Cryptic diversity in the mtDNA of the ornamental fish Carnegiella strigata

Phylogeography and population genetic structure of the cardinal tetra (Paracheirodon axelrodi) in the Orinoco basin and Negro River (Amazon basin): evaluating connectivity and historical patterns of diversification

The Neotropics contain one of the most diverse assemblages of freshwater fishes worldwide. Part of this diversity is shared between the Orinoco and Amazon basins. These basins have been separated for a long time due to the Vaupes Arch, rising between 10-11 Ma. Today, there is only one permanent connection between the Orinoco and Negro (Amazon) basins, known as the Casiquiare Canal. However, alternative corridors allowing fish dispersion between both basins have been proposed. The cardinal tetra (Paracheirodon axelrodi), the most important fish in the ornamental world market, is distributed in both basins. Here we investigated P. axelrodi phylogeography, population structure, and potential routes of migration and connectivity between the two basins. A total of 468 bp of the mitochondrial gene (COI), 555 bp of the nuclear gene fragment (MYH6), and eight microsatellite loci were analyzed. As a result, we found two major genetic clusters as the most likely scenario (K = 2), but they were not discreetly distributed between basins. A gradient of genetic admixture was observed in Cucui and São Gabriel da Cachoeira, between the upper Negro River and the upper Orinoco. Samples from the middle-lower Negro River were highly structured. Cucui (Negro basin) was more similar to the Orinoco than to the rest of the Negro basin populations. However, substructure was also observed by the discriminant analysis, fixation indices and other hierarchichal structure analyses (K = 3 - 6), showing three major geographic clusters: Orinoco, Cucui, and the remaining Negro basin. Unidirectional migration patterns were detected between basins: via Cucui toward Orinoco and via the remaining of the Negro basin toward Orinoco. Results from the Relaxed Random Walk analysis support a very recent origin of this species in the headwater Orinoco basin (Western Guiana Shield, at late Pleistocene) with a later rapid colonization of the remaining Orinoco basin and almost simultaneously the Negro River via Cucui, between 0.115 until about 0.001 Ma. Historical biogeography and population genetic patterns observed here for Cardinal tetra, seem to be better explained by river capture, physical, or ecological barriers than due to the geographic distance.

Discovering Hidden Diversity of Characins (Teleostei: Characiformes) in Ecuador's Yasuní National Park

BACKGROUND

Management and conservation of biodiversity requires adequate species inventories. The Yasuní National Park is one of the most diverse regions on Earth and recent studies of terrestrial vertebrates, based on genetic evidence, have shown high levels of cryptic and undescribed diversity. Few genetic studies have been carried out in freshwater fishes from western Amazonia. Thus, in contrast with terrestrial vertebrates, their content of cryptic diversity remains unknown. In this study, we carried out genetic and morphological analyses on characin fishes at Yasuní National Park, in eastern Ecuador. Our goal was to identify cryptic diversity among one of the most speciose fish families in the Amazon region. This is the first time that genetic evidence has been used to assess the species content of the Napo Basin, one of the richest regions in vertebrate diversity.

RESULTS

Phylogenetic analyses of partial mitochondrial 16S ribosomal RNA gene (∼600 pb) DNA sequences from 232 specimens of the family Characidae and its closest groups revealed eight candidate new species among 33 species sampled, representing a 24% increase in species number. Analyses of external morphology allowed us to confirm the species status of six of the candidate species.

CONCLUSIONS

Our results show high levels of cryptic diversity in Amazonian characins. If this group is representative of other Amazonian fish, our results would imply that the species richness of the Amazonian ichthyofauna is highly underestimated. Molecular methods are a necessary tool to obtain more realistic inventories of Neotropical freshwater fishes.