Landscape dynamics and diversification of the megadiverse South American freshwater fish fauna.

Landscape dynamics are widely thought to govern the tempo and mode of continental radiations, yet the effects of river network rearrangements on dispersal and lineage diversification remain poorly understood. We integrated an unprecedented occurrence dataset of 4,967 species with a newly compiled, time-calibrated phylogeny of South American freshwater fishes-the most species-rich continental vertebrate fauna on Earth-to track the evolutionary processes associated with hydrogeographic events over 100 Ma. Net lineage diversification was heterogeneous through time, across space, and among clades. Five abrupt shifts in net diversification rates occurred during the Paleogene and Miocene (between 30 and 7 Ma) in association with major landscape evolution events. Net diversification accelerated from the Miocene to the Recent (c. 20 to 0 Ma), with Western Amazonia having the highest rates of in situ diversification, which led to it being an important source of species dispersing to other regions. All regional biotic interchanges were associated with documented hydrogeographic events and the formation of biogeographic corridors, including the Early Miocene (c. 23 to 16 Ma) uplift of the Serra do Mar and Serra da Mantiqueira and the Late Miocene (c. 10 Ma) uplift of the Northern Andes and associated formation of the modern transcontinental Amazon River. The combination of high diversification rates and extensive biotic interchange associated with Western Amazonia yielded its extraordinary contemporary richness and phylogenetic endemism. Our results support the hypothesis that landscape dynamics, which shaped the history of drainage basin connections, strongly affected the assembly and diversification of basin-wide fish faunas.

Genetic assimilation and the evolution of direction of genital asymmetry in anablepid fishes.

Phylogenetic comparative studies suggest that the direction of deviation from bilateral symmetry (sidedness) might evolve through genetic assimilation; however, the changes in sidedness inheritance remain largely unknown. We investigated the evolution of genital asymmetry in fish of the family Anablepidae, in which males' intromittent organ (the gonopodium, a modified anal fin) bends asymmetrically to the left or the right. In most species, males show a 1 : 1 ratio of left-to-right-sided gonopodia. However, we found that in three species left-sided males are significantly more abundant than right-sided ones. We mapped sidedness onto a new molecular phylogeny, finding that this left-sided bias likely evolved independently three times. Our breeding experiment in a species with an excess of left-sided males showed that sires produced more left-sided offspring independently of their own sidedness. We propose that sidedness might be inherited as a threshold trait, with different thresholds across species. This resolves the apparent paradox that, while there is evidence for the evolution of sidedness, commonly there is a lack of support for its heritability and no response to artificial selection. Focusing on the heritability of the left : right ratio of offspring, rather than on individual sidedness, is key for understanding how the direction of asymmetry becomes genetically assimilated.

A new species of Cambeva (Siluriformes, Trichomycteridae) from the Rio Iguaçu basin, Paraná State, Brazil and redescription of Cambeva stawiarski (Miranda Ribeiro 1968).

This work aimed to describe Cambeva cauim, sp. nov., endemic to the Rio Iguaçu basin, Brazil and redescribe Cambeva stawiarski using external and internal morphological data through the revision of specimens deposited in fish collections, including the type material. In this process, we have also added comments on the possible type locality of C. stawiarski. C. cauim, sp. nov. and C. stawiarski are mainly diagnosed by the anatomy and number of procurrent caudal-fin rays in addition to colouration and several meristic and morphometric characters. Both species are compared with other possibly related species and their synapomorphic characters are discussed. C. cauim, sp. nov. and C. stawiarski along with eight other congeners are endemic to the Rio Iguaçu basin, a high impacted freshwater region which could be considered as a biodiversity hotspot to the genus.

Negative effect of turbidity on prey capture for both visual and non-visual aquatic predators.

Turbidity plays an important role in aquatic predator-prey interactions. Increases in turbidity are expected to reduce prey capture rates, especially for visually oriented predators. However, there is also evidence indicating that turbidity may have little or no effect on predation rates. Here, we conducted a systematic review and meta-analysis of the relationship between turbidity and capture rate. We explored possible sources of heterogeneity in the effect sizes (capture strategy, predator's body size, relative eye size and turbidity range in the experiments) while controlling for the dependence among effects sizes and phylogenetic relationships among predator species. We found a consistent negative effect of turbidity on prey capture and that turbidity range (manipulated in the experiments) was the main factor accounting for between-study variation in effect sizes. Also, capture rates of both visually and non-visually oriented predators decreased with an increase in turbidity. In addition, for visually oriented fish predators, the relative eye size did not influence the effect sizes. Despite the paucity of studies for some groups of aquatic predators (mainly in tropical regions), we provide corroborative evidence that turbidity is a critical environmental factor controlling predator-prey interactions. This result is especially relevant considering that changes in turbidity is a human-induced pervasive environmental alteration resulted from, among other mechanisms, runoff after deforestation, eutrophication or oligotrophication in reservoir cascades, which imply changes in predator-prey interactions.

A new species of Cambeva (Siluriformes, Trichomycteridae) from the Rio Ivaí basin, Upper Rio Paraná basin, Paraná State, Brazil.

A new species of Cambeva endemic to the Rio Ivaí basin, Upper Paraná basin, is described combining morphological and molecular data. This new species is distinguished from all congeners by characters related to the number of pectoral-fin rays, to the colour pattern of the dorsal and lateral surface of the body, to the presence of diffuse blotches in the ventral surface of body, to the presence of a pelvic-fin and pelvic girdle, to the number of odontodes in the inter-opercular and opercular patches, to the number of dorsal and ventral procurrent rays. In addition, the analysis of mitochondrial DNA sequences identified a satisfactory genetic distance between this new species and its congeners. The new species from the Rio Ivaí reinforces its characteristics as an area of endemism for fishes in the Upper Rio Paraná basin.

A new species of miniature Characidium (Characiformes: Crenuchidae) from the upper Rio Paraguay basin, Mato Grosso state, Brazil.

A new miniature species of Characidium is described from the upper Rio Paraguay basin, Brazil. The new species can be diagnosed from all congeners by the presence of a dark-brown humeral blotch, vertically elongated (spanning 5 to 7 horizontal scale rows), with the shape of an upside-down acute triangle. Additionally, it can be diagnosed by a short lateral line (6 to 8 perforated scales), the absence of a conspicuous peduncular blotch, a lower number of principal caudal-fin rays (14-16) and by absence of the adipose fin. The new species is the smallest species of the genus; the largest specimen was 19.3 mm standard length.