Our second day in Cuerici, I took a hike along the trail up the mountain searching for different moss morphotypes. Before reaching the stream about ¾ of the way up the trail, I noticed a large mushroom patch growing on a fallen log with quite a few Drosophila flies aggregating on top of the mushrooms. I saw that there were males on top of each mushroom and females flying around the mushrooms, occasionally landing and checking out the underside of the mushroom. There appeared to be a dominant male on each mushroom and any time another male landed on the mushroom, the male would aggressively chase the male off the mushroom. If the male refused to leave, the dominant male would physically fight the competitor until he left.
This was a tad more unique than moss growth along the trail, so I changed project ideas and tested if these flies were using the mushrooms as a food resource or territory to attract females (since Drosophila sometimes use fungi as a food source and the males seemed to be defending each mushroom as a separate territory). Within a 5 minute trial period, I counted the number of competing males and females that landed on the mushrooms. I also measured mushroom size and captured the dominant flies to see if their body size mattered in determining their dominant role. I saw a mating event on a mushroom but didn’t find any eggs underneath the mushrooms (where the females were going immediately after landing), indicating that the mushrooms weren’t being used as a food resource but, in fact, the male Drosophila were lekking!
Lekking is an unusual mating behavior (not often seen in Drosophila) in which males travel to a specific location to display and females come to watch and choose mates. Lekking is often seen in birds such as Manakins, but it also has been recorded in butterflies and fish.
If you had told me I would come to Costa Rica to study fly behavior and think it was cool, I would never have believed you. But I guess the Biology FSP is full of surprises for students from all backgrounds!