Author
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Hoberg, Eric |
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Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/5/2004 Publication Date: 2/8/2005 Citation: Hoberg, E.P. 2005. Coevolution and biogeography among Nematodirinae (Nematoda: Trichostrongylina) Lagomorpha and Artiodactyla (Mammalia): exploring determinants of history and structure for the northern fauna across the Holarctic. Journal of Parasitology. 91:358-369. Interpretive Summary: Nematodes of the subfamily Nematodirinae are characteristic components of a Holarctic fauna. In order to understand the occurrence of this group in North America, and to predict how these nematodes may respond to changing climate and ecological conditions a study integrating phylogeny, ecology and history was conducted. The topology of a generic-level phylogenetic hypothesis, patterns of diversity and geographic distributions for respective nematode taxa in conjunction with data for host occurrence are consistent with primary distributions determined across Beringia for species of Murielus, Rauschia, Nematodirus and Nematodirella. Ancestral hosts are represented by Lagomorpha (hares, rabbits, pikas), with evidence for a minimum of one host-switching-event and subsequent radiation in the Artiodactyla (even toed ungulates). 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, species of 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-Boreal fauna of zooparasitic nematodes (defined by latitude and altitude) adapted to transmission in extreme environments characterized by seasonally low temperatures and varying degrees of desiccation. The primary physiographic determinant of distribution was the Beringian nexus linking the Palearctic and Nearctic permanently through much of the Tertiary, and intermittently during the Pliocene and Quaternary along with the progressive development of tundra-steppe habitats. Beringia, as it became increasingly cold, insular and isolated with sharply defined seasons may have acted as a filter-bridge of high selectivity for parasite faunas that could not survive the expansion of rigorous climatic conditions in the late Pliocene and Pleistocene. Thus, such groups as the Haemonchinae (Haemonchus, Mecistocirrus), Cooperiinae, and Trichostrongylinae are either absent or poorly represented in the endemic Nearctic fauna, and represent groups with souther affinities. Distributions for species of these taxa are not strongly associated with wild ungulates, and their occurrence in the North America appears linked secondarily to introductions and dissemination with domestic sheep, cattle and goats at temperate/boreal latitudes coincidental with European contact after the 1500's. Structurally, and historically, this is further consistent with the overall mosaic nature of the North American fauna. In the context of global change, and climate/habitat modification, it would be predicted that such southern faunal elements (or introduced temperate/boreal faunas) will respond to ecological disruption by northern extensions of their ranges, which may currently be limited by temperature and moisture. Such a prediction is further supported in the context of long-term evolutionary histories for Haemonchus and Cooperia in tropical and subtropical habtiats of Africa. Northern faunas such as those represented by nematodirines, ostertagiines and some protostrongyles in ruminants may be influenced by latitudinal or altitudinal shifts in range, increasing rates for development, reductions in generation time, broadened windows for transmission, amplification and concomitant increases in the prevalence and intensity of infection. Increasingly northern faunas may be associated with regulation of host populations and emergence of disease conditions among both cervids and caprines. Technical Abstract: : Nematodes of the subfamily Nematodirinae are characteristic components of a Holarctic fauna. The topology of a generic-level phylogenetic hypothesis, patterns of diversity and geographic distributions for respective nematode taxa in conjunction with data for host occurrence are consistent with primary distributions determined across Beringia for species of Murielus, Rauschia, Nematodirus and Nematodirella. Ancestral hosts are represented by Lagomorpha, with evidence for a minimum of one host-switching-event and subsequent radiation in the Artiodactyla. 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, species of 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-Boreal fauna of zooparasitic nematodes (defined by latitude and altitude) adapted to transmission in extreme environments characterized by seasonally low temperatures and varying degrees of desiccation. The history and distribution of this fauna is examined in the context biotic and abiotic determinants for geographic colonization and host switching with an exploration of predicted responses of complex host-parasite systems to ecological perturbation under a regime of global climate change. |
