THEORETICAL MORPHOSPACE AND ITS RELATION TO FRESHWATER GOMPHONEMOID–CYMBELLOID DIATOM (BACILLARIOPHYTA) LINEAGES

Abstract

A number of basic forms in the gomphonemoid–cymbelloid diatom lineages were generated using three-dimensional (3D) parametric equations. The same boundary intervals and differentials for the parameters were used for all forms. From this, the absolute value of the Riemann sum of differences was determined for each variable between pairs of forms. The results were coordinate triplets, and they were plotted in 3D morphospace. Naviculoid forms occupied lower-valued morphospace in contrast to gomphonemoid and cymbelloid morphospaces. However, gomphonemoid and cymbelloid forms occupied different morphospaces. Forms representing Brebissonia occupied morphospace at the base of gomphonemoid forms, but occupied high-valued morphospace with respect to cymbelloid forms. Forms representing Encyonema had lower-valued coordinates compared to other cymbelloid forms. These results support hypotheses of Kociolek and Stoermer that state that naviculoid forms (and in particular, Placoneis) are ancestral to gomphonemoid and cymbelloid forms, Brebissonia is basal to gomphonemoid (but not cymbelloid) forms, and Encyonema is more primitive than other cymbelloid forms. This approach was useful in inferring the relation between theoretical morphospace and hypothesized phylogenies in the gomphonemoid–cymbelloid diatom lineages.