Burrow ornamentation in the fiddler crab (Uca leptodactyla): female mate choice and male–male competition

Abstract

Non-biological ornamentation is found in the nests and burrows of different kinds of animals. We evaluated here whether sand hoods constructed by male fiddler crabs (Uca leptodactyla) are one of the signals used by males to attract females during courtship. We observed females when they were walking among the males, and we quantified the proportion of females that visited male burrows with and without ornamentation and the choice to stay in a male’s burrow. Females visited more burrows with hoods than burrows without hoods, and they chose significantly more builder males. Male investment in ornamentation nevertheless decreased when the proportion of females increased in the area. Male investment was not correlated with the proportion of non-builder males nearby, but was positively correlated with overall density. The density sex ratio, however, was more male-biased in high-density than in low-density areas suggesting that even if building attracts females, the function could be related to male competition for mates.