I know, I know. Despite the nature of this tumblr, I am always cautioning against anthropomorphising. But some male water striders really can be total dicks.
In many species of animals, males court females with visual or acoustic displays that may also attract predators - the cost to fitness of potential predation is balanced against the fitness benefits of having more sex. After all, there’s no point living if you’re never going to have sex (that’s another life lesson for you all right there).
However, in this particular species of water strider, Gerris gracilicornis, males actually attract underwater predators by tapping the water. Why the hell would they do this? Well, males want to mate with as many females as possible - this means they have the greatest chance of fertilising lots of eggs and having lots of offspring, and so ensuring that their genes get to the next generation. For females, however, one mating is enough - anything more than that is unnecessary, and can actually be damaging. This discrepancy in the ideal mating rate for males and females is just one example of what is called ‘sexual conflict’.
Sexual conflict can create evolutionary ‘arms races’ between males and females, and this species is no exception. The females have evolved a ‘shield’ over what we shall demurely refer to as their ‘opening’; males which mount them cannot actually start the mating process until the female exposes her genitalia. Oh, ladies. It was almost so foolproof. Unfortunately, predatory aquatic insects and fish are attracted to vibrations on the surface… giving the mounting male a route for some rather serious intimidation.
A female can, of course, attempt to throw the male off her back, but this will also cause vibrations. A failure to dislodge him quickly means that death from below may not be far away. So, again, there’s a trade-off: accept the costs of unwanted excess mating, or dice with death…
Read the full paper here:
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Sexual conflict driving the elaboration of a sexually dimorphic trait.
Original image copyright Chang S. Han.
Advice* on life, love and sex (mainly sex) from the natural world...
