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1. Evolutionary time best explains the latitudinal diversity gradient of living freshwater fish diversity

   https://doi.org/10.1111/geb.13253  

   Miller, Elizabeth Christina ; Román‐Palacios, Cristian ; Tomašových, ed., Adam ( January 2021 , Global Ecology and Biogeography)

   The evolutionary causes of the latitudinal diversity gradient are debated. Hypotheses have ultimately invoked either faster rates of diversification in the tropics or more time for diversification owing to the tropical origins of higher taxa. Here, we perform the first test of the diversification rate and time hypotheses in freshwater ray‐finned fishes, a group comprising nearly a quarter of all living vertebrates.

   Global.

   368–0 Ma.

   Extant freshwater ray‐finned fishes.

   Using a mega‐phylogeny of actinopterygian fishes and a global database of occurrence records, we estimated net diversification rates, the number of colonizations and regional colonization times of co‐occurring species in freshwater drainage basins. We used generalized additive models to test whether these factors were related to latitude. We then compared the influence of diversification rates, numbers of colonizations, colonization times and surface area on species richness, and how these factors are related to each other.

   Although both diversification rates and time were related to richness, time had greater explanatory power and was more strongly related to latitude than diversification rates. Other factors (basin surface area and number of colonizations) also helped to explain richness but were unrelated to latitude. The most diverse freshwater basins of the world (Amazon and Congo rivers) were dominated by lineages having Mesozoic origins. The temperate groups dominant today arrived near the Cretaceous–Palaeogene boundary, leaving comparatively less time to build richness. Diversification rates and colonization times were inversely related: recently colonized basins had the fastest rates, whereas ancient species‐rich faunas had slower rates.

   We concluded that time is the leading driver of latitudinal disparities in richness in freshwater fish faunas. We suggest that the most likely path to building very high species richness is through diversification over long periods of time, rather than through rapid diversification.

    

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2. Single-Species Co-management Improves Fish Assemblage Structure and Composition in a Tropical River

   https://doi.org/10.3389/fevo.2021.604170  

   Medeiros-Leal, Wendell M. ; Castello, Leandro ; Freitas, Carlos E. ; Siqueira-Souza, Flávia K. ( March 2021 , Frontiers in Ecology and Evolution)

   Co-management is increasingly recognized as an effective model for managing fisheries, but little information exists on whether co-management can produce effects in species other than the target species. Fishery co-management in the tropics, where fish diversity is high and fish catches tend to be multispecies, is prone to produce assemblage-wide effects via alterations in the food web and changes in the overall capture of non-target species. Here, we assessed the effects of co-management for the species Arapaima sp. in relation to the structure and composition of the overall fish assemblage in floodplain lakes of the central Amazon Basin. These floodplain lakes are managed under a system of zoning of fishing activities. We used data from surveys of six floodplain lakes, including two lakes of each of three categories (lakes where fishing is prohibited, limited-access lakes, and open fishing lakes). The surveys were carried out before and after implementation of co-management, through gillnet fishing. The study area was the lower Solimões River, in the Amazon Basin, Brazil. Statistical models showed significant changes in the composition and structure of the fish assemblages after the implementation of the co-management, regardless of the zoning category. Through regulation of gear use and fishing practices, co-management allowed the colonization of species that had not been present before, which lead to higher richness and consequently increased fish sizes, abundance and biomass. Species of sedentary habits, migrants of short and medium distances, with commercial importance benefited the most from co-management. In the results presented in temporal scale, it was possible to observe a potential spillover effect being provided by the lakes where fishing is prohibited (no-take zones) and those of limited access that benefited those open to fishing. Thus, co-management had positive effects in the structure and composition of fish assemblages in all lakes, regardless of zoning category. 

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3. Phylogeography, hybridization, and species discovery in the Etheostoma nigrum complex (Percidae: Etheostoma: Boleosoma)

   https://doi.org/10.1016/j.ympev.2022.107645  

   MacGuigan, Daniel J. ; Orr, Oliver D. ; Near, Thomas J. ( January 2023 , Molecular Phylogenetics and Evolution)

