Research Training ProgramSmithsonian
Institution
|
||
 Rachel A. Harden University of North Carolina Chapel Hill, NC |
 |
|
|
Jon L. Norenburg |
||
| "By far, the best part of this
summer has been meeting and working with some truly incredible people--l
thank them all." |
||
|
||
ABSTRACT |
||
The invertebrate phylum Nemertea (ribbon worms) is comprised of non-segmented, predominantly marine worms which are distinguished from all other invertebrates by a unique tube-like structure called the proboscis. Nemerteans are active, often bottom dwelling, predators which use their proboscis for capturing prey. Although they are commonly found in many parts of the world, nemertean worms have generally been neglected by biologists, mostly because their taxonomy is difficult. The external features of nemerteans, such as color and size, are frequently taxonomically uninformative and difficult to assess in terms of evolutionary significance. Using the internal anatomy of these worms is also problematic for taxonomic purposes. Histological study of serial sections is a very time consuming process and is subject to misinterpretation because of distortion which results when the worms are preserved. Fortunately, molecular data is now readily accessible for use in systematics. The DNA sequences of individuals provide researchers with an array of discrete characters that can be used to assess relationships through cladistic analyses. In this study, nucleotide sequence data from the 16S ribosomal gene of mitochondrial DNA were used to examine the evolutionary relationships among several common intertidal heteronemerteans. DNA sequences from individuals representing the three color morphs of Myoisophagos sanguineus (previously L. sanguineus, L. nigricans, and L. socialis) and from populations of three presumably closely related Lineus species, L ruber, L. viridis, and a cryptic species, were generated. The nucleotide data was analyzed using both parsimony (cladistic) and maximum likelihood (statistical) based methods. The resulting 16S mtDNA phylogeny supports a working hypothesis of these heteronemertean relationships. By investigating the molecules of these worms, researchers now have a better understanding of their evolution, an understanding that was previously inaccessible.