Wednesday, May 19, 2010

DNA sequence identifies a larval nemertean

Marley Jarvis has finished her rotation project in my lab. Her project was to try to identify several planktonic larvae using DNA sequence data, while learning some basic molecular techniques (DNA extraction, PCR, gel electrophoresis etc.). Among other things,  we have sequenced portions of two mitochondrial genes (16S rDNA and Cytochrome Oxidase Subunit I) from the pilidium, which based on its morphology, I preliminary identified as belonging to the palaeonemertean Family Hubrechtidae, and likely the genus Hubrechtella (see my earlier post this year). It was a surprise to find this larva, because, no hubrechtids are currently known to occur on the Pacific Coast of North America. We have matched the 16S sequence derived from this pilidium to the sequence, I obtained earlier from the hubrechtid species from the Sea of Japan, Hubrechtella juliae Chernyshev, 2003The uncorrected sequence divergence is 0.7% for 16S. Sequence divergence of less than 1% for this region of 16S, suggests that the larva belongs to Hubrechtella juliae, or a very closely related species (very likely morphologically indistinguishable). Because this pilidium larva is at a very early developmental stage (before formation of any of the juvenile rudiments, called imaginal discs), and because of what we know about the dominant currents in the Pacific Ocean, it is highly unlikely that this larva was carried here from the Sea of Japan. A more likely explanation is that Hubrechtella juliae occurs on the Pacific Coast of North America, but we have not found the adults yet.

Chernyshev AV. 2003. Novy vid roda Hubrechtella (Nemertea, Anopla) i obosnovanie semeistva Hubrechtellidae. [A new species of the genus Hubrechtella (Nemertea, Anopla) from the Sea of Japan, and establishement of the family Hubrechtellidae]. In Russian. Biologiya Morya. 29(5): 368-370. 

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