John C. Holmes

EFFECTS OF CONCURRENT INFECTIONS ON HYMENOLEPIS DIMINUTA (CESTODA) AND MONILIFORMIS DUBIUS (ACANTHOCEPHALA). I. GENERAL EFFECTS AND COMPARISON WITH CROWDING

The ecology of intestinal helminths has been extensively studied in the past few years, but one aspect of their ecology, the influence of other parasites, has received scant attention. Such attention as has been paid to this influence has generally been directed to cross-immune responses of the host. The possibility of interspecific competition between parasites, which might be important as a factor in the regulation of their distribution and abundance, has been generally overlooked, or, indeed, denied (Baer, 1952, p. 213). Read and Phifer (1959) described the results of a series of experiments in which they studied the interactions between individual Hymenolepis diminutaand H. citelli in hamsters under conditions of ample and limited carbohydrate (starch). Both tapeworms were reduced in weight in the concurrent infections, but the extent of this reduction, and the relative effect on the two species, were markedly affected by the quantity of available carbohydrate. Competition for the available carbohydrate seems to be a likely explanation of their results. Cross (1934) reported an inverse relationship between the numbers of Proteocephalus exigus(sic) parasitizing ciscoes and the numbers of an acanthocephalan of the genus Neoicanthorinchus (sic) in the same host. Beck (1951), in a study on the effects of various factors on the egg production of single-worm infections of Hymenolepis diminuta, encountered several cases of accidental dual infections with Moniliformis dubius. He concluded that there was little evidence of toxicity of the acanthocephalan toward the tapeworm, although there might be some effect due to crowding or to competition. These two studies indicated that the relationship between acanthocephalans and tapeworms might profitably be studied. The experiments reported below are an attempt to determine the effects of concurrent infections on Hymenolepis diminuta and Moniliformis dubius. MATERIALS AND METHODS

Parasites as threats to biodiversity in shrinking ecosystems

Shrinking ecosystems concentrate both individuals and species into restricted areas, promoting transmission and exchange of parasites. Fragmentation increases edge and brings an influx of new species into the disturbed or agricultural habitats between fragments, introducing new parasites and possibly leading to the development of new and more pathogenic strains of parasite. Environmental contaminants act as stressors, and may compromise immune systems. Global climate changes challenge the adaptability of organisms, and may allow the invasion of new parasites. Because each of these effects increases the potential for parasites to become pathogenic, the importance of disease is expected to increase in shrinking ecosystems, with the emergence of new diseases and increasing numbers of epidemics. Increased pathogenicity of generalist parasites may pose a threat to species with restricted distributions or small populations.

The structure of helminth communities

Abstract The existence of both interactive and isolationist communities of helminths, each of which may be produced by any one of several processes, necessitates a pluralistic view of helminth community structure. A scheme involving three hierarchical scales of communities of helminths is proposed. Interactions between species occur in infracommunities, and should be looked for there. Interactions are often clearer in smaller groups of species, either among core species or within guilds. Infracommunities are samples of helminth communities at two larger scales: the helminth community in the host population provides core species, largely specialists, and that in the host community provides the generalists and the satellite species. The richness of each of the two large-scale communities is affected by various ecological, historical and evolutionary factors. The different concepts which have been applied to parasite communities are based on these factors.

Functional relationships and microhabitat distributions of enteric helminths of grebes (Podicipedidae): the evidence for interactive communities.

The significance of interspecific interactions as a structuring force in the enteric helminth communities of 4 species of grebes (Aechmophorus occidentalis, Podiceps grisegena, P. nigricollis, and P. auritus) was evaluated. Patterns of microhabitat distribution revealed that helminths resided in predictable locations along the length of the small intestine. Individual species of helminths occupied a high proportion of the intestine and varied in position in different host species suggesting a broad tolerance for conditions along the intestine. However, in individual birds, helminths were much more restricted in distribution, overlapped considerably less than their overall ranges would suggest, congeners had complementary distributions, and there was evidence of interference by at least 1 core species, all suggesting that interactions are important in these communities. Nevertheless, vacant niches were present in most birds, and core species were not distributed more evenly than would be expected through random placement. This suggests that important resources may not be distributed evenly along the intestinal gradient.

Do macrophage centres in freshwater fishes reflect the differences in water quality

Abstract Macrophage centres have been considered as a potentially useful indicator of fish health. In this histological work we tested this hypothesis with macrophage centres (MCs) in the spleen, the liver and the hematopoietic part of the kidney of two common freshwater fish species in Finland, perch ( Perca fluviatilis ) and roach ( Rutilus rutilus ). Samples were collected over 5 seasons from a system of 4 lakes providing a gradation in water quality. The mean number of MCs/mm 2 and the area covered (μm 2 /mm 2 ) by them differed between individual fish, species, organs, and lakes, with interactions amongst these factors. Hemosiderosis was recorded from the spleen and liver of both fish species; amounts differed between species of fish, organs, and lakes. None of the observed patterns agreed with rankings of water quality, and we conclude that macrophage centres have limited usefulness as indicators of pollution.

