''Volvox aureus'' is a species of colonial

green algae The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...

in the family

Volvocaceae The Volvocaceae are a family of unicellular or colonial biflagellates algae, including the typical genus ''Volvox'', and are collectively known as the volvocine algae. The family was named by Ehrenberg in 1834, and it is known in older classifi ...

. It is a

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

alga with a

cosmopolitan distribution In biogeography, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and en ...

, and is probably the most commonly reported species of the genus ''

Volvox ''Volvox'' is a polyphyletic genus of chlorophyte green algae in the family Volvocaceae. ''Volvox'' species form spherical colonies of up to 50,000 cells, and for this reason they are sometimes called globe algae. First reported by Antonie van L ...

''. It is common in lowland lakes, rivers, ponds, ditches, and puddles, and is most abundant in late summer.

Description

''Volvox aureus'' consists of

motile Motility is the ability of an organism to move independently using metabolic energy. This biological concept encompasses movement at various levels, from whole organisms to cells and subcellular components. Motility is observed in animals, mi ...

, spherical colonies of cells, typically around 400–600 μm in diameter. Colonies contain approximately 500–3200 cells, arranged in one layer around the margin of a hollow sphere or ellipsoid. Cells are connected to each other by thin

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

ic strands, approximately the same thickness as the flagella. Cells are surrounded by a confluent gelatinous sheath of cells; the center of the colony has a homogeneous mass from which gelatinous strands radiate outward and connect with the inner layer of the colonial matrix. Within the colony, there are four to 12

gonidia A gonidium (plural gonidia) is an asexual reproductive cell or group of cells, especially in alga Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and ...

irregularly distributed in the posterior half. Gonidia are 18–22 μm in diameter; these divide successively to form

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

s 150–175 μm in diameter. During development, the cells of the embryo grow between cell divisions, and the rate of division is quite slow. Cell division is light-dependent.

Reproduction

''Volvox aureus'' is typically

dioecious Dioecy ( ; ; adj. dioecious, ) is a characteristic of certain species that have distinct unisexual individuals, each producing either male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproduction is ...

, with individuals producing either male or female gametes, but not both. It may be

heterothallic Heterothallic species have sexes that reside in different individuals. The term is applied particularly to distinguish heterothallic fungi, which require two compatible partners to produce sexual spores, from homothallic ones, which are capable ...

homothallic In fungi and algae, homothallism refers to the condition in which a single individual or thallus carries the genetic determinants (i.e., both mating types or sexes) required to undergo sexual reproduction without the need for a distinct mating partn ...

. Male colonies are not much smaller than their asexual counterparts, about 330–360 μm long; they contain 1,000–5,000 cells and 600–1,000 antheridial (sperm) packets. Sperm packets are plate-like, 15–18 μm in diameter, producing 32 sperm cells. Female colonies are about 340–415 μm long and have 7–21 (usually 10–14) eggs. Zygotes are 38–62 μm in diameter, with a smooth

cell wall A cell wall is a structural layer that surrounds some Cell type, cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, ...

. Immature zygotes are green, while mature ones are orange. In homothallic strains of ''Volvox aureus'', male colonies can produce a glycoprotein

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

which induces sexual differentiation, leading to the mass development of further male individuals. However, it appears that in nature, zygotes are rarely formed; instead, the dominant resting stage is a parthenospore formed by gonidia without division or fertilization.

Taxonomy

''Volvox aureus'' is part of the section ''Janetosphaera''. In ''Volvox'' sect. ''Janetosphaera'', individual cells are surrounded by a confluent gelatinous sheath (as opposed to individual gelatinous sheaths around each cell). In addition, colonies have a gelatinous strands radiating from the center to the periphery. The vegetative morphology of ''Volvox aureus'' is very similar to ''

Volvox pocockiae ''Volvox'' is a polyphyletic genus of chlorophyte green algae in the family Volvocaceae. ''Volvox'' species form spherical colonies of up to 50,000 cells, and for this reason they are sometimes called globe algae. First reported by Antonie van Le ...

'', the other species of ''Volvox'' sect. ''Janetosphaera''. Unlike ''V. aureus'', cells of ''V. pocockiae'' are not connected to each other by cytoplasmic strands in the anterior half. Also, in ''V. pocockiae'' the gonidia enlarge before cell division, while in ''V. aureus'' the gonidia do not enlarge. Finally, male spheroids of ''V. pocockiae'' are markedly smaller than their asexual and female counterparts. ''Volvox pocockiae'' is known only from a single collection in Mexico. However, because most reports of ''Volvox aureus'' have not been based on reproductive characters, it is possibly overlooked.

References

{{taxonbar, from=Q979947 Chlorophyta species Chlamydomonadales