Juan T. Timi

The importance of the compound community on the parasite infracommunity structure in a small benthic fish

The extent to which the structure of parasite infracommunities and component communities is determined by the composition of the compound community was assessed by determining the importance of unspecific larval parasites relative to the other guilds (ectoparasites and adult endoparasites). This was analyzed under the hypothesis that the infracommunities harbored by any fish species in coastal waters of the northern Argentine sea will be dominated by unspecific larval stages, which also will be the determinants of the infracommunity structure. These predictions were tested in the Atlantic sea robin, Prionotus nudigula. A total of 1,570 metazoans belonging to 11 species were found in the overall sample (total prevalenceu2009=u200998%). Larval endoparasites, especially Corynosoma australe and Grillotia sp., were the best represented species, with a deep influence on the infracommunity structure, accounting for the highest proportion of individuals, dominating about 60% of the infracommunities, greatly determining all infracommunity descriptors, and producing marked changes in the similarity among infracommunities. Given the abundance and broad distribution of unspecific larval parasites in the compound community, infracommunities can be considered as subsets of the species available regionally. They are obtained by passive sampling of infective stages as fish feed, and lead to predictable assemblages, with a non-random composition and structure modeled mainly by ecological filters.

Is there a trade-off between fecundity and egg volume in the parasitic copepod Lernanthropus cynoscicola?

Negative relationships between egg number and egg size are commonly seen in many animal taxa, supporting the idea that there is a trade-off between egg number and egg size resulting from the allocation of resources to either one or the other. In parasites, where availability of resources is presumably very high, there may be fewer energetic constraints acting on allocation strategies, and the trade-off may be weakened. We investigated the association between egg number and egg volume among females of the copepod Lernanthropus cynoscicola Timi and Etchegoin, 1996, parasitic on the fish Cynoscion guatucupa (Cuvier). Both egg number and egg volume were strongly correlated with female body size. After controlling for the effects of body size, we found absolutely no evidence of a trade-off, i.e. no negative relationship, between egg number and egg volume. For a given body length, females that produce many eggs do not tend to produce relatively small eggs, and vice versa. In contrast, under conditions in which resources are plentiful, large females produce large quantities of high-quality eggs, and have a marked fitness advantage over small females.

Causes of inter-individual variation in reproductive strategies of the parasitic nematode Graphidioides subterraneus

Several factors capable of affecting the amount of resources available to an individual parasite, such as the number of other parasites in the host or host quality, may cause variability in reproductive success among parasites. Variation in egg output and mean egg volume was investigated among adult females of the nematode Graphidioides subterraneus, parasitic in the herbivorous subterranean rodent Ctenomys talarum (Octodontidae). Female nematode body size correlated strongly with the number of eggs produced. However, neither host body mass nor the number of other nematodes per host had any influence on the number or volume of eggs produced by the parasites. There was also no evidence for a trade-off between the number of eggs produced and mean egg volume among female nematodes. All these results suggest that resource supply to individual worms is not limited by host size or by the number of conspecific parasites vying for the same resources, despite the 30-fold variation in intensity of infection and the twofold variation in host body mass observed in the present study. Instead, resource availability does not appear to constrain reproduction in G. subterraneus, with its host providing a stable, predictable environment.

Parasites of a marine benthic fish in the Southwestern Atlantic: searching for geographical recurrent patterns of community structure

Parasite communities of Raneya brasiliensis are described and its parasites used as biological tags to discriminate its populations. Fish were caught in two zones of the Argentine Sea: one sample from San Jorge Gulf (Patagonian Region) and three samples from off the coast of Buenos Aires (Bonaerense Region). A total of 183 fish were examined for parasites and 11 species were found. Host body size and its ecology are pointed out as drivers of the paucity of taxa found. Multivariate similarity analyses allowed the identification of three stocks: one in the San Jorge Gulf, and two other in the Bonaerense Region. The parasite species that contributed most to the separation of the samples were generally those identified as biological markers in previous studies in the area. Patterns of distance decay in similarity among communities in R. brasiliensis were found; with dissimilarity values between distant localities being higher than between close ones. Whereas the composition and structure of parasite assemblages in Bonaerense waters reflect those of other fish species in this region, being mainly determined by the composition of the compound community, no repeatable patterns were found in the composition of parasites assemblages when R. brasiliensis was compared with other hosts species in Patagonia.

