Molecular phylogeny and evolution of phenotype in silica‐scaled chrysophyte genus Mallomonas

Abstract

The evolution of phenotypes is highly understudied in protists, due to the dearth of morphological characters, missing fossil record, and/or unresolved phylogeny in the majority of taxa. The chrysophyte genus Mallomonas (Stramenopiles) forms species‐specific silica scales with extraordinary diversity of their ornamentation. In this paper, we molecularly characterized three additional species to provide an updated phylogeny of 43 species, and combined this with evaluations of 24 morphological traits. Using phylogenetic comparative methods, we evaluated phylogenetic signal in traits, reconstructed the trait evolution, and compared the overall phylogenetic and morphological diversity. The majority of traits showed strong phylogenetic signal and mostly dynamic evolution. Phylogenetic relatedness was often reflected by the phenotypic similarity. Both V‐rib and dome are very conservative structures that are presumably involved in precise scale overlap and bristle attachment, respectively. Based on modern species, it seems the dome firstly appeared on apical and/or caudal scales, and only later emerged on body scales. Bristle was presumably present in the common ancestor and gradually elongated ever since. However, most other morphological traits readily changed during the evolution of Mallomonas.

Diversity of Silica-Scaled Chrysophytes of Two Tropical Islands: Phu Quoc and Con Son (Viet Nam)

“…To date, a consistent system of morphological criteria for distinguishing taxa has only been developed for a small number of chrysophytes (orders Synurales and Paraphysomonadales and some representatives of Chromulinales and Ochromonadales). This morphological system is consistent with the available molecular genetic information on these taxa [ 2 , 3 , 4 , 5 , 6 , 7 ]. Although sexual reproduction is known among chrysophytes [ 8 , 9 , 10 , 11 ], the biological species concept is difficult to apply to this group, and the morphological species concept, which is based on the presence or absence of distinct taxonomic features, remains the most useful.…”

Diversity of Silica-Scaled Chrysophytes in Central Vietnam

“…However, among this large group, there are species with siliceous covers (scales, spines, and bristles), which have a complex ultrastructure and provide reliable characteristics for morphological species differentiation [29]. Moreover, the developed system of morphological criteria for distinguishing taxa (morphological species concept) is considered one of the best among the protists and, in general, has been confirmed with molecular data [29,[31][32][33][34][35]. Hence, the majority of the known species of silica-scaled chrysophytes can be identified correctly.…”

Studies on Algae from the Order Synurales (Chrysophyceae) in Northern Vietnam

“…Taking into account morphological characters and molecular data, it was proposed to distinguish synuralean algae into a separate class, Synurophyceae [9,10]; however, recent molecular studies of the chrysophytes phylogeny clearly showed their position among Chrysophyceae [1]. The species concept for this group is based on the morphology of siliceous structures (scales and bristles), studied by transmission or scanning electron microscopy (TEM or SEM) [3], and is considered one of the best among the protists and generally confirmed by molecular methods [11,12]. Electron microscopy studies of synuralean algae began in the 1950s [13][14][15][16][17].…”