In addition to operational difficulties caused by the tiny size of dicyemids; currently, methods to manipulate gene expression have not been established in dicyemids; so it is still difficult to execute functional tests. From so simple a beginning, endless forms most beautiful; and most wonderful have been, and are being, evolving.
Despite the potential challenges, the genome sequence of this unusual parasite represents a resource that will be useful for future analyses; providing molecular information that could be used to reveal the ways in which this organism is similar to other spiralians and animal parasites; as well as the ways in which it is wholly unique.
In order to gain a true understanding of the power; and limitations of evolution to produce such endless forms; it is important to study a variety of organisms from across the tree of life. Next-generation sequencing technologies have enabled in-depth genomic analysis of virtually any organism, expanding the scope of powerful evolutionary analyses beyond model organisms.
Tiny size of dicyemids
Dicyemida are microscopic organisms consisting of only about 30 cells each (Fig 1). They are parasites that live inside the renal sacs of cephalopods like the squid and octopus, deriving nutrients from the host’s urine. Despite a relatively complex life cycle, dicyemids lack differentiated tissues such as a digestive tract and circulatory system, and thus represent one of the most extreme cases of body plan reduction among animals.
Due to their small size and simplifying tissues; they were once thought to represent a link between single celled and multicellular organisms. However, their true phylogenetic position was long considering controversial. Dicyemid mesozoans a unique parasitic lifestyle and a reducing genome; providing further insight into this odd organism; and revealing convergent patterns that are sharing among parasites in general.
Host and parasite
Parasitism has been observing in 15 of the 35 animal phyla; and is thought to have evolving independently over 200 times. While each parasitism event reflects a specific interaction between a host and parasite, parasites often possess certain features; such as a simplified body plan and complex life cycle, that reflect the selective pressures commonly experienced by organisms that “make a living” off of other organisms.
In order to understand the evolution of parasitism; the authors sought to explore the genomic innovations that make this lifestyle possible. According to the authors, “Decoding the dicyemid genome not only improves our understanding of the biology of dicyemids, such as their complicated life cycle, but also provides us a rich resource for comparative studies to [better understand] the evolution of spiralians from a genomic perspective.