高溫熱壓力及空間擴大對孤雌胎生豌豆蚜生殖細胞發育之影響

Abstract

溫度為環境改變的關鍵，也是調控昆蟲生理反應重要的決定因子。然而，目前對於高溫熱壓力如何調控昆蟲胚胎發育，甚或是孤雌生殖昆蟲之胚胎發育，相關之研究仍付之闕如。因此本論文將分析探討一種在基因體學與發育生物學中新興的模式物種：孤雌胎生豌豆蚜 (Acyrthosiphon pisum) 之胚胎發育是如何受到高溫熱壓力所調控，本研究中，我以 30°C 作為高溫刺激之溫度，與適合豌豆蚜生存之溫度 20°C 作為控制組以比較。過去研究中發現 30°C 中飼養之豌豆蚜雖可發育至成蟲，卻無法產下子代，可能之肇因為卵巢中因高溫壓力影響而導致胚胎發育不全，抑或是即使能正常發育卻無法被產下。本研究結果顯示，30°C 飼養下發育至成蟲第一天的豌豆蚜，其體內胚胎皆未發育成熟；而在 20°C 則可發現發育正常的成熟胚胎，因此推測胚胎之發育不全可能是造成成蟲無法生育之原因。實驗過程中，我首次發現若將豌豆蚜之飼養空間放大至六倍以上，約有 55 % 之成蟲即可產下子代，是與過去研究不同之處。儘管子代皆於出生後一天內死亡，卻說明較大之飼養空間可以誘導豌豆蚜在高溫逆境中生育，但仍無法使子代正常存活。除了生存率與發育型態，我也進一步比較了生殖基因 Apvas1在 20°C 及 30°C 中之表現量差異，體內及體外實驗之結果皆顯示在 30°C 中，成蟲卵巢內多數胚胎之 Apvas1 表現量顯著減少，推測主因為高溫抑制 Apvas1 的表現。同時，我也發現豌豆蚜體內之主要內共生菌 Buchnera aphidicola 在高溫下含量顯著減少，推測其可能為造成豌豆蚜生育下降之原因。綜合上述可以得知高溫熱壓力抑制了豌豆蚜之生育力，抑制 Apvas1 基因之表現以及內共生菌之含量，而關於這三者彼此是否有所關聯，則仍需後續研究來作進一步釐清。

Temperature is a critical factor to environmental changes and is known to regulate physiological conditions in insects. To Date, however, how heat stress regulates embryogenesis is not well known and how asexual embryogenesis responds to the heat stress is even worse known. In this thesis, I aim to analyze how embryogenesis of the parthenogenetic and viviparous pea aphid Acyrthosiphon pisum, a rising insect model for developmental and genomic studies, is affected by the high temperature at 30°C. Embryonic development at 20°C, a common temperature for pea aphids in the wild, serves as a control for comparison. Previous studies showed that pea-aphid nymphs cultured at 30°C can mature into adults but all of them were sterile. This suggests that embryos derived from the heat-shocked aphids were either not fully developed or labor of the fully-developed embryos was blocked. Experimental results showed that sterile adults bore embryos whose development was incomplete on the first day when the mother aphids became adults. By contrast, adult aphids cultured at 20°C were already pregnant with mature embryos, suggesting that incomplete development of embryos may be a cause of sterility. When the space was expanded six times, about 55% of aphid adults were able to give birth, however, all of the nymphs deceased within a day. This implies that enlarged space induces fecundity of pea aphids at 30°C but it cannot save the life of new born offsprings. Moreover, I also compared the expression of Apvas1 mRNA, a germline marker of pea aphids, in embryos developing at 20°C and 30°C respectively. In vitro and in vivo results showed that Apvas1 expression became significantly weaker in embryos of aphid adults cultured at 30°C, suggesting that the heat stress suppresses Apvas1 expression. Meanwhile, that numbers of the primary endosymbiont Buchnera aphidicola reduced was also identified. Taken together, the heat stress suppresses the fecundity of adults, expression of Apvas1, and number of endosymbionts. Whether these three changes are correlated and, if so, how they are regulated with each other require further investigation.