Parasite communities of a fish assemblage from the intertidal rocky zone of central Chile: similarity and host specificity between temporal and resident fish

New Salinity Tolerant Species of Gyrodactylus (Platyhelminthes, Monogenea) on Intertidal and Supratidal Fish Species from the Chilean Coast

PURPOSE

The intertidal and supratidal coastal zone challenges the osmoregulatory capacity of aquatic inhabitants. Four new species of Gyrodactylus ectoparasites on two intertidal fishes from Chile are described based on molecular and morphological analyses.

METHODS

Monogeneans were found from two fish species, the clingfish Sicyases sanguineus Müller & Troschel, 1843 and the combtooth blenny Scartichthys viridis Valenciennes, 1836. The morphology was described by drawings, and minimal measurements. The parasites were barcoded via the sequencing of the ribosomal DNA over ITS1-5.8S-ITS2.

RESULTS

The air-breathing clingfish S. sanguineus carried Gyrodactylus amphibius sp. nov., hiding in the ventral sucker formed by the modified pectoral fins of the fish. The intertidal combtooth blenny S. viridis carried three other new species: Gyrodactylus scartichthi sp. nov., Gyrodactylus viridae sp. nov., and Gyrodactylus zietarae sp. nov.

CONCLUSION

The four new species were all phylogenetically related with the previously described G. chileani Ziętara et al. 2012 on triplefin Helcogrammoides chilensis Cancino, 1960 in the same habitat. Thus, the five Chilean Pacific Gyrodactylus species formed a statistically well-supported (100%) monophyletic clade together with three geographically distant species recorded in Europe. The Chilean Pacific parasites are not related to G. salinae and G. magadiensis, parasites described in extreme osmotic stress environments earlier.

Differential patterns of definitive host use by two fish acanthocephalans occurring in sympatry: Pomphorhynchus laevis and Pomphorhynchus tereticollis

Parasites with complex life-cycles and trophic transmission are expected to show low specificity towards final hosts. However, testing this hypothesis may be hampered by low taxonomic resolution, particularly in helminths. We investigated this issue using two intestinal fish parasites with similar life-cycles and occurring in sympatry, Pomphorhynchus laevis and Pomphorhynchus tereticollis (Acanthocephala). We used species-specific ITS1 length polymorphism to discriminate parasite species from 910 adult acanthocephalans collected in 174 individual hosts from 12 fish species. Both P. laevis and P. tereticollis exhibited restricted host range within the community of available fish host species, and transmission bias compared to their relative abundance in intermediate hosts. The two parasites also exhibited low niche overlap, primarily due to their contrasting use of bentho-pelagic (P. laevis) and benthic (P. tereticollis) fish. Furthermore, parasite prevalence in intermediate hosts appeared to increase with taxonomic specificity in definitive host use. Comparison of P. laevis and P. tereticollis adult size in the two main definitive hosts, barbel and chub, suggested lower compatibility towards the fish species with the lowest parasite abundance, in particular in P. laevis. The determinants of low niche overlap between these two sympatric acanthocephalan species, and the contribution of definitive host range diversity to parasite transmission success, are discussed.

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The fish acanthocephalans P. laevis and P. tereticollis show moderate specificity and low niche overlap.

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Transmission bias from shared intermediate hosts towards either benthic or bentho-pelagic fish is evidenced.

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Decreased taxonomic specificity towards fish hosts matches with lower prevalence in intermediate hosts.

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Lower worm size in the host with the lowest abundance calls for further investigation of compatibility filter.

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Low taxonomic resolution within some parasite species complex hinders accurate estimate of host use pattern.

Parasites of fish larvae: do they follow metabolic energetic laws?

Eumetazoan parasites in fish larvae normally exhibit large body sizes relative to their hosts. This observation raises a question about the potential effects that parasites might have on small fish. We indirectly evaluated this question using energetic metabolic laws based on body volume and the parasite densities. We compared the biovolume as well as the numeric and volumetric densities of parasites over the host body volume of larval and juvenile-adult fish and the average of these parasitological descriptors for castrator parasites and the parasites found in the fish studied here. We collected 5266 fish larvae using nearshore zooplankton sampling and 1556 juveniles and adult fish from intertidal rocky pools in central Chile. We considered only the parasitized hosts: 482 fish larvae and 629 juvenile-adult fish. We obtained 31 fish species; 14 species were in both plankton and intertidal zones. Fish larvae exhibited a significantly smaller biovolume but larger numeric and volumetric densities of parasites than juvenile-adult fish. Therefore, fish larvae showed a large proportion of parasite biovolume per unit of body host (cm(3)). However, the general scaling of parasitological descriptors and host body volume were similar between larvae and juvenile-adult fish. The ratio between the biovolume of parasites and the host body volume in fish larvae was similar to the proportion observed in castrator parasites. Furthermore, the ratios were different from those of juvenile-adult fish, which suggests that the presence of parasites implies a high energetic cost for fish larvae that would diminish the fitness of these small hosts.

