Although habitat fragmentation fosters extinctions, it also increases the probability of speciation by promoting and maintaining divergence among isolated populations. Here we test for the effects of ...two isolation factors that may reduce population dispersal within river networks as potential drivers of freshwater fish speciation: 1) the position of subdrain-ages along the longitudinal river gradient, and 2) the level of fragmentation within subdrainages caused by natural waterfalls. e occurrence of native freshwater fish species from 26 subdrainages of the Orinoco drainage basin (South America) was used to identify those species that presumably arose from in-situ cladogenetic speciation (i.e. neo-endemic species; two or more endemic species from the same genus) within each subdrainage. We related subdrainages fish diversity (i.e. total, endemic and neo-endemic species richness) and an index of speciation to our two isolation factors while controlling for subdrainages size and energy availability. The longitudinal position of subdrainages was unrelated to any of our diversity measures, a result potentially explained by the spatial grain we used and/or the contemporary connection between Orinoco and Amazon basins via the upstream Casiquiare region. However, we found higher neo-endemic species richness and higher speciation index values in highly fragmented subdrainages. These results suggest that habitat fragmentation generated by natural waterfalls drives cladogenetic speciation in fragmented subdrainages. More generally, our results emphasize the role of history and natural waterfalls as biogeographic barriers promoting freshwater biodiversity in river drainage basins.
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.
Neospora caninum is an apicomplexan parasite responsible for major economic losses due to abortions in cattle. Innate immune responses are crucial for host resistance against the infection, however ...the molecules involved in parasite recognition are still poorly understood. Nod2 is a cytosolic receptor that recognizes several pathogens and its role during N. caninum infection has not yet been described. In that sense, we evaluated the role of Nod2 in host response against this parasite. We found that infection of macrophages induced increased expression of Nod2, which colocalized with the parasites' vacuoles. Nod2-deficient macrophages showed an impaired induction of pro-inflammatory cytokines, increased production of modulatory molecules, and failure to restrict parasite replication. In vivo, Nod2-knockout mice showed a reduction of MAPK phosphorylation and proinflammatory cytokines, followed by decreased inflammation in target organs and increment in parasite burden. Surprisingly, these mice were partially resistant to lethal doses of tachyzoites. In addition, these phenomena were not observed in Rip2-/- mice. In conclusion, our study indicates that Nod2-dependent responses account for N. caninum elimination. On the other hand, the inflammatory milieu induced by this innate receptor provoked pathogenesis and death in severe experimental neosporosis.
Using the most comprehensive fish occurrence database, we evaluated the importance of ecological and historical drivers in diversity patterns of subdrainage basins across the Amazon system. Linear ...models reveal the influence of climatic conditions, habitat size and sub-basin isolation on species diversity. Unexpectedly, the species richness model also highlighted a negative upriver-downriver gradient, contrary to predictions of increasing richness at more downriver locations along fluvial gradients. This reverse gradient may be linked to the history of the Amazon drainage network, which, after isolation as western and eastern basins throughout the Miocene, only began flowing eastward 1-9 million years (Ma) ago. Our results suggest that the main center of fish diversity was located westward, with fish dispersal progressing eastward after the basins were united and the Amazon River assumed its modern course toward the Atlantic. This dispersal process seems not yet achieved, suggesting a recent formation of the current Amazon system.
Climate change is a major threat to biodiversity. Rainfall patterns over recent decades have changed and extreme events are intensifying. These are expected to affect the hydrological dynamics and ...structure of forest streams in the Amazon basin, which strongly depend on the local rainfall regime, with potential consequences for local fish assemblages.
Here we used four repeated surveys of stream fish assemblages across 10 × 10 km area of a pristine forest reserve in central Amazonia over an 18‐year (2001–2018) period to investigate the temporal dynamics of fish taxonomic and functional composition in relation to changes in stream habitats and local climatic regime. We investigated changes in magnitude, direction, and congruence of fish assemblage trajectories over time.
