INTRASEXUAL AGGRESSION IN METRIDIUM SENILE

¹ Institute of Animal Behavior, Rutgers University, 101 Warren Street, Newark New Jersey 07102

The dioeceous anemone Metridium senile reproduces both sexually (in summer) and asexually (year round). Asexual reproduction yields genetically identical clones via longitudinal fission or pedal laceration. Clonemates may form large aggregates, ranked together in close order, and become aggressive against neighboring clones. Interclonal aggression is frequently carried out with the use of hypertrophied tentacles referred to as catch tentacles. The present study indicates that catch tentacles do not maintain clonal segregation, and do not serve as aggressive appendages against all nonclonemates. Laboratory pairings of nonclonemates and observations of their movements in the field indicate that interclonal aggression in this species is mediated by sex. Nonclonemates will become aggressive only against same sexed individuals, males fighting males and females fighting females, while nonclonemates of opposite sex may exhibit nonaggressive interaction, with or without the use of catch tentacles. Interclonal/intrasexual aggression in this species may function to increase the probability of successful fertilization during sexual reproduction by increasing the proximity of males to females and vice versa.