Read Online The Folly of Fools by Robert Trivers - Free Book Online
Authors: Robert Trivers
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an adult female of the pollinator species in both appearance and smell, so as to induce pseudo-copulation by the aroused male. The plant takes care not to give the male a full copulation with ejaculation, presumably to keep him in a perpetually aroused state, driven to seek out new “female” after new “female,” pollinating the flowers all the way. Males who find pseudo-females do not linger and test nearby flowers as do males in plant species that have just given a nectar reward. Instead they fly immediately to a new patch of flowers, presumably in search of actual rewards. Thus, sexual mimics tend to be more outbred than closely related species that offer a real reward—a side effect of being deceived that may actually benefit the species itself.
Selection has also repeatedly favored males who mimic females within their species to fool territorial males into thinking they are females so they can get close enough to steal paternity of some or all of the eggs about to be laid by real females. These eggs will be cared for by the territorial male as his own. Sometimes selection for deception has been strong enough to mold morphs that are permanently committed to deception, that is, morphological forms whose strategy depends entirely on a life spent deceiving others. A classic example occurs in the bluegill sunfish, where a specialized male form has evolved that mimics a female in appearance and behavior, being one-sixth the size of a territorial male and roughly the size of an actual female. This female-mimic seeks out a territorial male, permits himself to be courted, and responds enough to keep the other male interested, so that when a true female spawns, the pseudo-female is ready nearby to help fertilize the eggs. It is as if the territorial male imagines he is in bed with two females when in fact he is in bed with one female and one male. The female almost certainly knows the truth.
The two kinds of males appear to be distinct forms that never turn into each other. To have persisted for so long, their long-term reproductive success must be identical—that is, over evolutionary time, the deceiver is doing exactly as well as the deceived—and this equality must, in turn, be enforced by frequency-dependent selection. When the female-mimic is relatively rare, he will do relatively well; when common, less so. Whether the female expresses any kind of preference for either male is unknown, but in general, females prefer rare males, that is, the less frequent of two choices. Perhaps one of the most spectacular cases of sexual mimicry is performed by a tiny blister beetle, itself a parasite on a solitary bee. To achieve dispersal, one hundred to two thousand individuals aggregate in groups that mimic in size, color, and perching location a single female of the host bee species, even moving as a unit up and down a tree. So here a kaleidoscopic falsehood is produced, its individual parts one-hundredth or less the size of the picture they are creating. In turn, a male bee copulating with the picture will serve to disperse the beetles to future bee nests since the beetles attach to him.
FALSE ALARM CALLS
Alarm calls occur in a variety of species, especially birds, and serve to warn other individuals (often relatives) that a predator is nearby. An alarm call is obviously a key moment—with little room for error on the receiving end. Thus, it is not surprising that true alarm calls have served as a template for the repeated evolution of false alarm calls. In mixed-species flocks of birds found in the tropics, an individual will give a false warning call when another bird has caught and is about to eat a large, tasty insect. Half the time, this causes the bird to drop the insect and dive for cover. In the other half of the cases, the bird is not fooled—while it always responds to a true alarm call with immediate flight. Thus, the birds have evolved to tell false from real alarm calls half the time.
In skuas, false
Selection has also repeatedly favored males who mimic females within their species to fool territorial males into thinking they are females so they can get close enough to steal paternity of some or all of the eggs about to be laid by real females. These eggs will be cared for by the territorial male as his own. Sometimes selection for deception has been strong enough to mold morphs that are permanently committed to deception, that is, morphological forms whose strategy depends entirely on a life spent deceiving others. A classic example occurs in the bluegill sunfish, where a specialized male form has evolved that mimics a female in appearance and behavior, being one-sixth the size of a territorial male and roughly the size of an actual female. This female-mimic seeks out a territorial male, permits himself to be courted, and responds enough to keep the other male interested, so that when a true female spawns, the pseudo-female is ready nearby to help fertilize the eggs. It is as if the territorial male imagines he is in bed with two females when in fact he is in bed with one female and one male. The female almost certainly knows the truth.
The two kinds of males appear to be distinct forms that never turn into each other. To have persisted for so long, their long-term reproductive success must be identical—that is, over evolutionary time, the deceiver is doing exactly as well as the deceived—and this equality must, in turn, be enforced by frequency-dependent selection. When the female-mimic is relatively rare, he will do relatively well; when common, less so. Whether the female expresses any kind of preference for either male is unknown, but in general, females prefer rare males, that is, the less frequent of two choices. Perhaps one of the most spectacular cases of sexual mimicry is performed by a tiny blister beetle, itself a parasite on a solitary bee. To achieve dispersal, one hundred to two thousand individuals aggregate in groups that mimic in size, color, and perching location a single female of the host bee species, even moving as a unit up and down a tree. So here a kaleidoscopic falsehood is produced, its individual parts one-hundredth or less the size of the picture they are creating. In turn, a male bee copulating with the picture will serve to disperse the beetles to future bee nests since the beetles attach to him.
FALSE ALARM CALLS
Alarm calls occur in a variety of species, especially birds, and serve to warn other individuals (often relatives) that a predator is nearby. An alarm call is obviously a key moment—with little room for error on the receiving end. Thus, it is not surprising that true alarm calls have served as a template for the repeated evolution of false alarm calls. In mixed-species flocks of birds found in the tropics, an individual will give a false warning call when another bird has caught and is about to eat a large, tasty insect. Half the time, this causes the bird to drop the insect and dive for cover. In the other half of the cases, the bird is not fooled—while it always responds to a true alarm call with immediate flight. Thus, the birds have evolved to tell false from real alarm calls half the time.
In skuas, false
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