Linking species abundance distributions and body size in monogenean communities

Patterns in parasite diversity and interactions with anurans from the Atlantic Forest

Knowledge of parasite-host interactions is essential for understanding factors associated with the ecology and evolution of both groups. Some aspects, such as host size and phylogeny, as well as parasite specificity, are significant predictors that help unveil the parasite-host relationship. Thus, the goals of this study were: (1) to describe parasite diversity in regions of the Atlantic Forest; (2) to analyze which host characteristics can influence parasite richness of anuran's parasite component community; and (3) to investigate if the prevalence of parasite infection is related to specificity metrics (ecological and phylogenetic), number of infected hosts and parasite's abundance. We identified 49 parasite taxa, classified into three phyla: Nematoda, Acanthocephala, and Platyhelminthes. Supporting the existing literature, our findings corroborate the positive relationship between host size and parasite richness, further emphasizing the significance of this predictor. Parasite prevalence in the host community is related to the number of infected host species and parasite abundance, but not to phylogenetic and ecological specificity indices. This shows that parasite prevalence is strongly associated with infection opportunity, host sampling effort, and high parasite abundance.

Geographic range, distribution patterns and interactions of Monogenea Van Beneden 1858, with species of native host freshwater fishes from Brazil

This paper investigated information on monogenean species using 312 scientific papers, to search for infection and geographic distribution patterns in native freshwater fish from Brazil. We used 1,698 samples of 296 fish species of 28 families distributed into Characiformes, Siluriformes, Cichliformes, Gymnotiformes, Perciformes, Mugiliformes, Osteoglossiformes and Clupeiformes, in addition to four hybrid fish. Among the hosts of the different orders and families, the greatest numbers of parasite-host associations were found for species of the families Serrasalmidae, Characidae, Loricariidae, Curimatidae and Anostomidae. The 578 species of monogeneans used in parasite-host interactions were distributed in 86 genera of six five families (Dactylogyridae, Gyrodactylidae, Diplectanidae, Microcotylidae, Ancylodiscoididae and Ancyrocephalidae), but with great predominance of Dactylogyridae species. There was variation in prevalence, intensity and abundance levels of monogeneans species among host fish species, as well as in infection sites that occurred predominantly in external organs. Positive correlations of prevalence, intensity and abundance with body length of hosts were observed. There was geographic distribution pattern of monogeneans limited mostly to two hydrographic basins those being the Amazon River and Paraná River. Just approximately 6% of potential monogeneans have been explored thus far, showing a clear need for further studies on this interesting group of parasites.

Phylogeny, species delimitation, and ecological and morphological diversity of Characithecium (Monogenoidea: Dactylogyridae)

Characithecium (Monogenoidea, Dactylogyridae) is a genus containing nine species that live on the gills of a characid clade containing genera Astyanax, Andromakhe, Psalidodon and Oligosarcus (Characiformes, Characidae) in South and Central America. Earlier studies suggest a tight coevolutionary history between these parasites and their hosts mainly due to the phylogenetic proximity between these genera of fish. Hence, this study explores phylogenetic relationships, species limits and extrinsic factors (geography and ecology) explaining parasite prevalence. To understand the evolutionary history of the genus, we constructed a time-calibrated phylogenetic hypothesis, which includes eight of the nine known species of Characithecium sampled from a broad spectrum of host species. The phylogeny supports the monophyly of Characithecium, with its most recent common ancestor dating from the Miocene. Using generalized mixed-yule coalescent and Bayesian Poisson tree process methods, species delimitation analyses suggested fewer species than the proposed delimitation based on morphology alone, recovering four and six entities, respectively. The results indicate that species of Characithecium have wider geographical and host distribution and higher prevalence on Oligosarcus species compared to Astyanax and Psalidodon. Correlation between parasite prevalence and biotic and abiotic traits, based on generalized linear models, indicates that the frequency of occurrence of different species of Characithecium is associated with distinct factors, such as host genus, high altitudes, rivers and streams, and different ecoregions. Our results suggest that species of Characithecium are highly opportunistic, exploring resources in different manner as our data reveal the ability of these parasites to explore a diverse environment of variable biotic (e.g. hosts) and abiotic features.

