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PubMed1992

Molecular phylogeny of the volvocine flagellates.

Phylogenetic studies of approximately 2,000 bases of sequence from the large and small nuclear-encoded ribosomal RNAs are used to investigate the origins of the genus Volvox. The colonial and multicellular genera currently placed in the family Volvocaceae form a monophyletic group that is significantly closer phylogenetically to Chlamydomonas reinhardtii than it is to the other unicellular green flagellates that were tested, including Chlamydomonas eugametos, Chlorella pyrenoidosa, and Haematococcus lacustris. Statistical analysis of 251 phylogenetically informative nucleotide positions rejects the "volvocine lineage" hypothesis, which postulates a monophyletic evolutionary progression from unicellular organisms (such as Chlamydomonas), through colonial organisms (e.g., Gonium, Pandorina, Eudorina, and Pleodorina) demonstrating increasing size, cell number, and tendency toward cellular differentiation, to multicellular organisms having fully differentiated somatic and reproductive cells (in the genus Volvox). The genus Volvox appears not to be monophyletic. Volvox capensis falls outside a lineage containing other representatives of Volvox (V. aureus, V. carteri, and V. obversus), and both of these Volvox lineages are more closely related to certain colonial genera than they are to each other. This implies either a diphyletic origin of Volvox from different colonial volvocacean ancestors, a phylogenetic derivation of some of the colonial genera from a multicellular (i.e., Volvox) ancestor, or both. Considered together with previously published observations, these results suggest that the different levels of organizational and developmental complexity found in the Volvocaceae represent alternative stable states, among which evolutionary transitions have occurred several times during the phylogenetic history of this group.

Animals↗
PubMed2006

Morphogenesis in the family Volvocaceae: different tactics for turning an embryo right-side out.

Green algae of the family Volvocaceae provide an unrivalled opportunity to analyze an evolutionary pathway leading from unicellularity to multicellularity with division of labor. One key step required for achieving multicellularity in this group was the development of a process for turning an embryo inside out: a morphogenetic process that is now known as "inversion," and that is a diagnostic feature of the group. Inversion is essential because at the end of its embryonic cleavage divisions, each volvocacean embryo contains all of the cells that will be present in an adult, but the flagellar ends of all cells are pointed toward the interior, rather than toward the exterior where they will need to be to function in locomotion. Inversion has been studied in greatest detail in Volvox carteri, but although all other volvocacean species have to struggle with the same awkward situation of being wrong-side out at the end of cleavage, they do it in rather different ways. Here, the inversion processes of six different volvocacean species (Gonium pectorale, Pandorina morum, Eudorina unicocca, Volvox carteri, Volvox tertius, and Volvox globator) are compared, in order to illustrate the variation in inversion patterns that exists within this family. The simplest inversion process occurs in the plate-shaped alga Gonium pectorale and the most complicated in the spherical alga Volvox globator. Gonium pectorale goes only from a concave-bowl shape to a slightly convex plate. In Volvox globator, the posterior hemisphere inverts completely before the anterior pole opens and the anterior hemisphere slides over the already-inverted posterior hemisphere; during both halves of this inversion process, the regions of maximum cell-sheet curvature move progressively, as radially symmetrical waves, along the posterior-anterior axis.

Cell Division↗
PubMed2004

Novel method for the cryopreservation of testicular sperm and ejaculated spermatozoa from patients with severe oligospermia: a pilot study.

OBJECTIVE: To investigate Volvox globator as an easy-to-handle vehicle and as a safe alternative for cryopreservation of functional motile sperm cells. DESIGN: Prospective, controlled, clinical pilot study. SETTING: Two in vitro fertilization (IVF) outpatient clinics for reproductive medicine. PATIENT(S): Fifteen patients with severe male infertility (density <100 motile sperm per milliliter) who were recruited from two IVF programs. The sperm cells were not intended for clinical use after thawing. INTERVENTION(S): In each case, a predetermined number (n = 8) of motile and morphologically intact sperm cells were injected into each Volvox sphere and then cryopreserved. The quality of the sperm cells and the handling of the Volvox spheres were verified. MAIN OUTCOME MEASURE(S): Postthaw recovery rate in cases of severe male infertility and the amount of motile sperm after thawing. RESULT(S): The postthaw recovery rate was 100%. At least 60% of the sperm cells were motile after thawing. CONCLUSION(S): The use of the spherical algae Volvox globator offers a promising, inexpensive, and easy approach to the cryopreservation of functional motile sperm cells. Volvox globator is an alternative in countries that prohibit the destructive use of oocytes, even after fertilization has failed.

Cryopreservation↗