Abstract: A new species of Characithecium, a genus of monogenean parasites of Neotropical characids, is described from specimens collected on the body surface and gills of Astyanax aff. fasciatus and Astyanax jacuhiensis from Lake Guaíba, State of Rio Grande do Sul, Brazil. The new species is similar to Characithecium costaricensis, but differs by having the haptor separated from the body by a long peduncle, and by having an accessory piece composed of 2 subunits in the male copulatory complex - 1 ventral pincer-shaped at the distal end, and 1 dorsal with an expanded rod-shaped proximal end and the distal end containing 3 elongated projections-, and the dorsal bar usually presenting a small median elevation in the anterior margin. This study increases the number of species of Characitecium to 7 and expands our knowledge on the diversity of monogenean parasites of characids.

Resumen: Una especie nueva de Characithecium, género que comprende especies de parásitos monogenéticos de carácidos neotropicales, se describe a partir de especímenes colectados de la superficie corporal y las branquias de los peces Astyanax aff. fasciatus y Astyanax jacuhiensis en el lago Guaíba, estado de Rio Grande do Sul, Brasil. Esta especie nueva es similar a Characithecium costaricensis pero se diferencia por tener el haptor separado del cuerpo por un pedúnculo largo y por presentar una estructura accesoria compuesta por 2 subunidades en el complejo copulador masculino -una ventral con forma de pinza en el extremo posterior y otra dorsal con forma de barra en el extremo anterior y posterior, la cual tiene 3 prolongaciones alargadas-. Además, la barra dorsal usualmente presenta una pequeña elevación media en el margen anterior. Este estudio aumenta el número de especies de Characitecium a 7 y mejora nuestro conocimiento sobre la diversidad de parásitos monogenéticos en carácidos.

Procamallanus (Spirocamallanus) hilarii parasitizes several fish species but only few studies on morphology and ecology have been published. In this study we describe the morphology of P. (S.) hilarii parasitizing Astyanax aff. fasciatus and Astyanax jacuhiensis , and compare ecological parameters of their populations. Seventy A. aff. fasciatus and 60 A. jacuhiensis individuals were captured in Lake Guaiba, Rio Grande do Sul State, Brazil, between March 2012 and December 2013. The specimens of P. (S.) hilarii presented an oval oral opening with 6 cuticular elevations and 2 groups of papillae (one internal and one external) in the anterior region of the body. Males have 8 pairs of sessile caudal papillae (4 pre-cloacal and 4 post-cloacal), spicules with distal bifurcation and lack caudal alae. The prevalence of P. (S.) hilarii was higher in A. aff. fasciatus (69%) than in A. jacuhiensis (18%), whereas there was no difference in mean intensity (respectively, 2 and 5) and mean abundance (respectively, 1.6 and 0.9) of infection between the 2 host species. We suggest that the consumption of copepods, intermediate hosts of P. (S.) hilarii , may explain this difference.

Procamallanus (Spirocamallanus) hilarii (P. (S.) hilarii) parasita varias especies de peces, pero son escasos los estudios publicados sobre su morfología y ecología. En este estudio describimos la morfología de P. (S.) hilarii que parasitan las mojarras Astyanax aff. fasciatus y A. jacuhiensis y comparamos diferentes parámetros ecológicos de sus poblaciones. Entre marzo de 2012 y diciembre de 2013, capturamos 70 individuos de Astyanax (A.) aff. fasciatus y 60 de A. jacuhiensis en el Lago Guaiba, estado de Rio Grande do Sul, Brazil. Los ejemplares de P. (S.) hilarii presentaron una abertura oral de forma oval con 6 elevaciones cuticulares y 2 grupos de papilas (una interna y otra externa) en la región anterior del cuerpo. Los machos presentaron 8 pares de papilas caudales sésiles (4 precloaca y 4 poscloaca), espículas con bifurcación distal y ausencia de ala caudal. La prevalencia de P. (S.) hilarii fue mayor en A. aff. fasciatus (69%) que en A. jacuhiensis (18%). Sin embargo, no existieron diferencias en la intensidad promedio (2 y 5 respectivamente) y la abundancia promedio (1.6 y 0.9 respectivamente) de infección entre las 2 especies hospederas. Sugerimos que el consumo de copépodos, hospederos intermediarios de P. (S.) hilarii , podría explicar esta diferencia.

Helminths with heteroxenous cycles provide clues for the trophic relationships of definitive hosts, representing important sources of information for assessing niche overlap between males and females of non-dimorphic species. We necropsied 151 rufous-bellied thrushes (Turdus rufiventris) captured in a metropolitan region in southern Brazil to analyze whether the structure of parasite communities is influenced by host sex or age. Most thrushes (93%) were parasitized by at least 1 species. The helminth community of Turdus rufiventris was composed of 15 species with prevalences from <1% to 60%. Although the prevalence of Conspicuum conspicuum, Microtetrameres pusilla and Aproctella stoddardi was higher in adults, Syngamus trachea was more prevalent in juveniles. Adults showed greater species richness of parasites than juveniles, probably as a consequence of an increase in the opportunities of infection with a larger set of parasites with aging. Adult males and females presented similar species richness of helminths and quite similar communities, allowing us to conclude that they prey upon the same invertebrates, including earthworms, snails, isopods, millipedes, cockroaches and grasshoppers. Therefore, trophic niche overlap between adult males and females is greater than between adults and juveniles.

