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Hisayoshi Nozaki - One of the best experts on this subject based on the ideXlab platform.
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A new preferentially outcrossing monoicous species of Volvox sect. Volvox (Chlorophyta) from Thailand.
PLOS ONE, 2020Co-Authors: Hisayoshi Nozaki, Wuttipong Mahakham, Wirawan Heman, Ryo Matsuzaki, Masanobu KawachiAbstract:Volvox sect. Volvox is an interesting group of green algae; it comprises mostly monoicous species, but evidence suggests an evolution towards dioicy. Based on cultured strains originating from Thailand, we describe Volvox longispiniferus, a novel species in Volvox sect. Volvox. This species is distinguished from others in the section by the large number of sperm packets in its monoicous sexual spheroids and by the long spines on its zygote wall. Phylogenetic analyses indicate that V. longispiniferus is distinct from the other species of two monophyletic groups within Volvox sect. Volvox. In addition, the novel species produces more zygotes when different cultures are combined compared with a single culture, suggesting a preference for outcrossing.
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Correction: Morphological and molecular identification of the dioecious “African species Volvox rousseletii (Chlorophyceae) in the water column of a Japanese lake based on field-collected and cultured materials
PLOS ONE, 2019Co-Authors: Ryosuke Kimbara, Ryo Matsuzaki, Masanobu Kawachi, Nanako Isaka, Hiroko Kawai-toyooka, Hisayoshi NozakiAbstract:Volvox rousseletii is a dioecious species belonging to Volvox sect. Volvox that has previously only been found in Africa. During field surveys in a large dam lake (Lake Sagami) in Kanagawa Prefecture, central Japan, we encountered a Volvox sect. Volvox species that produces dioecious sexual spheroids in the water column. Although sexual induction of this species in culture did not produce adequately well-developed sexual spheroids for species identification, molecular data directly obtained from field-collected sexual spheroids verified the identity of field-collected male and female sexual spheroids as well as cultured materials. Based on molecular and morphological data, the species was identified as V. rousseletii. This is the first record of a dioecious species of Volvox sect. Volvox in Japan.
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Morphological and molecular identification of the dioecious "African species Volvox rousseletii (Chlorophyceae) in the water column of a Japanese lake based on field-collected and cultured materials.
PLOS ONE, 2019Co-Authors: Ryosuke Kimbara, Ryo Matsuzaki, Masanobu Kawachi, Nanako Isaka, Hiroko Kawai-toyooka, Hisayoshi NozakiAbstract:Volvox rousseletii is a dioecious species belonging to Volvox sect. Volvox that has previously only been found in Africa. During field surveys in a large dam lake (Lake Sagami) in Kanagawa Prefecture, central Japan, we encountered a Volvox sect. Volvox species that produces dioecious sexual spheroids in the water column. Although sexual induction of this species in culture did not produce adequately well-developed sexual spheroids for species identification, molecular data directly obtained from field-collected sexual spheroids verified the identity of field-collected male and female sexual spheroids as well as cultured materials. Based on molecular and morphological data, the species was identified as V. rousseletii. This is the first record of a dioecious species of Volvox sect. Volvox in Japan.
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Morphology, reproduction and taxonomy of Volvox dissipatrix (Chlorophyceae) from Thailand, with a description of Volvox zeikusii sp. nov.
Phycologia, 2019Co-Authors: Hisayoshi Nozaki, Wuttipong Mahakham, Ryo Matsuzaki, Mari Takusagawa, Osami Misumi, Masanobu KawachiAbstract:ABSTRACTA strain of Volvox collected from Thailand produced a very large asexual spheroid with maximum diameter over 2 mm long. This Thai alga was identified as Volvox dissipatrix based on the deli...
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Strains of the three Volvox species used in the present study.
2017Co-Authors: Kayoko Yamamoto, Hiroko Kawai-toyooka, Fumio Takahashi, Patrick J. Ferris, Takashi Hamaji, Yuki Tsuchikane, Toshiyuki Mori, Hiroyuki Sekimoto, Hisayoshi NozakiAbstract:Strains of the three Volvox species used in the present study.
Raymond E. Goldstein - One of the best experts on this subject based on the ideXlab platform.
