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Image: R.T. HANLON The mating scene for giant Australian cuttlefish (Sepia apama) is rife with fighting and deception. Small males often scoop their much larger counterparts by pretending to be female themselves, which allows the runts to get closer to females of reproductive age. "In the blink of an eye they can pull out of it and go back to being a male," observes lead author Roger Hanlon of the Marine Biological Laboratory in Woods Hole, Mass. But although researchers had observed this behavior in the wild, it was unclear how successful the male mimics were at actually fertilizing females. Hanlon and his colleagues studied the creatures in their natural habitat and used DNA fingerprinting to analyze eggs and calculate the mimics' success rates. According to the report, the female impersonators fertilized female fish in 60 percent of their attempts, a success rate about twice that of honest male cuttlefish.
A second report by researchers at the University of East Anglia in Norwich, U.K., details a new example of mimicry in vertebrates, which usually lack the ability to switch appearances. Isabelle M. Cote and Karen L. Cheney found that the bluestriped fangblenny fish (Plagiotremus rhinorhynchos) is an exception and can turn its disguise on and off at will. By pretending to be a bluestreak cleaner fish (Labroides dimidiatus--an animal that helps other species by removing parasites--the fangblenny then ambushes its prey. Although the physiological basis of the animals' color changes is not yet understood, the scientists found that rapid shifts in hue are possible and that the fish can maintain the different appearance for several hours. This flexibility is beneficial because if there are no cleaner fish to impersonate, the fangblenny fish can revert to its signature blue stripe, which allows the creature to blend in better with the surroundings. --Sarah Graham< /I>
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Among snakes, sex appeal has benefits�even when it doesn't lead to mating. Findings reported today in the journal Nature suggest that male garter snakes emerging from hibernation impersonate females just so that other males will warm them up and conceal them from predators.
Previous explanations of female mimicry in various animal species have regarded it as an alternative mating strategy, in which impersonators may steal matings or avoid aggression from brawnier rival males. But when australian biologist Richard Shine of the University of Sydney and his colleagues examined the phenomenon in garter snakes, they could find no mating advantage to the she-males. Noting that she-maleness in these creatures occurs only during the first day or two after they emerge from their eight-month hibernation�a period during which the snakes are cold and weak�the researchers propose another explanation for female mimicry. Perhaps, they offer, this strategy evolved as a way to get warm and evade predators, such as crows.
Field observations show that when an alluring she-male snake exits its hibernation den, male suitors form a so-called mating ball around it almost immediately. Perhaps not surprisingly, this mass of amorous males provides a great deal of warmth and protection to the object of their affections. Moreover, subsequent laboratory experiments demonstrated that such warming does, in fact, speed the vulnerable snake's recovery from hibernation: she-males that were kept warm regained their fully male status within three hours, while those kept cool retained their she-maleness for more than five hours. Thus "although intuition would favour an interpretation that female mimicry has evolved within the context of alternative mating tactics," the authors write, "simpler explanations should also be investigated." --Kate Wong
Biologists have known for some time that among certain egg-laying reptiles�crocodiles, for example�the sex of the embryos depends on the temperature at which they develop. No one suspected that the phenomenon could occur in reptiles that bear live young because the mothers maintain fairly stable body temperatures. Findings reported today in the journal Nature, however, reveal that, in fact, a female lizard can determine the sex of her offspring through thermoregulation�a mechanism that helps the creatures to balance sex ratios in the wild.
Kylie A. Robert and Michael B. Thompson of the University of Sydney studied a captive female population of the Australian skink, Eulamprus tympanum, which normally dwells in high-elevation habitats in southeastern Australia. They found that, in the laboratory, the females all maintained body temperatures of 32 degrees Celsius and produced only male offspring. Observations of the skinks in the wild, on the other hand, reveal equal sex ratios.
The mechanism by which the mothers select body temperature to balance the population sex ratio remains a mystery. But the fact that these skinks are subject to temperature-dependent sex determination may explain why the species occupies only alpine regions: warmer areas could result in the production of males only, which would be a death sentence for the population. Indeed, the team's findings may portend the effects of global warming on these animals. "For alpine species, there can be no retreat to cooler climates, so a rise in environmental temperature would result in increased production of males," the authors note. "Models predict a temperature rise of [4 degrees C] by 2100, which could seriously alter the sex ratio and lead to extinction of species such as E. tympanum." --Kate Wong
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sex selection in humans will certanly come in the near future, as science advances ... Hopefullythis will curtail and/or erase infanticide due to gender
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