National Geographic : 2009 Aug
to bird dung gives you enough of an edge that you survive to breed, your progeny may inherit your lucky guano cast. Maybe one will even top you as a droppings imposter, and within a few hundred generations the trait will have spread through the whole population and be the gold standard for your kind. Mimicry also reveals just how messy evo- lution can be, how ad hoc and make-do. For example, Ximena Nelson and Robert Jackson report in the Proceedings of the Royal Society on the dilemma of the male Myrmarachne, a jumping spider. Like a number of the world s jumping spiders, these arachnids have evolved to look like ants, a strategy that plays into the antipathy many predators have for the aggres- sive, noxiously armed, and ecologically domi- nant social insects. But the male spiders have a problem with the basic strategy, for mat- ing rituals demand that they sport elongated mouthparts, which could detract from the overall antlike e ect. Evolution has hammered out a compromise: Whereas the female spiders look like ordinary ants, the males with their en- larged fangs have come to resemble ants carry- ing bundles in their mandibles, as worker ants sometimes do. Ingenious, yes, but not perfect. It turns out that although the male jumping spiders are as effective as their female coun- terparts at deterring the generally ant-phobic among hunters, the males alone fall prey to predators that target ants least likely to fight back---those encumbered with bundles. Scientists are particularly intrigued by imper- fect mimicry, where one organism only vaguely resembles another. In some cases, the crude form may indicate a lineage newly embarked on the mimicry path, when evolution has only be- gun to hone the simulation. In other instances, the disjunction is a result of the mimicked spe- cies pulling away from its unwanted copycats. If the warning colorations that you have evolved to advertise your hard-won unpalatability are mimicked by too many edible free riders, your brand name will be cheapened and lose its pro- tective value. Mimicry can also be a great way to preen, or learn, or make a new friend. Among songbirds and humpback whales, competing males seem to imitate each other s songs. And some dol- phins duplicate each other s ying leaps. Parrots are masters at parroting, and ape is what the great apes do, which is why orangutans can learn to cook pancakes and chimpanzees to hunt with tools, and we compare each other to a summer s day and mirror each other s joy with a smile. j Resembling flora more than fauna, a female walking leaf of Malaysia stems from a long line of extreme leaf mimics. This insect group is little changed over 47 million years, judging from a recent fossil find in Germany. The largest of thousands of leaflike species, Phyllium giganteum can unfurl to some four inches in length.