Male Water Striders Grab Females by the Eyes for Sex Using Barbed Hooks

Posted on May 6, 2012

Male water striders have developed elaborate antennae as part of an ongoing evolutionary battle between males and females over mating. Discover Magazine reports that female water striders try to resist the eager males that jump on them as they skate over lakes and ponds. The females struggle and try to buck off the males, but the male water striders have developed special hooks and barbs on their antennae. They use these to grab the female by the eyes and make it more difficult for her to throw them off. Take a look:

Male water striders have developed increasingly elaborate antennae as females have developed new ways to avoid and resist the males in this evolutionary sex war. The main reason for the conflict is male striders want to mate as often as possible. However, New Scientist reports that female water striders can store sperm and only need to mate about once a week. The image below shows just how different the antennae are in male and female Rheumatobates rileyi, a special of water strider. The grasping structures in the male antennae are highlighted in purple.

Rheumatobates rileyi antennae

A team of researchers came up with a unique way to investigate how these barbs and hooks came to be on the male antennae of water striders. A research team led by Locke Rowe of the Department of Ecology and Evolutionary Biology at the University of Toronto with collaborators Ehab Abouheif of the Biology Department at McGill University, and Abderrahman Khila of Toronto and McGill, found a way to recreate the incremental steps in water stride antennae development. They turned back the evolutionary clock and watched the transformation of simple antennae into more elaborate ones.

Using high-speed video to observe mating, the researchers noted that each structure - hooks, enlarged segments and spikes - on the antennae appeared precisely designed to grasp females. They then looked at which genes were being expressed during development of the male antennae (just prior to maturation). Knowing the gene provides the opportunity to modify its expression, and therefore modify the male antennae. One gene looked promising so the researchers knocked down its expression during development using RNA interference.

The researchers then tested a set of these males with differing antennae to determine their utility in grasping females. They found that as the antennae became more elaborate, mating success increased.

Rowe says, "This means that the struggle over mating could account for the ever increasing elaboration of these antennae."

The research was reported here in the journal, Science.

Image: A. Khila