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. 2015 Nov 12;10(11):e0142632.
doi: 10.1371/journal.pone.0142632. eCollection 2015.

Delineating a New Heterothallic Species of Volvox (Volvocaceae, Chlorophyceae) Using New Strains of "Volvox africanus"

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Delineating a New Heterothallic Species of Volvox (Volvocaceae, Chlorophyceae) Using New Strains of "Volvox africanus"

Hisayoshi Nozaki et al. PLoS One. .

Abstract

The volvocine algae represent an excellent model lineage in which to study evolution of female and male genders based on comparative analyses of related species. Among these species, Volvox carteri has been extensively studied as a model of an oogamous and complex organism. However, it may have unique derived features that are not present in other species of Volvox. Therefore, information regarding the characteristics of sexual reproduction of other species of Volvox is also important. In 1971, Starr studied four types of sexuality in several global strains identified as Volvox africanus; however, further taxonomic studies of these strains have been lacking, and strains of three of the four sexual types are not available. Here, we studied the morphology, sexual reproduction, and taxonomy of two V. africanus-like species isolated recently from Lake Biwa, Japan. These two species were very similar to two sexual types described by Starr in 1971: one producing dioecious sexual spheroids in heterothallic strains and the other forming both male spheroids and monoecious spheroids in a single strain. The former species produced zygotes with a reticulate cell wall, whereas a smooth zygote wall was observed in the latter species as in V. africanus previously reported from various localities around the world. Our multigene phylogenetic analysis demonstrated that these are sister species to each other. However, the presence of a compensatory base change in the most conserved region of the secondary structure of nuclear ribosomal DNA internal transcribed spacer-2, hybrid inviability demonstrated by intercrossing experiments, and morphological differences in the density of abutment between the gelatinous material of adjacent cells (individual sheaths) in the spheroid supported the recognition of the two species, V. africanus having a smooth zygote wall and V. reticuliferus Nozaki sp. nov. having a reticulate zygote wall.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Nomarski interference microscopy of Volvox reticuliferus Nozaki sp. nov.
(A) Surface view of asexual spheroids showing small somatic cells and larger reproductive cells (gonidia). (B, C) Somatic cells in the anterior portion of asexual spheroid showing lack of cytoplasmic bridges between cells. (B) Surface view showing stigma. (C) Optical section showing pyrenoid. (D, E) Asexual spheroid stained with dilute aniline blue, showing a broad secondary boundary layer (asterisk) of the gelatinous matrix surrounding each somatic cell. (D) Front view of somatic cells. (E) Side view of somatic cells. (F) Surface view of chloroplast of gonidium of asexual spheroid. Note presence of radial striations in the chloroplast surface. (G) Pre-inversion stage. Note morphological differentiation of gonidia of the next generation. (H, I) Mature male spheroids with sperm packets. (J) Female spheroid with eggs. (K, L) Two views of mature zygotes with a reticulate wall. Abbreviations: e, egg; g, gonidium; p, pyrenoid; s, stigma; sp, sperm packet. (A-C, H, I) Strain VO123-F1-7. (D-G) Strain VO123-F1-6. (D-G) Strain 2013-0703-VO2. (K, L) Strains 2013-0703-VO2x3.
Fig 2
Fig 2. Phylogenetic positions of Volvox reticuliferus Nozaki sp. nov. and V. africanus G. S. West within the advanced members of the Volvocaceae (Eudorina group [8, 23]), as inferred from 6021 base pairs of five chloroplast genes.
The tree was constructed by Bayesian inference unlinked GTR+I+G, F81+I+G and GTR+I+G models for the first, second and third codon positions in the five concatenated genes, respectively. Branch lengths are proportional to the genetic distances, which are indicated by the scale bar above the tree. Numbers on the left, middle, or right side at the branches represent posterior probabilities (PP) of BI (≥0.95), bootstrap values (≥50%, based on 1,000 replicates) obtained with the maximum likelihood and maximum parsimony analyses, respectively. Asterisks at the branches indicate 1.00 PP and 100% bootstrap values by the two methods. For details of the methods, see the text. Longitudinal dashed lines associated with "M" represent species of Volvox sect. Merrillosphaera sensu Smith [2].
Fig 3
Fig 3. Phylogenetic relationships of various strains of Volvox reticuliferus Nozaki sp. nov. and V. africanus G. S. West, as inferred from internal transcribed spacer region 2 (ITS-2) of nuclear ribosomal DNA.
The tree was constructed by the maximum likelihood (ML) method (based on T92+G model). Branch lengths are proportional to the genetic distances, which are indicated by the scale bar above the tree. Numbers on the left or right side at the branches represent bootstrap values (≥50%, based on 1,000 replicates) obtained with the ML calculation and maximum parsimonious analysis (using a branch-and-bound search), respectively. Sexual types (S1 Table) are shown right to the strain designations.
Fig 4
Fig 4. Comparison of the most conserved region (near the YGGY motif of helix III [39]) of nuclear rDNA ITS-2 secondary structure between lineage RT (corresponding to Volvox reticuliferus Nozaki sp. nov., see Discussion of the main text), lineage AF (including V. africanus G. S. West) and "V. africanus" strain UTEX 1889 (Fig 3).
Note the modified YGGY motif (boldface). For secondary structures of ITS-2, see S5 Fig. Compensatory base changes between lineages RT/AF and "V. africanus" strain UTEX 1889 are marked with dotted open boxes, and those between lineages RT and AF are indicated by open boxes.

References

    1. Linnaeus C. Systema naturae Regnum animalae. Ed. 10, Stockholm; 1758.
    1. Smith GM. A comparative study of the species of Volvox Trans. Am. Microsc. Soc. 1944; 63: 265–310.
    1. Nozaki H. Morphology, sexual reproduction and taxonomy of Volvox carteri f. kawasakiensis f. nov. (Chlorophyta) from Japan Phycologia 1988; 27: 209–220.
    1. Kirk DL. Volvox: Molecular Genetic Origins of Multicellularity and Cellular Differentiation. Cambridge: Cambridge University Press; 1998.
    1. Nozaki H, Coleman AW. A new species of Volvox sect. Merrillosphaera (Volvocaceae, Chlorophyceae) from Texas. J. Phycol. 2011;47: 673–679. - PubMed

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