The life cycle of Prosorhynchoides carvajali (Trematoda: Bucephalidae) involving species of bivalve and fish hosts in the intertidal zone of central Chile

We describe the life cycle of the bucephalid Prosorhynchoides carvajali from the intertidal rocky zone of central Chile. To elucidate the life cycle of this digenean, two mytilid bivalves, Semimytilus algosus and Perumytilus purpuratus, and ten intertidal fish species belonging to the families Blenniidae, Tripterygiidae, Labrisomidae, Kyphosidae and Gobiesocidae were analysed for natural infections. In addition, experimental infections of fish were undertaken and molecular analyses were performed of several developmental stages of the digeneans in various host species. Experimental infections of fish were made from infected mytilids to determine which fish species were suitable for the metacercarial stage of Prosorhynchoides. We also determined the abundance and prevalence of metacercariae in natural infections in fish and found that they were lower than in the experimental infections. A molecular analysis showed that sporocysts from S. algosus were identical to metacercariae from five fish species and P. carvajali adults. Sporocysts isolated from P. purpuratus were similar to metacercaria found in one fish species only (G. laevifrons) but were different from P. carvajali, with 1.9-2.0% genetic divergence. Therefore, the complete life cycle of P. carvajali consists of the mytilid species S. algosus as the first intermediate host, at least five intertidal fish species as second intermediate hosts (Scartichthys viridis, Auchenionchus microcirrhis, Hypsoblennius sordidus, Helcogrammoides chilensis and Gobiesox marmoratus), two carnivorous fish as definitive hosts (Auchenionchus microcirrhis and A. variolosus) and one occasional definitive host (Syciases sanguineus). This is the second description of a life cycle of a marine digenean from Chile.

Morphological and molecular analyses of larval trematodes in the intertidal bivalve Perumytilus purpuratus from central Chile

The bivalve Perumytilus purpuratus is a common species that is widely distributed throughout rocky intertidal zones in Chile. This bivalve is the first intermediate host for three trematode species: one bucephalid (an undetermined species) and two fellodistomids (Proctoeces lintoni and one undetermined species). A few studies based on morphological comparisons, experimental infection and molecular analyses have been performed to ascertain the taxon (at least at the family level) to which these trematodes belong; yet, there remains no clarification about the specific identity of these trematodes. Therefore, in this study, we compared the V4 region nucleotide sequences of the 18S rRNA of these three sporocyst species, classified as morphotypes, found in P. purpuratus and nine adult trematode species from intertidal fishes that are likely definitive hosts for these parasites. The sequences from two of the sporocyst morphotypes matched with adult trematodes from the intertidal fish: type 1 sporocyst was similar to Prosorhynchoides carvajali (Bucephalidae), with a mean genetic divergence of 0.78%, and type 2 sporocyst was similar to Proctoeces sp. (but not P. lintoni), with 0% genetic divergence. The third species (type 3 sporocyst) was classified to the family Fellodistomidae; however, the sequence from this species differed greatly from the three other fellodistomid species documented in the marine fish of Chile and from other fellodistomids in public databases. Moreover, this morphotype has a particular cercarial morphology that greatly differs from other fellodistomid species described thus far. Therefore, this intriguing trematode remains a mystery.

Host selection and niche differentiation in sucking lice (Insecta: Anoplura) among small mammals in southwestern China

Understanding factors that shape host selection has been a classic issue in ecology, evolutionary biology, and epidemiological investigation. During the survey from 2000 to 2009, a total of 11,216 individuals of small mammals were captured from Yunnan Province in southwestern China. The captured small mammalian hosts belong to five orders, ten families, 35 genera, and 65 species and from their body surface, 38,885 individuals of ectoparasitic sucking lice were collected, which represent five families, seven genera, and 31 species. Based on niche overlap of dominant sucking lice on their primary hosts, we used hierarchical cluster analysis to sort different sucking louse species' resource utilizations of similar kind into respective categories. Given λ<5, there are only two groups clustered, however, sucking louse species' resource utilization was sorted into eight respective categories at λ=15. The results revealed that most species of sucking lice usually had high host specificity and a certain species of sucking louse usually restricted to one or few small mammalian species as their dominant hosts. Correspondence analysis was used to visualize associations between parasitic sucking lice and their small mammalian hosts, which suggested three different patterns of host resource utilization: species specialists, genera generalists, and multiple selections. For example, Sathrax durus (Johnson) only parasitized on species of Tupaia belangeri (Wagner), Hoplopleura edentula (Fahredholz) predominatly on genus of Eothenomys, and Polyplax reclinata (Nitzsch) on Family of Soricidae. Our results demonstrate that sucking lice have high host specificity and this might be due to coevolution between sucking lice and their hosts.