Evolution's Rainbow. Joan Roughgarden
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Название: Evolution's Rainbow
Автор: Joan Roughgarden
Издательство: Ingram
Жанр: Биология
isbn: 9780520957978
isbn:
But in the minds of deceit theorists, “excess” mating between members of a pair has nothing to do with building relationships; rather, it represents females using sexuality to manipulate males into giving them free food—a dinner date followed by sex. According to one model for the evolution of “female sexuality” in monogamous birds, males keep buying dinner because they can’t “risk leaving.” As a result, “females benefit from the presence of males in such a way that males get nothing in return.”6
For the record, biology provides no evidence whatsoever that the function of sexuality in monogamous relationships is deceit. Instead, theories of male/female cooperation should have been considered as a rationale for sexuality in the monogamous family.
WHEN FEMALES LOOK LIKE MALES
What does female-to-male cross-dressing tell us about the role of female choice? Reports on feminine males are marked by deceit rhetoric and sensationalism. Reports of masculine females are scanty, suggesting underreporting. What emerges is that some females signal receptiveness with colors that coincidentally resemble male colors, whereas other females modify their attractiveness to males to control how often males solicit them.
At the northwestern tip of the Iberian peninsula lies the seaport city of A Coruña, Spain, where Bocage’s wall lizard (Podarcis bocagei) lives. This lizard is the only vertebrate animal species so far in which females have been reported to imitate males, but the case isn’t convincing.7 Males have an intense green color on their back. Female wall lizards are usually brown, but when they have fertilized eggs already in their oviducts or have recently laid an egg, they turn green to signal that they won’t accept courtship. Is being green masculine and therefore romantically unappealing to other males, as some scientists have speculated? Whereas feminine males are cast as deceivers, masculine females are cast as unattractive. Or could green simply be a gender-neutral signal telling males not to bother courting?
The green color seems to be a gender-neutral signal rather than a masculine presentation that males find unattractive, because males do occasionally try to mate with green females and are rebuffed. These males are presumably learning what green means. If males found green females unattractive, they wouldn’t court them to begin with.
Interestingly, the phrase “male mimicry” is not introduced. Females are not seen as deceiving males. If this was a case of male mimicry, the males who do try to mate with green females would have to be mistaking the females as males and soliciting a same-sex courtship, something not (yet?) described in this species.
A comparable lizard species in western Ecuador, Microlophus occipitalis, also has females that display a special color when unreceptive to courtship.8 Hatchlings of both sexes have red throats and chins for about a month. Then males lose the red pigment, while females retain some of the red in skin folds on the side of the neck. The males develop black markings on their back and grow larger than the females.
During the reproductive season, some females develop bright red pigmentation covering the throat and chin similar to that of juveniles. Imagine painting Texas-red on your chin and neck, all the way down to your breastbone: you’ll get noticed. Females wear red on their chin and neck when carrying undeveloped eggs in their oviducts or after laying eggs. Males were found to make more courtship approaches to nonred females and pursue the courtship with them more ardently. Conversely, red females rejected courtship advances more than nonred females did. Out of thirty-eight matings observed during three years of study, thirty-three involved either unpigmented females or ones with but a small trace of red, whereas only five involved fully red-throated females.
Thus females in both Spanish and Ecuadorian lizards signal when they are not receptive. In the Spanish species, the signal (green on the back) is a color that males coincidentally also have on their backs, whereas in the Ecuadorian species the signal (red on the chin and neck) is distinctive from the color that males have on their chins and necks. Bright colors have been described in the females of more than thirty species of lizards so far, and in eighteen of these, the bright colors are expressed when the females are carrying oviductal eggs.9 Thus females using color to signal to males to back off is apparently quite general in lizards.
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