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Female lizards desire males of many colours

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    Female lizards desire males of many colours * 18:30 24 April 2008 * NewScientist.com news service * Rachel Nowak  redhead... (Image: Mo Healey)
    Message 1 of 1 , Apr 24, 2008
      Female lizards desire males of many colours

          * 18:30 24 April 2008
          * NewScientist.com news service
          * Rachel Nowak


      redhead... (Image: Mo Healey)

      ...yellowhead... (Image: Mo Healey)

      ...and orangehead (Image: Mo Healey)

      A newborn dragon lizard (Image: Mo Healey)

      Vive la difference – between men. That's the attitude of the female painted dragon lizard, which lives across the southern states of Australia.

      The females are polyandrous, and mate with as many males as possible. That is easy, because they only need to copulate for 10 seconds before males ejaculate.

      What is more, they store ejaculates inside their reproductive tracts for up to five months, forcing sperm from different males to compete to fertilise their eggs.

      Evolutionarily speaking, this all makes good sense. By encouraging competition the female increases her chances of getting hold of good-quality sperm.

      What has been a mystery is the fact that the brightly-coloured male dragons come in more than one version: some have red heads, some yellow heads, and a third version – discovered last year – have orange heads.
      Spice of life

      Usually natural selection weans out inferior versions of an organism, so the fact that all versions of male painted dragons exist in the population has been hard to explain.

      Now a team of evolutionary ecologists believe that they have solved a major piece of the puzzle.

      They think female dragons deliberately choose to mate with males with different coloured heads, perhaps as a means of ensuring they are not mating with the same male twice. That in turn helps ensure that the different head colours persist.

      "Given the choice, they go for variety," says Mo Healey of the University of Wollongong in New South Wales, Australia, who led the study. "This is the major selective pressure driving and maintaining the trait."
      Feisty red-heads

      Healey points out, however, that the female preference for variety isn't the only driving force. "The males also use head colour to assess each other's willingness to fight," she says. Red heads are better fighters.

      In the study, female lizards were allowed to approach male lizards in Perspex-sided cages. Given the option of either a single red-headed male or a single yellow-headed one, eight females choose yellow and 10 choose red, a difference that is not significant.

      Then 76 females were allowed to approach two pairs of males, one pair with the same, the other with different coloured heads. Two thirds of the females chose the pair with different coloured heads.

      "It's yet another demonstration that these little creatures with brains much smaller than a pea are taking in information about who is who, and using it to make extraordinarily subtle reproductive decisions about who to pursue to enhance fitness," says zoologist Rick Shine of the University of Sydney.
      Male hunt

      Healey and her colleagues also found that females that mated with multiple males hatched 12% more of their eggs than those who only mated with one male. In other words, multiple mating improves reproductive success.

      But there is a danger to females who mate with lots of males. When the researchers released lizards back into the bush, 20% of females released with males of one colour were recaptured over 13 weeks, compared to only 7% of females released with a mixture of red- and yellow-headed males.

      "They travel around more going to males, and time away from the burrow is dangerous," says Healey.

      Journal reference: Ethology (DOI: 10.1111/j.1439-0310.2007.01469.x)

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