What advantages does multicellular volvox have over unicellular chlamydomonas?

Answer 1

the family of volvocine green algae is remarkably well suited to studying the evolution of multicellularity. The volvocine algae include both unicellular and multicellular organisms that are closely related and exist today (Kirk 1998). The unicellular species in this group is named Chlamydomonasreinhardtii (hereafter Chlamydomonas), and its best-studied, close multicellular relative is a species named Volvox carteri (hereafter Volvox). What are these organisms like? Chlamydomonas are single-celled organisms with two apical flagella, which they use for sensory transduction and for moving around in a wet environment (Figure 2F). But Chlamydomonas unicells don't always have these flagella. They resorb them in preparation for cell division, so the Chlamydomonas life cycle consists of alternation between a swimming phase during which the cells grow, and an aflagellate/immotile reproductive phase during which they replicate their DNA and divide. When Chlamydomonas cells divide, they use what is called a multiple fission mode of division: They usually undergo sequential rounds of DNA replication and mitosis, and produce four, eight, or sixteen unicellular, asexual daughter cells. In Volvox, these two functions - swimming and reproduction - have been segregated into distinct cell types (Figure 2A-E; Kirk 1998).

Cells of one type, called somatic cells, number about 2,000 and closely resemble Chlamydomonas unicells. Somatic cells are small, have two flagella, and reside in a monolayer at the surface of a sphere of gelatinous extracellular matrix (ECM). Their job is to swim and keep Volvox in the light so that it can photosynthesize. Unlike Chlamydomonas unicells, Volvox somatic cells cannot divide, and this distinction is very important - Volvox has multicellularity with division of labor because its somatic cells lost the capacity for reproduction. Reproduction is carried out by a second type of specialized cell, called the gonidium. Gonidia are large and do not have flagella (see Figure 2E), so they cannot swim (and must therefore rely on somatic cells for motility), but they can divide. Each of the approximately sixteen gonidia has the capacity to generate a new individual through a series of ten to eleven embryonic cell divisions that generate all the cells present in the next generation. Is this sort of division of labor unique to Volvox? Probably not. Some scientists believe that the segregation of somatic functions (like swimming) and reproduction into distinct cell types was one of the first key steps in the evolution of multicellularity in animals as well (Buss 1987; King 2004).

Answer 2

The movement is coordinated among cells and the colonial organization borders on multicellularity