(Trichostrongyloidea) with Comments on the Evolution of Nematodirus Spp

Proc. Helminthol. Soc. Wash. 55(2), 1988, pp. 160-164

Morphology of the Synlophe of Nematodirus maculosus (Trichostrongyloidea) with Comments on the Evolution of Nematodirus spp. Among the Caprinae (Artiodactyla)1

ERIC P. HOBERG2 AND LORA G. RlCKARD2'3 2 College of Veterinary Medicine, Oregon State University, Corvallis, Oregon 97331 and 3 Department of General Science, Oregon State University, Corvalis, Oregon 97331

ABSTRACT: The synlophe of male specimens of Nematodirus maculosus is characterized. The 16-ridge bilaterally symmetrical system in the cervical region appears to be unique when compared to those species of Nematodirus that have been studied in detail. Nematodirus maculosus appears most similar to those species from the Bovidae, characterized by long lateral ridges, a small number of ridges (generally 14) at the midbody, and short symmetrical spicule tips. Results of this study and previous investigations allowed alternative hypotheses to be developed for the evolution and historical biogeography of some Nematodirus spp. among the Caprinae (tribes Caprini and Rupicaprini) in the Holarctic. KEY WORDS: Nematodirus maculosus, Nematodirus spp., Trichostrongyloidea, Bovidae, synlophe, coevolu- tion, biogeography, cuticle.

The synlophe is a useful character for differ- had not been recognized as a significant character entiation of genera (Durette-Desset, 1983) and in nematode systematics. Although Becklund related species of trichostrongyloid nematodes (1965) enumerated the ridges for both male and (Lichtenfels, 1983). In those studies 2 method- female specimens, an interpretation of the cer- ologies were generally employed: (1) a relatively vical synlophe was not provided. In the current narrow approach that stresses the number and study we present a detailed description of the axis of orientation of cuticular ridges at the mid- synlophe of male specimens of N. maculosus, body (Durette-Desset, 1983) or (2) a more syn- from the type host and Ovis canadensis Shaw, optic examination of the number of ridges, their that will allow a comparison to ridge-patterns pattern in the cervical region, and the longitu- known for other species from ruminants, partic- dinal extent of the synlophe (Lichtenfels and Pi- ularly bovids of the tribes Caprini and Rupicap- litt, 1983a, b). Accurate evaluations of the syn- rini in the Holarctic. lophe were generally not included among early descriptions of trichostrongyloid nematodes, and Materials and Methods relatively few species have been studied using modern techniques. Specimens of Nematodirus maculosus were studied using interference-contrast light microscopy (Leitz) and Detailed descriptions of the cuticular ridge sys- scanning electron microscopy. Prior to examination, tems for Nematodirus spp. from domestic ru- material for light microscopy was transferred to 70% minants in North America and Europe have been ethanol/5% glycerine and cleared in glycerine by evap- provided by Durette-Desset (1979), Lichtenfels oration. Eight specimens were prepared as temporary whole mounts and 2 specimens were studied in trans- and Pilitt (1983a), and Hoberg et al. (1986), but verse sections cut by hand with a scalpel blade or from relatively little information is available on species paraffin-embedded material (latter provided by J. R. parasitizing sylvatic hosts (Rossi, 1983). Ne- Lichtenfels). A single specimen was examined using matodirus maculosus Becklund, 1965, is 1 of 4 scanning electron microscopy (stub deposited as part species (N. tarandiHadwin, 1922; N. archariSo- of USNM Helm. Coll. 58180). The description of the synlophe is consistent with kolova, 1948; and N. odocoilei Becklund and the methodology and terminology presented by Lich- Walker, 1967) that parasitize sylvatic bovids and/ tenfels and Pilitt (1983a) for other species of Nema- or cervids in North America. At the time of the todirus from domestic ruminants. The current study original description, from Oreamnos americanus was based solely on male specimens as females were not available. In the description all measurements are (Blainville) (subfamily Caprinae), the synlophe given in micrometers unless stated otherwise. SPECIMENS EXAMINED: N. maculosus from Oream- nos americanus, USNM Helm. Coll. No. 58180 (5 males ' Published as Oregon Agricultural Experiment Sta- from Rattlesnake Creek, Montana), No. 58747 (1 male tion Technical Paper No. 8291, Oregon State Univer- embedded in paraffin and sectioned, from Canada), sity. and No. 66613 (4 males from South Dakota); and from 160 Copyright © 2011, The Helminthological Society of Washington 161

Ovis canadensis, No. 66607 (1 male from Alberta, Can- ada).

