CAUDAL POLYMORPHISM AND CEPHALIC MORPHOLOGY FOR FIRST STAGE LARVAE OF PARELAPHOSTRONGYLUS ODOCOILEI (PROTOSTRONGYLIDAE: ELAPHOSTRONGYLINAE) IN DALL'S SHEEP FROM THE MACKENZIE MOUNTAINS, CANADA

Authors: Hoberg, Eric; JENKINS, EMILY - UNIV SASKATCHEWAN; Rosenthal, Benjamin; Wong, Mayee; Erbe, Eric; KUTZ, SUSAN - UNIV SASKATCHEWAN; POLLEY, LYDDEN - UNIV SASKATCHEWAN

Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2005
Publication Date: 12/10/2005
Citation: Hoberg, E.P., Jenkins, E.J., Rosenthal, B.M., Wong, M., Erbe, E.F., Kutz, S.J., Polley, L. 2005. Caudal polymorphism and cephalic morphology for first stage larvae of Parelaphostrongylus odocoilei (Protostrongylidae: Elaphostrongylinae) in dall's sheep from the Mackenzie mountains, Canada. Journal of Parasitology. 91(6):1318-1325.

Interpretive Summary: Nematodes of the family Protostronglidae have significant economic impact among domestic and wild ungulates throughout the world. In North America various species are documented as serious pathogens that occur in the pulmonary system, skeletal musculature or central nervous system of domestic and wild sheep, and cervid hosts. Identification of larval parasites has remained problematic and this has limited our ability to carryout extensive geographic surveys or to fully understand epidemiology and the dynamics of transmission among intermediate hosts (gastropods) and final hosts that harbor adult worms. Recently molecular-based methods have been dedveloped for definitive diagnosis and have been applied to studies of Parelpahostrongylus odocoilei. We have applied thes techniques, based on comparisons of sequences from the mitochondrial and nuclear genomes to resolve the identification of certain larval parasites. We demonstrated unequivocally the occurrence of polymorphism in the structure of the tail among first-stage larvae representing a single species, Parelaphostrongylus odocoilei, among the Protostronglidae. Two distinct larvae, with a characteristic dorsal spine, include: 1. a morphotype with a conical tail marked by 3 distinct transverse folds or joints and a symmetrical terminal tail-spike; and 2. a morphotype with a digitate terminal region lacking folds or joints and with an asymmetrical, subterminal tail-spike. These divergent larval forms had been postulated as reprenting distinct species of elaphostrongyline nematodes. Application of a multi-locus approach using ITS-2 sequences from the nuclear genome and COX-II sequences from the mitochrondrial genome seved to confirm the identity of these dorsal-spined larvae as P. odocoilei. Ours is the first demonstration of structural polymorphism among larvae of a single species in the Metastrongloidea and Strongylida. The basis for this polymorphism remains undetermined, but such phenomena if discovered to be more widespread may contribute to continued confusion in discriminating among first-stage larvae for species, genera and subfamilies within the economically important Protostrongylidae.

Technical Abstract: We demonstrate unequivocally the occurrence of polymorphism in the structure of the tail among first-stage larvae representing a single species, Parelaphostrongylus odocoilei, among the Protostrongylidae. Two distinct larvae, with a characteristic dorsal spine, include: 1. a morphotype with a conical tail marked by 3 distinct transverse folds or joints and a symmetrical terminal tail-spike; and 2. a morphotype with a digitate terminal region lacking folds or joints and with an asymmetrical, subterminal tail-spike. These divergent larval forms had been postulated as representing distinct species of elaphostrongyline nematodes. Application of a multi-locus approach using ITS-2 sequences from the nuclear genome and COX-II sequences from the mitochondrial genome served to confirm the identity of these dorsal-spined larvae as P. odocoilei. Additionally, based on scanning electron microscopy (low temperature field emission), the cephalic region of these larvae consisted of a cuticular triradiate stoma surrounded by six single circumoral papillae of the inner circle, 10 papillae of the outer circle (4 paired, and 2 single) and 2 lateral amphids. Ours is the first demonstration of structural polymorphism among larval conspecifics in the Metastrongyloidae and Strongylida. The basis for this polymorphism remains undetermined, but such phenomena, if discovered to be more widespread, may contribute to continued confusion in discrminating among first-stage larvae for species, genera and subfamilies within Protostrongylidae.