Composition, abundance and biomass of a fish assemblage in a southern Brazilian coastal stream during polyhaline/euhaline condition / Composição, abundância e biomassa de uma assembléia de peixes em um arroio costeiro do sul do Brasil durante condição polihalina/euhalina

Abstract: The coastal streams of southernmost Brazil, Rio Grande do Sul state, are marked by a period of regular marine intrusion resultant from intense oceanic winds. In the present study we aimed to investigate the species composition, abundance and relative biomass of the ichthyofauna in the lower stretch of a coastal stream during summer, a period of regular marine intrusion. Estreito is a coastal hydrological complex composed by lakes, swamps and a perennial stream, located at the central-south portion of the coastal plain of Rio Grande do Sul state. During the summer of 2018, the ichthyofauna of lower Estreito stream was sampled by beach hauls applied in 17 random points distributed in a stretch of ca. 2km. Measurements at the sampled stretch revealed salinities between 19.3 to 31.3 ppt, characterizing the studied system as polyhaline/euhaline during summer. The sample of 4,533 specimens revealed the occurrence of 20 species, being the great majority marine-dwelling. The most abundant species were the anablepid Jenynsia lineata (70.3%), the cichlid Geophagus brasiliensis (19.3%) and the the mugilid Mugil curema (7.5%). The highest relative biomass was recorded for J. lineata, followed by M. curema and G. brasiliensis. The dominance of marine-dwelling species in the assemblage composition and the high abundance of limnic-estuarine J. lineata corroborate previous studies conducted in other washouts of Rio Grande do Sul.

Resumo: Os arroios costeiros do extremo sul do Brasil, estado do Rio Grande do Sul, são marcados por um período de regular intrusão marinha resultante de intensos ventos oceânicos. No presente estudo nós tivemos como objetivo investigar a composição de espécies, abundância e biomassa relativa da ictiofauna no trecho inferior de um arroio costeiro durante o verão, período de regular intrusão marinha. Estreito é um complexo hidrológico costeiro composto por lagoas, pântanos e um arroio perene, localizados na porção centro-sul da planície costeira do Rio Grande do Sul. Durante o verão de 2018, a ictiofauna do baixo arroio Estreito foi amostrada por arrastos de praia aplicados em 17 pontos aleatórios distribuídos em um trecho de cerca de 2 km. Medidas no trecho amostrado revelaram salinidades entre 19.3 e 31.3 ppt, caracterizando o sistema estudado como polialino/euhalino durante o verão. A amostra de 4.533 espécimes revelou a ocorrência de 20 espécies, sendo a grande maioria habitantes marinhos. As espécies mais abundantes foram o anablepídeo Jenynsia lineata (70,3%), o ciclídeo Geophagus brasiliensis (19,3%) e o mugilídeo Mugil curema (7.5%). A maior biomassa relativa foi registrada para J. lineata, seguido por M. curema e G. brasiliensis. A dominância das espécies marinhas na composição da assembléia e a alta abundância da espécie límnica-estuarina J. lineata corrobora estudos prévios conduzidos em outros sangradouros do Rio Grande do Sul.

Trends of karyotypical evolution in the pearl cichlid, Geophagus brasiliensis, from southern Brazil.

Chromosomal rearrangements such as inversions can facilitate speciation even in the presence of gene flow. The present study aims to analyze the karyotypic variation in six populations of Geophagus brasiliensis from southern Brazil. All specimens showed 2n=48 chromosomes, but three karyotypes were found to have one, two or three pairs of submetacentric chromosomes. Although G. brasiliensis did not exhibit variation in the diploid number, it presented a wide interpopulational variation mainly regarding the karyotype formula and specific chromosomal markers. Differences in the location of the major and minor rDNA loci were observed among the populations. Moreover, different patterns were observed in the distribution of the constitutive heterochromatin, presenting intra- and interpopulational variation. This supports the hypothesis that this taxon represents a complex species or that cryptic species are included in this group, indicating a possibleprocess of sympatric speciation. By potentially restricting gene flow between heterokaryotypes, the segregating chromosome rearrangements we describe for G. brasiliensis may play a role in diversification in this species complex.

Pequenos mamíferos não-voadores (Didelphimorphia, Rodentia) em dois fragmentos de mata de restinga de Rio Grande, planície costeira do Rio Grande do Sul / Non-volant small mammals ((Didelphimorphia, Rodentia) in two forest fragments in Rio Grande, Rio Grande do Sul coastal plain, Brazil