A new species of Hysterothylacium (Ascaridoidea, Anisakidae) parasitic in Zenopsis conchifer (Zeiformes, Zeidae) from Argentinean waters

A new species of parasitic nematode, Hysterothylacium spirale sp. nov. (Ascaridoidea, Anisakidae), is described based on specimens collected from the intestine and pyloric caeca of the silvery john dory Zenopsis conchifer (Lowe) (Zeiformes, Zeidae), from the Argentinean Shelf (35°05′–40°46′S, 53°03′–58°07′W). Among the 66 valid species described so far in the genus, the new species most closely resembles H. zenis (Baylis, 1929). Both species, apparently specific for fishes of the family Zeidae, share the shape of the dorsal lip, the long expanded lateral alae originating from subventral interlabia and the ornamentation of the tail tip, as well as general morphometry. The combination of these shared features distinguishes both species from all congeners so far known. However, the new species is distinguishable from H. zenis by having shorter interlabia, and consequently the lateral alae originating more posteriorly, shorter spicules, a smaller number of postcloacal papillae and the presence of two pairs of double postcloacal papillae.

Parasites of Urophycis brasiliensis (Gadiformes: Phycidae) as indicators of marine ecoregions in coastal areas of the South American Atlantic

The potential value of parasites as ecosystem markers was tested by analyzing the metazoan assemblages of Urophycis brasiliensis caught in four locations distributed in three ecoregions of the Warm Temperate Southwestern Atlantic. A total of 5,001 metazoan parasites belonging to 33 species were found. The identified parasites varied across locations in terms of presence, prevalence, and abundance, and their multivariate analyses resulted in clear similarity patterns. No differences were observed between two locations of the same ecoregion, whereas an evident separation of samples was observed across ecoregions in support of the existing hypotheses regarding the ecoregional division of the southwestern Atlantic. We proposed that parasite assemblages, which are composed of several metazoan phyla, are potentially useful as ecosystem indicators. This suggestion is derived from the combined evidence of the evolutionary history and biogeography of multiple lineages, which is expected to be more efficient in capturing recurrent patterns in overall biodiversity than individual lineages. Furthermore, as many parasites have complex life cycles, their distribution patterns are dependent not only on environmental conditions but also on the distribution and population density of all hosts involved in their life cycles, adding further sources of distributional variability that act synergistically to define robust geographical patterns. The selection of long-lived parasites and their comparative analysis provided evidence supporting the existence of three different stocks in the four sampled areas. The best parasite tags were those with low specificity in fish hosts, constituting promising biological tags for the stock discrimination of other fish species in the region.

Parasite assemblages of Nemadactylus bergi (Pisces: Latridae): the role of larval stages in the short-scale predictability

The short-scale temporal repeatability in the structure and composition of parasite communities of Nemadactylus bergi were analyzed by comparing population and infracommunity descriptors in five samples caught off Mar del Plata, Argentina (38º 27′ S, 57º 90′ W) at intervals of 20xa0days. This is the first study aiming to detect relevant local or short-term processes in an area where larval endohelminths dominate the parasite assemblages and are expected to provide predictability to the communities they belong. The parasite fauna of this host species was composed by 18 species, 16 of them being endoparasites, among which larval stages accounted for most of both the number of parasite individuals found and the highest percentages of average similarity among infracommunities. The structure of parasite communities of N. bergi was, as predicted, repeatable across samples at short spatial and temporal scales and, as expected, this predictability was mainly provided by larval stages, namely Corynosoma australe and Grillotia carvajalregorum. These results imply that a single sample of N. bergi from this locality will be enough to catch the structure and intrinsic variability of their component communities in further studies aiming to compare parasite assemblages at larger spatial scales. These studies should, however, take into account the heterogeneity in the size of fish among samples, which proved to be an important confounding factor in comparisons among samples by affecting their similarity.