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motility and phototaxis of gonium the simplest differentiated colonial alga
Physical Review E, 2020Co-Authors: Helene De Maleprade, Takuji Ishikawa, Frederic Moisy, Raymond E. GoldsteinAbstract:Green algae of the Volvocine lineage, spanning from unicellular Chlamydomonas to vastly larger Volvox, are models for the study of the evolution of multicellularity, flagellar dynamics, and developmental processes. Phototactic steering in these organisms occurs without a central nervous system, driven solely by the response of individual cells. All such algae spin about a body-fixed axis as they swim; directional photosensors on each cell thus receive periodic signals when that axis is not aligned with the light. The flagella of Chlamydomonas and Volvox both exhibit an adaptive response to such signals in a manner that allows for accurate phototaxis, but in the former the two flagella have distinct responses, while the thousands of flagella on the surface of spherical Volvox colonies have essentially identical behavior. The planar 16-cell species Gonium pectorale thus presents a conundrum, for its central 4 cells have a Chlamydomonas-like beat that provide propulsion normal to the plane, while its 12 peripheral cells generate rotation around the normal through a Volvox-like beat. Here we combine experiment, theory, and computations to reveal how Gonium, perhaps the simplest differentiated colonial organism, achieves phototaxis. High-resolution cell tracking, particle image velocimetry of flagellar driven flows, and high-speed imaging of flagella on micropipette-held colonies show how, in the context of a recently introduced model for Chlamydomonas phototaxis, an adaptive response of the peripheral cells alone leads to photoreorientation of the entire colony. The analysis also highlights the importance of local variations in flagellar beat dynamics within a given colony, which can lead to enhanced reorientation dynamics.
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flagellar phenotypic plasticity in volvocalean algae correlates with peclet number
Journal of the Royal Society Interface, 2011Co-Authors: Carlos Álvarez Solari, Knut Drescher, Sujoy Ganguly, Richard E. Michod, John O. Kessler, Raymond E. GoldsteinAbstract:Flagella-generated fluid stirring has been suggested to enhance nutrient uptake for suffi- ciently large micro-organisms, and to have played a role in evolutionary transitions to multicellularity. A corollary to this predicted size-dependent benefit is a propensity for pheno- typic plasticity in the flow-generating mechanism to appear in large species under nutrient deprivation. We examined four species of volvocalean algae whose radii and flow speeds differ greatly, with Peclet numbers (Pe) separated by several orders of magnitude. Populations of unicellular Chlamydomonas reinhardtii and one- to eight-celled Gonium pectorale (Pe 0.1-1) and multicellular Volvox carteri and Volvox barberi (Pe 100) were grown in diluted and undiluted media. For C. reinhardtii and G. pectorale, decreasing the nutrient concen- tration resulted in smaller cells, but had no effect on flagellar length and propulsion force. In contrast, these conditions induced Volvox colonies to grow larger and increase their flagellar length, separating the somatic cells further. Detailed studies on V. carteri found that the oppos- ing effects of increasing beating force and flagellar spacing balance, so the fluid speed across the colony surface remains unchanged between nutrient conditions. These results lend further sup- port to the hypothesized link between the Peclet number, nutrient uptake and the evolution of biological complexity in the Volvocales.
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THE FLAGELLAR PHOTORESPONSE IN Volvox SPECIES (VOLVOCACEAE, CHLOROPHYCEAE)1.
Journal of Phycology, 2011Co-Authors: Carlos Álvarez Solari, Knut Drescher, Raymond E. GoldsteinAbstract:Steering their swimming direction toward the light is crucial for the viability of Volvox colonies, the larger members of the volvocine algae. While it is known that this phototactic steering is achieved by a difference in behavior of the flagella on the illuminated and shaded sides, conflicting reports suggest that this asymmetry arises either from a change in beating direction or a change in beating frequency. Here, we report direct observations of the flagellar behavior of various Volvox species with different phyletic origin in response to light intensity changes and thereby resolve this controversy: Volvox barberi W. Shaw from the section Volvox sensu Nozaki (2003) changes the direction of the flagellar beating plane, while species encompassed in the group Eudorina (Volvox carteri F. Stein, Volvox aureus Ehrenb., and Volvox tertius Art. Mey.) decrease the flagellar beating frequency, sometimes down to flagellar arrest.
