 |
The parallel evolution of this malevolent mating tactic in insects, arachnids, and other taxonomic groups shows that traumatic insemination is more than just an oddball zoological curiosity. Rather, it could be an important driving force in the evolution of mating systems across diverse taxonomic groups. "It tells us that there's some level of generality behind the selective pressures and the mechanisms that have generated traumatic insemination," said Göran Arnqvist, an evolutionary biologist at the University of Uppsala in Sweden who was not involved in the research. "It's a dramatic male adaptation to sperm competition, basically." __H. sadistica__ females and closely related spiders all have round, cul-de-sac shaped sperm storage organs. These structures allow males to scoop out any sperm already present from past suitors before they mate, and so, ordinarily, the last male to mate is the first to fertilize the eggs. But by going the way of the abdomen rather than the sperm-storing genitalia, traumatically inseminating __H. sadistica__ males keep their sperm out of the reach of later-mating males. Thus, with this mating tactic, it's first come, first to sire. But Řezáč only studied the spider's behavior and didn't examine the sperm itself, so he never showed this experimentally, noted Ted Morrow, another Uppsala evolutionary biologist. "The crucial bit of data that he doesn't have is patterns of sperm precedence," he said. The parallels between __H. sadistica__ and other traumatic inseminators go beyond the painful pas de deux. Unlike other spider eggs, which are fertilized in the uterus shortly before being laid, __H. sadistica__ eggs are fertilized in the ovaries and laid as early-stage embryos up to one month later. Such internal fertilization is also found in bed bugs and related traumatically-inseminating insects, noted Siva-Jothy. Thus, "there's an awful lot of convergence that's going on between the two groups, but exactly what that means is still unclear," he said. It's impossible to say whether this form of reproduction evolved because of internal fertilization or the other way around, because the two are found in lock-step with each other, Siva-Jothy said. But __H. sadistica__ might offer a good system to tease this apart, because, unlike bed bugs, closely related species in the spider's genus do not engage in traumatic insemination. Comparative studies open up "interesting experimental possibilities," noted Arnqvist.
**__Related stories:__***linkurl:Wham, bam, now I'll die, ma'am;http://www.the-scientist.com/article/display/13971/
[28th July 2003]*linkurl:Spider's web;http://www.the-scientist.com/article/display/19558/
[27th March 2001]
