Date of Award
Doctor of Philosophy
Jiménez, F. Agustín
Heligmosomidae are gastrointestinal nematodes of rodents; members of this family are distributed through the Holarctic and Nearctic regions. Traditionally, the classification of Heligmosomidae was built based on basic morphological characteristics of the cuticle and sexual characteristics of the males. To this date, there is no revision that summarizes the geographic distribution and diversity of this group across North America. Thus, the primary goal of this dissertation was to produce a monograph of Heligmosomidae in the continent that helps in the understanding of the geographical distribution of the members of the family using museum records and peer-reviewed publications. To achieve this, holdings of scientific museums were used to examine the morphological variability, reconstruct phylogeny, establish species limits and identify, name and describe three new species. Thus, this compendium is based on the examination of 209 lots representing 18 species.Re-examination of the available holotypes gives scientists the ability to characterize intra- and interspecific character variability. By examining the holotype of a species, one is able to compare and evaluate structures that would have been ignored in the original description. As a consequence, I was able to characterize the cuticular ornamentation of two nematode species described over 100 years ago. Further, these efforts supported the proposal of three new species, two of Citellinema and one of Heligmosomoides. The new species of Heligmosomoides Hall, 1916 is proposed for nematodes collected from Peromyscus maniculatus (Deer Mouse) in western Canada; this species of parasite is diagnosed by the presence of two internal bursal membranes and number of ridges in the synlophe. The description of the species of Citellinema is based on the examination of materials collected in Alaska and western Canada. These organisms can be diagnosed based on the structure of their male genitalia and cuticular ornamentation. An assessment of the six recognized species in the genus is offered as well as a discussion to reinstate two of these species. I offer a brief characterization of specimens of Ohbayashinema and Heligmosomum since sequences from North America and Russia are available for analyses. The reconstruction based on 28S shows that Citellinema, Heligmosomoides, Heligmosomum, and Ohbayashinema are a monophyletic group, yet the topology suggests that Heligmosomoides is not a natural group. This topology is supported by the analysis of one nuclear and three mitochondrial genes. The genetic distance among these taxa is used as ancillary evidence to support the proposal of the new species.
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