Results The synlophe of Nematodirus maculosus is composed of a bilaterally symmetrical system of 16 ridges, with an orientation parallel to the longitudinal body axis, in the cervical region (Fig. 1). Eight ridges extend to the base of the cephalic capsule: a pair of minute lateral ridges (unpaired and unnumbered) and dorsal-ventral ridges numbered 3-5 (paired) are continuous in the cervical zone. Four pairs of lateral ridges are discontinuous: ridges numbered 1 and 7 terminate anteriorly at the level of the cervical papillae; those numbered 2 and 6 end about 100-150 from the base of the cephalic capsule (Figs. 1, 2). The fourth ventral ridge is interrupted at the level of the excretory pore (Fig. 3). All lateral ridges are narrow and become diminished in height anteri- ad. Ventral-dorsal ridges are relatively robust with the fourth pair being finlike and hypertrophied. The spacing of the lateral ridges is narrow compared to those in the ventral and dorsal fields. The number of ridges decreases extending posteriad from the cervical region. Minute lateralmost ridges terminate before the midbody. Lat- eral ridges numbered 1, 2, 7, and 6 are continuous; those numbered 1 and 7 are briefly interrupted for approximately 20 at a distance about 230 posterior to the cervical papillae. A reduction in height of the lateral ridges is evident toward the midbody (Figs. 4-6). The ventral and dorsal synlophe continues with a slight gradient in height (dorsal smaller than ventral) until the dorsal ridges become markedly attenuated 2-3 mm from the prebursal papillae. Robust ridges continue on the ventral surface to within 190 from the prebursal papillae where they become reduced in height. The synlophe extends from this region as a series of minute ridges, not discernible with the light microscope, that terminate 50 from the base of Figure 1. Synlophe in the cervical region of Nem- the copulatory bursa (Fig. 7). atodirus maculosus showing right lateral view (from camera lucida) and schematic of transverse section near Discussion the level of the excretory pore; D = dorsal, V = ventral. Observations from the present study in part confirm those of Becklund (1965) who reported (Lichtenfels and Pilitt, 1983a). Thus, it is antic- 14 longitudinal ridges for male and female spec- ipated that females of TV. maculosus may be iden- imens of TV. maculosus. Although 16 ridges were tified by the low number of cuticular ridges in found in the cervical zone of male specimens, 14 the cervical region and by the unique structure were found at the midbody during the present of the synlophe anterior to the cervical papillae study. Previous studies of Nematodirus spp. have and excretory pore. Specimens of N. maculosus indicated the similarity in the pattern of the cer- have fewer cervical ridges than any species of vical synlophe in male and female conspecifics Nematodirus so far examined, although a rela-

Figures 2-7. Scanning electron microscopy and interference-contrast microscopy of the synlophe of N. maculosus. 2. Right lateral view in cervical region, anterior to cervical papilla, showing narrow lateralmost ridge and termination of ridge 2 (arrows). 3. Synlophe in cervical region at level of excretory pore (exp) and right cervical papilla (cp); anterior is to the left. 4. Synlophe in midbody, lateral view. 5. Transverse section in postcervical region showing 16 ridges; note minute lateralmost ridges (arrows). 6. Transverse section in midbody showing 14 ridges; note minute lateral ridges (arrows) numbered 1 and 7. 7. Posterior, toward distal end of spicules; ridges not discernible in transverse section with the light microscope. AH scale bars = 20 jim. In Figures 5-7, v = ventral, d = dorsal. lively great number are continuous to the ce- these ridges are larger and extend posteriad be- phalic capsule. yond the cervical papillae, potentially repre- Criteria developed by Lichtenfels and Pilitt senting a hypertrophied condition. (1983a) suggested that N. maculosus was most The cervical synlophe has been examined in similar to N. fdicollis (Rudolphi, 1802) and N. detail for only 7 species of Nematodirus from davtiani Grigorian, 1949. These 3 species are domestic ruminants in North America (Lichten- characterized by the lateralmost pairs of ridges fels and Pilitt, 1983a; Hoberg et al., 1986). How- extending anteriorly more than lh of the cervical ever, data are available for the midbody region distance, 14 ridges at the midbody, finlike dorsal of 16 species from the Bovidae (Bovinae, Cap- and ventral ridges, a large copulatory bursa, and rinae), Cervidae, and Camelidae in the Holarctic short symmetrical spicule tips. The characters of and Neotropics (Durette-Desset, 1978, 1979; the synlophe have been postulated as synapo- Rossi, 1983). In addition to N. maculosus, N. morphies for N. fdicollis and N. davtiani (see filicollis, and N. davtiani, only 2 other species, Lichtenfels and Pilitt, 1983a), thus, the morpho- viz. N. hugonotae Rossi, 1983, and N. ibicisBioc- logical similarity of N. maculosus could have a ca, Balboa, and Costantini, 1982, were described historical phylogenetic basis. Additionally, the with 14 ridges (all others have 18 or more). Pre- minute, unpaired, discontinuous, lateralmost liminary studies of TV. archari have also indicated ridges in the cervical zone of N. fdicollis, N. dav- the presence of 14 ridges in this species (Rickard tiani, and N. maculosus appear to be homolo- and Lichtenfels, pers. comm.). Thus, there are at gous. However, in specimens of N. maculosus least 6 species, characterized by a postulated syn-

