雄性利用雌性感官偏好以保證生殖機會之探討：綠豆象及四紋豆象之實例

Abstract

植食性昆蟲的雌蟲會因產卵本能而受到寄主訊息的吸引而聚集至寄主植物上。若這些寄主職務上的雌蟲可接受再次交尾，則對雄蟲來說，寄主植物便是一個有豐富生殖資源的地方。因此，雄蟲除依靠雌蟲性費洛蒙來搜尋配偶之外，若額外具有搜尋寄主的能力，便可得到較多交尾機會。本研究以綠豆象 (Callosobruchus chinensis)、四紋豆象 (Callosobruchus maculatus)、敏豆象 (Acanthoscelides obtectus) 以及巴西豆象 (Zabrotes subsfaciatus) 為對象，檢驗雌蟲與雄蟲對寄主氣味的反應，結果顯示四個物種的雌蟲皆顯著受到寄主氣味吸引，但僅綠豆象的雄蟲展現搜尋寄主行為。在豆象科中，綠豆象為分歧年代最短的物種，顯示此雄蟲行為是演化自對既存的雌蟲行為偏好的利用。推測造成綠豆象的雄蟲會搜尋寄主的原因可能是雌蟲聚集地從他處轉換到寄主植物上，或是雌蟲因產卵壓力導致聚集於寄主植物的程度增加，因此雄蟲若能夠搜尋寄主，則能大幅增加交尾機會。此外，在這類物種中，雌蟲亦可能因為雄蟲的搜尋寄主行為而得利，因雄蟲若能夠搜尋寄主，即代表其有較佳的搜尋配偶能力，具此行為的雄蟲可遭遇較多配偶，雌蟲若與帶有寄主氣味、已證明具搜尋寄主能力的雄蟲交尾，便可確保其雄性子代亦會有相同行為，並進一步確保其雄性子代可遭遇較多配偶。實驗結果顯示，僅綠豆象的雌蟲在給予選擇時會偏好與帶有寄主氣味的雄蟲交尾，雄蟲不具搜尋寄主能力的物種，如四紋豆象，則無此交尾偏好。且由於綠豆象雄蟲帶有的寄主氣味不會提高雌蟲之產卵量，推測雌蟲做此配偶選擇的原因是來自間接的遺傳利益。

Mated females of Callosobruchus chinensis and their distant-related species, C. maculatus, Acanthoscelides obtectus and Zabrotes subfaciatus, show pre-existing sensory preference toward the odour of the host bean for oviposition. Females of these species that aggregate at host sites are capable of accepting further mating if males are present. Consequently, males that actively search for host sites enjoy increased chance of mating with gravid females. However, only males of C. chinensis, but not its ancestral species, are attracted by the host odour. This result indicates that the behavioral trait evolves from exploiting females’ pre-existing sensory bias. The establishment of male host-searching behavior may bring benefit to females. In detail analysis of mating behavior, C. chinensis females’ host-searching behavior is not affected by the presence of males, but they prefer to mate with males carried with the host odour regardless of age, body weight, or courtship performance. As there is no increase in fecundity in females that mate with males with host odour, the bias in mate choice may confer genetic advantage to females in term of ensuring her male offspring’s ability to locate host, and consequently, mates.