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- Title
Eunuch supremacy: evolution of post-mating spider emasculation.
- Authors
Kuntner, Matjaž; Pristovšek, Urška; Cheng, Ren-Chung; Li, Daiqin; Zhang, Shichang; Tso, I-Min; Liao, Chen-Pan; Miller, Jeremy; Kralj-Fišer, Simona
- Abstract
Emasculation-males becoming effectively sterile by self-removing their genitals-has long been considered a peculiar evolutionary phenomenon with unknown function, taxonomically restricted to few spiders and flies. In spiders, emasculation results in half or full eunuchs when males sever one or both sperm transferring organs, palps. Three types of emasculation, pre-maturation, mating, and post-mating are known in spiders, all having evolved multiple times. Males practicing pre-maturation emasculation sever one of their palps while still immature, then engage in strict monogyny via genital plugging and spontaneous death. Emasculation during mating also results in genital plugs, but half eunuchs have another chance to mate. So far, the behavior of those males that become eunuchs post-mating by self-removing disfigured palps has not been investigated empirically. We test the mechanism and adaptive significance of post-mating emasculation in coin spiders ( Herennia multipuncta) and use phylogenetic reconstruction to understand its evolutionary history. Our laboratory assays corroborate three hypotheses related to mate monopolization: (1) The plugging hypothesis-predicting genital plugs to prevent female remating; (2) The better-fighter hypothesis-predicting enhanced eunuch aggressiveness toward rivals; and (3) The gloves-off hypothesis-predicting increased eunuch endurance. The support for these hypotheses in spiders practicing emasculation during and after mating reinforces recent phylogenetic interpretations of these two emasculation types being evolutionarily linked in the family Nephilidae. We weigh the evidence in support of three different, but equally parsimonious scenarios of nephilid emasculation evolution. We conclude that emasculation is an adaptive, sexually selected trait that calls for further comparative and experimental research.
- Subjects
EUNUCHS; BIOLOGICAL evolution; CASTRATION; SPIDERS; SPERM competition; ANIMAL sexual behavior
- Publication
Behavioral Ecology & Sociobiology, 2015, Vol 69, Issue 1, p117
- ISSN
0340-5443
- Publication type
Article
- DOI
10.1007/s00265-014-1824-6