Understanding the Origins of Animal Multicellularity through the Studies of Choanoflagellates

Choanoflagellates are the closest living relative of animals (Alegado, 2014; King, 2015; King 2016; Rokas, 2008). This has been confirmed through multiple lines of phylogenetic analyses, comparative genomics, and similarities in cell biology (Alegado, 2014; King, 2001). Previous studies of the choanoflagellate Salpingoeca rosetta suggest that bacteria may have played an important role in the early origins of animals (Alegado, 2014; King, 2016; Levin, 2011). One such study showed that the Bacteriodetes Algoriphagus machinoponensis can release lipid signaling molecules that induces choanoflagellates to grow into multicellular colonies known as rosettes (Alegado, 2016; Beemelmanns, 2014). Another study showed that when grown in the presence of Vibrio fischerii, choanoflagellates will exhibit swarming behavior and sexually reproduce (Levin, 2013). Choanoflagellates have been repeatedly proven to be an experimentally tractable, phylogenetically relevant model system for investigating the unicellular ancestry of animals. Through the use of molecular and comparative genomic approaches, we can possibly study the origins and evolution of animals through choanoflagellates. M may be defined as the differentiation and organization of cells into functioning tissues within an organism (Anderson, et al., 2016; Rokas, 2008). Multicellularity arose independently several times in life’s history (Abedin, 2010; Alberts, 2002; King, 2016). The morphological diversity of multicellular organisms such as animals, fungi, and plants stem from the fact that each lineage obtained multicellularity in different ways (Abedin, 2010; Alberts, 2002; King, 2016). One way each lineage varies is in their method of adhesion or cell-cell connections (Abedin, 2010). Another property crucial to all multicellular organisms is their method of intercellular communications (Alberts, 2002). How each eukaryotic lineage achieves these unique multicellular challenges is partly what distinguishes them from each other (Abedin, 2010). Surprisingly, the origin and evolution of animal multicellularity is still largely unknown (Anderson, et al., 2016; King, 2016). However, by studying closely related extant species, we may be able to learn more about the current state of life today (Anderson, 2016; King & Carroll, 2001; King, 2016). For animals, the closest living relative is considered to be the choanoflagellate, a singlecelled eukaryote with a complex lifestyle (Alberts, 2002; King & Carroll, 2001; King, 2016; Rokas, 2008). There are multiple lines of evidence that support the idea of animals sharing a common ancestor with choanoflagellates, including several independent phylogenetic analyses, comparative genomics, and similarities in cell biology (Alegado, et al., 2014; King & Carroll, 2001). Choanoflagellates are also characterized by their complex life cycle, which consists of a single celled form, a chain form, and a multicellular spherical form known as a rosette (Alegado, et al., 2014; King, 2016). Rosette formation is induced by its prey, Algoriphagus, which releases lipid based signaling molecules that induce incomplete cytokinesis to promote rosette formation (Beemelmanns, et al., 2014). Review of Literature