The 2015-2016 El Niño increased infection parameters of copepods on Eastern Tropical Pacific dolphinfish populations

The oceanographic conditions of the Pacific Ocean are largely modified by El Niño (EN), affecting several ecological processes. Parasites and other marine organisms respond to environmental variation, but the influence of the EN cycle on the seasonal variation of parasitic copepods has not been yet evaluated. We analysed the relation between infection parameters (prevalence and mean intensity) of the widespread parasitic copepods Caligus bonito and Charopinopsis quaternia in the dolphinfish Coryphaena hippurus and oceanography during the strong 2015–16 EN. Fish were collected from capture fisheries on the Ecuadorian coast (Tropical Eastern Pacific) over a 2-year period. Variations of sea surface temperature (SST), salinity, chlorophyll a (Chl-a), Oceanic Niño Index (ONI), total host length (TL) and monthly infection parameters of both copepod species were analysed using time series and cross-correlations. We used the generalised additive models for determine the relationship between environmental variables and infection parameters. The total body length of the ovigerous females and the length of the eggs of C. bonito were measured in both periods. Infection parameters of both C. bonito and Ch. quaternia showed seasonal and annual patterns associated with the variation of environmental variables examined (SST, salinity, Chl-a and ONI 1+2). Infection parameters of both copepod species were significantly correlated with ONI 1+2, SST, TL and Chl-a throughout the GAMLSS model, and the explained deviance contribution ranged from 16%-36%. Our results suggest than an anomaly higher than +0.5°C triggers a risen in infection parameters of both parasitic copepods. This risen could be related to increases in egg length, female numbers and the total length of the ovigerous females in EN period. This study provides the first evidence showing that tropical parasitic copepods are sensitive to the influence of EN event, especially from SST variations. The observed behaviour of parasitic copepods likely affects the host populations and structure of the marine ecosystem at different scales.

Body size and ecological traits in fleas parasitic on small mammals in the Palearctic: larger species attain higher abundance

We studied the relationships between body size and (a) abundance and (b) host specificity in fleas parasitic on small mammals (rodents and shrews) in the Palearctic taking into account the confounding effect of phylogeny. We tested these relationships both across 127 flea species and within separate phylogenetic clades, predicting higher abundance and lower host specificity (in terms of the number or diversity of hosts used by a flea) in smaller species. We also tested for the relationships between body size and abundance separately for species that spend most of their lives on a host's body (the "body" fleas) and species that spend most of their lives in a host's burrow or nest (the "nest" fleas). A significant phylogenetic signal in body size was detected across all fleas, as well as in five of six separate clades. Across all fleas and in majority of phylogenetic clades, mean abundance significantly increased with an increase in body size. The same pattern was found for both the "body" and the "nest" fleas, although the slope of the relationship appeared to be steeper in the former than in the latter. Neither measure of host specificity demonstrated a significant correlation with body size regardless of the subset of flea species analysed. We explain higher abundance attained by larger flea species by higher fecundity and/or competitive advantage upon smaller species at larval stage. We conclude that the macroecological patterns reported to date in parasites are far from being universal.

Seasonal variation in metazoan parasites of Trichiurus lepturus (Perciformes: Trichiuridae) of Rio de Janeiro, Brazil

This work aimed to study the temporal variation of metazoan parasites of Trichiurus lepturus from the coastal zone of Rio de Janeiro, Brazil. Between July 2006 and June 2007, there were four seasonal quarterly samples of 30 specimens of T. lepturus. In addition to a group composed of anisakid larvae, we collected a total of 14 species of metazoan parasites: five digenean; five monogenean, two cestode larvae, one acanthocephalan larvae; and one copepod. With the exception of Lecithochirium microstomum and Lecithochirium sp., all species showed peaks of prevalence and abundance especially those fishes collected in summer, which may indicate a seasonal variation of these parasites in T. lepturus from the coast of Rio de Janeiro.

Four species of Pseudorhabdosynochus (Monogenea: Diplectanidae) from the camouflage grouper Epinephelus polyphekadion (Perciformes: Serranidae) off New Caledonia

Gill diplectanid monogeneans from the camouflage grouper Epinephelus polyphekadion (Bleeker) collected in the coral reef lagoon of New Caledonia, South Pacific, comprise four species. Very few monogeneans were found in most fish examined. Pseudorhabdosynochus dionysos n. sp. has a sclerotised vagina with a robust trumpet, a robust primary canal and two chambers of similar size; it is close to P. bacchus Sigura, Chauvet & Justine, 2007. P. viscosus n. sp. has a sclerotised vagina with a robust trumpet, long primary canal with an extremely thin wall and two small chambers, and a male quadriloculate organ with a characteristic thickening at the extremity of its cone. P. crassus n. sp., the most abundant species, has a sclerotised vagina with a thin-walled trumpet, thin-walled primary canal which is always coiled anteriorly and two small chambers. P. huitoe Justine, 2007, P. manifestus Justine & Sigura, 2007 and P. crassus have very similar sclerotised vaginae; however, species of this 'huitoe complex' can be distinguished by measurements of the haptoral hard parts. A few diplectanid specimens found in a single specimen of E. polyphekadion were attributed to P. huitoe, a species originally described from E. maculatus (Bloch) and also rarely found in E. cyanopodus Richardson in New Caledonia; specimens from these three fish species are morphologically indistinguishable.

