Evolution and Speciation in Protozoa

Protozoa are unicellular organisms that have evolved to perform almost all metazoan functions with a few subcellular organelles. Their unicellularity, structural simplicity, and diverse life cycles have limited their diversity, restricted their spatial distribution, demonstrated the dominance of clonality, reduced sexualization, facilitated the use of vegetative gametes, and secondary loss of sex. They occur in high densities of 105-106 cell/ml and have a dynamic cyst stage that allows for clonal or sexual reproduction. Their mean body size ranges from 2 μm to 2 mm, and they are twice as efficient as metazoans in trophic dynamics. Foraminifers serve as ecological sensitive indicators in petroleum exploration and rise in sea level.

Format: Hardback
Length: 180 pages
Publication date: 24 February 2023
Publisher: Taylor & Francis Ltd

The polyphyletic Protozoa have delved into the remarkable potential of utilizing a mere handful of subcellular organelles to perform nearly all metazoan functions. Their unicellular nature and architectural simplicity have resulted in (i) a limited diversity of 32,950 species, (ii) a constrained spatial distribution primarily inhabiting aquatic habitats (94% compared to 15% in Metazoa), (iii) a pervasive dominance of clonality, (iv) a reduction in sexualization in approximately 50% species, (v) the facilitation of vegetative gamete utilization in 40% species, and (vi) the secondary loss of sex in approximately 10% species. These organisms boast the fastest multiplication rates, occurring once every 6 to 60 hours, leading to high densities of 105 to 106 cells/ml. Their intricate and diverse life cycles are documented in 30 distinct types, showcasing their risky nature. The cycle encompasses clonality, hermaphroditism, and motility, with motility varying from 2 to 3 μm for Rhizopoda to 400 to 2,000 μm for Ciliophora. Surprisingly, over 6,800 species of arcellinids, filosians, and formainifers are testated or shelled. Within the 1,229 sessile species, the peritrichid and suctorian ciliates exhibit superior adaptations to coloniality. Unlike many Metazoa, the protozoan cyst serves as a dynamic stage where clonal or sexual reproduction can occur. Remarkably, over 81% of protozoans undergo encystment, which ensures (i) a survival rate of 90% in unfavorable conditions (compared to 15% in non-encysted protozoans), (ii) the transmission of genes across generations, (iii) dispersal into new habitats, and (iv) the potential for transmission to new hosts. Their mean body size spans from 2 μm to 2 mm, representing a staggering range over 1,000-times greater than that of only 8% of aquatic metazoans. In contrast, 77% of Metazoa are macrophagy predators, while only 46% of protozoans fall into this category. Within motile microphagy, protozoans filter 3-2 times smaller food particles at a significantly lower clearance cost, thereby expanding the scope of microphagy.

Weight: 517g
Dimension: 234 x 156 (mm)
ISBN-13: 9781032347516