紅樹林鱂魚(Kryptolebias marmoratus)之勝者效應與睪固酮、皮質醇之關係研究

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2010

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許多研究發現獲勝經驗使動物在後續打鬥時有較高的攻擊性及獲勝機率 (勝者效應,winner effect),落敗經驗則有相反的影響 (敗者效應,loser effect)。相較於敗者效應,勝者效應通常較不易偵測到,使得研究勝者效應的生理機制較為困難。睪固酮 (testosterone) 及皮質醇 (cortisol) 是與打鬥行為有密切相關的固醇類荷爾蒙,經常伴隨著動物的獲勝或落敗而變化,因此被推測可能是獲勝經驗調控後續打鬥行為的生理機制之一。雌雄同體且行自體授精的紅樹林鱂魚Kryptolebias marmoratus (former : Rivulus marmoratus) 具有顯著的勝者效應,而且打鬥行為與體內的睪固酮及皮質醇濃度有關聯性,是研究勝者效應與荷爾蒙關係的合適物種。本研究透過強制給予K. marmoratus個體連續三次的獲勝經驗,探討獲勝經驗前後個體體內睪固酮及皮質醇濃度是否有顯著改變,以及經驗後睪固酮及皮質醇濃度是否對後續打鬥的行為及勝率有顯著影響。此外,本研究亦探討K. marmoratus個體得到獲勝經驗後,再次參與打鬥時與對手的互動、打鬥結果以及經驗後荷爾蒙濃度,是否影響其打鬥後的體內荷爾蒙濃度。結果顯示,連續三次的獲勝經驗顯著地提高個體率先展示、率先攻擊、率先鰓蓋展示及獲勝的機率。然而,獲勝經驗前後,K. marmoratus體內睪固酮及皮質醇濃度沒有顯著的改變。經驗後睪固酮及皮質醇濃度亦未對後續的打鬥行為造成顯著的影響。然而,打鬥後荷爾蒙濃度卻受到後續打鬥時與對手的互動及打鬥結果的影響:相較於在後續打鬥中落敗的個體,打鬥後獲勝個體有顯著較高的睪固酮及顯著較低的皮質醇濃度。根據本研究的結果,獲勝經驗應非透過改變K. marmoratus個體體內睪固酮及皮質醇的濃度以引發勝者效應。本論文並針對其他可能與勝者效應相關之生理機制如血清素(serotonin)、或其他荷爾蒙等進行討論。
Recent winning and losing experiences have been found to increase and decrease an individual’s aggressiveness and probability of winning a subsequent contest, respectively (winner and loser effect). It is harder to find a suitable organism to investigate the physiological mechanisms of the winner effect because it is not as common as the loser effect. Testosterone and cortisol have been shown to correlate with contest behavior and outcome in many animal species and are thus considered possible candidates for the physiological mechanisms underlying winner and loser effect. K. marmoratus displays both winner and loser effects and its contest behaviors correlate with its testosterone and cortisol levels, which makes the fish ideal for investigating the relationship between the winner effect and the two hormones. I gave individuals of the fish three winning experiences to investigate whether testosterone and cortisol played important roles in mediating the winner effect in the fish. The results of the study showed that the winning experiences did not have significant effects on post-experience testosterone or cortisol levels, and that post-experience testosterone and cortisol levels did not have significant relationships with the fish’s subsequent contest behavior or outcome. Interestingly, the fish’s subsequent contest behavior and outcome appeared to influence its post-contest testosterone and cortisol levels: winners of the subsequent contests had higher testosterone but lower cortisol levels than the losers. I concluded from these results that although these two hormones may have important relationships with the fish’s contest behavior, they are not responsiblefor mediating the winner effect in the fish. Physiological mechanisms that might be important to the winner effect of the fish are discussed.

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打鬥行為, 勝者效應, 類固醇荷爾蒙, 皮質醇, 睪固酮, 挑戰者假說, Kryptolebias marmoratus, contest behaviors, winner effect, steroid hormones, cortisol, testosterone, the challenge hypothesis, Kryptolebias marmoratus

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