The Choanoflagellates: Evolution, Biology and Ecology

The Choanoflagellates: Evolution, Biology and Ecology

Barry S. C. Leadbeater

Language: English

Pages: 350

ISBN: 0521884446

Format: PDF / Kindle (mobi) / ePub

Choanoflagellates have three distinctive claims to fame: they are the closest, living, unicellular relatives of animals; they are a major component of aquatic microbial foodwebs; and one group is remarkable for its siliceous basket-like coverings. This landmark book offers a unique synthesis of over forty years of choanoflagellates research. Key areas are covered, from the phylogenetic evidence supporting the sister-group relationship between choanoflagellates and Metazoa, to choanoflagellate distribution and diversity in marine and freshwater environments. The structure and assembly of choanoflagellate loricae is also presented together with a full discussion of a novel example of 'regulatory evolution', suggesting that the switch from nudiform to tectiform cell division and lorica production was achieved by a sudden reorganisation of existing structures and mechanisms. Providing an authoritative summary of what is currently known about choanoflagellates, this title will serve as a foundation upon which future research and discussion can take place.

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(arrows). Bar ¼ 2 mm. Fig. 7.45 The lorica cup is now fully formed; the petaloid strips (1) are on the outside, strips of the anterior ring (arrowheads 6) are on the outside of the anterior edge of the lorica cup and the strips that will form the future intermediate and posterior transverse costae are within the lorica cup (arrow). Bar ¼ 2 mm. Reproduced from Leadbeater (2010). Didymoeca costata 171 Fig. 7.46 Didymoeca costata. Sequence of drawings of a cell undergoing division illustrating

can be seen to almost encircle the nucleus (Fig. 2.54). Frequently, the distal surface of the mitochondrial reticulum is overlain by cisternae of the endoplasmic reticulum 37 (ER) (Figs 2.55, 2.56). In some instances this can be almost continuous, giving the impression that the mitochondrion is located in a compartment bounded proximally by the nuclear envelope and distally by the ER (Fig. 2.57). The mitochondrial surface is bounded by two membranes, the inner of which is folded to give

comprising six thickened strips. There are between four and six longitudinal costae surrounding the cell, each costa comprising two strips. A second transverse costa is located below the anterior transverse ring. Posteriorly, the lorica terminates in a long spine (Fig. 4.77). Acanthocorbis haurakiana presents a more elaborate arrangement of costae but, in common with Calliacantha, has anterior and posterior spines (Fig. 4.74). In the specimen shown in Fig. 4.74 there are six spines that are

110 Requirement for silicon and its deposition in costal strips Fig. 5.13 Stephanoeca diplocostata. Effect of colchicine on population growth in stirred culture at 20 C. Control culture (open circles) contains cells grown in Erdschreiber seawater with 80 mg ml–1 proteose peptone and 16 mg ml–1 yeast extract. Treated culture (closed circles) involved identical conditions to control but after 40 hours (arrow) 5 ml of an aqueous colchicine solution was added to give a final concentration of 0.8

the posterior intermediate ring, are not protected on their inner surface by an organic investment and are therefore completely exposed to the medium. Costal strips in the posterior chamber are covered on their inner surface by an organic investment which partially limits immediate access to the surrounding medium. 5.7.3 Batch culture growth of Stephanoeca diplocostata in silicon depleted conditions The S. diplocostata experiments that provided the data on growth and silicon turnover in

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