Abstract
Although complex behaviour in marine zooplankton has been considered strong evidence of adaptation, ethological studies of marine zooplankton generally have not employed either the comparative approach or evolutionary perspective necessary to distinguish adaptation from any alternative. Consequently, the potential for intra-specific variation in the behavior of marine zooplankton has received insufficient attention and conclusions of adaptation remain poorly substantiated. Intraspecific comparison of patterns of migration and behaviour for seven populations of golden jellyfish, Mastigias (Scyphozoa: Rhizostomeae), inhabiting isolated marine lakes and semi-enclosed lagoon coves in Palau document population specific differences in patterns of horizontal migration, vertical migration, pulse rate, swimming speed, and turning behavior. Evidence was found for symplesiomorphic behaviours, canalization, exaptation, adaptation, and probably once-deleterious traits. Behavioural evolution likely proceeded via, at least, relaxation of selection, trade-offs with morphology, and natural selection effected by predation. Behavioural patterns also may change with ontogeny. Geographic variation in the behaviour of marine plankton therefore can be substantial and patterns of evolution complex. Behavioural evolution can rapidly generate coastal biodiversity. Thus, geographic variation in marine plankton is of potential interest to ethologists, evolutionary biologists, biogeographers, and conservation biologists.