表皮碳氫化合物（Cuticular hydrocarbon）由烷烴和烯烴組成，是昆蟲表皮的重要成分，它們保護陸生昆蟲免於乾燥，並在各種化學傳遞過程中作為訊號，果蠅在適應不同環境過程中，會演化出相應的表皮碳氫化合物。在此研究中，我分析了牽牛花果蠅（Drosophila elegans）和高山果蠅（Drosophila gunungcola）兩近緣種的表皮碳氫化合物組成，同時透過分析牽牛花果蠅自然存在的不同體色型和體色基因突變品系，了解體色與表皮碳氫化合物可能的關聯性。經由氣相層析（Gas chromatography）分析，我發現第13、23、24、25號等四種化合物為牽牛花果蠅特有，且其中後三種化合物僅出現在雄蟲表皮中。另外第7號化合物則僅在高山果蠅的雄蟲表皮中偵測到，值得一提的是，第18號化合物在牽牛花果蠅中皆可偵測到，但在高山果蠅卻單僅在雄蟲中偵測到。進一步地定量分析中，我發現不同表皮碳氫化合物普遍存在著性別差異，其中第2、4、12號化合物一致性地在兩物種顯現性別差異。當我進行同性別牽牛花果蠅兩體色型與高山果蠅碳氫化合物定量分析時，發現不論是種內或種間之比較，相對量有顯著差異的碳氫化合物種類在雄蟲皆多於雌蟲。原先帶有yellow基因突變的果蠅品系中，我發現有幾種碳氫化合物相對量與對照野生型品系不同，但是經由遺傳背景控制交配後所帶有yellow突變的果蠅，與帶有野生型等位基因的果蠅並無差異。我的研究結果顯示，表皮碳氫化合物組成在這兩近緣種存在著種內多樣性和種間分的現象，潛在性影響種內和種間的生殖隔離，雄蟲表皮碳氫化合物相對量有較多的種內和種間差異的現象，也符合fast male hypothesis。另外，不同體色型的牽牛花果蠅，其體表碳氫化合物有一定的差異，但是這些差異是否與影響體色的遺傳變異有關，則有待釐清。

Cuticular hydrocarbons (CHCs), comprising alkanes and alkenes, are key components of insect cuticles. They protect terrestrial insects from desiccation and serve as signal molecules in various chemical communication processes. Fruit flies have evolved corresponding CHC profiles to adapt to different environments. In this study, I examined the CHC profiles of two closely related species, Drosophila elegans and Drosophila gunungcola, mainly focusing on the body color morphs and pigmentation gene mutant to investigate the possible association between body color and CHC profiles. According to gas chromatography analysis, I found that the number 13, 23, 24, and 25 compounds are D. elegans specific, and the last three compounds only appeared in male cuticle extracts. Conversely, the number 7 compound was only found in D. gunungcola males. More interestingly, the number 18 compound could be found in D. elegans and male D. gunungcola, but not in female D. gunungcola. Further quantitative comparisons suggested a substantial sex difference in CHC profiles. Among those differences, the number 2, 4, and 12 compounds exhibited consistent sex differences across strains and species. When the CHCs of the same sex were compared, no matter intra- or inter-specifically, the numbers of compounds exhibiting significant differences in male comparisons were higher in female comparisons. Several CHCs of the yellow mutant strain significantly differed from the wildtype counterpart in my original analysis. However, those differences diminished after the flies were undergone a cross for genetic background control. Overall, my study showed the inter-specific diversity and inter-specific diversification of CHC profiles, potentially involved in reproductive isolation, in this pair of closely related species. That more compounds exhibiting intra- and inter-specific differences in male cuticles is also consistent with the fast male hypothesis. Moreover, there are substantial differences in CHC profiles between two body color morphs of D. elegans. But whether those CHC differences are determined by the genetic variants controlling body color difference is uncertain.

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