Cordero-Rivera Adolfo
ECOEVO Lab, Departamento de Ecoloxía e Bioloxía Animal, Universidade de Vigo , Pontevedra, Galiza , Spain.
PeerJ. 2016 May 24;4:e2077. doi: 10.7717/peerj.2077. eCollection 2016.
Postcopulatory sexual selection may favour mechanisms to reduce sperm competition, like physical sperm removal by males. To investigate the origin of sperm removal, I studied the reproductive behaviour and mechanisms of sperm competition in the only living member of the oldest damselfly family, Hemiphlebia mirabilis, one species that was considered extinct in the 1980s. This species displays scramble competition behaviour. Males search for females with short flights and both sexes exhibit a conspicuous "abdominal flicking". This behaviour is used by males during an elaborate precopulatory courtship, unique among Odonata. Females use a similar display to reject male attempts to form tandem, but eventually signal receptivity by a particular body position. Males immobilise females during courtship using their legs, which, contrarily to other damselflies, never autotomise. Copulation is short (range 4.1-18.7 min), and occurs in two sequential stages. In the first stage, males remove part of the stored sperm, and inseminate during the second stage, at the end of mating. The male genital ligula matches the size and form of female genitalia, and ends by two horns covered by back-oriented spines. The volume of sperm in females before copulation was 2.7 times larger than the volume stored in females whose copulation was interrupted at the end of stage I, indicative of a significant sperm removal. These results point out that sperm removal is an old character in the evolution of odonates, possibly dating back to the Permian.
交配后的性选择可能有利于减少精子竞争的机制，比如雄性通过物理方式清除精子。为了探究精子清除行为的起源，我研究了最古老的豆娘科现存的唯一成员——奇异半脉豆娘（Hemiphlebia mirabilis）的繁殖行为和精子竞争机制，该物种在20世纪80年代曾被认为已灭绝。这个物种表现出争夺式竞争行为。雄性通过短距离飞行寻找雌性，两性都会表现出明显的“腹部轻弹”。在蜻蜓目独特的精心求偶过程中，雄性会使用这种行为。雌性用类似的展示来拒绝雄性形成串联的企图，但最终会通过特定的身体姿势表示接受。在求偶过程中，雄性用腿固定雌性，与其他豆娘不同的是，它们的腿从不自行脱落。交配时间很短（4.1 - 18.7分钟），分两个连续阶段进行。在第一阶段，雄性清除部分储存的精子，在交配结束时的第二阶段进行授精。雄性生殖叶与雌性生殖器的大小和形状相匹配，并以两个覆盖着向后的刺的角结束。交配前雌性体内的精子量比在第一阶段结束时交配被打断的雌性体内储存的精子量多2.7倍，这表明存在显著的精子清除现象。这些结果指出，精子清除是豆娘进化过程中的一个古老特征，可能可追溯到二叠纪。
