Comparatively little attention has been paid to the life histories of many modular, sessile organisms such as sponges, bryozoans and cnidarians, as well as terrestrial and marine animals and plants (9). Vernon et al. (23) have noted that while clonal reproduction is commonly reported in literature describing metazoan life cycles, there is yet little understanding of how these organisms deal with natural enemies or habitat, and how such elements affect the expression of a modular lifestyle. Presented here are studies which describe selected clonal organisms, relating such aspects as reproduction, genetic and phenotypic diversity, and growth to the highly specialized mode of clonal life cycles.
Sackville Hamilton et al. (19) have observed that it has been difficult to assign a role--and even a consistent name--to describe acceptably the individual when this concept is examined from the viewpoints of animal and plant biologists. Individual clonal units are generally reviewed in terms of genets (the result of mitotic growth derived from a single zygote), and modules (the multicellular 'iterative unit', seen during the process of genet growth). Ramets or individuals that share the same genotype for all polymorphic loci can be described as a clone (11). This nomenclature impacts studies of clonal organisms in several ways. Reproductive success can be measured in terms of successful growth of genets, modules or both. Fitness can be examined similarly, with genetic descendants arising from varying proportions of these sources.
The creation of models to determine genetic relatedness and inbreeding in organisms has shed considerable light on the degree of genetic diversity seen in clonal organisms. Sackville Hamilton et al. (19) present an overview of the life history and population biology of clonal organisms, proposing a model to describe different strategies in relation to r and K-selection. A more recent work by Orive (17) further ...