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dancing Volvox hydrodynamic bound states of swimming algae
Physical Review Letters, 2009Co-Authors: Knut Drescher, Kyriacos C Leptos, Idan Tuval, Takuji Ishikawa, T J Pedley, Raymond E. GoldsteinAbstract:The spherical alga Volvox swims by means of flagella on thousands of surface somatic cells. This geometry and its large size make it a model organism for studying the fluid dynamics of multicellularity. Remarkably, when two nearby Volvox colonies swim close to a solid surface, they attract one another and can form stable bound states in which they ‘‘waltz’’ or ‘‘minuet’’ around each other. A surface-mediated hydrodynamic attraction combined with lubrication forces between spinning, bottom-heavy Volvox explains the formation, stability, and dynamics of the bound states. These phenomena are suggested to underlie observed clustering of Volvox at surfaces.
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Volvox BARBERI, THE FASTEST SWIMMER OF THE VOLVOCALES (CHLOROPHYCEAE)(1).
Journal of Phycology, 2008Co-Authors: Carlos Álvarez Solari, Richard E. Michod, Raymond E. GoldsteinAbstract:Volvox barberi W. Shaw is a volvocalean green alga composed of biflagellated cells. Vovocales with 16 cells or more form spherical colonies, and their largest members have germ-soma separation (all species in the genus Volvox). V. barberi is the largest Volvox species recorded in terms of cell number (10,000-50,000 cells) and has the highest somatic to reproductive cell ratio (S/R). Since they are negatively buoyant, Volvocales need flagellar beating to avoid sinking and to reach light and nutrients. We measured V. barberi swimming speed and total swimming force. V. barberi swimming speeds are the highest recorded so far for volvocine algae (~600 μm · s⁻¹). With this speed, V. barberi colonies have the potential to perform daily vertical migrations in the water column at speeds of 2-3 m · h⁻¹, consistent with what has been reported about Volvox populations in the wild. Moreover, V. barberi data fit well in the scaling relationships derived with the other smaller Volvox species, namely, that the upward swimming speed Vup[is proportional to]N⁰.²⁸ and the total swimming force FS[is proportional to]N⁰.⁷⁷ (N = colony cell number). These allometric relationships have been important supporting evidence for reaching the conclusion that as size increases, colonies have to invest in cell specialization and increase their S/R to increase their motility capabilities to stay afloat and motile.
Masanobu Kawachi - One of the best experts on this subject based on the ideXlab platform.
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A new preferentially outcrossing monoicous species of Volvox sect. Volvox (Chlorophyta) from Thailand.
PLOS ONE, 2020Co-Authors: Hisayoshi Nozaki, Wuttipong Mahakham, Wirawan Heman, Ryo Matsuzaki, Masanobu KawachiAbstract:Volvox sect. Volvox is an interesting group of green algae; it comprises mostly monoicous species, but evidence suggests an evolution towards dioicy. Based on cultured strains originating from Thailand, we describe Volvox longispiniferus, a novel species in Volvox sect. Volvox. This species is distinguished from others in the section by the large number of sperm packets in its monoicous sexual spheroids and by the long spines on its zygote wall. Phylogenetic analyses indicate that V. longispiniferus is distinct from the other species of two monophyletic groups within Volvox sect. Volvox. In addition, the novel species produces more zygotes when different cultures are combined compared with a single culture, suggesting a preference for outcrossing.
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Correction: Morphological and molecular identification of the dioecious “African species Volvox rousseletii (Chlorophyceae) in the water column of a Japanese lake based on field-collected and cultured materials
PLOS ONE, 2019Co-Authors: Ryosuke Kimbara, Ryo Matsuzaki, Masanobu Kawachi, Nanako Isaka, Hiroko Kawai-toyooka, Hisayoshi NozakiAbstract:Volvox rousseletii is a dioecious species belonging to Volvox sect. Volvox that has previously only been found in Africa. During field surveys in a large dam lake (Lake Sagami) in Kanagawa Prefecture, central Japan, we encountered a Volvox sect. Volvox species that produces dioecious sexual spheroids in the water column. Although sexual induction of this species in culture did not produce adequately well-developed sexual spheroids for species identification, molecular data directly obtained from field-collected sexual spheroids verified the identity of field-collected male and female sexual spheroids as well as cultured materials. Based on molecular and morphological data, the species was identified as V. rousseletii. This is the first record of a dioecious species of Volvox sect. Volvox in Japan.
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Morphological and molecular identification of the dioecious "African species Volvox rousseletii (Chlorophyceae) in the water column of a Japanese lake based on field-collected and cultured materials.
