營養操弄影響果蠅在求偶上的偏好性

Abstract

動物一生當中最重要的使命就是傳承基因、繁衍後代，動物的求偶行為一直是個有趣且重要的課題，過去的研究指出公果蠅會選擇年輕的處女果蠅而非年老或者已交配過的母果蠅。另外一方面，對於繁衍後代的成功率，母親的充分營養攝取是個重要指標。本研究探討當公果蠅面對飼養在不同營養狀態(1%，5%或20%酵母)的母果蠅時，公果蠅選擇的交配對象以及其原因。我們確定在果蠅食物的主要成分：酵母的濃度操弄十天之下，處女果蠅的體重、下蛋數量隨著濃度而提升，在飲食量、活動力方面則反之；公果蠅的體重隨著濃度而提高，在飲食量則下降，但在活動力方面則無影響；並且飼養在中等酵母濃度食物的果蠅比低濃度或高濃度較長壽；而類胰島素因子則隨食物酵母濃度而增高。我們發現在一公對一母的求偶實驗中，公果蠅對不同營養環境下飼養的母果蠅有相似的求偶分數；但在一公對二母或是三母的競爭實驗中，公果蠅對於飼養在高酵母濃度的母果蠅有較高的求偶分數，並且公果蠅總求偶分數隨著母果蠅隻數而上升，但年老公果蠅的總求偶分數顯著降低且不會對高酵母環境生長的母果蠅產生偏好；移除視覺的公果蠅同樣也會對高酵母濃度的母果蠅有較高的偏好，且會有更高的總求偶分數；並且將母果蠅的頭去除以限制其行動力時，公果蠅還是對飼養在高濃度酵母食物的母果蠅有較高的求偶分數，這些結果顯示公果蠅的視覺以及母果蠅的行動力都不是影響公果蠅偏好的主因；有趣的是，飼養在不同酵母濃度的母果蠅如果類胰島素突變或破壞oenocyte細胞時，公果蠅則不會有求偶的偏好性，我們也發現抑制母果蠅oenocyte細胞上，類胰島素以及表皮長鏈碳的表現也會使公果蠅不會有偏好性。綜合以上結果，我們發現母果蠅來自酵母的營養攝取，透過類胰島素以及在oenocyte細胞的表現，調節表皮長鏈碳表達量使公果蠅產生偏好。

Choosing an appropriate partner to mate with is an important part of animal reproduction. In Drosophila melanogaster, it has been shown that male flies prefer to mate with virgin and young females rather than mated or aged females. Since nutritional availability plays a key role in regulating aspects of fly physiology such as lifespan and fecundity, we investigated the effect of nutrient intake on male courtship preference by altering the concentration of yeast (1%, 5% and 20% yeast) in fly foods. We found that flies on higher yeast diets for 10 days showed differentiation in body weight, fecundity, locomotor activity (during light periods), food intake, lifespan, and insulin-like signaling. Moreover, male flies had higher courtship indexes to females raised in higher yeast diets when placed in 1-male to 3-female courtship choice assays, each lasting 30 minutes. Similar trends were observed in eye ablated male mutant flies. This preference was also displayed even when the females were decapitated. These results suggest that neither male visual signals nor female locomotor activities could mediate male courtship preference in this experimental context. Intriguingly, this preference was not present when insulin-like signaling (IIS) was specifically disrupted in oenocytes of female mutant flies or when females were masked with the same cuticular hydrocarbons (CHCs). We also found that diet could induce alterations in IIS and CHCs expression in female flies. In summary, we found that nutrition, especially from yeast, controls male courtship preference by modulating insulin-like signaling on female oenocytes, which in turn regulates the production of CHCs for sexual attractiveness.