Human impacts and the loss of Neotropical freshwater fish diversity

Identification of fish specimens of the Tocantins River, Brazil, using DNA barcoding

The fish fauna of the Tocantins River possesses many endemic species; however, it is little studied in molecular terms and is quite threatened by the construction of several hydroelectric dams. Therefore, the objective of this study was to identify the ichthyofauna of the Tocantins River using DNA barcoding. For this, collections were carried out in five points of this river, which resulted in the capture of 725 individuals from which partial sequences of the cytochrome oxidase subunit I (COI) gene were obtained for genetic analysis. A total of 443 haplotypes were recovered with the mean intraspecific K2P genetic distance of 1.82%. Altogether, 138 species were identified based on morphological criteria, which was a quantity that was much lower than that indicated by the four molecular methods (assemble species by automatic partitioning [ASAP], barcode index number [BIN], generalized mixed Yule coalescent (GMYC), and Bayesian Poisson tree processes [bPTP]) through which 152-157 molecular entities were identified. In all, 41 unique BINs were obtained based on the data generated in the BOLDSystems platform. According to the result indicated by ASAP (species delimitation approach considered the most appropriate in the present study), there was an increase of 17 molecular entities (12.32%), when compared to the number of species identified through their morphological criteria, as it can show cryptic diversity, candidates for new species, and misidentifications. There were 21 incongruities indicated between the different identification approaches for species. Therefore, it is suggested that these taxonomic problems be cautiously evaluated by experts to solve such taxonomic issues.

Ecosystem variables importance in the presence and abundance of a globally invasive fish

Changes in physical habitat that are associated with anthropogenic disturbances facilitate the establishment and expansion of non-native species in receiving environments. Here, we evaluated the relative importance of ecosystem variables for the presence and abundance of the invasive fish Poecilia reticulata in Brazil. We collected fish species and assessed environmental variables through an established physical habitat protocol in 220 stream sites located in southeastern and midwestern Brazil. A total of 14,816 P. reticulata individuals were collected in 43 stream sites, and 258 variables that describe the physical characteristics of streams were assessed, including measures of channel morphology, substrate size and type, habitat complexity and cover, riparian vegetation cover and structure, and human influence. Dimensionality reduction methods were employed to limit redundancy, resulting in a smaller set of the most relevant environmental variables. Subsequently, we used random forest models to assess the relative importance of these variables in determining the presence and abundance of P. reticulata. The presence of this invasive fish was primarily explained by human disturbance variables related to urbanization (total impact, pavement, artificial structure areal cover, riparian canopy cover, electrical conductivity, mean thalweg depth, and sand), whereas channel morphology (mean bank full height) and fish cover variables (natural fish cover, and aquatic macrophyte areal cover) were important predictors of its abundance. Identifying which ecosystem variables are favorable to the establishment of non-native species is an important step in preventing future biological invasions, as well as managing those that already occur.

Chromosomal rearrangements and the first indication of an ♀X1 X1 X2 X2 /♂X1 X2 Y sex chromosome system in Rineloricaria fishes (Teleostei: Siluriformes)

Rineloricaria is the most diverse genus within the freshwater fish subfamily Loricariinae, and it is widely distributed in the Neotropical region. Despite limited cytogenetic data, records from southern and south-eastern Brazil suggest a high rate of chromosomal rearrangements in this genus, mirrored in remarkable inter- and intraspecific karyotype variability. In the present work, we investigated the karyotype features of Rineloricaria teffeana, an endemic representative from northern Brazil, using both conventional and molecular cytogenetic techniques. We revealed different diploid chromosome numbers (2n) between sexes (33♂/34♀), which suggests the presence of an ♀X₁ X₁ X₂ X₂ /♂X₁ X₂ Y multiple sex chromosome system. The male-limited Y chromosome was the largest and the only biarmed element in the karyotype, implying Y-autosome fusion as the most probable mechanism behind its origination. C-banding revealed low amounts of constitutive heterochromatin, mostly confined to the (peri)centromeric regions of most chromosomes (including the X₂ and the Y) but also occupying the distal regions of a few chromosomal pairs. The chromosomal localization of the 18S ribosomal DNA (rDNA) clusters revealed a single site on chromosome pair 4, which was adjacent to the 5S rDNA cluster. Additional 5S rDNA loci were present on the autosome pair 8, X₁ chromosome, and in the presumed fusion point on the Y chromosome. The probe for telomeric repeat motif (TTAGGG)_n revealed signals of variable intensities at the ends of all chromosomes except for the Y chromosome, where no detectable signals were evidenced. Male-to-female comparative genomic hybridization revealed no sex-specific or sex-biased repetitive DNA accumulations, suggesting a presumably low level of neo-Y chromosome differentiation. We provide evidence that rDNA sites might have played a role in the formation of this putative multiple sex chromosome system and that chromosome fusions originate through different mechanisms among different Rineloricaria species.

