鉤盲蛇的食性與覓食行為

Abstract

藉由覓食，動物獲得代謝、活動和繁殖的能量。為了獲得最大的適存度(fitness)以順應各種環境限制，生物應會演化出最佳的覓食行為(optimal foraging behavior)，掠食者(predator)得在取得食物與自身安全中取得平衡。蛇類受生理構造的限制，缺乏四肢、無法咀嚼，且壓制獵物的機制較為單純，遭獵物反擊(prey retaliation)的風險較高。其中盲蛇類群(Scolecophidia)具掘地性、生性隱密，我們所知甚少。盲蛇主要以螞蟻、白蟻這兩種具有護幼行為的社會性昆蟲為食，與真蛇(Alethinophidia)有許多不同的特質，且較真蛇缺乏纏勒(constriction)和注射毒液(envenomation)等制伏獵物的能力，因而易受螞蟻和白蟻反擊。受到口寬與張嘴幅度之生理限制，盲蛇僅能吃食比嘴巴小的食物；牠們視覺退化，僅能靠嗅覺搜索移動緩慢或無法移動且聚集在一起的獵物。台灣僅有一種盲蛇──鉤盲蛇(Ramphotyphlops braminus)分布，本研究主要探討：鉤盲蛇的攝食量以及在蟻窩中覓食的時間是否會因遭遇的螞蟻體型、攻擊能力不同而異，換言之，鉤盲蛇的覓食策略是否會隨遭遇的螞蟻體型而變更。此外我於飼養期間觀察到，鉤盲蛇在取食白蟻時偶爾會將白蟻的頭部去除後才吞下。由於鉤盲蛇張嘴幅度有限，我認為鉤盲蛇為避免因吞嚥困難、增加覓食的時間，因而表現出對白蟻的去頭行為。初步推論肇因於白蟻大小以及盲蛇的口寬限制，本研究亦對此假說加以探討。 鉤盲蛇屬於廣食性的掠食者，本實驗紀錄到鉤盲蛇取食的物種涵蓋 42種螞蟻、 5種白蟻和一種擬步行蟲。實驗結果顯示，嘴寬較小的鉤盲蛇對白蟻的去頭率較高，較大隻的白蟻亦會引發鉤盲蛇表現出較高的去頭率。鉤盲蛇遭遇較大隻的螞蟻時，螞蟻成功攻擊鉤盲蛇、表現出疼痛反應的機會隨之增加。表現出疼痛反應的鉤盲蛇於蟻窩中停留的時間，較無疼痛反應者為短。鉤盲蛇的攝食量與其在蟻窩內的停留時間呈正相關。

By foraging, organisms acquire the energy for sustaining metabolism, doing activities, and for propagation. In order to achieve highest fitness, animals developed all kinds of optimal foraging behaviors, and predators are to make the right balance between foraging and their own safety. Snakes are limbless, unable to chew, they have only few methods to subdue preys, and thus are vulnerable to prey retaliation. Among snakes, the blind snakes are tiny fossorial species of the clade Scolecophidia. They primarily feed on ants and termites which are social insects that defend their offspring. Compared to the advanced snakes, snakes of Alethinophidia, the blind snakes are lacking of constriction behavior and the ability to envenom. As a result, they tend to be struck by the ants and termites when preying. The blind snakes are bound by their gape limitation and are only able to eat relative small prey items. Due to their degraded vision, they can only hunt with olfactory clue, and prey on immobile or slow-moving preys. Ramphotyphlops braminus is the only blind snake in Taiwan. In my research, I test if the amount of food intake and the duration of R. braminus in ant hives are affected by the size of ants, which is related to the ability of attacking blind snakes. I also notice that R. braminus often remove some heads of termites before swallowing, which has not been reported before. I believe this novel behavior is due to their gape limitation. I test this prediction in my research as well. The results supported my prediction and showed that R. braminus with smaller mouth or encountering bigger termites had higher head-removing rate on termites. When R. braminus encountered bigger ants, there was higher chance of ants attacked the snakes effectively, which made the snakes acted painfully. R. braminus with agony behavior had shorter duration in the hives, and intaked less food. However, the relationship between the amount of food intake of R. braminus and ant sizes was not significant.