Fish-stashe

You know how you can hear about something and it just sticks in your brain until you have to look it up? That's how this story went for me. I mean, how can you not remember a story about mustachioed fish?

When it comes to sexual selection in the animal world, it is the usually the sex that puts more effort (and has more to lose) into the results that gets to be the choosy sex. Usually this means females get to be picky. After all, eggs are more expensive than sperm and females often end up contributing quite a bit with parental care. This choosiness means that males need to impress females through the evolution of secondary sexual traits. This could be, and usually is, just about anything: elaborate feathers, complicated dances or mating calls, gift giving, etc.

In the world of the Mexican molly, Poecilia sphenops, its all about the mustaches. In a new paper published in Behavioral Ecology and Sociobiology, researchers performed mate choice experiments where they varied the presence/absence and sizes of the fish-stashes. These fish-stashes consist of epidermal outgrowths at the edge of the scales, they appear to have no sensory function, and are not linked to male body size polymorphism. It is thought that the mustache functions as tactile sexual stimulation for the female, contact of the mustache to the female fish's genital region before copulation. The study found that female mollies spent over 60% of their time with the mustachioed males compared to the clean-shaven males, and they preferred the same males with large stashes rather than small. However, the presence of a mustache was not the only preferred variable - females liked larger males without mustaches rather than smaller males with mustaches. So, if you are a molly, and you want to score big you need to be a big guy with a big mustache.

This is your reference:
Schlupp, I., et al. (2010). A novel, sexually selected trait in poeciliid fishes: female preference for mustache-like, rostral filaments in male Poecilia sphenops Behavioral Ecology and Sociobiology: published online (DOI: 10.1007/s00265-010-0996-y)