Corals: pointing to a different evolution

摘要

For most marine organisms, ocean currents are the vehicles of larval dispersal and are therefore the pathways of genetic connectivity. These paths repeatedly and continuously change over time, creating changes to the distribution ranges and genetic compositions of species. Geographic space and evolutionary time interact: species units diverge, then re-form into different units. For corals, this creates 'reticulate' patterns in both space and time. In geographic space, species are typically distinct in any single region but loose their identity as taxonomic units over very great distances. When these patterns are envisaged in evolutionary time, species have no ti me or place of origin and there are no distinctions between sympatric and non-sympatric concepts of origination. Differences between species and subspecies taxonomic levels and between species and 'hybrids' are arbitrary and/or unrecognizable. Reticulate evolution is driven by the physical environment, not biological competition. Rates of evolution and extinction (which occur through fusions as well as terminations of lineages) are similar over long geological intervals. Reticulate evolution gives the overall impression of punctuated equilibria, as is frequently observed in fossil records. Taxonomic, systematic and biogeographic concepts of neo-Darwinian and reticulate evolution are mutually exclusive, except where single species form genetically cohesive, reproductively isolated, units. In the latter case, natural selection as the driving force of evolutionary change becomes dominant over environment-driven reticulate change.