Fueled by Symbiosis, Foraminifera have Evolved to be Giant Complex Protists

Abstract

One may wonder in the framework of this book, and in context with the well-balanced chapter by Stambler, why foraminifera have been singled out to be the focus of a separate chapter. The answer is simple. Foraminifera are generally less well known, and they exemplify the power by which symbiosis can drive evolution of a predisposed and malleable group of organisms. As foraminifera are relatively small, when compared with corals and other invertebrates in the same semi- and tropical well-illuminated marine habitats, they are easily overlooked. At times, they form beaches of “living” and “star-sands” (Fig. 1e), and are so abundant that they can be scooped up with a spoon. Snorklers and SCUBA divers can see them as underwater “Christmas tree ornaments” on sea grasses or on macrophyte algae (Fig. 1c). Their tests are composed of CaCO3 and they fossilize well. Testimonial to their abundance in the Tethys Sea are the mountains of fossilized limestone formed from their tests (Fig. 1a, b, d) and quarried to build the Egyptian pyramids. Also intriguing is the fact that different types of algae have driven various lines of foraminifera to evolve tens to hundreds of times larger in size and considerably more complex than their ancestors. Modern larger foraminifera are the hosts for a greater variety of symbionts than any other marine group (Lee, 2006). With respect to symbiont type, there is some specificity. Those larger foraminifera that normally host diatoms have never been observed to host dinoflagellates. Similarly, those that host dinoflagellates never host diatoms, chlorophytes, or rhodophytes and so forth.