Switching between mating tactics in the fiddler crab Uca uruguayensis

RIBEIRO, P; DALEO, P; IRIBARNE, O

Panama

Congreso; Meeting of the International Society of Invertebrate Reproduction and Development (ICIRD); 2007

Smithsonian Tropical Research Institute Panama

Abstract: It is common to find species to achieve alternative ways of mating, but the understanding of the mechanism through which the behavioral variation is accomplished is generally a source of controversies. Fiddler crabs show two different mating tactics: either females search and crabs mate underground in male?s burrows, or males search and crabs mate on the surface near female?s burrows. In general, each species develops only one mating tactic; however, some species (as Uca uruguayensis) develop both. This study explored the relationship between the density of crabs, the occurrence of both mating tactics, and the level of size-assortative mating in the fiddler crab U. uruguayensis. An experiment of density manipulation showed that crabs mated mostly on the surface at low densities (70-75% matings), and underground at high densities (65-80% matings). Size-assortative mating (measured as the correlation between the sizes of male and female crabs) was found in underground matings from high-density areas, while in surface matings (both densities) or underground mating from low-density areas crabs mated randomly. Logistic regressions were used to estimate the size of crabs at which they switched the mating tactic (i.e. switching point). The proportion of male crabs from the population that mated underground was calculated by integrating their size-frequency distribution beyond the switching point. This proportion ranged between 0.57 and 0.72 at high density, and between 0.04 and 0.15 at low density. In overall, the results of this work suggest that switching between mating tactics in U. uruguayensis is a case of behavioral plasticity rather than a genetically-based polymorphism, and that the level sexual selection by female choice would not only change with the mating tactic, but also with the density at which the mating tactic is developed.