PLOS ONE, 2019Co-Authors: Ryosuke Kimbara, Ryo Matsuzaki, Masanobu Kawachi, Nanako Isaka, Hiroko Kawai-toyooka, Hisayoshi NozakiAbstract:Volvox rousseletii is a dioecious species belonging to Volvox sect. Volvox that has previously only been found in Africa. During field surveys in a large dam lake (Lake Sagami) in Kanagawa Prefecture, central Japan, we encountered a Volvox sect. Volvox species that produces dioecious sexual spheroids in the water column. Although sexual induction of this species in culture did not produce adequately well-developed sexual spheroids for species identification, molecular data directly obtained from field-collected sexual spheroids verified the identity of field-collected male and female sexual spheroids as well as cultured materials. Based on molecular and morphological data, the species was identified as V. rousseletii. This is the first record of a dioecious species of Volvox sect. Volvox in Japan.
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Morphology, reproduction and taxonomy of Volvox dissipatrix (Chlorophyceae) from Thailand, with a description of Volvox zeikusii sp. nov.
Phycologia, 2019Co-Authors: Hisayoshi Nozaki, Wuttipong Mahakham, Ryo Matsuzaki, Mari Takusagawa, Osami Misumi, Masanobu KawachiAbstract:ABSTRACTA strain of Volvox collected from Thailand produced a very large asexual spheroid with maximum diameter over 2 mm long. This Thai alga was identified as Volvox dissipatrix based on the deli...
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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
PLOS ONE, 2016Co-Authors: Hisayoshi Nozaki, Ryo Matsuzaki, Nanako Isaka, Noriko Ueki, Tokiko Saigo, Kayoko Yamamoto, Fumio Takahashi, Ken-ichi Wakabayashi, Masanobu KawachiAbstract: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.
Ryo Matsuzaki - One of the best experts on this subject based on the ideXlab platform.
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A new preferentially outcrossing monoicous species of Volvox sect. Volvox (Chlorophyta) from Thailand.
PLOS ONE, 2020Co-Authors: Hisayoshi Nozaki, Wuttipong Mahakham, Wirawan Heman, Ryo Matsuzaki, Masanobu KawachiAbstract:Volvox sect. Volvox is an interesting group of green algae; it comprises mostly monoicous species, but evidence suggests an evolution towards dioicy. Based on cultured strains originating from Thailand, we describe Volvox longispiniferus, a novel species in Volvox sect. Volvox. This species is distinguished from others in the section by the large number of sperm packets in its monoicous sexual spheroids and by the long spines on its zygote wall. Phylogenetic analyses indicate that V. longispiniferus is distinct from the other species of two monophyletic groups within Volvox sect. Volvox. In addition, the novel species produces more zygotes when different cultures are combined compared with a single culture, suggesting a preference for outcrossing.
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Correction: Morphological and molecular identification of the dioecious “African species Volvox rousseletii (Chlorophyceae) in the water column of a Japanese lake based on field-collected and cultured materials
PLOS ONE, 2019Co-Authors: Ryosuke Kimbara, Ryo Matsuzaki, Masanobu Kawachi, Nanako Isaka, Hiroko Kawai-toyooka, Hisayoshi NozakiAbstract:Volvox rousseletii is a dioecious species belonging to Volvox sect. Volvox that has previously only been found in Africa. During field surveys in a large dam lake (Lake Sagami) in Kanagawa Prefecture, central Japan, we encountered a Volvox sect. Volvox species that produces dioecious sexual spheroids in the water column. Although sexual induction of this species in culture did not produce adequately well-developed sexual spheroids for species identification, molecular data directly obtained from field-collected sexual spheroids verified the identity of field-collected male and female sexual spheroids as well as cultured materials. Based on molecular and morphological data, the species was identified as V. rousseletii. This is the first record of a dioecious species of Volvox sect. Volvox in Japan.
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Morphological and molecular identification of the dioecious "African species Volvox rousseletii (Chlorophyceae) in the water column of a Japanese lake based on field-collected and cultured materials.
PLOS ONE, 2019Co-Authors: Ryosuke Kimbara, Ryo Matsuzaki, Masanobu Kawachi, Nanako Isaka, Hiroko Kawai-toyooka, Hisayoshi NozakiAbstract:Volvox rousseletii is a dioecious species belonging to Volvox sect. Volvox that has previously only been found in Africa. During field surveys in a large dam lake (Lake Sagami) in Kanagawa Prefecture, central Japan, we encountered a Volvox sect. Volvox species that produces dioecious sexual spheroids in the water column. Although sexual induction of this species in culture did not produce adequately well-developed sexual spheroids for species identification, molecular data directly obtained from field-collected sexual spheroids verified the identity of field-collected male and female sexual spheroids as well as cultured materials. Based on molecular and morphological data, the species was identified as V. rousseletii. This is the first record of a dioecious species of Volvox sect. Volvox in Japan.
