Neotropical sisterhood: new species of Gyrodactylus von Nordmann, 1832 (Platyhelminthes: Monogenea) infecting Rhamdia guatemalensis and Rhamdia laticauda (Siluriformes: Heptapteridae) in Mexico.

We describe two new species of monogenean parasites of the genus Gyrodactylus von Nordmann, 1832 infecting Neotropical catfishes (Siluriformes) in southern Mexico: Gyrodactylus chulini n. sp. from 'chulín', Rhamdia laticauda collected in Oaxaca; and Gyrodactylus juili n. sp. from 'juil', Rhamdia guatemalensis from Veracruz. Morphologically, both new taxa are similar to Gyrodactylus spp. infecting catfishes (Siluriformes) in South America. Sequences of the internal transcribed spacers (ITS1-5.8S-ITS2 rDNA), the D2+D3 domains of the large ribosomal subunit (28S rDNA) and the cytochrome oxidase II (COII) gene were obtained from multiple parasite specimens and analysed using Bayesian inference. Phylogenetic hypotheses using ITS rDNA and COII genes, recovered two new Gyrodactylus species from Rhamdia spp.: G. chulini n. sp.; and Gyrodactylus juili n. sp., which are sister species to Gyrodactylus lilianae, a parasite of Rhamdia quelen in Brazil, and show strong affinity to other gyrodactytlids infecting Neotropical catfishes. This suggests that these new taxa, the first gyrodactylids described from Rhamdia spp. in Mexico, co-migrated to Tropical Middle America with their Neotropical catfish hosts, after the emergence of the Isthmus of Panama.

Morphological and molecular characterization of an enigmatic clinostomid trematode (Digenea: Clinostomidae) parasitic as metacercariae in the body cavity of freshwater fishes (Cichlidae) across Middle America.

The family Clinostomidae Lühe, 1901 contains 29 species allocated to seven genera, of which Clinostomum Leidy, 1856 is the most diverse, with c. 14 valid species. The diversity of Clinostomum has been assessed, combining morphological and molecular data. The genetic library for species in this genus has increased steadily, although there is little or no information for the other genera included in the family. Molecular phylogenetic relationships among the genera of clinostomids have not been assessed, and their classification is still based on morphological traits. The monotypic Ithyoclinostomum was described from a fish-eating bird in Brazil, and its metacercariae have been found in several locations in South America, parasitizing erythrinid freshwater fishes. We collected unusually large metacercariae from the body cavity of cichlids in several locations across Middle America. These metacercariae exhibited some resemblance to Ithyoclinostomum, although several differences prevent their inclusion in Ithyoclinostomum dimorphum, casting doubt on their taxonomic identification. The main objective of this paper was to characterize the metacercariae collected in cichlids using both morphology and molecular data from three molecular markers, and to assess the molecular phylogenetic relationships among the genera of Clinostomidae to establish the position of the newly generated sequences. We took a conservative position and tentatively placed the metacercariae as belonging to Ithyoclinostomum.

The use of mitochondrial and nuclear sequences in prospecting for cryptic species in Tabascotrema verai (Digenea: Cryptogonimidae), a parasite of Petenia splendida (Cichlidae) in Middle America.

In this study, we used sequences of mitochondrial and nuclear markers to test the hypothesis that Tabascotrema verai Lamothe-Argumedo and Pineda-López, 1990, a parasite of the cichlid Petenia splendida Günther, 1862 in Middle America, represents a single species, following a molecular prospecting approach. One-hundred and five individuals of T. verai were collected from the intestine of 43 specimens of P. splendida in eight localities of Mexico, Belize and Guatemala. A portion (n=53) of the collected specimens was used for molecular studies, whereas the remaining individuals were processed for morphological studies. Fifty-three partial sequences of the cytochrome c oxidase subunit I (cox1) gene were obtained. In addition, 36 sequences of the ITS (internal transcribed spacers 1, 5.8S rRNA gene, and ITS2) and of the 28S rRNA gene were generated from most of the specimens that showed nucleotide variation with the cox1 gene. A haplotype network obtained from cox1 sequences revealed three independent groups (haplogroups 1, 2, and 3). Independent phylogenetic analyses performed with maximum likelihood and Bayesian inference of cox1, ITS and the 28S rRNA gene recovered three genetically-distinct and reciprocally-monophyletic groups, corresponding with the 3 haplogroups obtained in the haplotype network. Values of genetic divergence between clades for cox1 sequences ranged between 8.3% and 11.9%, while for ITS and the 28S rRNA gene, these ranged from 0.08% to 1.2% and from 0.3% to 0.4%, respectively. Morphological observations, and measurements of 23 characters of 44 mounted individuals, showed that no morphological differences exist between individuals from the eight collecting sites, and that the ranges of most morphological traits overlap. Our results suggest that the digenean T. verai represents a complex of cryptic species; the haplotype network, phylogenetic analyses, and genetic differences, along with the morphological stasis recorded here support this notion. Finally, the three recovered lineages showed neither geographical association nor correlation with drainage basins.

Serotonin--a link between disgust and immunity?

Immune systems maintain the integrity of organisms by recognising and attacking foreign substances and/or pathogens. However, immune defences can only take place following direct contact with threats. Disgust can prevent infection before contact with potential pathogens: we propose that disgust is an evolved nervous response to a signal reliably co-occurring with infectious environmental disease threats, which motivates behaviour leading to the avoidance of infection. We hypothesize that disgust and immunity form a defensive continuum with overlaps: disgust acts prior to contact with the infectious agent and prevents it from getting into the body; emesis (vomiting) gets it out once inside the gastrointestinal tract, before penetration of the body boundaries; and immunity expels or kills infectious threats following penetration of the body proper. We further propose that serotonin (5-hydroxytryptamine, 5-HT) might be the link between disgust and immunity. 5-HT plays a central role in the induction of the emetic reflex and is possibly involved in the development of learned aversion; it is also a signal used by immune cells and modulates both innate and acquired immunity. We therefore propose 5-HT might mediate the interaction between these two defensive mechanisms.