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Aplodinotus grunniens represents one of the most common, widespread, and unique freshwater fishes in North America. Understanding the evolutionary history of this sciaenid is challenging though as published palaeontological records are lacking. Existing literature documenting skeletal remains and otoliths is summarised herein to better understand divergence and biogeography of the extant A. grunniens and extinct Aplodinotus species. Fossil evidence indicates that in addition to A. grunniens, three putative, extinct, marine species in North America and two in South America existed. The North American fossil Aplodinotus range from Oligocene to early Miocene, while the genus extends to the middle Miocene in South America. All described extinct fossil Aplodinotus have been recovered from shallow marine sediments with the oldest from the U.S.A. Gulf Coastal Plain. All sites with extant A. grunniens are from freshwater deposits ranging from middle to late Miocene to Holocene in age which very closely approximate the modern geographic distribution and include a variety of preserved skeletal elements and otoliths. The disappearance of the fossil marine Aplodinotus in the early Miocene in the Gulf is interpreted to represent the genus' transition to brackish and eventually freshwater habitats and development of the extant species by the late Miocene. [ABSTRACT FROM AUTHOR]

Neotropical freshwater stingrays (subfamily Potamotrygoninae) are carnivorous bottom feeder batoids widely distributed in most river basins of South America. They represent the unique extant group of elasmobranchs that evolved to live exclusively in freshwater environments. These species are exploited either by commercial fisheries (e.g., for food or ornamental industry) or by indigenous communities allocated along with their natural range. Restrictive life history characteristics coupled with habitat degradation make Potamotrygoninae species highly vulnerable to human impacts and highlight the necessity of studies to inform basic biological aspects, from ecology to genetics, to guide their conservation and clarify the molecular basis of adaptation to the freshwater environment. We used available and newly assembled Potamotrygon spp. mitogenomes to perform a comparative investigation of their molecular evolution. A phylogenetic estimation using the mitogenome of Potamotrygon falkneri and other Elasmobranchii supports monophyly for Potamotrygonidae and indicates a close relationship to Dasyatidae. A synteny analysis comprising 3 Potamotrygon and other 51 batoids revealed a highly conserved mitogenomic context. We detected various amino acid sites under positive selection exclusively in Potamotrygon spp., within the sequences of ND4, ND5, ND6, and COXII genes. Positively selected mutational events in key genes of energetic metabolism may be related to the physiological adaptation of Potamotrygon spp. during the ancient incursion into freshwater. This broad comparative mitogenomic study provides novel insights into the evolutionary history of neotropical freshwater stingrays and their relatives and stands out as a valuable resource to aid in current and future research on elasmobranch molecular evolution. [ABSTRACT FROM AUTHOR]

Anthropogenic environmental degradation has led to an increase in the frequency and prevalence of aquatic hypoxia (low dissolved oxygen concentration, DO), which may affect habitat quality for water-breathing fishes. The weakly electric black ghost knifefish, Apteronotus albifrons, is typically found in well-oxygenated freshwater habitats in South America. Using a shuttle-box design, we exposed juvenile A. albifrons to a stepwise decline in DO from normoxia (> 95% air saturation) to extreme hypoxia (10% air saturation) in one compartment and chronic normoxia in the other. On average, A. albifrons actively avoided the hypoxic compartment below 22% air saturation. Hypoxia avoidance was correlated with upregulated swimming activity. Following avoidance, fish regularly ventured back briefly into deep hypoxia. Hypoxia did not affect the frequency of their electric organ discharges. Our results show that A. albifrons is able to sense hypoxia at non-lethal levels and uses active avoidance to mitigate its adverse effects. [ABSTRACT FROM AUTHOR]

Aim: Fish community composition is shaped by current and historical factors. In recently formed ecosystems, however, as the Quaternary coastal lagoons of South America, the influence of historical factors has less frequently been investigated. The low rate of endemism in these lagoons suggests a limited role for speciation while their dynamic formation history suggests local extinction and dispersal limitation could have affected present species composition. We aimed to assess the influence of past and current factors on the beta diversity of those communities and explore the main processes involved. Location: Atlantic coast of South America. Taxon: Fishes (173 species). Methods: We built a dataset of species occurrence in 129 lagoons across eight freshwater ecoregions of the world (FEOWs) located between latitudes 0° and 36°, and calculated beta diversity (βjac) and its turnover (βjtu) and nestedness (βjne) components. We used a partial Mantel test and multiple regressions on distance matrices to evaluate the importance of past and current factors, and of geographical distance in determining beta diversity. Past variables were those representing the historical freshwater habitat during the last glacial maximum (LGM), and contemporary variables were those related to current habitat. Results: We found high values of βjac within the FEOWs, with βjtu prevailing over βjne. Both past (palaeodrainage) and current (drainage area, salinity and lagoon area) factors affected species dissimilarity (βjac = 46%) and its components (βjtu = 44% and βjne = 20%), although explanation was, in part, shared with geographical distance. Individually, the influence of past factors was prevalent in beta diversity and its components. Main conclusions: The large influence of the past factors on beta diversity suggests that major changes in the availability of freshwater habitats and connectivity since the Pleistocene must have affected the colonization, extinction and recolonization processes of fishes along the eastern coast of South America. We suggest that the high beta diversity values result from limited dispersal after extinctions in the LGM. The dissimilar freshwater fish communities currently seen result from heterogeneous subsets of the regional species pool that persisted in landscape refuges during past sea level increases and then recolonized coastal lagoons. [ABSTRACT FROM AUTHOR]

