Structure, Biodiversity, and Historical Biogeography of Nematode Faunas in Holarctic Ruminants: Morphological and Molecular Diagnoses for Teladorsagia boreoarticus n. sp. (Nemadota:Ostertagiinae), Dimorphic Cryptic Species in Muskoxen (Ovibos moschatus)

Discovery of the ostertagiine nematode Teladorsagia boreoarcticus n. sp. in muskoxen, Ovibos moschatus, from the central Canadian Arctic highlights the paucity of knowledge about the genealogical and numerical diversity of nematode faunas characteristic of artiodactyls at high latitudes across the Holarctic. Teladorsagia boreoarcticus is a dimorphic cryptic species distinguished from Teladorsagia circumcinctalTeladorsagia trifurcata in domestic sheep by a 13% divergence in the ND4 region of mitochondrial DNA, constant differences in the synlophe, and significantly longer esophageal valve, spicules, gubernaculum, and bursa. Teladorsagia boreoarcticus represents an archaic component of the North American fauna and may have a Holarctic distribution in muskoxen and caribou. Recognition of T. boreoarcticus in muskoxen, in part, corroborates hypotheses for the existence of a cryptic species complex of Teladorsagia spp. among Caprinae and Cervidae at high latitudes and indicates the importance of climatological determinants during the late Tertiary and Pleistocene on diversification of the fauna. Also reinforced is the concept of the North American fauna as a mosaic of endemic and introduced species. Discovery of a previously unrecognized species of Teladorsagia has additional implications and clearly indicates that (1) our knowledge is incomplete relative to potentially pathogenic nematodes that could be exchanged among domestic and wild caprines; (2) we do not have sufficient knowledge of the fauna to understand the ecological control mechanisms (limitations) on dissemination and host range; and (3) an understanding of historical and geographical influences on the genealogical diversity and distribution of nematode faunas in domestic and wild ruminants is requisite to define the interface between agricultural and natural ecosystems across the Holarctic. The characteristic nematode fauna in ruminants from the Nearctic is a mosaic that has been assembled over temporal scales that are deep to relatively recent. For example, Holarctic distributions for some endemic and archaic parasite-host assemblages, particularly those associated with wild caprine bovids and cervids, were determined during the late Tertiary and Pleistocene across the Beringian nexus linking the Nearctic and Palearctic (Hoberg and Lichtenfels, 1994; Hoberg et al., 2000). In contrast, the relatively recent introduction and dissemination of parasites with domestic stock coinciding with European contact since the 1500s has had a substantial anthropogenic influence on patterns of parasite distribution in North America and other regions of the world (e.g., Hoberg 1997a; Hoberg and Lichtenfels, 1994; Lichtenfels et al., 1997). As a consequence of this deep history and recent introductions, the possible range of interactions between endemic versus introduced faunas, and the potential for exchange of nematodes among domestic stock and wild hosts is complex. Ostertagiine nematodes of several genera (e.g., Teladorsagia Andreeva and Satubaldin, 1954, Marshallagia (Orloff, 1933), Ostertagia Ransom, 1907) are components of an archaic and endemic fauna in the Nearctic. Introduction of related ostertagiines could have resulted in (1) displacement of the endemic fauna; (2) hybridization and introgression with an endemic fauna, assuming incomplete species cohesion and barriers to gene flow; or (3) existence of endemic and introduced faunas in alReceived 7 December 1998; revised 5 April 1999; accepted 5 April 1999. * Department of Zoology, Oregon State University, Corvallis, Oregon 97331. t Department of Veterinary Microbiology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5B4. lopatry and coexistence of a wild and domestic fauna in zones of contact with the possibility of cross-infection. These issues have not been considered previously with respect to the structure and diversity of the nematode fauna in Nearctic bovids and cervids. It is requisite to define clearly the genealogical and ecological diversity of the nematode faunas in both domestic and sylvatic hosts in order to delineate parasite distribution, faunal history, and potential patterns of interaction for hosts and parasites including responses to global climate change and the emergence of pathogens and disease (Hoberg, 1997a; Hoberg et al., 2000). Ostertagiine nematodes, particularly those distributed among the bovids of the subfamily Caprinae, provide the basis for examining these concepts. The Ostertagiinae (Skrjabin and Shul'ts, 1937) is a monophyletic group within the Trichostrongylidae (Durette-Desset, 1985; Hoberg and Lichtenfels, 1994). Among the polymorphic ostertagiine nematodes (see Drozdz, 1995), Teladorsagia circumcincta (Stadelman, 1894), including the minor morphotypes, Teladorsagia trifurcata (Ransom, 1907) and Teladorsagia davtiani Andreeva and Satubaldin, 1954, exhibit a particularly broad host and geographic distribution (e.g., Suarez and Cabaret, 1991) and exceptional morphometric variation (e.g., Becklund and Walker, 1971; Lichtenfels and Pilitt, 1991). Teladorsagia circumcincta is a cosmopolitan species in which geographic distribution has been influenced by dissemination throughout the world coincidental with the transport of domestic hosts, particularly sheep (Ovis aries L.), since the 1500s (e.g., Hoberg, 1997a; Hoberg et al., 2000). The species also occurs in historically isolated populations of wild caprine bovids and caribou at high latitudes in the Northern Hemisphere. Generally, it is considered a typical abomasal parasite in domestic and wild sheep, other Caprinae, and pronghorn, and occasionally has been reported in cervid hosts across