Experimental evidence that immediate neighbors affect male attractiveness

If female mate choice is based on comparison of locally available mates rather than absolute, fixed criteria, a male's attractiveness might depend on the attractiveness of his immediate competitors. We use robotic models to test whether the number of females that a male fiddler crab, Uca mjoebergi, attracts depends on his immediate neighbors' size. Larger males are, on average, more attractive to females and are also more likely to win male-male fights. Larger males can partially influence who their territorial neighbors are because they assist smaller neighbors to repel intruders that attempt to acquire the neighbor's burrow (defence coalitions). This assistance might allow a male to avoid the costs of renegotiating territorial boundaries with new neighbors, who will also tend to be larger than the previous neighbor. In this study, we show that males are more likely to attract females if they court immediately alongside smaller males. This represents an additional potential benefit of defence coalitions, by ensuring that large males compete against smaller neighbors when courting.