Sperm Races: live video report
Researchers at Syracuse University (New York State), working under the leadership of Scott Pitnick, with the help of fluorescent tagging technology, got an unprecedented opportunity to observe the competition taking place between the spermatozoa of different male Drosophila flies (Drosophila melanogaster), who fertilized the same female. The results of their work can be found in the article published on March 18 in the preliminary on-line version of the journal Science by Mollie K. Manier et al. «Resolving Mechanisms of Competitive Fertilization Success in Drosophila melanogaster».
Numerous works devoted to the study of the sexual behavior of various animals have shown that the mating of one female with several males in the wild is the rule rather than the exception. Apparently, the competitions of spermatozoa for speed and endurance taking place in the female reproductive tract are one of the mechanisms of natural selection and, accordingly, the evolution of the animal world.
However, until now, the mechanisms of these competitions have remained at the level of speculation based on counting the number of cubs conceived from each of the potential fathers, or on other indirect factors.
With the help of differential labeling of genes encoding the nuclear protein protamine (it provides a much denser DNA packing in sperm heads than the one histones are capable of), the researchers tracked the movement of two ejaculates belonging to males of different subspecies of drosophila along the reproductive tract of a female sperm. The pictures taken after the completion of the mating process of the female with the second male, as well as a 10-second video, show a complex dance performed by the sperm of one male, labeled with green fluorescent protein, the second, labeled with red.
The complexity of this action and the activity of the performers amazed scientists. Among the scenes they observed was the expulsion of sperm from the semen receptacle and spermatecas (organs of the female reproductive tract of drosophila, designed to preserve sperm in an active state), mixing of sperm from different males and the displacement of sperm from one male sperm of the second from the "storage chamber" of sperm.
However, scientists have failed to obtain evidence of a recently proposed theory, also based on the results of work with fruit flies, according to which the sperm of a later ejaculate negatively affects the competitiveness of the sperm of the first. Curiously, the authors of another article published this week in the same journal Science (Susanne P. A. den Boer et al., "Seminal Fluid Mediates Ejaculate Competition in Social Insects"), received confirmation of this theory when studying the sexual behavior of ants and bees. In these species, the seminal fluid, with the help of some unknown mechanisms, promotes the survival of its own spermatozoa, while simultaneously suppressing the viability of the spermatozoa of other males.
The application of the fluorescent tagging method proposed by the researchers to hymenopteran insects (ants and bees), other insect species, and, possibly, animals, will help in studying the features of the mechanisms of sperm competition used by various organisms. This technique is a very powerful tool for studying the mechanisms underlying the paternity options that are the direct result of such competitions.
The authors applied the methodology they developed to two more varieties of fruit flies and to Tribolium beetles (small flour crunch) and are working on creating several more models. However, they note that fruit flies are of particular value, different subspecies of which are able to interbreed with each other, and observing the mutual behavior of sperm cells of males of different subspecies who fertilized the same female can shed light on the mechanisms of speciation.
Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on the materials of The Scientist: Sperm sparring spotted.
22.03.2010