Biodiversity and biogeography of microalgae:progress and pitfalls

摘要

The role of microbial diversity in ecosystem functioning is becoming increasingly recognized. Microalgae are alarge group of organisms that are extremely diverse and heterogeneous from evolutionary and ecological viewpoints. However,estimates of their diversity are nebulous and require substantial input from systematics, dispersal analyses, and biogeography. Our generally poor understanding of microalgal biogeography has generated several hypotheses. According toone view, microalgae are cosmopolitan. However, use of advanced morphometric and molecular techniques suggest a restricteddistribution (i.e., endemism) for many microalgae that were previously considered as cosmopolitan. The quest tohave an exclusive theory of microalgal biogeography depends upon efforts to solve the problems related with appropriatetaxonomic unit, genotype–morphospecies relationship, extent of synonymy in known species, degree of coexistence of endemicand cosmopolitan species, reasons for apparent restricted distribution, and the relative importance of sympatric speciationin genotype variations. This review discusses microalgal diversity from a biogeographical perspective, which, inturn, is analyzed in the light of empirical evidence available for the group. Also discussed are the arguments emergingfrom ongoing debates on the biogeography of other microorganisms. In addition to their immense ecological importance,microalgae have emerged as a potential source for a range of precious products including neutraceuticals, energy, and therapeutic drugs. Therefore, an understanding of their diversity and spatial distribution is crucial for formulating the conservation strategies for the group.