Biology ETDs

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Mating durations have only recently become the object of detailed research. The stick insect Diapheromera velii mates from 3 to 136 hours, during which time the genitalia are often not inserted, and contact is maintained by a male clasping organ. Prolonged attachment of male D. velii in the absence of copulation is best explained as guarding that assures the efficiency of previously transferred ejaculates by avoiding sperm competition. Oviposition patterns in D. velii are relatively continuous when compared to those of many insects. The result is that female value to males is comparatively constant as well. The amount of time a male might optimally invest in guarding females under this condition is determined by the probability of finding other females to inseminate and how likely it is that past mates will copulate with other males. These are, in large part, functions of density and sex ratio. It is demonstrated by field surveys that density varies in time and space as does sex ratio. The latter, in particular, shows large fluctuations possibly because of differential mortality of adult females through predation. Due to this spatial and temporal heterogeneity of D. velii's sexual environment, the evolution of flexible mating duration is proposed and experimentally tested. Durations are found to decrease as sex ratios become increasingly female skewed, but show greater variance when unmated males are present. It is argued that this variance is the result of two factors: the adaptiveness of longer matings when male biases exist, and the difficulty of maintaining attachment due to male-male aggression. Intrasexual aggression, while common in the Orthopteroidea, has apparently not been previously documented in the Phasmatodea. Male size is shown to be important, but not the sole component of success in obtaining and maintaining copulations. Sexual dimorphism is minimal in D. velii compared to other stick insects, and it is suggested that this is a result of the unusually high density of the species and, hence, a particularly high degree of male-male competition. It has been hypothesized in another phasmid species that lengthy mating serves as a means of avoiding predation because the pair pools their chemical defenses. The antipredator adaptations of D. velii are examined, as is survivorship of single and mating insects during bird attacks. While D. velii are more apt to escape Mexican Jays while mating, it is concluded that predation is unlikely to affect selection for duration.



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Department Name

UNM Biology Department

First Committee Member (Chair)

Albert Randolph Thornhill

Second Committee Member

Clifford Smeed Crawford

Third Committee Member

Rex Gordon Cates

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