title: A New Morphological Type of Volvox from Japanese Large Lakes and Recent Divergence of this Type and V. ferrisii in Two Different Freshwater Habitats.
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.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan.
authors.forename: Hisayoshi
authors.initials: H
authors.lastname: Nozaki
authors.affiliation: Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, 226-8503, Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Ueki
authors.affiliation: Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan.
authors.forename: Nanako
authors.initials: N
authors.lastname: Isaka
authors.affiliation: Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan.
authors.forename: Tokiko
authors.initials: T
authors.lastname: Saigo
authors.affiliation: Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan.
authors.forename: Kayoko
authors.initials: K
authors.lastname: Yamamoto
authors.affiliation: Center for Environmental Biology and Ecosystem Studies, National Institute for Environmental Studies, Onogawa 16-2, Tsukuba-shi, Ibaraki, 305-8506, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Matsuzaki
authors.affiliation: College of Life Sciences, Ritsumeikan University, Nojihigashi 1-1-1, Kusatsu-shi, Shiga, 525-8577, Japan.
authors.forename: Fumio
authors.initials: F
authors.lastname: Takahashi
authors.affiliation: Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, 226-8503, Japan.
authors.forename: Ken-Ichi
authors.initials: KI
authors.lastname: Wakabayashi
authors.affiliation: Center for Environmental Biology and Ecosystem Studies, National Institute for Environmental Studies, Onogawa 16-2, Tsukuba-shi, Ibaraki, 305-8506, Japan.
authors.forename: Masanobu
authors.initials: M
authors.lastname: Kawachi
mesh_terms: D018744:DNA, Plant / Q000235:genetics*; D021903:DNA, Ribosomal Spacer / Q000235:genetics*; D017753:Ecosystem; D054627:Genome, Plastid; D007564:Japan; D060106:Lakes; D012639:Seeds / Q000166:cytology / Q000235:genetics / Q000254:growth & development; D044446:Volvox / Q000166:cytology / Q000235:genetics / Q000254:growth & development
chemical_list: D018744:DNA, Plant; D021903:DNA, Ribosomal Spacer