MOLECULAR DELINEATION OF SPECIES AND SYNGENS IN VOLVOCACEAN GREEN ALGAE (CHLOROPHYTA)¹

Abstract

Two species of the colonial green flagellate family Volvocaceae are worldwide in distribution yet exhibit contrasting species structure. Geographically disparate isolates of Gonium pectorale Mueller can interbreed while isolates of Pandorina morum Bory behave quite differently. More than 20 sexually isolated subpopulations occur within this species; these have been termed “syngens” (sensu Sonneborn). Because prezygotic barriers to mating cause intersyngen pairings to fail, breeding analyses cannot be used to estimate genetic relatedness among the syngens of P. morum. DNA comparisons provide an alternative method of assessing genetic relatedness. We compared the nucleotide sequence of the internal transcribed spacer (ITS) region of the nuclear ribosomal repeat among clones of P. morum and of G. pectorale. Members of syngens of P. morum with distribution restricted to one small geographical area show great similarity. Likewise, members of any syngen of worldwide distribution show near uniformity, even those from different continents. However, the ITS sequence of each syngen differs from that of other syngens. In contrast, G. pectorale, which has an ITS region that is remarkably uniform throughout the world, appears to consist of a single syngen within North America and Europe by mating tests. The molecular data are in complete conformity with previous syngen assignment. Because the latter is based on mating affinity, with two complementary mating types per syngen, the evolution of new mating type pairs appears to be the basis of microevolution in these algae. We infer that either P. morum is a more ancient species than G. pectorale or that P. morum has a less stable genome. In either case, the biogeographic distribution of certain syngens may reflect climatological changes of the past.

Molecular and Ecological Evidence for Species Specificity and Coevolution in a Group of Marine Algal-Bacterial Symbioses

“…was 4 to 7%, a level of variation similar to those observed among other algal ITS sequences used successfully for phylogenetic analysis (13,24,29). A limitation of the analysis of ITS sequence variation is the difficulty in defining suitable outgroups (relatives close enough that confident alignment is possible) for phylogenetic analyses.…”

Mollusc-Algal Chloroplast Endosymbiosis. Photosynthesis, Thylakoid Protein Maintenance, and Chloroplast Gene Expression Continue for Many Months in the Absence of the Algal Nucleus

“…In contrast, positive signals were obtained for both probes using the control algal total DNA. We chose the nuclear ribosomal DNA ITS region because of its rapid evolutionary change, which would prevent the V. litorea ITS probe from hybridizing to slug ITS and because of its presence in multiple copies (White et al, 1990;Coleman et al, 1994;Zechman et al, 1994;Manhart et al, 1995).…”

A taxonomic study ofEudorina unicocca(Volvocaceae, Chlorophyceae) and related species, based on morphology and molecular phylogeny

“…In addition, the internal transcribed spacer (ITS) regions of nuclear ribosomal DNA from three strains of E. unicocca (NIES-724, NIES-726 and UTEX 1221) and two aplanosporic strains (TKI-C-2 and 990601-IE-5) were sequenced, as described by Sakayama et al (2004), except for the primers used for polymerase chain reaction (PCR) and sequencing. The primers for the ITS regions were those of Coleman et al (1994) (Mai & Coleman, 1997;Coleman, 2002). The sequence alignment is available upon request from the corresponding author (H.N.).…”