Rivers and lake systems in the southern cone of South America have been widely influenced by historical glaciations, carrying important implications for the evolution of aquatic organisms, including prompting transitions between marine and freshwater habitats and by triggering hybridization among incipient species via waterway connectivity and stream capture events. Silverside fishes (Odontesthes) in the region comprise a radiation of 19 marine and freshwater species that have been hypothesized on the basis of morphological or mitochondrial DNA data to have either transitioned repeatedly into continental waters from the sea or colonized marine habitats following freshwater diversification. New double digest restriction‐site associated DNA data presented here provide a robust framework to investigate the biogeographical history of and habitat transitions in Odontesthes. We show that Odontesthes silversides originally diversified in the Pacific but independently colonized the Atlantic three times, producing three independent marine‐to‐freshwater transitions. Our results also indicate recent introgression of marine mitochondrial haplotypes into two freshwater clades, with more recurring instances of hybridization among Atlantic‐ versus Pacific‐slope species. In Pacific freshwater drainages, hybridization with a marine species appears to be geographically isolated and may be related to glaciation events. Substantial structural differences of estuarine gradients between these two geographical areas may have influenced the frequency, intensity and evolutionary effects of hybridization events. [ABSTRACT FROM AUTHOR]

Aim The South American fish fauna is renowned for its extraordinary diversity. The majority of this diversity is restricted to few major clades that have ancient associations to freshwater habitats. However, at a higher taxonomic level, the South American ichthyofauna is enriched by an extraordinary number of marine derived lineages - lineages that are endemic to freshwaters, but derived from marine ancestors. Here, we test palaeogeographical hypotheses that attempt to explain the origins and exceptional diversity of marine derived fishes in rivers of South America. Location South America. Methods We analysed time-calibrated molecular phylogenies, ancestral reconstructions and biogeographical patterns for multiple independent marine-derived lineages. Results Five of the ten marine-derived lineages in our analysis have biogeographical patterns and stem ages consistent with invasion from the Atlantic Ocean during the Oligocene or Eocene. Drums and pufferfishes reveal patterns and ages that were consistent with the Miocene marine incursion hypothesis. The Amazonian halfbeak is the only lineage younger than the Miocene and invaded Amazonian freshwaters less than a million years ago. Main Conclusion Our results suggest Miocene marine incursions and the Pebas Mega-Wetland may not explain the high diversity of marine derived lineages in South America. Instead, the Pebas Mega-Wetland may have created a fertile opportunity for diversification of some, but not all marine-derived lineages. [ABSTRACT FROM AUTHOR]

Limnoperna fortunei (Dunker, 1857) is an invasive freshwater bivalve native to rivers and streams of China and Southeast Asia. In 2001, it was discovered in Itaipú Reservoir, and its population has grown considerably since then. The aim of this study was to estimate density, recruitment, and individual growth of L. fortunei in a subtropical region from a field experiment using an artificial substrate. Samples were collected between December 2004 and December 2005 at Bela Vista Reservoir in Foz do Iguaçu, Brazil. Mussels were counted and measured to generate size-frequency and distribution data. Maximum and minimum densities (± standard deviation) were 204 ± 17 ind. 100 cm-2 and 94 ± 22 ind. 100 cm-2, respectively. Shell length ranged between 1 and 36 mm, and shell length frequency indicated presence of young mussels with variable densities throughout the period surveyed. The von Bertalanffy model fitted successfully in all cases explaining more than 96% of the variation in shell length. Measured growth parameters (k = 2.35 year-1, L∞ = 38 mm) were different from those estimated for populations of L. fortunei in a temperate region. [ABSTRACT FROM AUTHOR]

Few long-term demographic studies have been conducted on freshwater turtles of South America, despite the need for this type of inquiry to investigate natural variation and strengthen conservation efforts for these species. In this study, we examined the variation in demography of the Chocoan River Turtle (Rhinoclemmys nasuta) based on a population from an island locality in the Colombian Pacific region between 2005 and 2017. We calculated survival, recapture, and transition probabilities, and the effects of stream substrate and El Niño–Southern Oscillation (ENSO) phases (El Niño, Neutral, La Niña) on these variables using a multi-state model. We found differences in survival probabilities between ENSO phases, likely as a consequence of an increase in flood events. In addition, we found support for survival being greater in muddy streams than rocky streams, possibly because it is easier to escape or hide in mud substrates. Recapture probabilities varied by life stages; differences in the probability of recapture between size classes were associated with the high fidelity to territories by adults. The present increases in frequency and severity of El Niño and La Niña may exacerbate the consequences of climatic regimes on natural populations of turtles by increasing the mortality caused by drastic phenomena such as floods. [ABSTRACT FROM AUTHOR]