In continuation of this idea, I calculated that, if the morphology of a taxon can be scored as a set of X binary characters, and morphological species boundaries are defined by a minimum of a one-character difference, the theoretical number of morphologically diagnosable species (N) increases exponentially with the number of characters available (N = 2X). Consequently, chances of encountering multiple species with identical morphologies increase quickly in taxa of lower morphological complexity (Verbruggen et al. 2009b). While such reasoning is useful conceptually, it is unlikely that all theoretically possible

morphologies will be produced in the course of the evolution of a lineage. To obtain a more realistic image of morphospace occupancy, I have now simulated character data using sensible models of character evolution.

BAY 73-4506 cost BGJ398 ic50 In summary, this approach consists of generating phylogenetic trees containing a number of species (between 10 and 400), and subsequently letting a set of traits (i.e., morphological characters) evolve along this phylogeny at a rate that corresponds to those measured for a real algal morphometric data set. The result of this exercise is a set of values for each trait for each species in the phylogeny. Those can then be compared with each other to evaluate how many of the species can be reliably distinguished from one another. For a more detailed description of the simulations, see the author’s blog at http://phycoweb.wordpress.com/. As could be expected, only a small subset of all possible

character combinations were produced during the evolution of the simulated ADAM7 lineages. For example, when lineages of 400 species were simulated, only ~50 distinct morphologies were produced in lineages with 20 characters, and only ~20 morphologies in lineages with 10 characters (Fig. 2A). It is evident that more complex lineages (i.e., with more characters) reach higher actual numbers of diagnosable species than simpler lineages. Consequently, complex lineages have a higher fraction of species pairs that are distinguishable (Fig. 2B), and these fractions are not influenced by the number of species in the lineages. The same pattern returns if continuous rather than binary characters are used: 54.2% of species pairs could be distinguished for lineages with 10 characters, whereas this number increased to 72.5% for organisms with 20 characters (Fig. 3, 1st vs. 4th boxplot). In conclusion, it appears to be a general rule that species of more complex lineages (i.e., those having more characters) are more easily distinguishable from one another than species of simpler lineages. But how about selection? We know that habitat has a major influence on the morphology of organisms. For example, macroalgae from very different phylogenetic backgrounds (Rhodophyta, Ulvophyceae, and Phaeophyceae) have converged onto very similar body architectures in similar environments (e.g., Littler and Littler 1980, Steneck and Dethier 1994).