Genetic and Developmental Studies on Botryllus Schlosseri

Abstract

1. Properties of Botryllus schlosseri which give it outstanding promise for studies in developmental genetics are reviewed. 2. Laboratory culture procedures, in vitro fertilization, and a method for raising embryos in vitro are described. Controlled successions of complete life cycles can now be achieved in any laboratory. 3. Experiments involving colony fusion, subsequent vascular budding, and the analysis of color patterns in resultant systems suggest that cells of the simple vessel walls govern the morphology of the regenerated zooids. 4. Results of some preliminary genetic crosses are reported.

Botryllus schlosseri: A model ascidian for the study of asexual reproduction

“…Blastogenesis in Botryllus was initially described by several 19 th century researchers (Metschnikow, 1869;Della Valle, 1882;Oka, 1892;Hjort, 1893;Pizon, 1893) and in the 20th century by Ä rnbä ck-Christie-Linde (1923), Berrill (1941a,b), Watterson (1945), Sabbadin (1955a), Milkman (1967), and Izzard (1973. A bud primordium appears as a thickening of the peribranchial wall and the overlying epidermis, which then arches progressively to form a double vesicle.…”

“…4A1), ripen (only one or a few on either side) in primary buds (Fig. 1B), and ovulate when the primary buds are about to pass to the adult stage (10/7/1) (Milkman, 1967). Fertilization occurs just after siphon opening, and the larvae hatch when adults are almost at the end of their life cycle.…”

“…1B) and discharges most of the sperm 1-2 days after ovulation, thus avoiding selfing (Milkman, 1967;Sabbadin, 1971;Sabbadin and Zaniolo, 1979;Stewart-Savage et al, 2001).…”

Ascidians as models for studying invasion success

“…C. intestinalis can produce gametes continually as long as water temperature is suitable, and each mature individual can potentially spawn once daily over the spawning period and release approximately 500 eggs per day (Carver et al 2003). Compared with solitary species, colonial ascidians generally have a lower level of fecundity, even though a mature colony can release 7-20 well-developed tadpole larvae per week (Milkman 1967;Lambert 2005). Rapid growth and high fecundity enable invasive ascidians to overcome both survival and reproduction barriers at the establishment stage (Fig.…”

EVOLUTIONARY GENETICS OF ALLORECOGNITION IN THE COLONIAL HYDROID HYDRACTINIA SYMBIOLONGICARPUS

“…To the extent that this specificity is genetically controlled, the loci governing invertebrate allorecognition specificity may exhibit polymorphism that rivals, or exceeds, levels recorded at loci in the vertebrate Major Histocompatibility Complex (Potts and Wakeland 1990;Hughes and Nei 1992;Brown and Ecklund 1994;Hedrick 1994), as well as loci associated with gametophytic incompatibility systems in angiosperms (Ebert et al 1989). High levels of allotypic specificity could, however, result from any number of genetic alternatives, ranging from one or a few loci with tens to hundreds of alleles per locus (characteristic of populations of botryllid ascidians : Milkman 1967;Mukai and Watanabe 1975a,b;Scofield et al 1982;Grosberg and Quinn 1986;Rinkevich and Saito 1992;Yund and Feldgarden 1992;Rinkevich et al 1994) to numerous independent loci with relatively low levels of allelic variation (Curtis et al 1982). The ability to distinguish among these genetic alternatives, and to circumscribe the rules governing compatibility, determines how the expression of allorecognition-dependent behaviors influences the evolution of allotypic variation.…”