A new species of Dichelyne (Nematoda, Cucullanidae) parasitizing sciaenid fishes from off the South American Atlantic coast

A new nematode species Dichelyne (Cucullanellus) sciaenidicola sp. nov. is described based on specimens collected from the Whitemouth croaker Micropogonias furnieri (Desmarest) and the Argentine croaker Umbrina canosai Berg, from coastal waters of Argentina and Brazil. These nematodes were firstly identified as D. (C.) elongatus (Törnquist, 1931), a commonly reported species from M. furnieri in South American Atlantic waters. However, other species of Dichelyne have so far been reported from this host in the same area, namely D. (C.) rodriguesi (Pinto, Fábio et Noronha, 1970), D. (C.) amaruincai (Freitas, Vicente et Ibañez, 1969) and D. (Dichelyne) micropogonii Pereira et Costa, 1996. A careful re-examination of these parasites, as well as of type specimens of all species reported from M. furnieri, revealed that these nematodes represented a new species. The new species is distinguished from most of its congeners by having papillae 5–7 and 9 forming a subventral line close to cloaca, this feature is shared with other 6 species [D. (C.) dichelyneformis (Szidat, 1950), D. (C.) fraseri (Baylis, 1929), D. (C.) abbreviatus (Rudolphi, 1819), D. (C.) adriaticus (Törnquist, 1931), D. (C.) minutus (Rudolphi, 1819) and D. (C.) mariajuliae Alarcos, Timi, Etchegoin et Sardella, 2006)], which are readily distinguished by their body size, spicules length, distribution patterns of other papillae and position of the excretory pore and deirids. Also, D. (C.) elongatus from Umbrina canariensis (Valenciennes) from West Africa is established as a new species Dichelyne (Cucullanellus) yvonnecampanae sp. nov.; D. (C.) amaruincai from Pacific waters is considered as a valid species, D. (D.) micropogonii is regarded as species inquirendae and D. (C.) rodriguesi is identified as Cucullanus sp.

Strongyloides myopotami in ctenomyid rodents: transition from semi-aquatic to subterranean life cycle.

Strongyloides myopotami, a parasite of Myocastor coypus (nutria or coypu), was found during an extensive parasitological survey carried out on parasitic helminths of 5 species of subterranean rodents (tuco-tucos) belonging to the genus Ctenomys from Argentina and Uruguay. Strongyloides myopotami became known by causing “marsh itch” (also called “nutria itch” or “swimmer’s itch”), a severe rash caused by larvae that enter the skin in humans, and it is recognised as a zoonosis for people handling nutria fur. In the present study S. myopotami was found in 2 of the 5 examined species of Ctenomys (C. talarum from Argentina and C. pearsoni from Uruguay), both inhabiting the vicinity of water courses. Population descriptors of S. myopotami in C. talarum showed that a population of this parasite is well established in this rodent. The development of infective filariform larvae from eggs in the faeces of C. talarum and the prevalence of gravid parasitic females in this host can be considered as evidence of the establishment of a population of S. myopotami independent of the source population parasitizing M. coypus. Therefore, the presence of S. myopotami in these species of tuco-tucos indicates a change from a semi-aquatic to subterranean life cycle. Evidence that tuco-tucos are reservoirs for these nematodes and therefore may be a risk to human health in the areas studied is provided.

Digenetic trematodes of the Brazilian flathead, Percophis brasiliensis Quoy et Gaimard, 1825 (Percophidae, Perciformes), from Argentinean and Uruguayan waters

Based on the examination of 234 specimens of the Brazilian flathead, Percophis brasiliensis (Percophidae), caught in the Argentinean and Uruguayan Seas, the list of digenean species parasitizing P. brasiliensis is increased from 6 to 9, including the specific identification of two species previously reported at the generic level. The three news digenean records for P. brasiliensis are: Elytrophalloides oatesi, Parahemiurus merus and Aponurus laguncula, while that Ectenurus virgulus and Lecithocladium cristatum were identified to specific level. These reports showed the highest diversity of digeneans registered in fishes from the study region. The diversity of the digenean fauna of P. brasiliensis could be a consequence of the generalist food habits of this fish.