Molecular phylogeny and morphologic data of strains of the genus Coelastrella (Chlorophyta, Scenedesmaceae) from a tropical region in North America (Yucatan Peninsula)

Abstract

Background: Scenedesmaceae family exhibits great morphological variability. High phenotypic plasticity and the presence of cryptic species have resulted in taxonomic re-assignments of Scenedesmaceae members.
 Study strains: Strains CORE-1, CORE-2 and CORE-3 were characterized.
 Study site: Yucatan Peninsula
 Methods: Morphological analyses were executed by optical and scanning electron microscopy. Phylogenetic relationships were examined by ITS-2 and ITS1-5.8S-ITS2 rDNA regions.
 Results: Optical and scanning electron microscopy analyses indicated spherical to ellipsoidal cells and autospore formation correspond to members of the family Scenedesmaceae, as well as observable pyrenoid starch plates. Detailed morphology analysis indicated that CORE-1 had visible granulations dispersed on the cell wall, suggesting identity with Verrucodesmus verrucosus . However CORE-1 did not show genetic relations with this species, and was instead clustered close to the genus Coelastrella . CORE-2 did not show any particular structure or ornamentation, but it did show genetic relations with Coelastrella with good support. CORE-3 showed meridional ribs from end to end, one of them forked and well pronounced, and orange cells in older cultures characteristic of Coelastrella specimens. Phylogenetic trees of ITS-2 and ITS1-5.8S-ITS2 rDNA sequences indicated with good support that all strains were related to the genus Coelastrella despite their morphologic differences.
 Conclusions: This study reports freshwater Coelastrella strains from a tropical region in North America (Yucatan Peninsula) for the first time. The results contribute to knowledge of Coelastrella species, and the fact that they do not always show structures that are useful for taxonomic assignment, probably as a result of phenotypic plasticity.