ASEXUAL REPRODUCTION AND GENETIC POPULATION STRUCTURE IN THE COLONIZING SEA ANEMONEHALIPLANELLA LUCIAE

Abstract

Populations of Haliplanella luciae on the Atlantic coast of North America typically are composed of one or a few strictly asexual clones. The lack of genetic variability in one local population, that at Blue Hill Falls, Maine, is reflected in the population's response to extremes of temperature and salinity. As the limits of tolerance are approached, there is an abrupt and epidemic incidence of mortality, rather than a gradual one. Genetic and the concomitant physiological uniformity explain the well-known tendency for local populations of Haliplanella to disappear suddenly and illustrate a common outcome of the founder effect. The success of Haliplanella as a colonizer is due to its extreme hardiness toward physical environmental factors and to its prolific asexual nature. Asexual reproduction by longitudinal fission and by pedal laceration not only provides a means of rapid colonization of a new habitat, but also a means of producing multiple copies of genotypes that have proved to be successful under local conditions. The resultant population structure recalls that in other animal and plant colonizers, in which there is heavy reliance on general purpose genotypes in isolated populations. The comparative lack of colonizing success in the ecologically similar anemone, Diadumene leucolena, relates to its reproductive biology. Not only is the asexual potential for the rapid spread of successful genotypes lacking, but sexual reproduction typically requires a more optimal set of environmental circumstances which will not necessarily be met in a new habitat.