Infracommunity Richness Research Articles

Ecologia das comunidades de metazoários parasitos, do xaréu, Caranx hippos (Linnaeus) e do xerelete, Caranx latus Agassiz (Osteichthyes, Carangidae) do litoral do estado do Rio de Janeiro, Brasil

Sixty specimens of Caranx hippos (Linnaeus, 1766) and fifty-five specimens of Caranx latus Agassiz, 1831 collected from the coastal zone of the State of Rio de Janeiro (21-23oS, 41-45oW), Brazil, from October 1998 to October 1999, were necropsied to study their metazoan parasites. All specimens of C. hippos were parasitized, and the majority of specimens of C latus (96.4%) were parasitized by one or more metazoan species. Nineteen species of parasites were collected in C. hippos: 5 digeneans, 5 monogeneans, 2 cestodes, 5 nematodes, and 2 copepods. Seventeen species of parasites were collected in C. latus: 6 digeneans, 2 monogeneans, 3 cestodes, 4 nematodes, and 2 copepods. The endoparasites (digeneans, cestodes, and nematodes) were the majoriry, 76.4% and 63.3%, of the total number of parasite specimens collected in C. hippos and C. latus, respectively. The monogeneans Allopyragraphorus hippos (Hargis, 1956) and Cemocotyle carangis (MacCallum, 1913) were the most dominant species with the highest parasitic prevalence in the parasite community of C. hippos and C. latus, respectively. The metazoan parasites of the two host species showed the typical overdispersed pattern of distribution. Bucephalus varicus Manter, 1940. A. hippos, Protomicrocotyle mirabilis (MacCallum, 1918), Cucullanus pulcherrimus Barreto, 1918, and Lemanthropus giganteus KrΦyer, 1863 had a positive correlation only between the host's total length and abundance andlor prevalence in C. hippos. Bucephalus varicus, Tergestia pectinata (Linton, 1905), C. carangis, and Pseudoterranovo sp. had a positive correlation between the host's total length and abundance and/or prevalence in C. latus. In C. hippos, the copepod Caligus robustus Bassett-Smith, 1898 had the highest values of prevalence and abundance in the female hosts. No parasite species showed influence of the host's sex on their prevalence and abundance in C. latus. The mean diversity and the parasite species richness of the parasite infracommunities of C. hippos and C. latus were not significantly different. Only the parasite species diversity of C. hippos was correlated with the host's total length; in both host species the parasite diversity did not showed differences in relation to the sex of the host. Only one pair of ectoparasite species, A. hippos - P. mirabilis, showed significant positive co-occurrence and covariation in the parasite infracommunities of C. hippos. Two endoparasite species, B. varicus - Parahemiurus merus (Linton, 1910), showed negative co-occurrence and positive covariation; and the pair B. varicus - Pseudoterranova sp. had positive co-occurrence and covariation in the infracommunities of C. latus. The values of qualitative and quantitative simila rity coefficients between the parasite communities of C. hippos and C. latus were 55.5 and 30.4, respectively. The parasite communities of C. hippos and C. latus were defined as closest to isolationist type because there are few evidences of interspecific associations or covariations. Additional parasitological studies on other species of carangid fishes from the South American Atlantic Ocean are needed to evaluate the structure of carangid parasite communities in the Neotropical region.

Interactions between species and the structure of helminth communities.

The role of interspecific interactions in the structure of gastrointestinal helminth communities has been at the core of most research in parasite community ecology, yet there is no consensus regarding their general importance. There have been two different approaches to the study of species interactions in helminths. The first one consists of measuring the responses of helminth species in concomitant infections, preferably in laboratory experiments. Any change in numbers of parasite individuals or in their use of niche space, compared with what is observed in single infections, provides solid evidence that the species are interacting. The second approach can only provide indirect, circumstantial evidence. It consists in contrasting observed patterns either in the distribution of species richness of infracommunities from wild hosts, in their species composition, or in pairwise associations between helminth species among infracommunities, with the random patterns predicted by appropriate null models. In many cases, observed patterns do not depart from predicted ones; when they do, alternative explanations are usually as plausible as invoking the effect of interactions among helminth species. The present evidence suggests that the role of species interactions in helminth community structure is often negligible, but that it must always be evaluated on a case-by-case basis.