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Morphology, reproduction and taxonomy of Volvox dissipatrix (Chlorophyceae) from Thailand, with a description of Volvox zeikusii sp. nov.
Phycologia, 2019Co-Authors: Hisayoshi Nozaki, Wuttipong Mahakham, Ryo Matsuzaki, Mari Takusagawa, Osami Misumi, Masanobu KawachiAbstract:ABSTRACTA strain of Volvox collected from Thailand produced a very large asexual spheroid with maximum diameter over 2 mm long. This Thai alga was identified as Volvox dissipatrix based on the deli...
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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
PLOS ONE, 2016Co-Authors: Hisayoshi Nozaki, Ryo Matsuzaki, Nanako Isaka, Noriko Ueki, Tokiko Saigo, Kayoko Yamamoto, Fumio Takahashi, Ken-ichi Wakabayashi, Masanobu KawachiAbstract: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.
Richard E. Michod - One of the best experts on this subject based on the ideXlab platform.
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Distributions of reproductive and somatic cell numbers in diverse Volvox (Chlorophyta) species
Evolutionary ecology research, 2012Co-Authors: Deborah E. Shelton, A. G. Desnitskiy, Richard E. MichodAbstract:Background: Volvox (Chlorophyta) asexual colonies consist of two kinds of cells: a large number of small somatic cells and a few large reproductive cells. The numbers of reproductive and somatic cells correspond directly to the major components of fitness – fecundity and viability, respectively. Volvox species display diverse patterns of development that give rise to the two cell types. Questions: For Volvox species under fixed conditions, do species differ with respect to the distribution of somatic and reproductive cell numbers in a population of asexual clones? Specifically, do they differ with respect to the dispersion of the distribution, i.e. with respect to their intrinsic variability? If so, are these differences related to major among-species developmental differences? Data description: For each of five Volvox species, we estimate the number of somatic and reproductive cells for 40 colonies and the number of reproductive cells for an additional 200 colonies. We sampled all colonies from growing, low-density, asexual populations under standard conditions. Search method: We compare the distribution of reproductive cell numbers to a Poisson distribution. We also compare the overall dispersion of reproductive cell number among species by calculating the coefficient of variation (CV). We compare the bivariate (reproductive and somatic cell) dataset to simulated datasets produced from a simple model of cell-type specification with intrinsic variability and colony size variation. This allows us to roughly estimate the level of intrinsic variability that is most consistent with our observed bivariate data (given an unknown level of size variation). Conclusions: The overall variability (CV) in reproductive cell number is high in Volvox compared with more complex organisms. Volvox species show differences in reproductive cell number CV that were not clearly related to development, as currently understood. If we used the bivariate data and tried to account for the effects of colony size variation, we found that the species that have fast embryonic divisions and asymmetric divisions have substantially higher intrinsic variability than the species that have slow divisions and no asymmetric divisions. Under our culture conditions, the Poisson distribution is a good description of intrinsic variability in reproductive cell number for some but not all Volvox species.
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flagellar phenotypic plasticity in volvocalean algae correlates with peclet number
Journal of the Royal Society Interface, 2011Co-Authors: Carlos Álvarez Solari, Knut Drescher, Sujoy Ganguly, Richard E. Michod, John O. Kessler, Raymond E. GoldsteinAbstract:Flagella-generated fluid stirring has been suggested to enhance nutrient uptake for suffi- ciently large micro-organisms, and to have played a role in evolutionary transitions to multicellularity. A corollary to this predicted size-dependent benefit is a propensity for pheno- typic plasticity in the flow-generating mechanism to appear in large species under nutrient deprivation. We examined four species of volvocalean algae whose radii and flow speeds differ greatly, with Peclet numbers (Pe) separated by several orders of magnitude. Populations of unicellular Chlamydomonas reinhardtii and one- to eight-celled Gonium pectorale (Pe 0.1-1) and multicellular Volvox carteri and Volvox barberi (Pe 100) were grown in diluted and undiluted media. For C. reinhardtii and G. pectorale, decreasing the nutrient concen- tration resulted in smaller cells, but had no effect on flagellar length and propulsion force. In contrast, these conditions induced Volvox colonies to grow larger and increase their flagellar length, separating the somatic cells further. Detailed studies on V. carteri found that the oppos- ing effects of increasing beating force and flagellar spacing balance, so the fluid speed across the colony surface remains unchanged between nutrient conditions. These results lend further sup- port to the hypothesized link between the Peclet number, nutrient uptake and the evolution of biological complexity in the Volvocales.
