WORMING OUR WAY OUT OF A MESS: AN APPRAISAL OF THE NEW WORLD NIPPOSTRONGYLINAE (NEMATA, TRICHOSTRONGYLOIDEA, HELIGMONELLIDAE)
Date of Award
Master of Science
Nippostrongylinae are a globally distributed cosmopolitan subfamily of trichostrongylid nematodes that occur commonly in rodents of the families Gliridae, Hystricidae, Caviidae, Arvicolidae, Muridae, Cricetidae and Sciuridae. In the New World, there are about 80 described species in 11 genera. These worms are diagnosed based on a combination of characters, including the number and morphology of cuticularized ridges known as the synlophe, the morphology and arrangement of the rays in the copulatory bursa, and the structure of the female tail and reproductive apparatus. Further examination of previously collected worms has allowed the description and characterization of taxa that feature greater variation of characters; this variation is evident even in those characters used in the diagnosis of species and genera. Some of these characters include the symmetry of the bursa, orientation of the synlophe, and presence of caudal appendages in females. These appendages are projected dorsally in one species or ventrally in another one. Given the position of the anus relative to these caudal appendages, they cannot be proposed as homologous. Due to the practice of using the same characters to diagnose different hierarchical levels, there is uncertainty in diagnoses of genera within the Nippostrongylinae. To assess the relationships and expand the characters used for diagnosis and identification, I conducted the first phylogenetic analysis using nuclear DNA Internal Transcribed Spacer (ITS1, 5.8S, and ITS2), 28S Ribosomal RNA, and Mitochondrial DNA Cytochrome C Oxidase subunit 1 (CO1, a.k.a. cox1) for 46 species in 9 genera of New World Nippostrongylinae. I identified the signal in the phylogenies of each gene, and detected the same four internal clades. These four clades feature strong support, especially in slowly evolving genes (ITS and 28S). I used the topology resulting from the analysis of the concatenated genes to reconstruct the ancestral character states on each of the four internal nodes. Structures tested included the presence of spine on a female, which has the alternative states of being blunt or acute, and the arêtes in the synlophe, which may form a gradient or form a carene. The ancestral state reconstruction found that the gradient pattern of the arêtes of the synlophe, the carene type, and cuticular enlargement of the female tail are useful in diagnosing clades within the Nippostrongylinae. Because of the comparative nature of my investigation, I examined several individuals collected across the Americas, and propose a new species of Alippistrongylus based on preserved material from the elegant rice rats, Euryoryzomys nitidus, from Peru. This investigation estimated the first molecular phylogeny of the Nippostrongylinae as well as the first to asses the validity of characters that describe these worms.
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