Intraspecific density mediates sex-change in the territorial patellacean limpet Lottia gigantea

The effects of intraspecific density and agonistic interactions on sex-change were studied in the territorial limpet Lottia gigantea. In a one-year field experiment (1982–1983) on San Nicolas Island off the southern California coast, USA, male limpets transplanted to large enclosures changed sex more frequently than those transplanted to small enclosures (9 of 13 vs 1 of 10; p=0.013), indicating that intraspecific density can profoundly influence the probability of sex change. Large limpets were more likely to change sex than small ones. Observations of gender-age distributions as well as field behavior suggested that each limpet's territorial status prior to the experiment may have been an important component of this size effect, although other interpretations including an effect of age are possible. Pooling the results with those of two previous studies confirmed that sex-change is enhanced by low density. This enhancement was observed among the largest members of a local population in the first year of each experiment, while among the smaller members the enhancement was delayed until the second or third year. Low density may be a correlate of high mortality, and therefore an adaptive cue for an earlier age of sex change. Dominant territorial status correlates with an individual's size, and therefore egg-producing capacity, relative to its neighbors, and thus may also be a good cue for the initiation of sex-change.