林地領域性蝶種以視覺偵測配偶及從事求偶飛行與太陽光斑大小之相關性

photo by Zéza Lemos

Visual mate detection and mate flight pursuit in relation to sunspot size in a woodland territorial butterfly

Animal Behaviour Volume 78, Issue 1, July 2009, Pages 17-23
Martin BergmanCorresponding ^a ,Christer Wiklunda
^a Department of Zoology, Stockholm University, Sweden

據領域具有相當可觀的利益。雄性的斑點木蝶（Pararge aegeria）在開放森林棲地的太陽光斑上飛行，勝利的一方成為光斑的佔有者，而落敗的一方則沒有領地且只能在小的光斑中坐等雌蝶。先前研究發現,雖然雌性並未特別受到領地佔有者或者光斑領域本身的吸引，但是雄性佔有領地者的交配成功率較沒有領地者高。 作者在此測試以下假說：(1)雄性佔有領地者有較高交配成功率的原因在於在大型光斑中的配偶偵測比在小型光斑中更有效率 (2) 只有在某個特定大小以上的光斑能被界定為領域。領域光斑的田野評估顯示，被守禦的光斑大小顯著大於森林底層光斑的平均尺寸。作者以實驗測試雄蝶以視覺偵測一隻模型蝴蝶經過光斑時的能力，結果顯示在光斑中飛行長距離飛行的情形下,雄蝶能較為成功地追求並攔截經過的模型。因此，作者提出光的狀況、視覺配偶偵測與完整的配偶飛行追求可解釋雄性的斑點木蝶（Pararge aegeria）在開放森林棲地守禦大型光斑的理由。

Territory residency is associated with considerable benefits. In the speckled wood butterfly, Pararge aegeria, males fight over ownership of large sunspots in open forest habitats; winners become sunspot residents, and losers become nonterritorial and sit and wait for females in small sunspots. A previous study has shown that residents have higher mating success than nonterritorial males, although females are not more attracted to territorial males or sunspot territories per se. Here we tested the hypotheses (1) that the higher success of resident males is caused by visual mate detection being more efficient in a large than in a small sunspot, and (2) that only sunspots above a certain size are defended as territories. Field assessment of territorial sunspot size showed that defended sunspots were significantly larger than ‘average sunspots’ on the forest floor. Experimental tests of male ability to detect visually a model butterfly passing through a sunspot showed that males were more successful in pursuing and intercepting a passing model when flown a longer distance in the sunspot. Hence, we conclude that light conditions and associated visual mate detection and ability to complete mate flight pursuit can explain why P. aegeria males defend territories in large sunspots in forest habitats.

Keywords: butterfly vision; Lepidoptera; light gap; mate searching; Pararge aegeria; sexual selection; speckled wood butterfly; territoriality