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A New Morphological Type of Volvox from Japanese Large Lakes and Recent Divergence of this Type and V . ferrisii in Two Different Freshwater Habitats

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ABSTRACT

Volvox sect. Volvox is characterized by having unique morphological characteristics, such as thick cytoplasmic bridges between adult somatic cells in the spheroids and spiny zygote walls. Species of this section are found from various freshwater habitats. Recently, three species of Volvox sect. Volvox originating from rice paddies and a marsh were studied taxonomically based on molecular and morphological data of cultured materials. However, taxonomic studies have not been performed on cultured materials of this section originating from large lake water bodies. We studied a new morphological type of Volvox sect. Volvox (“Volvox sp. Sagami”), using cultured materials originating from two large lakes and a pond in Japan. Volvox sp. Sagami produced monoecious sexual spheroids and may represent a new morphological species; it could be clearly distinguished from all previously described monoecious species of Volvox sect. Volvox by its small number of eggs or zygotes (5–25) in sexual spheroids, with short acute spines (up to 3 μm long) on the zygote walls and elongated anterior somatic cells in asexual spheroids. Based on sequences of internal transcribed spacer (ITS) regions of nuclear ribosomal DNA (rDNA; ITS-1, 5.8S rDNA and ITS-2) and plastid genes, however, the Volvox sp. Sagami lineage and its sister lineage (the monoecious species V. ferrisii) showed very small genetic differences, which correspond to the variation within a single biological species in other volvocalean algae. Since V. ferrisii was different from Volvox sp. Sagami, by having approximately 100–200 zygotes in the sexual spheroids and long spines (6–8.5 μm long) on the zygote walls, as well as growing in Japanese rice paddies, these two morphologically distinct lineages might have diverged rapidly in the two different freshwater habitats. In addition, the swimming velocity during phototaxis of Volvox sp. Sagami spheroids originating from large lakes was significantly higher than that of V. ferrisii originating from rice paddies, suggesting adaptation of Volvox sp. Sagami to large water bodies.

No MeSH data available.


Maximum likelihood (ML) tree of Volvox sect. Volvox and other colonial Volvocales based on rbcL and psbC genes (S1 Table).Bootstrap values from ML (left) and maximum parsimony (right) analyses are shown on the branches.
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pone.0167148.g003: Maximum likelihood (ML) tree of Volvox sect. Volvox and other colonial Volvocales based on rbcL and psbC genes (S1 Table).Bootstrap values from ML (left) and maximum parsimony (right) analyses are shown on the branches.

Mentions: Phylogenetic relationships within Volvox sect. Volvox, resolved by the ITS rDNA and chloroplast rbcL-psbC gene trees (Figs 2 and 3) were essentially the same as those of a previous study [9], except for the phylogenetic position of Volvox sp. Sagami, which is a sister to V. ferrisii. These two species exhibited only a single nucleotide difference in ITS rDNA (S2 Fig), and a single difference in 780 base pairs of psbC coding regions but no differences in the 1128 base pairs of the rbcL genes.


A New Morphological Type of Volvox from Japanese Large Lakes and Recent Divergence of this Type and V . ferrisii in Two Different Freshwater Habitats
Maximum likelihood (ML) tree of Volvox sect. Volvox and other colonial Volvocales based on rbcL and psbC genes (S1 Table).Bootstrap values from ML (left) and maximum parsimony (right) analyses are shown on the branches.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120847&req=5

pone.0167148.g003: Maximum likelihood (ML) tree of Volvox sect. Volvox and other colonial Volvocales based on rbcL and psbC genes (S1 Table).Bootstrap values from ML (left) and maximum parsimony (right) analyses are shown on the branches.
Mentions: Phylogenetic relationships within Volvox sect. Volvox, resolved by the ITS rDNA and chloroplast rbcL-psbC gene trees (Figs 2 and 3) were essentially the same as those of a previous study [9], except for the phylogenetic position of Volvox sp. Sagami, which is a sister to V. ferrisii. These two species exhibited only a single nucleotide difference in ITS rDNA (S2 Fig), and a single difference in 780 base pairs of psbC coding regions but no differences in the 1128 base pairs of the rbcL genes.

View Article: PubMed Central - PubMed

ABSTRACT

Volvox sect. Volvox is characterized by having unique morphological characteristics, such as thick cytoplasmic bridges between adult somatic cells in the spheroids and spiny zygote walls. Species of this section are found from various freshwater habitats. Recently, three species of Volvox sect. Volvox originating from rice paddies and a marsh were studied taxonomically based on molecular and morphological data of cultured materials. However, taxonomic studies have not been performed on cultured materials of this section originating from large lake water bodies. We studied a new morphological type of Volvox sect. Volvox (“Volvox sp. Sagami”), using cultured materials originating from two large lakes and a pond in Japan. Volvox sp. Sagami produced monoecious sexual spheroids and may represent a new morphological species; it could be clearly distinguished from all previously described monoecious species of Volvox sect. Volvox by its small number of eggs or zygotes (5–25) in sexual spheroids, with short acute spines (up to 3 μm long) on the zygote walls and elongated anterior somatic cells in asexual spheroids. Based on sequences of internal transcribed spacer (ITS) regions of nuclear ribosomal DNA (rDNA; ITS-1, 5.8S rDNA and ITS-2) and plastid genes, however, the Volvox sp. Sagami lineage and its sister lineage (the monoecious species V. ferrisii) showed very small genetic differences, which correspond to the variation within a single biological species in other volvocalean algae. Since V. ferrisii was different from Volvox sp. Sagami, by having approximately 100–200 zygotes in the sexual spheroids and long spines (6–8.5 μm long) on the zygote walls, as well as growing in Japanese rice paddies, these two morphologically distinct lineages might have diverged rapidly in the two different freshwater habitats. In addition, the swimming velocity during phototaxis of Volvox sp. Sagami spheroids originating from large lakes was significantly higher than that of V. ferrisii originating from rice paddies, suggesting adaptation of Volvox sp. Sagami to large water bodies.

No MeSH data available.