Los helmintos que presentan ciclos heterogéneos proveen pistas importantes sobre las relaciones tróficas que mantienen con sus hospederos definitivos. Estas pistas son además importantes fuentes de información que permiten evaluar el sobrelapamiento de sus nichos cuando comparamos machos y hembras en especies no dimórficas. Así, se practicaron necropsias en 151 zorzales colorados (Turdus rufiventris) que fueron capturados en una región metropolitana al sureste de Brasil, a fin de analizar de qué manera la estructura de la comunidad de parásitos podría estar influenciada por la edad o sexo del hospedero. La mayoría de los zorzales (93%) fueron parasitados por al menos 1 especie. La comunidad de helmintos de Turdus rufiventris estuvo compuesta por 15 especies, con prevalencias entre 1% a 60%. Aunque la prevalencia de Conspicuum conspicuum, Microtetrameres pusilla y Aproctella stoddardi fue más alta en adultos, Syngamus trachea tuvo una mayor prevalencia en juveniles. Los adultos mostraron una mayor riqueza de parásitos que los juveniles. Probablemente, ésto sea consecuencia de una mayor posibilidad de infectarse conforme avanza la edad de los individuos; sin embargo, machos y hembras adultos presentaron una riqueza similar en la concentración de helmintos en comunidades semejantes. Esto podría apoyar a concluir que podrían estar alimentándose del mismo tipo de invertebrados como son: lombrices, caracoles, isópodos, ciempiés, cucarachas y saltamontes. Concluimos que la sobreposición del nicho trófico es mas clara entre machos y hembras adultos que entre los juveniles.

A introdução de espécies tem alterado a diversidade dos parasitos e seus hospedeiros em todo o mundo. No caso dos hospedeiros introduzidos, a idade da população parece ser um bom preditor da riqueza parasitária. A alteração do habitat é outra variável que pode ter impacto sobre as interações parasito-hospedeiro, pois afeta a disponibilidade de hospedeiros intermediários. O pardal (Passer domesticus (Linnaeus, 1758)) é um bom modelo para testar essas predições. Ele foi introduzido em várias partes do mundo e pode ser encontrado ao longo do gradiente urbano-rural. Um total de 160 pardais, provenientes de Porto Alegre, Rio Grande do Sul, Brasil, foram necropsiados, dos quais 19 % (30) estavam parasitados com pelo menos uma das cinco espécies de helmintos encontradas (Digenea: Tamerlania inopina Freitas, 1951 and Eumegacetes sp.; Eucestoda: Choanotaenia passerina (Fuhrmann, 1907) Fuhrmann, 1932; Nematoda: Dispharynx nasuta (Rudolphi, 1819) Stiles & Hassall, 1920 and Cardiofilaria pavlovskyi Strom, 1937). Não houve diferença entre machos adultos e fêmeas adultas e entre adultos e juvenis na prevalência e intensidade de infecção das espécies, na riqueza de parasitos e na diversidade das comunidades de helmintos. Também não houve diferença significativa no número de pardais infectados em cada estação e na riqueza de helmintos e abundância das espécies entre as paisagens rural e urbana. Somente a prevalência de C. passerina variou sazonalmente (p=0,0007). Uma redução no número de espécies de parasitos de P. domesticus desde a sua distribuição original (13) ao seu ponto de entrada no Brasil, a cidade do Rio de Janeiro (nove), até Porto Alegre (cinco), é compatível com a hipótese de que a idade da população hospedeira é um bom preditor da riqueza de parasitos.

Species introductions have altered host and parasite diversity throughout the world. In the case of introduced hosts, population age appears to be a good predictor of parasite richness. Habitat alteration is another variable that may impact host-parasite interactions by affecting the availability of intermediate hosts. The house sparrow (Passer domesticus (Linnaeus, 1758)) is a good model to test these predictions. It was introduced in several parts of the world and can be found across rural-urban gradients. A total of 160 house sparrows from Porto Alegre, state of Rio Grande do Sul, Brazil, were necropsied. Thirty house sparrows (19 %) were parasitized with at least one out of five helminth species (Digenea: Tamerlania inopina Freitas, 1951 and Eumegacetes sp.; Eucestoda: Choanotaenia passerina (Fuhrmann, 1907) Fuhrmann, 1932; Nematoda: Dispharynx nasuta (Rudolphi, 1819) Stiles & Hassall, 1920 and Cardiofilaria pavlovskyi Strom, 1937). Overall, there was no difference in prevalence and intensity of infection of any parasite species, parasite richness and community diversity between adult males and females and adults and juveniles. The number of infected sparrows among seasons, the richness of helminths and the abundance of species were also similar between rural and urban landscapes. Only the prevalence of C. passerina varied seasonally (p=0.0007). A decrease in the number of parasite species from the original range of P. domesticus (13) to its port of entrance in Brazil, the city of Rio de Janeiro (nine), to Porto Alegre (five) is compatible with the hypothesis that host population age is a good predictor of parasite richness.