Search

The neotropical fish genus Astyanax (Characidae) and its associated helminths migrated northward from South America following the Great American Biotic Interchange (GABI): ca. 150 Astyanax spp. are found throughout South and Central America, up to the Mexico-USA border. Most characids are distributed south of the Trans-Mexican Volcanic Belt (TMVB), which bisects the country and represents a major transition zone between the neotropical and nearctic realms. Here, we characterize parasites of the monogenean genus Gyrodactylus infecting Astyanax spp. in Mexico: Astyanax aeneus south of the TMBV, Astyanax mexicanus north of it. Based on morphological, phylogenetic (internal transcribed spacer (ITS) and cytochrome oxidase subunit II (cox 2)) and statistical analyses of morphometric data, we confirmed the validity of Gyrodactylus pakan and Gyrodactylus teken, and erected two new species, Gyrodactylus aphaa n. sp. and Gyrodactylus ricardoi n. sp. These four gyrodactylids are part of a complex of morphologically cryptic species, which are phylogenetically closely related to each other, and sister species to Gyrodactylus carolinae and Gyrodactylus heteracanthus, parasites of characins in Brazil. Four gyrodactylid lineages (G. pakan, G. ricardoi n. sp., G. teken, Gyrodactylus sp. A) are distributed north of the TMVB; G. pakan is also widely distributed south of the TMVB, together with G. aphaa n. sp. Based on the ITS phylogeny, Brazilian parasites form a sister clade to all Mexican gyrodactylids, whose derived clades are distributed in progressively more northerly latitudes in Mexico - the three most-derived species north of the TMVB. This would suggest that gyrodactylid species diverged gradually, presumably as their characid fish hosts colonized and adapted to new environments north of the TMVB., (Copyright © 2024 Australian Society for Parasitology. Published by Elsevier Ltd. All rights reserved.)

The family Profundulidae includes some one of the most enigmatic freshwater fishes of Mesoamerica: despite many attempts, a robust phylogenetic framework to delimit species is lacking, mainly due to limited morphological variation within the group. The accumulation of molecular data of profundulid fishes has led to advances in the description of new taxa, but relatively less progress has been made estimating evolutionary and phylogenetic relationships for this fish family. Here, we adopt an integrative taxonomy approach including the use of nuclear and mitochondrial DNA sequences, morphometric and ecological data, to test species boundaries in profundulid fishes in the westernmost area of their known distribution range in the states of Guerrero and Oaxaca, Mexico. Using a combination of methods for species discovery and validation based on Bayesian gene tree topologies, our analyses support the delimitation of 15 valid species of profundulid fishes - a combination of previously described species validated by this study, the synonymy of unsupported taxa, and the description of two new species. Using species delimitation methods, examination of phenotypic variation, and ecological niche characterization, we also identify five potentially new lineages which require further evidence to be erected as new species. We demonstrate that the use of an integrative taxonomy approach provides a robust methodology to delimit species in a taxonomically complex group like Profundulidae. Accurate taxonomic and ecological information is crucial for the conservation of these microendemic fishes, as several species are endangered., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The genus Gyrodactylus von Nordmann, 1832 is one of the most diverse within the class Monogenea; it contains mainly parasites of freshwater and marine teleost fishes. Around 40 species of Gyrodactylus have been described from gobiid fishes; mainly in Europe, as only two species are known from the Americas. In this study, we describe three new gyrodactylids from the body surface and fins of the goby Sicydium salvini (Gobiidae, Sycydiinae), which has a wide distribution on the Pacific coast, from Mexico to Panama. We describe Gyrodactylus oaxacae n. sp., G. atoyacensis n. sp. and G. salvini n. sp. collected from rivers draining to the eastern Pacific in the state of Oaxaca, Mexico. Morphologically, G. atoyacensis n. sp. and G. salvini n. sp. are very similar, and both are easily differentiated from G. oaxacae n. sp. Phylogenetic hypotheses based on sequences of the Internal Transcribed Spacers (ITS1-5.8S-ITS2 rDNA) and the D2 + D3 domains of the large ribosomal subunit (28S rDNA) support the erection of the three new taxa; and suggest that G. atoyacensis n. sp. and G. salvini n. sp. are sister species. These gyrodactylids are the first monogeneans described from gobies of the genus Sicydium in Mexico., Competing Interests: Declaration of Competing Interest The authors declare that they have no conflict of interest., (Copyright © 2022 Elsevier B.V. All rights reserved.)

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.

Trematode taxonomy is mainly based on the morphological traits of adults. The identification of metacercariae is challenging because such traits are not developed in larval forms, and they even may show some level of morphological variability. Studies testing the potential correspondence between morphological differences and genetic variation of parasites are still lacking. The metacercariae of Posthodiplostomum minimum are probably the diplostomids more widely distributed in North and Middle American freshwater fish, and their intraspecific morphological variability has been attributed to the effect exerted by the host. Here, we tested the hypothesis whether they represent a single species, or a species complex by assessing the genetic divergence and phylogenetic relationships of metacercariae sampled from several host species in a wide geographical range across Middle America. The internal transcribed spacers (ITS1-5.8S-ITS2), and the mitochondrial COI gene were sequenced for 124 and 55 metacercariae, respectively. Phylogenetic analysis inferred from ITS sequences uncovered six well-supported monophyletic lineages. The six lineages show no correspondence to any Posthodiplostomum species for which sequences are available thus far in GenBank. Lineages exhibit some degree of host specificity; Lineages I, II, IV and V are primarily parasites of cyprinodontiforms of the families Poeciliidae, Goodeidae, Profundulidae and Fundulidae. In poeciliids there are at least four candidate species of Posthodiplostomum, some of them occurring in sympatry; instead, Lineages II and VI are exclusively parasites of cichlids. This study contributes to our understanding of the diversity of larval forms of diplostomids and provides an opportunity to further study their life cycles.