Michael A. Barger

The transmission of digenetic trematodes: style, elegance, complexity.

Abstract Traditionally, the field of parasitology has dealt with eukaryotic animals, to the exclusion of viruses, bacteria, fungi, etc., which is the way it will be approached here. The focus of the present paper will be on certain ecological aspects of the life cycles and life-history strategies employed by the Digenea, a diverse group of platyhelminths that includes some 25,000 species. More specifically, the review will consider the nature of host/parasite interactions within molluscan intermediate hosts and the manner in which these interactions, or lack thereof, function in structuring trematode infracommunities within these molluscan intermediate hosts. Literature in this area suggests that predation/competition may be a significant structuring force for infracommunities in certain marine prosobranchs, but not others, and that temporal/spatial factors may be involved as structuring mechanisms in at least some freshwater pulmonates.

HOST SPECIFICITY AND THE DISTRIBUTION–ABUNDANCE RELATIONSHIP IN A COMMUNITY OF PARASITES INFECTING FISHES IN STREAMS OF NORTH CAROLINA

A positive relationship between distribution and local abundance is often observed among species in a community. The resource-breadth hypothesis suggests that this pattern is the result of differential abilities among species to utilize available resources, such that generalists are widely distributed and locally abundant, and specialists are narrowly distributed and locally sparse. This hypothesis was tested in a community consisting of 22 species or morphospecies of parasites infecting members of 18 species of fish among 14 sites in 7 small streams in the Appalachian Mountains of North Carolina. A positive relationship between distribution (fraction of sites occupied) and abundance (average local abundance) was evident among parasite species. The number of host species infected by each parasite species was positively related to both distribution and average local abundance; both relationships held after statistical removal of the distribution and abundance of the hosts, respectively. These results support the resource-breadth hypothesis as an explanation for the distribution–abundance relationship in this system.

Downstream changes in the composition of the parasite community of fishes in an Appalachian stream

The spatial distribution of 6 parasite species (Myxobolus sp., Dactylogyrus sp., Sterliadochona ephemeridarum, Plagioporus sinitsini, Allopodocotyle chiliticorum, Allocreadium lucyae) was studied in 5 species of fishes (Oncorhynchus mykiss, Clinostomus funduloides, Notropis chiliticus, Rhinichthys atratulus, Semotilus atromaculatus) in Basin Creek, an Appalachian stream in North Carolina. Nonmetric multidimensional scaling and vector fitting were used to determine if the proximity of sampling sites was related to community similarity. Position along Basin Creek was significantly related to parasite community structure. Breaks in parasite community composition were imposed by waterfalls at upstream areas of Basin Creek that restricted distributions of C. funduloides, N. chiliticus, and S. atromaculatus and at the downstream limit of the study area by a break in the distribution of S. ephemeridarum coincident with the existence of a dam but were independent of suitable piscine host distributions. These discontinuities in parasite community composition imply that the relationship between proximity of sites and community similarity is predictive because distance between sites is related to the probability that fish at different sampling sites recruit parasites from different species pools. This relationship is not the same for all component communities.

Effects of coinfection with Pomphorhynchus bulbocolli on development of leptorhynchoides thecatus (Acanthocephala) in amphipods (Hyalella azteca).

The effect of the presence of Pomphorhynchus bulbocolli on the development of Leptorhynchoides thecatus (Acanthocephala) in amphipod intermediate hosts (Hyalella azteca) was examined. Two groups of amphipods were exposed either to eggs of both species (experimental) or only to L. thecatus eggs (control). Amphipods of both groups were dissected 39 days postexposure. The percentage of L. thecatus at the cystacanth stage and mean abundance of cystacanths and precystacanths per amphipod were determined. Contingency table analysis and Fishers exact tests demonstrated that a significantly smaller proportion of L. thecatus reached the cystacanth stage in coinfected amphipods of the experimental group than either worms in the control group or worms in L. thecatus-only infections of the experimental group. Interspecific interaction between acanthocephalans in intermediate hosts has not been reported previously. Coinfection reduces the number of L. thecatus in amphipods available for transmission to definitive hosts. Habitat separation by eggs of L. thecatus and P. bulbocolli might reduce this effect if amphipods are less likely to become coinfected when eggs are in different microhabitats than when they are not.

Structure of Leptorhynchoides thecatus and Pomphorhynchus bulbocolli (Acanthocephala) eggs in habitat partitioning and transmission.

