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Evidence for Evoluti16 - Therefore in the control cage(with...

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Evidence for Evolution Experimental reversal of parental investment In their paper, the authors (Gwynne and Simmons, 1990) experiment on a katydid of, as yet, unnamed species and genus. This species of katydid was observed to be highly variable in male contribution to parental investment. In these insects, the males transfers a spermatophore to the female after copulation. The spermatophore contains the ampulla, which contains the sperm, and the spermatophylax, which the female eats. The spermatophylax has been demonstrated to increase both the number and fitness of offspring sired by the male (it is a source of nutrition to the female). In their experiment the authors set up two cages. In cage one (the control) the katydids were allowed to feed on the pollen of their host plants. In cage two the katydids were allowed to feed on the pollen, but were also provided a nutritional supplement (the experimental cage).
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Unformatted text preview: Therefore, in the control cage (with limited food) the value of the males spermatophore is much greater to the female. Females were introduced to both cages and their behavior was observed. In the control cage (with limited food) the males exerted a mating preference and females competed for mating opportunities with males. This is because, with a scarcity of food, the male spermatophore became a valuable asset. In the experimental cage, the females exerted the mating preference because with an abundance of food, the male spermatophore was not such a valuable asset. In this way the authors showed that (in katydids at least) the parental investment is the determining factor in courtship roles (i.e. which sex exerts the mating preference)...
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