It is extremely interesting!
The topic of competition and collaboration for the benefit of maximized self fitness has significant social science applications … with regards to the current population status in Haiti, this new paper just stimulates me a lot of random thoughts.
Nature advance online publication 20 January 2010
doi:10.1038/nature08736
Received 24 September 2009; Accepted 7 December 2009; Published online 20 January 2010Competition drives cooperation among closely related sperm of deer mice
Heidi S. Fisher1,2 & Hopi E. Hoekstra1,2
1. Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology,
2. Center for Brain Science, Harvard University, Cambridge, Massachusetts 02138, USACorrespondence to: Heidi S. Fisher1,2 Correspondence and requests for materials should be addressed to H.S.F. (Email: hfisher@oeb.harvard.edu).
Among the extraordinary adaptations driven by sperm competition is the cooperative behaviour of spermatozoa1. By forming cooperative groups, sperm can increase their swimming velocity and thereby gain an advantage in intermale sperm competition 1, 2. Accordingly, selection should favour cooperation of the most closely related sperm to maximize fitness 3. Here we show that sperm of deer mice (genus Peromyscus) form motile aggregations, then we use this system to test predictions of sperm cooperation. We find that sperm aggregate more often with conspecific than heterospecific sperm, suggesting that individual sperm can discriminate on the basis of genetic relatedness. Next, we provide evidence that the cooperative behaviour of closely related sperm is driven by sperm competition. In a monogamous species lacking sperm competition, Peromyscus polionotus, sperm indiscriminately group with unrelated conspecific sperm. In contrast, in the highly promiscuous deer mouse, Peromyscus maniculatus, sperm are significantly more likely to aggregate with those obtained from the same male than with sperm from an unrelated conspecific donor. Even when we test sperm from sibling males, we continue to see preferential aggregations of related sperm in P. maniculatus. These results suggest that sperm from promiscuous deer mice discriminate among relatives and thereby cooperate with the most closely related sperm, an adaptation likely to have been driven by sperm competition.
The following parts are from the original paper which I thought are very intriguing:
“Why then do sperm of P. polionotus aggregate at all if the species is strictly monogamous and lacks sperm competition? Sperm cooperation may benefit monogamous males if the increased swimming velocity of aggregated sperm allows them to migrate faster through a potentially hostile female tract 3 or manoeuvre around obstacles while travelling to the fertilization site 26.”
“P. maniculatus sperm discriminate equally against sperm of a brother and a heterospecific. Such highly selective aggregations are similar to cooperative phenotypes seen in social amoebas (Dictyostelium discoideum) 28 and budding yeast (Saccharomyces cerevisiae) 29. In these microbes, a single gene encodes for a homophilic adhesion protein 28,29, suggesting that sperm aggregation may also operate under a simple genetic mechanism.”
“… temporary alliances among sperm are not passively formed, rather they represent a complex discriminatory behaviour driven by sexual selection“
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New in 'Theory'
http://f1000biology.com/article/id/1797996/evaluation
Hunter Fraser
Stanford University, United States of America
In this work, Fisher and Hoekstra show that sperm from mice can cooperate with one another in a highly selective fashion, by forming fast-swimming aggregates specifically with other sperm from the same male. This fascinating behavior is a vivid example of the effects of competition for fertilization.
By fluorescently tagging sperm from multiple males with different colors and then mixing these together, preferential aggregation of sperm from the same male was observed. This was seen only in a promiscuous mouse species, and not in a monogamous species, suggesting that competition between sperm from different males may be driving this behavior. Intriguingly, sperm could even differentiate between self vs sperm from a brother (to an equal extent as they could discriminate sperm from an unrelated male), suggesting that genetic similarity between sperm is unlikely to be responsible for this discrimination ability. The mechanism underlying this behavior is not known, but will surely be an exciting subject for future work.