無效卵及幼蟲密度對貓蚤同類相食之影響

同類相食 (Cannibalism) 被定義為殺死並取食同種生物而獲得能量的行為，此行為通常和年齡或體型大小相關。自然界許多生物都有這樣的行為，包括寄生性昆蟲 - 貓蚤 (Ctenocephalides felis (Bouche))。貓蚤幼蟲生活環境資源有限以致於同類成員成為牠們可選擇的食物之一。經過觀察發現幼蟲會以咀嚼式口器取食卵、較小的幼蟲或裸蛹。雖然三個齡期都有同類相食的行為，但在取食傾向和成功率都不盡相同。卵常被老熟幼蟲取食，但裸蛹的取食就不被齡期所侷限。貓蚤常會造繭以防止被其他幼蟲攻擊或取食而有較高的羽化率。環境因素常影響同類相食的劇烈程度，當缺乏豬血粉或幼蟲密度高時，他們會傾向吃掉更多的卵。然而在缺乏豬血粉的情況下，高密度反而會減低取食卵的行為，這兩個因子之間的相互影響仍需多加探討。雌蚤交配後仍會產生的無效卵也會影響同類相食的行為。基於有效卵 (viable egg) 的渾圓形狀使取食行為較難進行，當兩種卵同時存在時幼蟲會偏好去選擇較易取食且扁平凹陷的無效卵 (non-viable egg) (尤其是一齡幼蟲)。雖然可讓最多幼蟲發育為成蟲的最適宜有效卵的比例並沒有被找到，但雌蚤產生無效卵的現象也許可視為一種具有保護子代、提高生存機會的一種親代照顧 (parental care)，在演化上對族群延續可能具有重要意義。

關鍵字

貓蚤；幼蟲；同類相食；無效卵；親代投資

並列摘要

Cannibalism, defined as killing and consuming conspecifics for energy gain, tends to be size or age dependent, and is common in many creatures including cat fleas, Ctenocephalides felis (Bouche). Since the flea larvae normally live in habitat with limited resource, their conspecifics might be an accessible choice for additional energy. In my laboratory experiment, cat flea larvae are found to consume conspecific eggs, smaller larvae or naked pupae by their chewing mouthparts. Although cat flea displayed cannibalistic behavior in all three larval instars, differences are still showed in their preference or successful rate. Eggs were under higher risk of being attacked by late instar larvae while the age did not affect larvae to cannibalize the naked pupa. The pupa can be protected by cocoon which keeps the larvae from consuming them. Environment factor can influence the cannibalistic tendency, flea larvae consume more eggs under high density or lack of food. However, high larval density reduces the egg consumed of each larva when no porcine blood curd powder is provided as additional food. The interaction between these two factors should be further considered. The non-viable eggs produced by mated females also influence the cannibalistic behavior. The viable eggs are round and may be relatively difficult for the larvae, especially the first instar, to consume. Since the non-viable eggs are flat and it may be easier for larvae to feed on them, more non-viable eggs were consumed by larvae when both eggs were available. Although I did not calculate a credibly optimal ratio of viable egg among all eggs laid, the protective and nutrition providing function might trigger the female flea to produce non-viable eggs to reduce egg cannibalism. It can be seen as a kind of parental care which plays an important role in cat flea population sustaining.

並列關鍵字

cat flea ； larvae ； cannibalism ； non-viable egg ； parental care

參考文獻

Annis B, Bismo Sarojo UTI, Hamzah N, Trenggono B. 1990. Laboratory studies of larval cannibalism in Toxorhynchites amboinensis (Diptera: Culicidae). J Med Entomol 27: 777-783.

Bartlett J. 1987. Filial cannibalism in burying beetles. Behav Ecol Sociobiol 21: 179-183.

Borries C, Launhardt K, Epplen C, Epplen JT, Winkler P. 1999. DNA analyses support the hypothesis that infanticide is adaptive in langur monkeys. Proc Roy Soc London Ser B Biol Sci 266: 901-904.

Casill D. 2002. Brood care strategies by newly mated monogyne Solenopsis invicta (Hymenoptera: Formicidae) queens during colony founding. Ann Entomol Soc Am 95: 208-212.

Claessen D, de Roos AM, Persson L. 2004. Population dynamic theory of size-dependant cannibalism. Proc Roy Soc London Ser B Biol Sci 271: 333-340.

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無效卵及幼蟲密度對貓蚤同類相食之影響

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