Adam Clayton and Dr. Byron Adams, Department of Biology
Nematodes are known to play important roles in ecosystem functioning, however their specific roles may vary across different taxonomic levels. Correct identification of nematode species is necessary when analyzing their diversity in order to effectively assign their functional role(s). Several different kinds of nematodes are known to inhabit the dry valleys of the Antarctic McMurdo Long-Term Ecological Research site, but the ecological roles of each of these taxa is still a mystery. One genus of particular interest is called Plectus. There is currently a debate regarding what species of Plectus actually exists in Antarctica. To resolve this Dr. Byron Adams has collected both terrestrial and aquatic samples belonging to the Plectus genus identifying them using physical characteristics. By gathering sequences of certain genes that have been proven useful in separating nematodes into differing species I have found that more than one species of Plectus exists in the Dry Valleys.
In order for any ecological roles of nematodes to be assigned, individual species must first be categorized. My goal in focusing on Plectus was to solve a debate regarding the actual species of Plectus found on the Antarctic continent. It was previously believed that only a single species of Plectus (P. antarcticus) was found in the dry valleys of Antarctica and that this species was restricted to the soils (Andrassy 1998). Plectus antarcticus was the second nematode species identified from Antarctica.
Subsequent authors have explored whether P. antarcticus is a valid species. Micoletzky (1922) considered it P. rhizophilus. De Man, (1880) Andrassy, (1984, 1985) and Zell (1993) supposed it to be P. cirratus, while Bastian (1865), Maggenti (1961) and Goodey (1963) related it with P. parietinus. Several authors have given accurate descriptions of Plectus species named “antarcticus.” Their nematode descriptions, however, do not agree (Andrassy 1998).
Dr. Adams and his team on the ice have collected and examined specimens broadly distributed across the Dry Valleys using physical characteristics established by Andrassy and accepted by all nematologists. In order to place these specimens in an evolutionary context, I have attempted to sequence three gene regions (18S, ITS and 28S rDNA). Following gene amplification and sequencing of the aforementioned regions we proceeded to construct alignments of the forward and reverse sequences for each sample using the computer program Sequencher 4.0. After that the collection of sequences of each gene region were aligned together using another program ClustalX. The alignment of sequences was compared and edited using the program, MacClade, and then further analyses and tree construction were done using another program called Paup 4.0b10.
My results indicate first that Plectus is not solely a soil dweller. Furthermore my sequencing results indicate the presence of at least two species. It is likely, due to the level of similarity in the aforementioned gene regions that the Plectus we collected belong to the species P. frigophilus and P. murrayi. Ironically neither of these species was theorized to exist on the continent. There are many differences among our samples in one of the gene regions (ITS) both on a population level and an individual level, which indicates that our Plectus may have undergone some degree of divergent evolution from its closest relatives P. frigophilus and P. murrayi.
This work is vital to the future because now ecological roles can be assigned to the Antarctic Plectus, which will tell us what Plectus does in Antarctica and what it may be doing in other environments. With this knowledge Plectus may eventually be used as a means of improving agriculture or bioremediation.
I presented my work at the 2009 Long-Term Ecological Research All Scientists Meeting in Estes Park, CO. The data collected is in the process of being compiled and edited before submission to the Journal of Nematology early next year.
References
- Andrassy, I. (1998). Nematodes in the sixth continent. Journal of Nematode Morphology and Systematics, 1(2): 107-186.
- Freckman, D. W., and R. A. Virginia. 1997. Low-diversity Antarctic soil nematode communities: distribution and response to disturbance. Ecology, 78: 363-369.
- Holovachov, O. (2004). Morphology, phylogeny and evolution of the superfamily Plectoidea Örley, 1880 (Nematoda: Plectida). Annales Zoologici 54: 631-672.