SIBLING SPECIES IN THE SEA

Sibling species are common in all major marine groups and habitats. Their abundance reflects both inadequate study of morphological features of living organisms (''pseudo-sibling species'') and divergence in habitat, life history, and chemical recognition systems without parallel divergence in morphology. Many marine sibling species are quite distinct genetically. Others, however, exhibit slight genetic differences whose significance is only clear in sympatry and in combination with other subtle but concordant patterns of differentiation. A large number of abundant, well-studied, or economically important taxa have recently been shown to be complexes of sibling species. The broad habitat and geographic distributions characteristic of many marine species require reevaluation in this context.