Parasitofauna y alimentación de Notothenia c.f. angustata Hutton, 1875 (Pisces: Nototheniidae) en el intermareal de dos localidades del Golfo de Arauco, Chile

We studied the parasite fauna and food contents of 38 juvenile of Notothenia c.f. angustata specimens captured in the intertidal of Island Santa María and Maule, in the Arauco Gulf, Chile. Trophic habits of Notothenia c.f. angustata were not different between localities, which was mainly algae. A total 11 parasitic taxa among were found with the digenean Lecitasther macrocotyle, cestode larvae Tetraphyllidea and Diphyllidea and nematode Ascarophis sp. being the dominant taxa. The abundance of parasites was similar in the two localities, although the infracommunity richness was higher in fish from Maule. The most abundant parasite was L. macrocotyle in hosts from Isla Santa María, while those from Maule they were the Diphyllidea larvae and nematodes Ascarophis sp. The body length of the hosts was not a good predictor of the variations in abundance and richness at infracommunities, probably because of the early ontogenetic stage of fishes.

Helminth Communities in Audouin's Gulls, Larus audouinii from Chafarinas Islands (Western Mediterranean)

A survey of intestinal helminth communities of Audouin's gulls Larus audouinii, from their breeding colonies in Chafarinas Islands, western Mediterranean, Spain was conducted to determine the abundance and species diversity of intestinal parasites of these birds. The sample of 58 gulls harbored intestinal helminth infracommunities composed of species that are gull generalists, including the digeneans Cardiocephalus longicollis, Knipowitschiatrema nicolai, Condylocotyla pilodora, and Aporchis massiliensis, and the cestode Tetrabothrius cylindraceus. Two nematodes are waterfowl generalists (Cosmocephalus obvelatus and Paracuaria adunca), whereas the digenean Acanthotrema armata is an Audouin's gull specialist. The relative high values of species richness and diversity of the helminth infracommunities are comparable to those of other gulls (Larus philadelphia, Larus canus), probably reflecting the specialized, nonselective fish diet of L. audouinii.

A new index of interactivity in parasite communities

A new index of interactivity which allows objective evaluation and comparison of interactivity in communities between different host species is presented. The index is derived from the equations for species-accumulation curves generated using non-linear regression (with the Levenberg–Marquardt algorithm) of sample infracommunity richness data. It is advantageous in that it requires only presence/absence data to calculate, is applicable to all parasite taxa (including asexual species), is largely independent of sample size and allows objective comparison of parasite communities while correcting for differences in total richness. Iterative randomisation of infracommunity richness values to generate a mean value for the index avoids spurious results which may be generated by heterogeneity in infracommunity richness and the variation this produces in the non-linear regression results.

Composition and diversity of helminth communities in eels anguilla anguilla in the river tiber: long-term changes and comparison with insular europe

Most studies of helminth communities in the European eel Anguilla anguilla have been undertaken in the British Isles, and there are very few analyses of community composition and structure from continental Europe. To fill this gap and test the hypothesis that helminth communities in freshwater eels in the British Isles are not typical of those of continental Europe, helminth communities of eels in the River Tiber below Rome were analysed by season using data collected in 1980 and new data from 1996. The intestinal helminth communities in the Tiber eels were species poor and characterized by low diversity. Most eels harboured one or no parasite species and communities were heavily dominated by the acanthocephalan Acanthocephalus clavula. Intestinal helminth infracommunity richness and diversity did not differ between seasons within a year or between the same seasons in 1980 and 1996, although some changes in composition were apparent. Intestinal infracommunities from Tiber eels were very similar in characteristics to those analysed from the British Isles, and their temporal changes also showed close similarities to those reported from rivers in the UK. It seems likely therefore that conclusions derived from British studies can be applied to helminth communities of eels on the continent.

