6/15/2016)... June 15, 2016 Transparency ... titled "Gesture Recognition Market by Application Market - Global Industry Analysis ... 2024". According to the report, the  global gesture recognition ... 2015 and is estimated to grow at a ... by 2024.  Increasing application of gesture ...
(Date:6/2/2016)... , June 2, 2016 The ... has awarded the 44 million US Dollar project, for ... Embossed Vehicle Plates including Personalization, Enrolment, and IT Infrastructure ... leader in the production and implementation of Identity Management Solutions. ... January, however Decatur was selected for ...
Breaking Biology News(10 mins):
(Date:6/27/2016)... ... 2016 , ... Parallel 6 , the leading software as a service ... Virtual Patient Encounter CONSULT module which enables both audio and video telemedicine communication ... , Using the CONSULT module, patients and physicians can schedule a face to face ...
(Date:6/27/2016)... , ... June 27, 2016 , ... ... for Amgen, will join the faculty of the University of North Carolina ... professor of strategy and entrepreneurship at UNC Kenan-Flagler, with a focus on the ...
(Date:6/27/2016)... June 27, 2016   Ginkgo Bioworks , a ... engineering, was today awarded as one of the ... the world,s most innovative companies. Ginkgo Bioworks is ... the real world in the nutrition, health and ... directly with customers including Fortune 500 companies to ...
(Date:6/24/2016)... SAN DIEGO , June 24, 2016 /PRNewswire/ ... that more sensitively detects cancers susceptible to PARP ... individual circulating tumor cells (CTCs). The new test ... of HRD-targeted therapeutics in multiple cancer types. ... therapies targeting DNA damage response pathways, including PARP, ...
Breaking Biology Technology: