INTRASPECIFIC AGGRESSION AND POPULATION DISTRIBUTIONS OF THE SEA ANEMONEMETRIDIUM SENILE

Abstract

Aggregations of the sea anemone M. senile in Monterey Harbor sometimes contained only 1 clone (genetically identical individuals) but often contained 2 or more intermingled clones. The frequent occurrence of mixed clonal aggregations was perplexing, because M. senile uses fighting (catch) tentacles in intraspecific agonistic interactions. A photographic survey of 19 quadrats showed that mixed clonal aggregations of anemones persisted throughout the 3.5-yr study. Locomotion by the anemones, low frequency of nonclonemate contact, low population density, and infrequent occurrence of fighting tentacles were eliminated as possible explanations for the persistence of mixed clonal aggregation. Laboratory studies revealed differences among clones in the frequencies of fighting tentacle inflation and of injury to nonclonemates. Low expression of these aggressive traits might permit intermingling of clones. High expression of aggressive traits was not found consistently in clones which were not intermingled, and thus may not cause the segregation of such clones. Apparently, the most important factor contributing to the intermingling of clones was habituation of anemones to nonclonemate contact. The decrease in fighting tentacle inflation observed during two 6-day laboratory experiments was not due to fatigue, because contact with unfamiliar nonclonemates renewed aggression. Habituation to nonclonemate contact probably occurs in situ and loss of habituation must occur occasionally to account for the occurrence of fighting tentacles.