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Animavore wrote:So what's the intermediate? Males with bad aim?
Calilasseia wrote: If a male H. cochimiensis inseminates a female H. sonorensis, the result is a massive, rapid and lethal immune reaction. Which means that cochimiensis may use cross-species sex in order to remove food rivals from the scene, by using shagging as a biological weapon.
Clive Durdle wrote:And I think another barnacle has the largest penis in comparison to body size.
Řezáč, 2009 wrote:The males of invertebrates from a few phyla, including arthropods, have been reported to practise traumatic insemination (TI; i.e. injecting sperm by using the copulatory organ to penetrate the female’s body wall). As all previously reported arthropod examples have been insects, there is considerable interest in whether TI might have evolved independently in other arthropods. The research reported here demonstrates the first case of TI in the arthropod subphylum Chelicerata, in particular how the genital morphology and mating behaviour of Harpactea sadistica (Řezáč 2008), a spider from Israel, has become adapted specifically for reproduction based on TI. Males have needle-like intromittent organs and females have atrophied spermathecae. In other spiders, eggs are fertilized simultaneously with oviposition, but the eggs of H. sadistica are fertilized in the ovaries (internal fertilization) and develop as embryos before being laid. Sperm-storage organs of phylogenetically basal groups to H. sadistica provide males with last male sperm priority and allow removal of sperm by males that mate later, suggesting that TI might have evolved as an adaptive strategy to circumvent an unfavourable structure of the sperm-storage organs, allowing the first male to mate with paternity advantage. Understanding the functional significance of TI gives us insight into factors underlying the evolution of the genital and sperm-storage morphology in spiders.
Nessler et al, 2007 wrote:The morphology of male genitalia often suggests functions besides sperm transfer that may have evolved under natural or sexual selection. In several species of sexually cannibalistic spiders, males damage their paired genitalia during mating, limiting them to one copulation per pedipalp. Using a triple-mating experiment, we tested if genital damage in the orb-web spider Argiope bruennichi increases male fitness either through facilitating his escape from an aggressive female or by obstructing the female’s insemination ducts against future copulation attempts from other males. We found no survival advantage for males damaging their pedipalps; however, copulations into a previously used insemination duct were significantly shorter when the previous male had left parts of his genitalia inside the insemination duct. Because copulation duration determines paternity in this species, our result suggests that male genital damage in A. bruennichi is sexually selected. By breaking off parts of their intromittent organs inside a virgin female, males can reduce sperm competition and thereby increase their paternity success.
Kuntner et al, 2009 wrote:Genital morphology is informative phylogenetically and strongly selected sexually. We use a recent species-level phylogeny of nephilid spiders to synthesize phylogenetic patterns in nephilid genital evolution that document generalized conﬂict between male and female interests. Speciﬁcally,we test the intersexual coevolution hypothesis by deﬁning gender-speciﬁc indices of genital complexity that summarize all relevant and phylogenetically informative traits. We then use independent contrasts to show that male and female genital complexity indices correlate signiﬁcantly and positively across the phylogeny rather than among sympatric sister species, as predicted by reproductive character displacement. In effect, as females respond to selection for fecundity-driven ﬁtness via giantism and polyandry (perhaps responding to male-biased effective sex ratios), male mechanisms evolve to monopolize females (male monogamy) via opportunistic mating, pre- and postcopulatory mate guarding, and/or plugging of female genitalia to exclude subsequent suitors. In males morphological symptoms of these phenomena range from self-mutilated genitalia to total castration. Although the results are compatible with both recently favored sexual selection hypotheses, sexually antagonistic coevolution, and cryptic female choice, the evidence of strong intersexual conﬂict and genitalic damage in both sexes is more easily explained as sexually antagonistic coevolution due to an evolutionary arms race.
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