An annotated list of parasites (Isopoda, Copepoda, Monogenea, Digenea, Cestoda and Nematoda) collected in groupers (Serranidae, Epinephelinae) in New Caledonia emphasizes parasite biodiversity in coral reef fish

Abstract: Over a 7-year period, parasites have been collected from 28 species of groupers (Serranidae, Epinephelinae) in the waters off New Caledonia. Host-parasite and parasite-host lists are provided, with a total of 337 host-parasite combinations, including 146 parasite identifications at the species level. Results are included for isopods (5 species), copepods (19), monogeneans (56), digeneans (28), cestodes (12), and nematodes (12). When results are restricted to those 14 fish species for which more than five specimens were examined and to parasites identified at the species level, 109 host-parasite combinations were recorded, with 63 different species, of which monogeneans account for half (32 species), and an average of 4.5 parasite species per fish species. Digenean records were compared for 16 fish species shared with the study of Cribb et al. (2002); based on a total of 90 parasite records identified at the species level, New Caledonia has 17 new records and only seven species were already known from other locations. We hypothesize that the present results represent only a small part of the actual biodiversity, and we predict a biodiversity of 10 different parasite species and 30 host-parasite combinations per serranid. A comparison with a study on Heron Island (Queensland, Australia) by Lester and Sewell (1989) was attempted: of the four species of fish in common and in a total of 91 host-parasite combinations, only six parasites identified at the species level were shared. This suggests strongly that insufficient sampling impairs proper biogeographical or ecological comparisons. Probably only 3% of the parasite species of coral reef fish are already known in New Caledonia.

Two new species of Pseudorhabdosynochus Yamaguti, 1958 (Monogenea: Diplectanidae) from the deep-sea grouper Epinephelus morrhua (Val.) (Perciformes: Serranidae) off New Caledonia

Three species of monogeneans were collected from Epinephelus morrhua, a deep-sea grouper from the external slope of the coral reef, off New Caledonia, South Pacific, and are the first parasites recorded from this fish species. Pseudorhabdosynochus morrhua n. sp. is characterised by: a sclerotised vagina with small sclerotised chambers and a short secondary canal; squamodiscs with central rows of rodlets which form closed ovals; and a scaly tegument. P. variabilis n. sp. has: a male quadriloculate organ with a characteristic structure; a sclerotised vagina in which the primary canal, secondary canal and accessory structure are very long and the different parts have various arrangements in different specimens; its squamodiscs have central rows of rodlets which form closed circles; and a smooth tegument. A prominent vaginal structure, comparable to that of P. variabilis, has been found only in P. dolicocolpos Neifar & Euzet, 2007, but the species can be distinguished by details of the vagina and other structures. A species of Haliotrema Johnson & Tiegs, 1922 (Ancyrocephalidae) is reported but not described. Specimens of each of the three species were present in similar numbers.

Species abundance distributions and numerical dominance in gastrointestinal helminth communities of fish hosts

The abundances of different species in a parasite community are never similar: there is typically one or a few numerically dominant species and many species with low abundance. Here, we determine whether basic features of parasite communities are associated with strong dominance by one or a few species, among 39 component communities of gastrointestinal helminths in marine fishes from Brazil. First, we tested whether the shape of the species abundance distribution in these communities fits that predicted by several theoretical models, using a goodness-of-fit procedure. Only the canonical lognormal model could be rejected for 5 out of 39 communities; all other comparisons of observed and predicted abundance distributions showed no significant differences, although this may be due to limited statistical power. Second, we used the ratio between the abundance of the most abundant species and either the second or third most abundant species, as indices of dominance; these show, for instance, that the dominant species in a community is typically twice, but sometimes over ten times, as abundant as the next most abundant species. We found that these ratios were not influenced by either the community's species richness, the mean number of individual parasites per host, or the taxonomic identity of the dominant species. However, the abundance ratio between the first and third most abundant species in a community was significantly correlated with an independent index of species interactivity, based on the likelihood that the different parasite species in a component community co-occur in the same host individuals: the difference in abundance between the dominant and third most abundant species was greater in communities characterized by weak interactions. These findings suggest that strong interactions may lead to greater evenness in the abundance of species, and that numerical dominance is more likely to result from interspecific differences in recruitment rates.