Copyright © 2011, The Helminthological Society of Washington OF WASHINGTON, VOLUME 55, NUMBER 2, JULY 1988 163 apomorphy (14 midbody ridges), that are also of these ruminants (see Kurten and Anderson, primarily parasites of the Caprinae (tribes Cap- 1980; Geist, 1985, 1987) suggest that Nemato- rini and Rupicaprini). dirus initially became parasites of the Caprinae The association between the Caprinae and in the Palearctic during the late Tertiary. Thus, Nematodirus spp. is thought to be of relatively only a single event of colonization of the Capri- recent origin in the Pleistocene (Rossi, 1983). nae (from camelids) during the Pliocene is pos- Current hypotheses for the evolution and bio- tulated. Dispersal from the Palearctic by precur- geography of this assemblage postulate multiple sors of Ovis spp. and Oreamnos, already events of long-range dispersal and widespread parasitized by Nematodirus, into the Nearctic colonization of the Caprini and Rupicaprini late during the Pleistocene would then account for in the history of these host groups. Both tribes the contemporary distribution of some sylvatic of the Bovidae originated in the Palearctic during hosts and their evolutionarily derived parasites the Miocene and Pliocene. However Nem- in North America. This contention is further atodirus (and Nematodirinae) is considered to be supported by the high diversity of Nematodirus of Nearctic origin among the Camelidae (Du- spp. associated with sylvatic sheep, goats, and rette-Desset and Chabaud, 1977; Rossi, 1983). antelope in Eurasia (see Kulmamatov, 1974) and Camels had dispersed across Beringia to Eurasia the paucity of nematodes with Holarctic distri- by the Pliocene, postdating the early evolution butions among these hosts. Additionally, the lack of the Caprinae, but became extinct in the Nearc- of endemic species of Nematodirus among bo- tic by the late Pleistocene (Kurten and Anderson, vids in Africa (Durette-Desset, 1979) and the 1980; Thenius, 1980). Rossi (1983) and Durette- history of bovid tribes (including the Caprini) in Desset (1985) contended that Nematodirus spp. sub-Saharan Africa (see Vrba, 1985) suggests that became parasites of the Caprinae via coloniza- the Caprinae were colonized in the Palearctic tion from camelids only after the former host during the late Pliocene. Among other Nema- group had dispersed into North America during todirinae, it has been postulated that host- the Pleistocene. Thus, the widespread occurrence switching from camelids to bovids by species of of Nematodirus spp. among some contemporary Nematodirella Yorke and Maplestone, 1926, also Caprinae in the Palearctic would have resulted occurred in Eurasia prior to the Pleistocene from a subsequent event of dispersal (from the (Lichtenfels and Pilitt, 1983b). Continued stud- Nearctic) and broad colonization and speciation ies of Nematodirus spp. and eventual phyloge- of nematodes among sylvatic sheep and antelope netic analyses will be required to fully evaluate during the late Pleistocene. Current evidence these hypotheses. however indicates that the primary movements of caprine bovids were from west to east across Acknowledgments Beringia during the Wisconsin (and earlier dur- Partial funding for this study was provided by ing the Pleistocene), with little indication of dis- a grant from the General Research Council, Or- persal into the Palearctic (Kurten and Anderson, egon State University, to G. L. Zimmerman and 1980;Geist, 1985). E. P. Hoberg. Dr. J. R. Lichtenfels kindly pro- Results from the present study and those provided specimens of N. maculosus from the USNM vided by Lichtenfels and Pilitt (1983a) support Helminthological Collections, USDA, Beltsville, alternative hypotheses for the evolution of Nem- Maryland, and critically evaluated an earlier draft atodirus among the Caprini and Rupicaprini. Two of the manuscript. Mr. A. H. Soeldner, of the postulated synapomorphies may unite N. mac- Electron Microscopy Facility, Oregon State Uni- ulosus and other species (14 ridges at the mid- versity, prepared specimens and assisted with body and anterior extent of the lateral cervical scanning electron microscopy. ridges), suggesting that some Nematodirus spp. have coevolved with these host groups. Species Literature Cited with a low number of midbody ridges that occur Becklund, W. W. 1965. Nematodirus maculosus sp. among the Caprini and Rupicaprini appear to be n. (Nematoda: Trichostrongylidae) from the highly derived and otherwise do not share syn- mountain goat, Oreamnos amcricanus, in North America. Proceedings of the Helminthological So- apomorphic characters with species typical of ca- ciety of Washington 51:945-947. melids or other hosts. Such observations along Durette-Desset, M. C. 1978. Nouvelles donnees mor- with the biogeographic and evolutionary history phologiques sur des Nematodes Trichostrongy-

