Old-male paternity advantage is a function of accumulating sperm and last-male precedence in a butterfly

Old-male mating advantage has been convincingly demonstrated in Bicyclus anynana butterflies. This intriguing pattern may be explained by two alternative hypotheses: (i) an increased aggressiveness and persistence of older males during courtship, being caused by the older males' low residual reproductive value; and (ii) an active preference of females towards older males what reflects a good genes hypothesis. Against this background, we here investigate postcopulatory sexual selection by double-mating Bicyclus anynana females to older and younger males, thus allowing for sperm competition and cryptic mate choice, and by genotyping the resulting offspring. Virgin females were mated with a younger virgin (2–3 days old) and afterwards an older virgin male (12–13 days old) or vice versa. Older males had a higher paternity success than younger ones, but only when being the second (=last) mating partner, while paternity success was equal among older and younger males when older males were the...多项研究已确凿证实，泽苔眼蝶（Bicyclus anynana）存在老年雄性交配优势现象。这一有趣的研究结果可通过两种对立假说加以解释：其一，老年雄性在求偶过程中攻击性与坚持性更强，这源于其剩余繁殖价值较低；其二，雌性对老年雄性存在主动偏好，这符合优秀基因假说（good genes hypothesis）。基于上述研究背景，本研究通过让泽苔眼蝶（Bicyclus anynana）雌蝶先后与老年、年轻雄性进行两次交配，以此模拟精子竞争与隐蔽性配偶选择，并对所得子代进行基因分型，以探究交配后性选择机制。实验中，处女雌蝶先与2~3日龄的年轻处女雄蝶交配，随后再与12~13日龄的老年处女雄蝶交配，或采用相反的交配顺序。结果显示，老年雄性的父权成功率高于年轻雄性，但仅当其为第二次（即末次）交配对象时成立；而当老年雄性为……时，二者的父权成功率并无显著差异。