Do specific choices made by female insects and spiders, when selecting a mate, influence the evolution of male insect and spider genitalia? "There is convincing empirical evidence for postmating sexual selection mechanism of genital evolution, according to research comparing pairs of related clades of insects that differ in mating system. This research also indicates that sexual selection could be responsible for the evolutionary elaboration of both primary and secondary sexual traits." (Arnqvist 1998) Which forms of sexual selection are responsible for genital evolution? To answer this question we should look at the most common reasons for female insects and spiders to choose or reject a potential mate.

Size does not appear to be the deciding factor. The factors seem to differ from species to species, depending on their specific needs. We will take a look at a few species of insects and spiders and attempt to discover what circumstances lead to successful matings between males and females. We will also att

In their 1997 paper on insect genitalia, William G. Eberhard, Bernhard A. Huber, Rafael Lucas Rodriguez S., R. Daniel Brinceno, Isabel Salas and Viterbo Rodriguez compared allometric values of male genitalia size in twenty species of insects and spiders. They compared these results to the allometric values of other body parts, (usually of the thorax in insects, of the cephalothorax in spiders), in order to determine whether larger genitalia size had any bearing on the likelihood of that male being selected by a female as a mate. They determined that the allometric values showed that females do not use large genitalia size as a factor to determine if a male will be chosen as a mate."Sexual selection on male courtship structures that are brought into contact with the females in precise ways may favor relatively low allometric values, in contrast to the high values seen in other sexual characters (usually visual display devices) that have been studied previously, because a female's own size will influence her perception of the contact courtship devices of a male." (Eberhard, Huber, Rodriguez S., Brinceno, Salas, and Rodriguez 1998). "Analyses at two levels revealed a trend for the allometric values of genitalia to be lower than those of nongenitalic structures" (Eberhard, Huber, Rodriguez S., Brinceno, Salas, and Rodriguez 1998). "The allometric values of genitalic structures (the slopes in log-transformed regressions of genitalia on body size)are usually lower than those of other body parts in the same species". So what are the determining factors? "Several other adaptive hypotheses could explain the low allometric values of genitalia documented. Low values are predicted by species isolation by mechanical fit between females and males ("mechanical lock and key"), and species isolation via stimulation of specific female receptors by male genitalia ("sensory lock and key") What characteristics must a male display in order to be selected by a mate and therefore have the chance to pass on his genes?

A final factor for selecting a mate could stem from the lock and key theory, which suggests that females of some species of insect and spiders choose their mates, based on the shape of their genitalia. Species in which male genital structures contact rigid female genitalia structures. Males and females of certain species have evolved with a system of intricately fitting genitalia. Among insects, male reproductive organs differ dramatically from one species to another. One theory is that male penile organs are diversely proportioned mainly to serve as a barrier against cross-copulations between members of two different species, an act that would either be a sterile waste of reproductive energy, or would result in the birth of genetically weak offspring. "The longstanding lock and key hypothesis, still popular among taxonomists, suggests that genitalia evolve by a pre-insemination hybridization avoidance; that is, hybrid inferiority drives the evolution of male genitalia with a proper mechanical fit to female genitalia" (Arnqvist 1998). The females therefore must have genitalia that exactly matches the diversely proportioned males, suggesting that females might choose mates based on the 'mechanical fit' of their genitalia. Although in their experiments Eberhard et al. found this to have no more effect on the choice of the female than when the male genital structures came

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Salas Rodriguez, Arnqvist Stallmann, , Viterbo Rodriguez, Maydianne Andrade, Robert Stallmann, Eberhard Gutierrez, American Naturalist, allometric values, Stallmann R, Gutierrez E, sexual selection, water striders, australian redback, watson arnqvist, salas rodriguez, arnqvist stallmann, genital structures, watson arnqvist stallmann, rodriguez brinceno salas, rodriguez brinceno, huber rodriguez, eberhard huber rodriguez, brinceno salas rodriguez, huber rodriguez brinceno,
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