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Document Type

Grand Teton National Park Report

First Page

53

Last Page

57

Abstract

Cyphoderris strepitans Morris and Gwynne is a common species of nocturnal insect in many sagebrush areas within Grand Tetons and Yellowstone National Parks. It is a primitive orthopteran group, a relict of the ancient family Haglidae. Only five species in three genera are currently known (Morris and Gwynne 1978, Storozhenko 1980). Males produce a calling song by rubbing their forewings together. Females are attracted to male song; during mating the female feeds on the tissues of the male's fleshy underwings. Virgin and non-virgin males can, therefore, be distinguished by examining their underwings. At the end of mating the male transfers a large proteinaceous spermatophore which the female also consumes. The main objective of this study has been to investigate the role and consequences of the male investment in his underwings and spermatophore (see Morris and Gwynne 1979). Female katydids use spermatophore proteins for egg production (Gwynne and Toalson unpublished) so these nutrients can be regarded as an important male investment likely to influence patterns of sexual selection within this group. Trivers (1972) outlined the theory of parental investment and its influence on sexual selection. Females, because they produce fewer larger gametes (eggs) are usually the limiting sex for the males which have a relatively large number of small gametes (sperm). As a result, males are predicted to maximize reproductive success by competing with each other to inseminate as many females as possible. Females, because they are limited by their fewer gametes will not gain by competing for copulations. Instead they should enhance reproductive success by being selective about which males fertilize their eggs. Sexual selection should, therefore, be stronger on males since competition for mates should produce a greater variance in the reproductive success of this sex (i.e., some males obtain few or no mates while others mate frequently). Males can offset the initial disparity of investment in gametes by investing parentally via paternal care of eggs or offspring or, as in many insects, by feeding the female with prey items or glandular products (Thornhill 1976). These sorts of male investments should decrease the variance in reproductive success of these males because the males are more "female like" in their reproductive strategy i.e., competing less because they reduce the number of potential copulations engaged in due to the large nutrient investment in each copulation. In orthopterans such as Cyphoderris where females feed on male-produced nutrients the following predictions emerge: (1) females should select a mate who is likely to provide more of the nutrient; (2) as mentioned above, the variance in male reproductive success should be low; few males should go unmated. Previous work in Grand Teton National Park has indicated that females may prefer Cyphoderris males who can supply more nutrients. Significantly more virgin males are mated than non-virgins (Morris and Gwynne 1979). Virgins are likely to be a better mate choice for females since they have not only more wing material but also would have large reproductive accessory glands capable of producing a full sized spermatophore. The main purpose of this season's work was to investigate the variance in reproductive success of males. An effort was also made to further collect information on the distribution of C. strepitans in and around Grand Teton and Yellowstone national parks. This information is presented first. (* Erratum: pp. 51 and 52 should be 56 and 57)

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