As matas de restinga representam formações vegetais originais na Planície Costeira do estado do Rio Grande do Sul. O objetivo deste trabalho foi avaliar a composição de espécies de pequenos mamíferos não-voadores em dois fragmentos de matas de restinga (mata palustre e mata arenosa ciliar) no município de Rio Grande, região sul da Planície Costeira do Rio Grande do Sul. Um total de 234 indivíduos pertencentes a três espécies de marsupiais (Didelphidae: Cryptonanus guahybae, Didelphis albiventris, Lutreolina crassicaudata) e oito espécies de roedores (Cricetidae: Deltamys kempi, Holochilus brasiliensis, Oligoryzomys flavescens, O. nigripes, Oxymycterus nasutus, Scapteromys tumidus; Muridae: Mus musculus, Rattus rattus) foi capturado. As espécies C. guahybae, D. albiventris, D. kempi, H. brasiliensis, O. nigripes, S. tumidus e M. musculus foram registradas no fragmento de mata palustre, enquanto que C. guahybae, D. albiventris, Lutreolina crassicaudata, D. kempi, O. flavescens, O. nigripes, S. tumidus e R. rattus ocorreram no fragmento de mata arenosa ciliar. Oligoryzomys nigripes e S. tumidus foram as espécies mais abundantes no fragmento de mata palustre, representando respectivamente 40,4 e 22,1% do total de indivíduos capturados. No fragmento de mata arenosa ciliar, as espécies mais abundantes foram O. nigripes e D. albiventris, representando respectivamente 63,4 e 12,4% do total de indivíduos capturados. Indivíduos de C. guahybae e O. nigripes foram capturados em estrato arbóreo (alturas entre 0,50 e 1,65 m) enquanto que todos os indivíduos das demais espécies foram capturados no solo.

The restinga forests represent original vegetal formations in Coastal Plain of Rio Grande do Sul state. This work aimed to evaluate the species composition of non-volant small mammals in two restinga forests (peat forest and sandy riparian forest) in Rio Grande, Southern Rio Grande do Sul Coastal Plain. A total of 234 individuals belonging to three species of marsupials (Didelphidae: Cryptonanus guahybae, Didelphis albiventris, Lutreolina crassicaudata) and eight species of rodents (Cricetidae: Deltamys kempi, Holochilus brasiliensis, Oligoryzomys flavescens, O. nigripes, Oxymycterus nasutus, Scapteromys tumidus; Muridae: Mus musculus, Rattus rattus) was captured. The species C. guahybae, D. albiventris, D. kempi, H. brasiliensis, O. nigripes, S. tumidus and M. musculus were recorded in the peat forest while C. guahybae, D. albiventris, Lutreolina crassicaudata, D. kempi, O. flavescens, O. nigripes, S. tumidus and R. rattus occurred in the riparian sandy forest. Oligoryzomys nigripes and S. tumidus were the most abundant species in the peat forest, representing 40.4 and 22.1% of the total of captured individuals, respectively. The most abundant species in the riparian sandy forest were O. nigripes e D. albiventris, representing 63.4 and 12.4% of the total of captured individuals. Individuals of C. guahybae and O. nigripes were captured on trees (heights between 0.50 and 1.65 m) while all individuals of the remaining species were captured on the ground.

A hybrid zone of the genus Ctenomys: A case study in southern Brazil.

We describe variation at microsatellite loci and the chromosomal polymorphisms of a hybrid population, and hybridizing populations of Ctenomys minutus (the minor tuco-tuco) from the coastal plain of Rio Grande do Sul, southern Brazil. Cytogenetic analysis and a survey of six microsatellite loci included 101 specimens of C. minutus from the parental populations (2n/AN = 42/74 and 48a/76) and their contact zone. Cytogenetic analysis recorded 26 different karyotypes exhibited by 50 individuals from the hybrid population. Of the 26 karyotypes, only 14% presented a parental-like configuration, and none had the combinations of 2n and AN expected for an F1 hybrid. The remaining karyotypes were alternative hybrid forms, with 2n varying from 42 to 46 and AN from 68 to 80. These results suggest chromosomal rearrangements are only of minor significance in the establishment of reproductive barriers for this species.

Inter and intra-specific hybridization in tuco-tucos (Ctenomys) from Brazilian coastal plains (Rodentia: Ctenomyidae).

The present work describes chromosomal polymorphisms in zones of contact between divergent populations of Ctenomys minutus parapatrically distributed in the coastal plain of southern Brazil, and inter-specific hybridization with C. lami a closely related species. A sample of 171 specimens from 32 sample sites distributed along 161 km of the coastal plain was cytogenetically analyzed. Nine polymorphic populations were found: four with specimens with 2n = 46-48 (autosomal arm number (AN) = 76); three only have specimens with 2n = 47 and 48; one population sampled presented specimens with 2n = 43-46 (AN = 74-76) and one population with 2n = 50-52 (AN = 76-80). The remainder populations were fixed for 2n = 42, 46 or 48. The variation is the result of Robertsonian mechanisms of chromosomal evolution and a fusion in tandem rearrangement. The polymorphisms have been considered the result of secondary contact of populations after divergence in allopatry. The geomorphological evolution of the coastal plain provides clues to the possible existence of past geographic barriers acting over populations of Ctenomys, during the Holocene.