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EVOLUTION OF DEVELOPMENTAL PROGRAMS IN Volvox (CHLOROPHYTA)1
Journal of Phycology, 2010Co-Authors: Matthew D. Herron, A. G. Desnitskiy, Richard E. MichodAbstract:The volvocine green algal genus Volvox includes ∼20 species with diverse sizes (in terms of both diameter and cell number), morphologies, and developmental programs. Two suites of characters are shared among distantly related lineages within Volvox. The traits characteristic of all species of Volvox—large (>500) numbers of small somatic cells, much smaller numbers of reproductive cells, and oogamy in sexual reproduction—have three or possibly four separate origins. In addition, some species have evolved a suite of developmental characters that differs from the ancestral developmental program. Most multicellular volvocine algae, including some species of Volvox, share an unusual pattern of cell division known as palintomy or multiple fission. Asexual reproductive cells (gonidia) grow up to many times their initial size and then divide several times in rapid succession, with little or no growth between divisions. Three separate Volvox lineages have evolved a reduced form of palintomy in which reproductive cells are small and grow between cell divisions. In each case, these changes are accompanied by a reduction in the rate of cell division and by a requirement of light for cell division to occur. Thus, two suites of characters—those characteristic of all Volvox species and those related to reduced palintomy—have each evolved convergently or in parallel in lineages that diverged at least 175 million years ago (mya).
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triassic origin and early radiation of multicellular volvocine algae
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Matthew D. Herron, Jeremiah D Hackett, Frank O Aylward, Richard E. MichodAbstract:Evolutionary transitions in individuality (ETIs) underlie the watershed events in the history of life on Earth, including the origins of cells, eukaryotes, plants, animals, and fungi. Each of these events constitutes an increase in the level of complexity, as groups of individuals become individuals in their own right. Among the best-studied ETIs is the origin of multicellularity in the green alga Volvox, a model system for the evolution of multicellularity and cellular differentiation. Since its divergence from unicellular ancestors, Volvox has evolved into a highly integrated multicellular organism with cellular specialization, a complex developmental program, and a high degree of coordination among cells. Remarkably, all of these changes were previously thought to have occurred in the last 50–75 million years. Here we estimate divergence times using a multigene data set with multiple fossil calibrations and use these estimates to infer the times of developmental changes relevant to the evolution of multicellularity. Our results show that Volvox diverged from unicellular ancestors at least 200 million years ago. Two key innovations resulting from an early cycle of cooperation, conflict and conflict mediation led to a rapid integration and radiation of multicellular forms in this group. This is the only ETI for which a detailed timeline has been established, but multilevel selection theory predicts that similar changes must have occurred during other ETIs.
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Volvox BARBERI, THE FASTEST SWIMMER OF THE VOLVOCALES (CHLOROPHYCEAE)(1).
Journal of Phycology, 2008Co-Authors: Carlos Álvarez Solari, Richard E. Michod, Raymond E. GoldsteinAbstract:Volvox barberi W. Shaw is a volvocalean green alga composed of biflagellated cells. Vovocales with 16 cells or more form spherical colonies, and their largest members have germ-soma separation (all species in the genus Volvox). V. barberi is the largest Volvox species recorded in terms of cell number (10,000-50,000 cells) and has the highest somatic to reproductive cell ratio (S/R). Since they are negatively buoyant, Volvocales need flagellar beating to avoid sinking and to reach light and nutrients. We measured V. barberi swimming speed and total swimming force. V. barberi swimming speeds are the highest recorded so far for volvocine algae (~600 μm · s⁻¹). With this speed, V. barberi colonies have the potential to perform daily vertical migrations in the water column at speeds of 2-3 m · h⁻¹, consistent with what has been reported about Volvox populations in the wild. Moreover, V. barberi data fit well in the scaling relationships derived with the other smaller Volvox species, namely, that the upward swimming speed Vup[is proportional to]N⁰.²⁸ and the total swimming force FS[is proportional to]N⁰.⁷⁷ (N = colony cell number). These allometric relationships have been important supporting evidence for reaching the conclusion that as size increases, colonies have to invest in cell specialization and increase their S/R to increase their motility capabilities to stay afloat and motile.
