Marcelo Loureiro

Diet of four annual killifishes: an intra and interspecific comparison

inhabiting temporal ponds of southeastern Uruguay, by analysis of stomach contents.Fishes were captured from fifty ephemeral ponds of Castillos Lagoon basin, in the region of the Humedales del Este. Weidentified 13099 individual prey items extracted from 669 stomachs of the four captured species. In the studied system, annualkillifishes represents the most abundant and conspicuous top predators. Killifishes are generalist key predators at the ephemer alponds of the studied system, consuming mostly aquatic items. Zooplancton represented the bulk of the diet in the fouranalyzed species, followed by eggs, algae and diatoms. Insects are the next group in prey number, as follows: Diptera larvae(especially Chironomidae and Cullicidae), Ephemeroptera (especially Betidae), and coleopteran larvae (especially Dytiscidae).Acari are also important prey in number. The four fish species differ in diet composition and in diet richness. A general patte rnof differences in diet richness among killifish species and demographic groups could be related to variations in body sizes. Astop predators annual killifishes are an important component of the temporal pond ecosystems. Understanding the naturalhistory of this species and their communities is necessary in order to conserve them.Nos examinamos a dieta de 4 peixes anuais,

A new species of Austrolebias Costa (Cyprinodontiformes: Rivulidae) from northeastern Uruguay, with comments on distribution patterns

A new species of Austrolebias is described based on individuals from the middle and upper rio Negro (rio Uruguay basin) and rio Yaguaron (Patos-Merin system). The new species can be differentiated from all other species of the genus by the unique presence in males of uniform bluish gray pigmentation on flanks (without vertical bands) and unpaired fins. The new species is also distinguished by the combination of characters associated with a reduction of the squamation of the abdominal, preopercular, and opercular regions. The new species presents some morphological characteristics similar to A. gymnoventris and A. luteoflammulatus. The distribution of the new species is concordant with three other species of Austrolebias and may represent a case of drainage rearrangement of the rio Negro upstream tributaries (rio Uruguay basin) and tributaries of laguna Merin system.

Intra- and intersexual selection on male body size in the annual killifish Austrolebias charrua

Since many traits are involved in both female mating decisions and male contest outcomes, female mate choice and male competition can act in concert to intensify sexual selection on male traits, or in opposition to weaken it. In the sexually dimorphic annual killifish, Austrolebias charrua, we evaluated the effect of male body size on female mate choice, male-male competition, and their interaction. We carried out an experiment with three consecutive stages: (i) female choice test between males of different size in a classic two-choice device, (ii) agonistic interactions between males used in the previous stage, and (iii) a second female choice test to evaluate preference consistency in females that either were allowed or were prevented from observing the male competition. Larger males were preferred by females and became socially dominant in agonistic interactions. Further, females were consistent in their choices, and this consistency was independent of whether they had observed or not the male contest. Our research shows that, in A. charrua, intrasexual competition and female mate choice act in concert with respect to male body size. The unique life-history of Austrolebias and the high repeatability of mate-choice assays make this system a promising candidate for studies of behavioural evolution.

Feeding habits and morphometry of Iheringichthys labrosus (Lütken, 1874) in the Uruguay River (Uruguay)

Body size and diet of organisms are fundamental attributes which determine their ecology and natural history. Iheringichthys labrosus is one of the most common fish species of the Uruguay River. However, its natural history is poorly known and there is little information about its diet and interactions with other species. This paper describes the feeding habits of this species, relating feeding patterns to the size classes and morphometry of individuals and to the temporal variations. Fishes were captured in May and November of 2006 in three zones of the lower Uruguay River. A total of 101 stomach contents was analyzed (standard length: 60-224 mm). The species exhibited a broad feeding spectrum with most items belonging to the benthic community. We found significant diet differences between size classes and studied months. However, we have not found a close relationship between changes in morphometric variables and diet shifts between size classes.

New records of freshwater fish for Uruguay

Based on National Collections records, this article presents the first report of eight freshwater fish species for Uruguay in the middle and lower Uruguay River basin, extending their current distribution: Cyanocharax alegretensis Malabarba and Weitzman, 2003; Leporinus lacustris Amaral Campos, 1945; Microglanis aff. eurystoma Malabarba and Mahler, 1998; Tatia boemia Koch and Reis, 1996; Lepthoplosternum pectorale (Boulenger, 1895); Crenicichla missioneira Lucena and Kullander, 1992; C. minuano Lucena and Kullander, 1992; Apistogramma borellii Regan, 1906. These species were previously recorded either for upper Uruguay River or Parana River.