The role of egg structure in transmission and habitat use of Leptorhynchoides thecatus and Pomphorhynchus bulbocolli (Acanthocephala) was investigated. During storage in tap water at 4 C, the outer membrane of L. thecatus eggs was lost, releasing ribbonlike filaments of the fibrillar coat. After similar storage, the outer membrane and fibrillar coat of P. bulbocolli eggs remained intact. Eggs of L. thecatus entangled in algae, whereas those of P. bulbocolli settled to the substratum. Leptorhynchoides thecatus infections in amphipod intermediate hosts were significantly more prevalent and dense when eggs were allowed to entangle than when they were not. Prevalence and relative density of P. bulbocolli infections in amphipods were not significantly different between trials in which entanglement was possible and those in which it was not. These results indicate that although the same species of amphipod, Hyalella azteca, is the intermediate host for both acanthocephalan species, mechanisms of transmission differ. Differences in fibrillar coats result in segregation of the environment in a manner that affects transmission and occurrence in intermediate hosts.

A New Species of Neoechinorhynchus (Acanthocephala: Neoechinorhynchidae) from a Red-Eared Slider (Trachemys scripta elegans) in Mexico

Abstract Neoechinorhynchus schmidti n. sp. is described from the red-eared slider, Trachemys scripta elegans, from the state of Tabasco, Mexico. A large, prominent process at the posterior end of females distinguishes the new species from all others of the genus except Neoechinorhynchus chelonos, Neoechinorhynchus lingulatus, and Neoechinorhynchus magnapapillatus, also parasites of turtles. Neoechinorhynchus schmidti n. sp. can be distinguished from these taxa by the structure of the eggs. The eggs of N. schmidti have numerous small, nearly spherical inclusions not found in N. chelonos, N. lingulatus, and N. magnapapillatus.

Spatial heterogeneity in the parasite communities of creek chub (Semotilus atromaculatus) in southeastern Nebraska.

The intestinal helminth communities of creek chub (Semotilus atromaculatus) were studied in the streams of southeastern Nebraska to characterize spatial variation, to determine whether drainages act as regional species pools, and to examine the spatial patterning of individual parasite species within and among drainages. Creek chub were sampled in the summer of 2003 and the spring of 2004 at each of 12 sites distributed evenly among 3 drainages in the Big Nemaha River watershed. Four intestinal helminths were recovered: Allocreadium lobatum, Proteocephalus sp., Rhabdochona canadensis, and Paulisentis missouriensis. Host size had little or no effect on the composition of the parasite communities of creek chub, either among individual fish or among samples. In contrast, drainage and sample date explained 82% of the variation in mean infracommunity species richness among samples, and 62% of the variation in mean infracommunity abundance among samples. Drainage differences were determined by the distributions of P. missouriensis and R. canadensis; whereas, A. lobatum and Proteocephalus sp. were more uniformly distributed among drainages. Each drainage was characterized by a unique pattern of species diversity at infracommunity, component community, and drainage levels of organization.

Host specificity of Rhabdochona canadensis (Nematoda: Rhabdochonidae) in Nebraska.

Intermediate and definitive host specificity of Rhabdochona canadensis in Nebraska were investigated. Mayfly nymphs Trichorythodes sp. and Caenis sp. were found to serve as experimental intermediate hosts. Development inside the nymphs required approximately 10 days, with the worms passing through 2 molts and then becoming encapsulated in the hemocoel as infective third-stage juveniles. Survey data revealed that only the red shiner Cyprinella lutrensis serves as definitive host for R. canadensis in nature. Laboratory infections of Notropis dorsalis, N. stramineus, and Fundulus zebrinus, all of which were uninfected in nature, were attempted to determine if observed specificity was due to physiological or ecological factors. Two individuals of N. dorsalis became infected with R. canadensis, but no development was observed. Both N. stramineus and F. zebrinus were incapable of becoming infected. Thus, definitive host specificity in this system seems to be mediated by both physiological and host ecological factors.

A Key to the Species of Neoechinorhynchus (Acanthocephala: Neoechinorhynchidae) from Turtles

Abstract A dichotomous key to the species of Neoechinorhynchus (Acanthocephala: Neoechinorhynchidae) occurring in turtles is presented based on characters of the posterior extremity of fully gravid females and the egg. The 9 recognized species of Neoechinorhynchus in turtles can be identified reliably based on these characters alone. Identification requires fully gravid females that have been properly killed and fixed. Immature females and males cannot be identified using the key presented herein.

Redescription of Oligacanthorhynchus major (Machado-Filho, 1963) Schmidt, 1972 (Acanthocephala: Oligacanthorhynchidae) from the white-lipped peccary (Tayassu pecari) in Bolivia

Abstract Oligacanthorhynchus major (Machado-Filho, 1963) Schmidt, 1972 (Acanthocephala: Oligacanthorhynchidae) was redescribed using specimens from 2 white-lipped peccaries (Tayassu pecari) collected in the department of Santa Cruz, Bolivia. The male and the egg of O. major were described for the first time. The female worm is 241-824 mm long; the trunk is narrowest at the anterior end and widest in the middle of the worm. The male worm (120 mm) is substantially smaller than the female, the testes are confined to the posterior region, and an instance of monorchism is documented for a member of this species.