July 8, 2009 -- Females may be outwardly choosy when selecting sexual partners -- accepting or shunning mates in very public ways -- but males may get the last say in this battle of the sexes. New research found that males can adjust the speed and effectiveness of their sperm by allocating more or less seminal fluid to copulations. The determining factor is whether the male finds the female attractive. The study, conducted on red junglefowl, a director ancestor of chickens, adds to the growing body of evidence that males throughout many promiscuous species in the animal kingdom, including humans, can mate with many females, but chances of fertilization are greater when the female is deemed to be attractive. Desirable female red junglefowl are easy to identify. "Female attractiveness is determined by the expression of a sexual ornament -- the comb -- which is phenotypically and genetically correlated to the number and mass of eggs females lay," according to study co-authors Charlie Cornwallis of the University of Oxford and the Royal Veterinary College's Emily O'Connor. For the study, published in the current Proceedings of the Royal Society B, the researchers collected natural ejaculates from dominate and subordinate red junglefowl males housed at the University of Stockholm. The males had either just mated with attractive or unattractive females. Related Content:
The scientists next separated the sperm from the seminal fluid and analyzed the quantity and characteristics of both. "There was a strong relationship between sperm velocity and the volume of the ejaculate sperm came from," Cornwallis and O'Connor determined, adding that males allocated "larger ejaculates to attractive females." The mechanism behind this remains a mystery for now, but the scientists have an intriguing theory. "Males may alter the velocity of sperm they allocate to copulations by strategically firing their left and right ejaculatory ducts, which can operate independently," they explained. Stimulation from sexy, attractive females, therefore, leads to the double firing. "Furthermore," they added, "differential firing of left and right ejaculatory ducts may contribute to how males strategically change the number of sperm in their ejaculates, a phenomenon that is widespread, but for which the mechanism remains unknown." Get More NewsSpiders, Scorpions Among World's Oldest CreaturesMany creepy crawlies have been on Earth much longer than previously believed.Blood-Sucking Vampire Bats Sing DuetsWhite-winged vampire bats "harmonize" with separated roost mates.Oldest Hebrew Writing Possibly FoundAncient inscriptions on a 3,000-year-old pottery shard could make history.Rare, Prehistoric-Age Reptile Found in N.Z.A tuatara has been spotted on the New Zealand mainland for the first time in 200 years.Iceman Has No Living RelativesOetzi, the 5,300 year-old frozen mummy, left no living genetic legacy.SLIDE SHOW: Landscapes of TerrorWhat makes a place feel scary? There are scientific explanations.It's Official: People Are Warming the PolesHumans are conclusively to blame for polar warming, say scientists.Eight-Armed Animal Preceded DinosaursWhat may be one of Earth's first animals was no bigger than a coaster and had eight arms.Phoenicians Live on in People's GenesOne in 17 Mediterranean men may be descended from ancient Phoenicians.Pesticides, Fertilizers Linked to Frog DeclineA pesticide is found to promote parasites among amphibians.Hubble Telescope Taking Photos AgainThe Hubble Space Telescope is once again snapping stunning photos of the universe.Andean Mummy Hairs Show Hallucinogen UseScientists find direct evidence of hallucinogenic drug use among ancient Andeans.Opals on Mars Reveal Planet's Long Wet PastOpals found on Mars suggest the planet has been wet for much longer. |
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