Evolutionary Significance of Sexual and Asexual Modes of Propagation in Neogene Species of the Bryozoan Metrarabdotos in Tropical America

摘要: Three new Miocene-Pliocene species of the cheilostome bryozoan Metrarabdotos from Venezuela are atypical in showing significant evidence that as many half colonies originated asexually (clonally) by “regeneration” previously existing colonies, rather than almost exclusively ancestrular zooids (products metamorphosis sexually produced larvae), is characteristic genus. The extremely low proportion (less two percent) recognizably committed to producing larvae (ovicelled) these Venezuelan agrees with reported a variety Danian (Paleocene) genera which clonal propagation has been predominate. However, all but 17 other living and fossil also have fewer percent their ovicelled, even though one more 250 colony bases examined ancestrulae. lack correlation between frequencies ovicelled suggests may not diverted resources sexual reproduction. This inference supported retention level heritable morphologic variation (estimated partitioning among-colonies within-colonies variance zooid characters) commensurate estimated for was apparently entirely means. Thus, reproduction throughout genus sufficient maintain genetic diversity speciation could proceed at normal rates. As both cladistic nearest-neighbor morphologic-stratigraphic methods, three occupy quite different positions inferred phylogeny Metrarabdotos. elevated appears be response local conditions, most probably high productivity associated upwelling, promoted rapid vegetative growth while leaving unchanged.