Back to the trees – can barcodes really advance the rate of microbial and invertebrate species discovery?

Ecological and evolutionary perspectives are fundamentally linked in biodiversity research. A good example of this linkage is the increasing use of DNA in the ecological study of microbial and macroinvertebrate communities. DNA sequences provide a promising means of species delineation in ecological studies, but only if we can recognize evolutionary entities from sequence data that are comparable to species. The generalized mixed Yule-coalescent (GMYC) model identifies independently evolving lineages as a transition from coalescent to speciation branching patterns on a phylogenetic tree. Applied here to benthic invertebrates (Madagascar), cyanobacteria (Germany), and actinobacteria (Europe), the model produced encouraging results. A critical factor in the success of the model was sample size, where between 7-10 individuals represented a threshold above which there was minimal increase in genetic diversity, broadly agreeing with coalescent theory and other empirical studies. For insects, GMYC delineated 370 putative species from 1480 individuals. These were compared to data from the nuclear genome and morphological identification and found to be highly congruent (98% and 94%). The GMYC model enables rapid species discovery using sequence data from mixed or environmental samples, providing an evolutionary basis for large-scale (pyrosequencing) studies of microbial ecology and biodiversity the near future.