loides des collections du United States National Kulmamatov, A. 1974. O vidovom sostave roda Museum. Bulletin du Museum National d'His- Nematodirus Ransom 1907. Materially Nauch- toire Naturelle, Paris, Zoologie 352:135-147. nykh Konferentsii Vsesouznogo Obshchestva —. 1979. Les Nematodirinae (Nematoda) chez Gel'mintologov. 26:137-140. les Ruminants et chez les Lagomorphes. Annales Kurten, B., and E. Anderson. 1980. Pleistocene mam- de Parasitologie Humaine et Comparee 54:313- mals of North America. Columbia University 329. Press, New York. —. 1983. Keys to the genera of the superfamily Lichtenfels, J. R. 1983. The synlophe and species Trichostrongyloidea. In R. C. Anderson and A. determination of Trichostrongyloidea. Pages 273- G. Chabaud, eds. CIH Keys to the Nematode Par- 291 in A. R. Stone, H. M. Platt, and L. F. Khalil, asites of Vertebrates. No. 10. 85 pp. Common- eds. Concepts in Nematode Systematics. Academ- wealth Agricultural Bureaux, Farnham Royal, En- ic Press, New York. gland. , and P. A. Pilitt. 1983a. Cuticular ridge pat- —. 1985. Trichostrongyloid nematodes and their terns of Nematodirus (Nematoda: Trichostrongy- vertebrate hosts: reconstruction of the phylogeny loidea) parasitic in domestic ruminants of North of a parasitic group. Advances in Parasitology 24: America, with a key to species. Proceedings of the 239-306. Helminthological Society of Washington 50:261- -, and A. G. Chabaud. 1977. Essai de classifi- 274. cation des Nematodes Trichostrongyloidea. An- -, and . 1983b. Cuticular ridge patterns nales Parasitologie 52:539-558. of Nematodirella (Nematoda: Trichostrongylo- Geist, V. 1985. On Pleistocene bighorn sheep: some idea) of North American ruminants, with a key to problems of adaptation, and relevance to today's species. Systematic Parasitology 5:271-285. American megafauna. Wildlife Society Bulletin 13: Rossi, P. 1983. Sur le genre Nematodirus Ransom, 351-359. 1907 (Nematoda: Trichostrongyloidea). Annales . 1987. On speciation of Ice Age mammals, de Parasitologie Humaine et Comparee 58:557- with special reference to cervids and caprids. Ca- 581. nadian Journal of Zoology 65:1067-1084. Thenius, E. 1980. Grundziige der Faunen-und Ver- Hoberg, E. P., G. L. Zimmerman, and J. R. Lichtenfels. breitungs-geschichte der Saugetiere. Gustav Fisch- 1986. First report of Nematodirus battus (Nem- er Verlag, Stuttgart. atoda: Trichostrongyloidea) in North America: re- Vrba, E. S. 1985. African Bovidae: evolutionary description and comparison to other species. Pro- events in the Miocene. South African Journal of ceedings of the Helminthological Society of Science 81:263-266. Washington 53:80-88.

A History of Animal Parasitology in USDA

A chapter entitled "Animal Parasitology in the United States Department of Agriculture, 1886- 1984," by the late Dr. John S. Andrews, is included in pages 113-166 of "100 Years of Animal Health, 1884-1984," published as Journal of NAL Associates, Vol. 11(1-4), January/December 1986. This publication commemorates the centennial of the establishment of the Bureau of Animal Industry in USDA. It is available for $17.00 U.S. from: Associates of the National Agricultural Library, Inc., Room 203, 10301 Baltimore Boulevard, Beltsville, Maryland 20705, U.S.A.