Impacts of river fragmentation on limiting individual dietary specialization of Amazonian predatory fish

Individual dietary specialization is one of the factors that promotes variation in resource use at the individual level. Here we used stable isotope analysis of multiple tissues with different turnover rates to examine the degree of individual specialization in two sub-populations of the predator Cichla temensis inhabiting both fragmented and undammed rivers within the Uatumã River basin of the Amazon. Our results showed that the undammed river provides better conditions to promote individual dietary specialization than the fragmented river. This study contributes to the understanding of how specific life history characteristics of populations of generalist predators are impacted by fragmentation within megadiverse environments such as the Amazon basin.

Physical habitat in conterminous US streams and rivers, Part 1: Geoclimatic controls and anthropogenic alteration

Anthropogenic alteration of physical habitat structure in streams and rivers is increasingly recognized as a major cause of impairment worldwide. As part of their assessment of the status and trends in the condition of rivers and streams in the U.S., the U.S. Environmental Protection Agency's (USEPA) National Aquatic Resource Surveys (NARS) quantify and monitor channel size and slope, substrate size and stability, instream habitat complexity and cover, riparian vegetation cover and structure, anthropogenic disturbance activities, and channel-riparian interaction. Like biological assemblages and water chemistry, physical habitat is strongly controlled by natural geoclimatic factors that can obscure or amplify the influence of human activities. We developed a systematic approach to estimate the deviation of observed river and stream physical habitat from that expected in least-disturbed reference conditions. We applied this approach to calculate indices of anthropogenic alteration of three aspects of physical habitat condition in the conterminous U.S. (CONUS): streambed sediment size and stability, riparian vegetation cover, and instream habitat complexity. The precision and responsiveness of these indices led the USEPA to use them to evaluate physical habitat condition in CONUS rivers and streams. The scores of these indices systematically decreased with greater anthropogenic disturbance at river and stream sites in the CONUS and within ecoregions, which we interpret as a response of these physical habitat indices to anthropogenic influences. Although anthropogenic activities negatively influenced all three physical habitat indices in the least-disturbed sites within most ecoregions, natural geoclimatic and geomorphic factors were the dominant influences. For sites over the full range of anthropogenic disturbance, analyses of observed/expected sediment characteristics showed augmented flood flows and basin and riparian agriculture to be the leading predictors of streambed instability and excess fine sediments. Similarly, basin and riparian agriculture and non-agricultural riparian land uses were the leading predictors of reduced riparian vegetation cover complexity in the CONUS and within ecoregions. In turn, these reductions in riparian vegetation cover and complexity, combined with reduced summer low flows, were the leading predictors of instream habitat simplification. We conclude that quantitative measures of physical habitat structure are useful and important indicators of the impacts of human activities on stream and river condition.

Ichthyofauna of Santa Helena Relevant Ecological Interest Area (REIA), Paraná, Brazil

Abstract The Relevant Ecological Interest Area (REIA), popularly known as “Refúgio Biológico de Santa Helena”, is part of the Atlantic Forest Biome and one of the 78 ecoregions mapped by IBAMA as basic unit for planning priorities focused on national biodiversity conservation. Quarterly collections were carried out from November 2017 to November 2019 to inventory the ichthyofauna of this Conservation Unit. Specimens were captured with the aid of gillnets, fishing sieve and seine. In total, 3,919 specimens belonging to two class, eight orders, 27 families and 74 species were sampled. Characiformes and Siluriformes presented the highest species richness; they accounted for 40 (54%) and 17 (23%) species, respectively. Geophagus sveni (181 individuals = 17%), Trachelyopterus galeatus (109 individuals = 10%) and Schizodon borellii (105 individuals = 10%) were the most abundant fish species captured with gillnet. Moenkhausia was the most abundant genus captured with seine and fishing sieve, with emphasis on species Moenkhausia bonita (930 individuals = 33%) and Moenkhausia gracilima (845 individuals = 30%). Moreover, two “endangered” species (Brycon orbignyanus and Pseudoplatystoma corruscans) were registered. Therefore, we present an updated inventory of species belonging to the ichthyofauna of REIA, and it may contribute to future management plans focused on this Conservation Unit.

Freshwater fishes of the Río de la Plata: current assemblage structure

Abstract Few studies have addressed the composition of fish assemblages of the freshwater Río de la Plata (RdlP) and have only been limited to species lists gathered over the last two centuries. As such inventories have never been reviewed or validated by fish sampling, the richness and structure of RdlP fish assemblage are poorly known. Hence, we conducted an exhaustive literature review and a fieldwork in six coastal points of Argentina to update the species composition and determine the hierarchical structure of the fish assemblage. From the 206 species registered in the literature, 48 were not confirmed, 13 were absent, five were taken as synonymized species, 29 were supported by literature and 107 were confirmed; one was an established exotic species, and three were a non-established exotic species. The findings reported here suggest that the fish assemblage currently comprises 141 species, including four new records. Analysis of fieldwork data in number and weight of fish captured resulted in an assemblage hierarchical structure of five dominant, 22 frequent, and 45 rare species; 16 dominant, 11 frequent, and 45 rare taxa, respectively. These results could be used as baseline to monitor, manage, and preserve neotropical fish species in their southern distribution boundary.