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United States Department of Agriculture

Agricultural Research Service

Title: Phylogeny for Genera of Nematodirinae (Nematoda: Trichostronglyina)

Authors
item HOBERG, ERIC
item Rickard, L - MISSISSIPPI STATE U
item Lichtenfels, James

Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 14, 2004
Publication Date: N/A

Interpretive Summary: Nematodirine nematodes globally represent serious pathogens in wild mammals and domestic stock. The speciose genus, Nematodirus contains an array of helminth pathogens that infect ruminants throughout the world, and species such as N. battus continue to be regarded as the most economically significant parasites in domestic sheep, Ovis aries Linnaeus, across the Northern Hemisphere. Although there has been considerable effort and research to define epizootiology, and the host-parasite interface for species of Nematodirus, our understanding of the broader evolution and history for these and related nematodes remains to be fully elucidated. We conducted the first phylogenetic studies of the Nematodirinae. Monophyly for the Nematodirinae, with 5 inclusive genera, Murlieus, Rauschia, Nematodiroides, Nematodirus and Nematodirella was confirmed based on comparative morphology and phylogenetic analysis of structural characters. This concept for the nematodirines excludes the monotypic Lamanema chavezi, but otherwise corroborates inclusive generic-level diversity as defined in prior studies. Ancestral hosts are represented by Lagomorpha, with evidence for a minimum of one host-switching-event and subsequent radiation in the Artiodactyla, particularly among the sheep and goats. The structure of the phylogenetic hypothesis, patterns of diversity and geographic distributions for respective taxa in conjunction with data for the occurrence of species within inclusive genera is consistent with primary distributions determined across Beringia for Murielus, Rauschia, Nematodirus and Nematodirella. Diversification may reflect vicariance of respective faunas along with episodic or cyclical range expansion and isolation across the Beringian land mass linking North America and Eurasia during the late Tertiary and Quaternary. Secondarily, Nematodirus attained a distribution in the Neotropical region with minimal diversification of an endemic fauna represented by N. molini among tayassuids, N. lamae among camelids and N. urichi in cervids during the Pleistocene. Nematodirines are a core component of an Arctic fauna (defined by latitude and altitude) adapted to transmission in extreme environments characterized by seasonally low temperatures and varying degrees of dessication. Knowledge of the history and distribution of this fauna provides a foundation for examining and predicting the response by hosts and parasites to global change and ecological perturbation at temperate, Boreal and Arctic latitudes.

Technical Abstract: Monophyly for the Nematodirinae, with 5 inclusive genera, Murlieus, Rauschia, Nematodiroides, Nematodirus and Nematodirella was confirmed based on comparative morphology and phylogenetic analysis of structural characters. This concept for the nematodirines excludes the monotypic Lamanema chavezi, but otherwise corroborates inclusive generic-level diversity as defined in prior studies. Exhaustive analysis,resulted in one most parsimonious tree (37 steps; CI= 0.95; HI= 0.08; RI= 0.92; RC= 0.87; excluding phylogenetically uninformative characters, CI= 0.92; HI= 0.08). As an inclusive group, Nematodirinae was diagnosed by 7 synapomorphies: (i) large eggs; (ii.) long filiform spicules; (iii) basal division of the dorsal ray; (iv) symmetrical membrane enveloping the spicules; (v) fused structure of the spicule tips; (vi) absence of the gubernaculum; and (vii) development of the third stage larva within the egg. Ancestral hosts are represented by Lagomorpha, with evidence for a minimum of one host-switching-event and subsequent radiation in the Artiodactyla. The structure of the phylogenetic hypothesis, patterns of diversity and geographic distributions for respective taxa in conjunction with data for the occurrence of species within inclusive genera is consistent with primary distributions determined across Beringia for Murielus, Rauschia, Nematodirus and Nematodirella. Diversification may reflect vicariance of respective faunas along with episodic or cyclical range expansion and isolation across Beringia during the late Tertiary and Quaternary. Secondarily, Nematodirus attained a distribution in the Neotropical region with minimal diversification of an endemic fauna represented by N. molini among tayassuids, N. lamae among camelids and N. urichi in cervids during the Pleistocene. Nematodirines are a core component of an Arctic fauna (defined by latitude and altitude) adapted to transmission in extreme environments characterized by seasonally low temperatures and varying degrees of dessication. The history and distribution of this fauna is examined in the context of global climate change.

Last Modified: 9/29/2014