Morphological Variation in the South American Snake-Necked Turtle Hydromedusa tectifera (Testudines: Chelidae)

Abstract Morphological variation in size and shape of organisms has physiological, ecological, and evolutionary relevance. In this context, an important step in the identification of evolutionary units is to identify groups of populations occupying a continuous geographic space, at both genetic and morphological levels. The freshwater turtle Hydromedusa is endemic to the Neotropical region and inhabits water bodies of the Paraná–La Plata basin of Argentina and coastal streams of Brazil and Uruguay. The genus is present in the fossil record since the Paleocene (56 mya) and currently consists of only 2 extant species. Hydromedusa tectifera has the widest distribution, from Santiago del Estero in Argentina to the State of Sao Paulo in Brazil. The goal of this work was to study the patterns of morphological variation of H. tectifera through most of its geographical range. Herein, we report morphological variation of carapace shape in this species associated with developmental and historical parameters. Our results support the hypothesis that at least part of the morphological variation found is associated with population variation among basins, possibly as a result of reduced gene flow among their populations. This variation is shown in both linear and geometric morphometry analyses. Sea level fluctuations that occurred in the region during the last 15 million years could have caused the current differentiation.

Perciformes, Cichlidae, Crenicichla tendybaguassu Lucena and Kullander, 1992: first record for Uruguay

The present note is the first record of the pike cichlid Crenicichla tendybaguassu for Uruguay, extending its distribution about 400 km to the South. The presence of C. tendybaguassu and their co-occurrence with other priority species for conservation in Uruguay adds greater value to conservation of the Cuareim River (Middle Uruguay River). Coloration of live breeding females is described for first time.

Phylogenomics of pike cichlids (Cichlidae: Crenicichla): the rapid evolution and trophic diversification of an incipient species flock

The rapid rise of phenotypic and ecological diversity in independent lake‐dwelling groups of cichlids is emblematic of the East African Great Lakes. In this study, we show that similar ecologically based diversification has occurred in pike cichlids (Crenicichla) throughout the Uruguay River drainage of South America. We collected genomic data from nearly 500 ultraconserved element (UCEs) loci and >260 000 base pairs across 33 species, to obtain a phylogenetic hypothesis for the major species groups and to evaluate the relationships and genetic structure among five closely related, endemic, co‐occurring species (the Uruguay River species flock; URSF). Additionally, we evaluated ecological divergence of the URSF based on body and lower pharyngeal jaw (LPJ) shape and gut contents. Across the genus, we recovered novel relationships among the species groups. We found strong support for the monophyly of the URSF; however, relationships among these species remain problematic, likely because of the rapid and recent evolution of this clade. Clustered co‐ancestry analysis recovered most species as well delimited genetic groups. The URSF species exhibit species‐specific body and LPJ shapes associated with specialized trophic roles. Collectively, our results suggest that the URSF consists of incipient species that arose via ecological speciation associated with the exploration of novel trophic roles.

First report of four characiform fishes (Ostariophysi: Characiformes) for Uruguay

In this article the authors present the first report of four characiform fish species for Uruguay, extending their current distribution to the middle and lower Uruguay River basin: Astyanax saguazu Casciotta, Almiron and Azpelicueta, 2003; Hypobrycon poi Almiron, Casciotta, Azpelicueta and Cione, 2001; Leporinus amae Gody, 1980; Cyphocharax saladensis (Meinken, 1933). These species were previously recorded from either the upper Uruguay River, Patos-Merin lagoon system or Parana River. Color pattern in life for A. saguazu and H. poi are described for the first time.

Female masculinization and reproductive success in Cnesterodon decemmaculatus (Jenyns, 1842) (Cyprinodontiforme: Poeciliidae) under anthropogenic impact

Aquatic organisms are exposed to a myriad of chemical compounds, with particular concerns focused on endocrine disruptors. Growing scientific evidence indicates that these compounds interfere with normal endocrine function and could affect the reproductive system of humans and wildlife. We analyzed the proportion of masculinized females, defined by elongation and fusion of the anal fin rays, and the extent of masculinization, masculinization index, defined by anal fin length divided by the standard length, of Cnesterodon decemmaculatus resident to areas of agricultural and urban-industrial activities in the Arroyo Colorado basin. Additionally, a bioassay was carried out to assess the potential effects of masculinization on reproductive success, measured as the number of viable progenies, using pregnant females from the site downstream of the urban–industrial zone. Masculinized females were observed in all sampling sites, particularly downstream of the urban–industrial area, where over 80% of females presented abnormal sexual characteristics and the highest masculinization index was registered. In the laboratory, masculinized adult females showed male mating behavior, and survival of their progeny was lower than those of normal females. To our knowledge, this is the first report of endocrine disruption in field-collected C. decemmaculatus, and the first evaluation of the reproductive success of masculinized females. Finally, our results support C. decemmaculatus as an excellent sentinel species due to its wide distribution, easy culture in laboratory conditions, and its potential capability to respond to sources of pollution, particularly endocrine disruptors.