Rediscovery of the “ancestralVolvox” species: Morphology and phylogenetic position ofPleodorina sphaerica(Volvocales, Chlorophyceae) from Thailand

Abstract

Iyengar was considered to be a phylogenetic link between and the type species Shaw because it has small somatic cells distributed from the anterior to posterior poles in 64- or 128-celled vegetative colonies. However, cultural studies and molecular and ultrastructural data are lacking in , and this species has not been recorded since 1951. Here, we performed light and electron microscopy and molecular phylogeny of based on newly established culture strains originating from Thailand. Morphological features of the present Thai species agreed well with those of the previous studies of the Indian material of and with those of the current concept of the advanced members of the Volvocaceae. The present strains exhibited homothallic sexuality; male and facultative female colonies developed within a single clonal culture. Chloroplast multigene phylogeny demonstrated that was sister to two other species of ( and Nozaki) without posterior somatic cells, and these three species of formed a robust clade, which was positioned distally in the large monophyletic group including nine taxa of sect. and (sect.) Ehrenberg. Based on the present phylogenetic results, evolutionary losses of posterior somatic cells might have occurred in the ancestor of and . Thus, might represent an ancestral morphology of , rather than of.

Evolution of the Two Sexes under Internal Fertilization and Alternative Evolutionary Pathways

“…This could alter the relationship between zygote size and zygote survival (function s; table 2), an integral component of GD models. Published photographs show no apparent increase in zygote size between immature and fully mature zygotes (e.g., Pleodorina japonica [Nozaki et al 1989], Pleodorina sphaerica [Nozaki et al 2017], Volvox carteri f. kawasakiensis [Nozaki 1988], Volvox capensis [Nozaki et al 2015]), suggesting no significant maternal provisioning after fertil-ization. However, parental care could come in the form of reduced mortality risk in the relatively protected internal colony environment.…”

The Genetics of Fitness Reorganization During the Transition to Multicellularity: The Volvocine regA-Like Family as a Model

“…Algae in the genera Eudorina, Pandorina, Volvulina, Yamagishiella and Colemanosphaera all have spheroidal body plans with between 16 -64 cells (cell numbers vary between genera) with no germ-soma cellular differentiation under standard growth conditions. Species in the Pleodorina genus have 32 to 128 cells with specialized somatic cells in the anterior portion of the colony, except for one species, Pleodorina sphaerica, that has somatic cells distributed in both the anterior and posterior of the colony (Coleman, 2012;Nozaki et al, 2017). Finally, species in the genus Volvox are the largest and most complex members of the Volvocaceae, with several hundred to several thousand cells and two distinct cell types, specialized germ and specialized soma (Coleman, 2012).…”

The Genetics of Fitness Reorganization during the Transition to Multicellularity: The Volvocine regA-like Family as a Model

“…Algae in the genera Eudorina, Pandorina, Volvulina, Yamagishiella, and Colemanosphaera all have spheroidal body plans with between 16 and 64 cells (cell numbers vary between genera) with no germ–soma cellular differentiation under standard growth conditions. Species in the Pleodorina genus have 32 to 128 cells with specialized somatic cells in the anterior portion of the colony, except for one species, Pleodorina sphaerica , that has somatic cells distributed in both the anterior and posterior of the colony [ 26 , 34 ]. Finally, species in the genus Volvox are the largest and most complex members of the Volvocaceae, with several hundred to several thousand cells and two distinct cell types, specialized germ and specialized soma [ 26 ].…”