EFFICACY OF IVERMECTIN AGAINST NEMATODES INFECTING FIELD POPULATIONS OF SNOWSHOE HARES (LEPUS AMERICANUS) IN YUKON, CANADA

From July 1990 to February 1991, nematode numbers in free-ranging snowshoe hares (Lepus americanus) at Kluane Lake, southwestern Yukon, Canada, were manipulated by subcutaneous injection (0.4 mg/kg) of ivermectin. Three field experiments were conducted to determine the degree of helminth loss associated with a single administration of ivermectin; the length of time that ivermectin was effective in reducing worm numbers; and the effect of repeated ivermectin administration in reducing worm numbers. Numbers of the nematodes, Protostrongylus boughtoni and Nematodirus triangularis were reduced by approximately 80% 2 wk after treatment with a single dose of ivermectin, and were still significantly lower than controls at 4 wk. However, beyond 2 wk, ivermectin did not affect the rate of acquisition of new worms of either species. All treated groups contained one or more hares in which numbers of P. boughtoni and N. triangularis were not reduced. In addition, ivermectin had no effect on numbers of Trichuris leporis or Passalurus sp. Overall, ivermectin was not as effective against the nematodes of free-ranging hares as has been reported for nematodes of domestic and laboratory animals.

Isopod (Asellus Aquaticus) size and acanthocephalan (Acanthocephalus lucii) infections.

We examined the effect of isopod size and age on the success of an acanthocephalan infection and on the effects of that infection on the growth and survival of the isopods. Groups of isopods (Asellus aquaticus) belonging to 4 size classes (juveniles, maturing adults, young adults, and older adults) were exposed to infective acanthors of Acanthocephalus lucii. At the end of the experiment, survival of the isopods, lengths of male and female isopods, and numbers of different developmental stages of A. lucii larvae in infected isopods were assessed. Acanthocephalus lucii prevalence was significantly lower in juvenile isopods than in adults. Intensity of infection increased with the size of isopods at exposure, and cystacanth intensity correlated positively with isopod size at the end of the experiment. Exposed juveniles and maturing adults survived significantly better than unexposed individuals, but the opposite was true of the 2 largest size classes. At the end of experiment, exposed isopods, and, especially, cystacanth-infected isopods, were significantly larger than unexposed isopods in every size class. We suggest that isopod size not only affects the success of A. lucii infection but also affects the ability of A. lucii to affect the survival (and perhaps the growth) of the isopod hosts.

EXPERIMENTAL INFECTIONS OF FREE-RANGING ROCKY MOUNTAIN BIGHORN SHEEP WITH LUNGWORMS (PROTOSTRONGYLUS SPP.; NEMATODA: PROTOSTRONGYLIDAE)

Twelve free-ranging Rocky Mountain bighorn lambs (Ovis canadensis canadensis), each exposed experimentally to 125–1,000 infective third-stage larvae of Protostrongylus stilesi and P. rushi, shed significantly more first-stage larvae in their feces than did control lambs, but showed no clinical signs of illness and had equivalent summer and overwinter survival as control lambs. Two adult ewes, each exposed to 925 infective larvae, showed no increase in numbers of first-stage larvae in their feces; both survived at least 14 mo postexposure. Experimentally exposed lambs did not differ from control lambs in numbers of larvae in their feces in the following summer. Three experimental lambs had 313–402 adult P. stilesi and 0–97 adult P. rushi on necropsy; two control lambs had 255 and 270 P. stilesi and no P. rushi. The presence of these numbers of lungworms did not appear to be sufficient to precipitate lungworm pneumonia in bighorn lambs under the conditions of this study.

Niche separation and the broken-stick model: use with multiple assemblages

Application du modele de MacArthur (broken-stick) a la prediction des distances entre niches ecologiques. Exemples pour des cestodes parasitant des oiseaux

Plicatrium visayanensis new species (Digenea: Hemiuridae) from Hydrophis ornatus (Serpentes: Hydrophiidae) from the Visayan Sea, Philippines

Bush A. O. and Holmes J. C. 1984. Plicatrium visayanensis new species (Digenea: Hemiuridae) from Hydrophis ornatus (Serpentes: Hydrophiidae) from the Visayan Sea, Philippines. International Journal for Parasitology14: 35–38. A new species of hemiurid is described from a sea snake. The diagnosis of the genus Plicatrium is emended.