Total annual rainfall increased over time, with stormy days (i.e. daily rainfall above 20 mm) becoming more frequent during recent decades and a concomitant change of stream substrates from litter‐dominated to free sand. The overall taxonomic and functional composition of fish assemblages changed consistently over time, with stronger differences between the first and last surveys due to alterations in relative abundances of some of the most abundant species. Functional composition moved from open water species (compressed‐bodied species with less developed fins and terminal‐oriented mouths) to species adapted to lateral pools and shallow marginal areas (species with fusiform body shape, more developed fins, and superior‐oriented mouth)
We provide evidence of a concerted directional change of fish assemblages associated with increased precipitation and a higher frequency of stormy days over the last 2 decades. Considering the short time interval and the subtleness of the climatic changes assessed in this study, as well as the historically assumed structural stability of Amazonian streams, these findings are surprising and indicate those stream fish assemblages may respond quickly to climate changes.
Aim: We studied the underlying biotic and abiotic drivers of network patterns in marine cleaning mutualisms (species feeding upon ectoparasites and injured tissues of others) at large spatial scales. ...Location: Eleven marine biogeographical provinces. Time period: 1971–2018. Major taxa studied: Reef fish and shrimps. Methods: We combined field and literature data to test whether recurrent patterns in mutualistic networks (nestedness, modularity) describe the distributions of marine cleaning interactions. Nested network structures suggest that some cleaner species interact with many clients while the others clean fewer, predictable subsets of these clients; modular network structures suggest that cleaners and clients interact within defined, densely connected subsets of species. We used linear mixed models to evaluate whether the life-history traits of cleaners contribute to the emergence of these patterns locally and whether environmental and geographical factors influence the network structures. Results: Marine cleaning networks were more nested than modular. Nestedness was prevalent in communities with dedicated cleaners (ones that feed exclusively by cleaning), whereas communities with only facultative cleaners (ones that clean opportunistically) were generally unstructured. Cleaner type and taxa were the only traits shaping networks, with dedicated fish cleaners contributing disproportionally more than facultative cleaners and shrimps to the emergence of nestedness. Although cleaner species seem concentrated around the tropics and biodiversity centres, we did not detect an influence of environmental and geographical factors on network structures. Main conclusions: Dedicated species are key in shaping the structure of marine cleaning mutualistic networks. By relying exclusively on cleaning to feed, dedicated cleaners interact with most of the available clients and form the network core, whereas the opportunistic facultative species tend to clean the most common clients. We hypothesize that trophic niche variation and phenotypic specialization are major drivers of this asymmetry in marine mutualisms. Our study strengthens the links between biotic interactions at the community level and the distribution of species and specializations at larger spatial scales.
Aim
Functional diversity encapsulates whole‐community responses to environmental gradients mediated by species traits. Under trait convergence, similar responses may cause distantly related taxa to ...exhibit spatially correlated functional diversity. We investigated whether similar responses of reef fish, coral and algal functional richness and disparity to the environment produce spatially correlated functional diversity patterns.
Location
Brazilian marine biogeographical province.
Taxon
Reef fish, corals, algae.
Methods
We analysed data from 40 coastal and oceanic sites distributed across 27 degrees of latitude in the Brazilian province. Using traits, we measured functional richness (FRic) and disparity (Rao's Q) and calculated Pearson's correlation (ρobs) between pairs of metrics and taxa. We used Bayesian multivariate linear models to model taxa functional richness and disparity relative to sea surface temperature (SST), turbidity, salinity, species richness and region, and to estimate the residual correlation (ρres) between metrics after accounting for these variables.
Results
The best fitted model contained SST, species richness and region, and explained about 56% of the variation in FRic and Rao's Q across taxa. Yet, FRic and Rao's Q of fish, algae and corals responded differently to environmental variables. Functional diversity metrics were less correlated between algae and corals than compared to fish. Observed correlations of FRic and Rao's Q were low to intermediate across taxa (average ρobs = 0.14), and residual correlations were even lower (average ρres = 0.02).
