| Summary: | 碩士 === 東海大學 === 生命科學系 === 101 === Fluctuating asymmetry (FA), random deviation of bilaterally symmetrical traits, is considered as an effective indicator of developmental stability (DS) which can be affected by environmental or genetic stress. However, there is an ongoing debate of whether FA of phenotypic traits can reliably reflect developmental stress. The variation of phenotypic traits can be maintained by two major processes: canalization and DS. Canalization reduces among-individual phenotypic variation, whereas DS reduces within-individual variation of traits. Phenotypic traits under natural and sexual selection had been hypothesized to generate different patterns of trait variation and FA. But whether canalization and DS share the same mechanism to regulate overall variation of traits was not clear. The stag beetle, Cyclommatus mniszechi, was reared in high and low nutritional treatments to investigate three questions: (1) Does environmental stress of low larval nutrition cause elevated FA of adult morphological traits? (2) Does DS share a common mechanism with canalization? (3) Do traits under directional and stabilizing selection show predicted patterns of FA and trait variation? The results showed that for C. mniszechi the size of the mandible, head, thorax, elytra and femur of the foreleg were all significantly larger for beetles in high nutritional treatment. However, the level of signed FA of all measured traits did not differ between the two nutritional treatments. No consistent relationship of variance of morphological traits and their FAs suggested that the mechanism of canalization and DS of C. mniszechi were not the same, and DS may be trait-specific in C. mniszechi. As predicted, two sexual traits, the mandible and head, showed greater FA and trait variation than that of non-sexual traits. The elytra, which was expected to be largely under natural selection for protection and flight, showed smaller FA and trait variation. Earlier behavioral studies of the male-male fighting in C. mniszechi suggested that both thorax and foreleg were involved in territorial contests. This study supported that, in addition to natural selection, these two structures were partly under strong sexual selection and showed similarly small trait variation but greater FA than that of elytra.
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