Intestinal helminth communities in the green lizard, lacerta viridis, from bulgaria

A data set comprising individual host/parasite lists from 100 Lacerta viridis (Reptilia: Lacertidae) belonging to four isolated populations in Bulgaria was studied. A total of seven helminth species was recovered (Leptophallus nigrovenosus, Plagiorchis molini, Oswaldocruzia filiformis, Spauligodon extenuatus, Skrjabinelazia hoffmanni, Physaloptera clausa and Mesocestoides sp.). Lacerta viridis is a new host record for the first five of these species. Communities of intestinal helminths of L. viridis consist of a few species which resulted in a low species richness, abundance and diversity of infracommunities, which exhibit substantial homogeneity among the four samples. A similar pattern of dominance of two nematode species leading to a relatively high community similarity at both infra- and component community levels was observed. While intestinal helminth communities in lizards from 'marginal' habitats were dominated by the host generalist, O. filiformis, those in hosts from 'typical' habitats were dominated by the lizard specialist S. extenuatus. The results indicate that the characteristics of the host's habitat are important in determining the composition rather than structure of intestinal helminth communities in L. viridis.

The number of niches in intestinal helminth communities of Anguilla anguilla: are there enough spaces for parasites?

SUMMARYThe suggestion that there may be a limit to the number of niches available to helminth species in the intestine of Anguilla anguilla was investigated by examining the frequency distributions of the number of helminth species per eel and the relationships between maximum and mean infracommunity richness and component community richness in 1 locality over 17 years and in 64 localities throughout Ireland and England. The maximum number of species per eel did not exceed 4 in the 1 locality, or 3 in the 64 localities. In both the single and the several localities, the relationship between maximum and mean infracommunity richness and component community richness was curvilinear and best described by a power or polynomial function. This was interpreted to mean that infracommunity richness became increasingly independent of component community richness, and that infracommunities were saturated at values well below the higher level of helminth richness immediately available for colonization i.e. component community richness. It is argued that these findings cannot be explained by supply-side ecology, pool exhaustion or transmission rates, but only by infracommunity processes acting to impose a fixed limit to the number of species in an infracommunity. Most infracommunities are species poor, and the limiting factors will only operate as species richness rises to determine a maximum. Acceptance of a limit to the number of niches available also resolves the apparent inconsistency between the occurrence and importance of interspecific competition and the nature of isolationist communities.

Richness, nestedness, and randomness in parasite infracommunity structure.

Within a host population, parasite infracommunities vary in both richness and species composition. If interspecific interactions among parasites are important in shaping infracommunities, the structure of these assemblages is expected to differ from the one predicted by null models, i.e. from the one that would result from chance alone. Using data from the literature, I tested for discrepancies between observed and random patterns in the richness and composition of gastrointestinal helminth infracommunities of birds and mammals. Both the Poisson distribution and a more sophisticated null model, derived from prevalence of the different parasite species in the host population, usually provided a good fit to the observed distributions of infracommunity richness among hosts. This suggests that parasite species do not co-occur more or less frequently than expected by chance. In mammals, the co-occurrence of all available parasite species in the same host individual, or maximum potential infracommunity richness, was less likely to be observed when several parasite species were available; this is also a phenomenon expected from the random assembly of parasite species. Finally, there was no evidence for a nested subset pattern among parasite species in a host population: rate species were distributed independently of common ones. The overall picture emerging from these results is one in which parasite assemblages are more likely to be the product of random events than of predictable and repeatable processes.

The role of positive and negative interspecific associations in the organization of communities of intestinal helminths of bats

Twelve populations of bats were examined to determine the extent of interspecific associations in determining the species richness of intestinal helminth infracommunities. The pool of helminth species which was available to individual bats ranged from 2 to 21. The 'summed binomial' distribution was determined to underlie the host frequency distribution of the number of helminth species per host. Overall covariation in occurrences of species in replicated communities can be detected by testing for the equality of the observed variance of the host frequency distribution to the variance expected when species are allocated to hosts at random. Where statistically significant the covariance was indicative of a majority of positive rather than negative interspecific associations. As the mean number of species per host in a host population increases not only does the number of positive associations increase but so does the proportion of species pairs which exhibit positive associations. Although there is an increase in the proportion of species pairs which exhibit positive associations as the number of species increases, the magnitude of the associations (as indicated by the mean positive or the mean negative pairwise covariances) does not. Therefore, we concluded that positive interactions are more common than negative interactions in determining the species richness of helminth infracommunities of bats. Further, positive associations become even more important as the community becomes more complex. However, the increased importance is derived from the number rather than the strength of the associations.