Main conclusions
SST, species richness and region had a widespread role in determining spatially congruent functional diversity offish, algae and corals across Brazilian reefs, despite their fundamentally different evolutionary histories. Low residual spatial correlations suggest that other mechanisms might also contribute to functional diversity patterns of reef taxa independently. Given the role of SST, species richness and region, the functional structure of these reefs might be compromised by climate change, pollution and overfishing.
Diversity patterns are determined by biogeographic, energetic, and anthropogenic factors, yet few studies have combined them into a large‐scale framework in order to decouple and compare their ...relative effects on fish faunas. Using an empirical dataset derived from 1527 underwater visual censuses (UVC) at 18 oceanic islands (five different marine provinces), we determined the relative influence of such factors on reef fish species richness, functional dispersion, density and biomass estimated from each UVC unit. Species richness presented low variation but was high at large island sites. High functional dispersion, density, and biomass were found at islands with large local species pool and distance from nearest reef. Primary productivity positively affected fish richness, density and biomass confirming that more productive areas support larger populations, and higher biomass and richness on oceanic islands. Islands densely populated by humans had lower fish species richness and biomass reflecting anthropogenic effects. Species richness, functional dispersion, and biomass were positively related to distance from the mainland. Overall, species richness and fish density were mainly influenced by biogeographical and energetic factors, whereas functional dispersion and biomass were strongly influenced by anthropogenic factors. Our results extend previous hypotheses for different assemblage metrics estimated from empirical data and confirm the negative impact of humans on fish assemblages, highlighting the need for conservation of oceanic islands.
In Amazonia reduced-impact logging, which is meant to reduce environmental disturbance by controlling stem-fall directions and minimizing construction of access roads, has been applied to large areas ...containing thousands of streams. We investigated the effects of reduced-impact logging on environmental variables and the composition of fish in forest streams in a commercial logging concession in central Amazonia, Amazonas State, Brazil. To evaluate short-term effects, we sampled 11 streams before and after logging in one harvest area. We evaluated medium-term effects by comparing streams in 11 harvest areas logged 1-8 years before the study with control streams in adjacent areas. Each sampling unit was a 50-m stream section. The tetras Pyrrhulina brevis and Hemigrammus cf. pretoensis had higher abundances in plots logged ≥3 years before compared with plots logged <3 years before. The South American darter (Microcharacidium eleotrioides) was less abundant in logged plots than in control plots. In the short term, the overall fish composition did not differ two months before and immediately after reduced-impact logging. Temperature and pH varied before and after logging, but those differences were compatible with normal seasonal variation. In the medium term, temperature and cover of logs were lower in logged plots. Differences in ordination scores on the basis of relative fish abundance between streams in control and logged areas changed with time since logging, mainly because some common species increased in abundance after logging. There was no evidence of species loss from the logging concession, but differences in log cover and ordination scores derived from relative abundance of fish species persisted even after 8 years. For Amazonian streams, reduced-impact logging appears to be a viable alternative to clear-cut practices, which severely affect aquatic communities. Nevertheless, detailed studies are necessary to evaluated subtle long-term effects.
Animals and plants worldwide are structured in global biogeographic regions, which were shaped by major geologic forces during Earth history. Recently, humans have changed the course of events by ...multiplying global pathways of introduction for nonindigenous species and propagating local species extirpations. Here, we report on how introductions and extirpations have changed the distributions of freshwater fishes worldwide and how it affected their natural biogeographic regions. We found major shifts in natural regions, with the emergence of an intercontinental region arising from the fusion of multiple faunas, which we named Pan-Anthropocenian Global North and East Asia (PAGNEA). The PAGNEA region is evocative of the Pangea supercontinent, as flows of introductions show that dispersal has become possible again across multiple continents, suggesting that human activities have superseded natural geological forces. Our results constitute evidence on the expected modification of biostratigraphic boundaries based on freshwater fish, which are abundant in the fossil record, thereby supporting the concept of the Anthropocene epoch.
The worldwide geography of freshwater fish biodiversity has been redefined by humans, superseding geological forces.
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