   The history of riverine fish diversification is largely a product of geographic isolation. Physical barriers that reduce or eliminate gene flow between populations facilitate divergence via genetic drift and natural selection, eventually leading to speciation. For freshwater organisms, diversification is often the product of drainage basin rearrangements. In young clades where the history of isolation is the most recent, evolutionary relationships can resemble a tangled web. One especially recalcitrant group of freshwater fishes is the Johnny Darter (Etheostoma nigrum) species complex, where traditional taxonomy and molecular phylogenetics indicate a history of gene flow and conflicting inferences of species diversity. Here we assemble a genomic dataset using double digest restriction site associated DNA (ddRAD) sequencing and use phylogenomic and population genetic approaches to investigate the evolutionary history of the complex of species that includes E. nigrum, E. olmstedi, E. perlongum, and E. susanae. We reveal and validate several evolutionary lineages that we delimit as species, highlighting the need for additional work to formally describe the diversity of the Etheostoma nigrum complex. Our analyses also identify gene flow among recently diverged lineages, including one instance involving E. susanae, a localized and endangered species. Phylogeographic structure within the Etheostoma nigrum species complex coincides with major geologic events, such as parallel divergence in river basins during Pliocene inundation of the Atlantic coastal plain and multiple northward post-glacial colonization routes tracking river basin rearrangements. Our study serves as a nuanced example of how low dispersal rates coupled with geographic isolation among disconnected river systems in eastern North America has produced one of the world’s freshwater biodiversity hotspots. 

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4. Population genomic response to geographic gradients by widespread and endemic fishes of the Arabian Peninsula

   https://doi.org/10.1002/ece3.6199  

   DiBattista, Joseph D. ; Saenz‐Agudelo, Pablo ; Piatek, Marek J. ; Cagua, Edgar Fernando ; Bowen, Brian W. ; Choat, John Howard ; Rocha, Luiz A. ; Gaither, Michelle R. ; Hobbs, Jean‐Paul A. ; Sinclair‐Taylor, Tane H. ; et al ( April 2020 , Ecology and Evolution)

   Genetic structure within marine species may be driven by local adaptation to their environment, or alternatively by historical processes, such as geographic isolation. The gulfs and seas bordering the Arabian Peninsula offer an ideal setting to examine connectivity patterns in coral reef fishes with respect to environmental gradients and vicariance. The Red Sea is characterized by a unique marine fauna, historical periods of desiccation and isolation, as well as environmental gradients in salinity, temperature, and primary productivity that vary both by latitude and by season. The adjacent Arabian Sea is characterized by a sharper environmental gradient, ranging from extensive coral cover and warm temperatures in the southwest, to sparse coral cover, cooler temperatures, and seasonal upwelling in the northeast. Reef fish, however, are not confined to these seas, with some Red Sea fishes extending varying distances into the northern Arabian Sea, while their pelagic larvae are presumably capable of much greater dispersal. These species must therefore cope with a diversity of conditions that invoke the possibility of steep clines in natural selection. Here, we test for genetic structure in two widespread reef fish species (a butterflyfish and surgeonfish) and eight range‐restricted butterflyfishes across the Red Sea and Arabian Sea using genome‐wide single nucleotide polymorphisms. We performed multiple matrix regression with randomization analyses on genetic distances for all species, as well as reconstructed scenarios for population subdivision in the species with signatures of isolation. We found that (a) widespread species displayed more genetic subdivision than regional endemics and (b) this genetic structure was not correlated with contemporary environmental parameters but instead may reflect historical events. We propose that the endemic species may be adapted to a diversity of local conditions, but the widespread species are instead subject to ecological filtering where different combinations of genotypes persist under divergent ecological regimes.

    

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5. Biogeographic reconstruction of the migratory Neotropical fish family Prochilodontidae (Teleostei: Characiformes)

   https://doi.org/10.1111/zsc.12531  

   Frable, Benjamin W. ; Melo, Bruno F. ; Fontenelle, João P. ; Oliveira, Claudio ; Sidlauskas, Brian L. ( March 2022 , Zoologica Scripta)

   Geographically, widespread Neotropical fish lineages offer opportunities to reconstruct historical biogeography patterns and infer processes leading to modern ichthyological diversity and distribution. The characiform family Prochilodontidae is well suited for such reconstruction because their migrations limit population substructure within river systems. Therefore, their biogeographic history should match closely the history of connectivity among Neotropical river basins. Here, we combine a time‐calibrated phylogeny with biogeographic model testing to recover the history of this family's diversification. Results support the Miocene rise of the Andean Eastern Cordillera as a dispersal barrier, but also indicate a much earlier Eocene origin of the trans‐Andean genusIchthyoelephas. Despite the early origin of the family and its three constituent genera, most prochilodontid lineages originated during the Miocene in Greater Amazonia, likely due to drainage reorganizations caused by Andean uplift. Subsequent speciation appears linked to interbasin exchanges and expansions of Amazonian lineages into Brazilian coastal systems. The modern richness ofProchilodusin easterly drainages appears to be relatively young, with onlyProchilodus vimboideslikely reaching that region prior to the late Miocene. The rise of the Vaupes Arch coincides with two splits between Orinocoan and Amazonian lineagescirca9 million years ago (Ma). However, two instances of later dispersal between these drainages reveal the permeability of the Vaupes Arch, suggesting that it may promote periodic speciation. This study illustrates how model‐based biogeographic studies of widespread groups can reconstruct historic paths of dispersal and help reveal how landscape evolution promoted modern diversity patterns.

    

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