Coastal Plain Of Southern Brazil Research Articles

MICROSATELLITE ANALYSIS OF A HYBRID ZONE BETWEEN CHROMOSOMALLY DIVERGENT POPULATIONS OF CTENOMYS MINUTUS FROM SOUTHERN BRAZIL (RODENTIA: CTENOMYIDAE)

This paper describes variation at 6 microsatellite loci in 107 specimens of Ctenomys minutus from a chromosomal hybrid zone on the coastal plain of southern Brazil. Of the 56 alleles uncovered in this study, 39.2% are exclusive to alternative cytotypes or the contact populations. Clinal variation is not obvious because there are no microsatellite fixed differences among chromosomally divergent populations, but variation at Hai 2 locus is gradual across the zone. The local populations are highly differentiated and structured. The moderate estimated values of gene flow follow an isolation-by-distance model, which predicts concentration of an allele or a homozygous genotype in patches with generations of individuals with limited dispersal and mating by proximity. Analysis of populations distantly localized from the contact zone probably will provide further insights in the genetic relationship among cytotypes.

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This is a paleoclimatic synthesis based on the results of seven cores from the Brazilian Coastal Plain and adjacent low areas (Central Depression and Serra Geral, southern foothill valley) of Rio Grande do Sul, published by different authors. The objective is asses to the Holocene history of the Atlantic rain forest stricto sensu ( str. s. ), a dense ombrophilous forest in the extreme southern Brazil. The comparative analysis indicates scarce presence of the first taxa of the Atlantic rain forest str. s. at the beginning of the Holocene (probably due to warmer and wetter climate) and sea-level oscillations. Subsequently marsh forest expansion took place after 4,000 BP on the coast, after sea regression and desalination of the soils. In the adjacent low areas from the coast, favored by this warmer and wetter climate without marine influence, expansion of the forest seems to have occurred earlier, at about 4,000 BP. In the Serra Geral southern foothill valleys and Central Depression forest expansion occurred much earlier, at ca . 6,000 BP. These data agree with the coastward migration of the Atlantic rain forest str. s. from inner continental areas colonizing the Coastal Plain of southern Brazil in the Late Holocene.

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.

A rapid fish radiation associated with the last sea-level changes in southern Brazil: the silversideOdontesthes perugiaecomplex

Coastal freshwater fishes provide valuable models for studying the role of the last glaciations in promoting speciation. To date, the great majority of studies are of Northern Hemisphere taxa, and reflect the influence of vicariant events during, or prior to, the Pleistocene. Microsatellite markers and mitochondrial DNA sequences were used to investigate patterns of population divergence and evolutionary relationships in a freshwater group of silverside fishes (Odontesthes perugiae complex), endemic to the recently formed coastal plain of southern Brazil. Lacustrine morphotypes showed concordant patterns of genetic and morphological divergence consistent with the geographical history of the coastal plain. The results support the proposal of a silverside radiation chronologically shaped by the sea-level changes of the Pleistocene and Holocene. The radiating lineage comprises a minimum of three allopatric and two sympatric lacustrine species. Four species displayed extremely high levels of genetic variation and some of the most rapid speciation rates reported in fishes. These features were related to a marine-estuarine origin of the radiation. To the best of our knowledge, this study represents the first molecular phylogeographic survey of a coastal radiation in South America.

ENVIRONMENTAL ANALYSIS OF THE LOWER CAMAQUÃ RIVER WATERSHED (BRAZIL) — A STUDY OF PLANNING AND ENVIRONMENTAL EDUCATION

The Lower Camaquã River Watershed is settled within two major geologic systems: the Pre-Cambrian basement and the Southern Brazilian Coastal Plain. Geological, environmental and socio-economic characteristics of this section of the watershed provide a heterogeneous landscape mosaic of interconnected natural and anthropic elements. In this work, the Sapato Creek watershed is used as a case study for an environmental analysis of the Lower Camaquã system. Landscape elements were identified, described and modelled as a way to understand their structure and dynamics. Satellite images (1:100,000) and field checking were utilised in the characterisation of the landscape elements and identification of land use categories. The results supported the characterisation of the structural and functional organisation of the watershed, potential impacts and the suitability of land use for the system. A conceptual methodological strategy is presented as an effective tool for transferring the recommendations produced in this work to decision-makers directly involved with environmental management in the region. The strategy relies on the interaction between scientists, decision-makers and watershed stakeholders to foster the identification of possible educational actions that could lead to a rational use of land and natural resources in the watershed.

Microsatellite loci isolated from Odontesthes argentinensis and the O. perugiae species group and their use in other South American silverside fish.

Odontesthes (Atheriniformes: Atherinopsidae) is a diverse and widespread genus of silverside fish, containing between 15 and 22 recognized species distributed across marine, estuarine and freshwater environments of temperate South America (Dyer 1993). The marine-estuarine O. argentinensis ranges from the south-east coast of Brazil (25 ° S) to Chubut, in Argentina (43 ° S) (Dyer 1993). It is an economically significant resource for local fisheries in Brazil, Uruguay and Argentina (de Buen 1953) and a suitable organism for bioassay studies (Phonlor & Cousin 1997). The freshwater O. perugiae species group is composed of morphotypes mostly distributed along the complex system of lagoons of the coastal plain of southern Brazil (Dyer 1993). We are using molecular markers to understand historical and recent biogeographic scenarios that have shaped the evolution of Odontesthes. Results based on sequences of three mitochondrial DNA genes revealed that O. argentinensis and O. perugiae are closely related and have recently radiated in the coastal areas of southern Brazil (L. Beheregaray, unpublished). We developed microsatellites for these taxa to identify population structures, clarify taxonomic problems and reconstruct their phylogeographic history. Evidence for the application of these primers in a wide range of Neotropical silverside species is presented. To our knowledge, these are the first microsatellite loci isolated from fish native to South America, a continental area with one of the most diverse ichthyofaunas of the planet. Genomic DNA of O. argentinensis and the O. perugiae species group was extracted by salting-out (Sunnucks & Hales 1996), pooled together, and digested with Hae III, Eco RV and Alu I. Fragments ranging between 430 and 550 bp were cloned into Sma I cut pUC18 and a resulting library of approximately 25 000 colonies was screened with radiolabelled CA/GT and GA/CT co-polymers according to Taylor et al . (1994). Putative positive clones were rescreened, and 31 clones encompassing different hybridization intensities were selected for sequencing. This strategy increased our chances of choosing both long and short repeats as they are expected to inform at different levels of divergence (see below). Thirteen of the clones sequenced contained microsatellites with appropriate flanking regions for primer design. Variation at each of the 13 loci was assessed by the polymerase chain reaction (PCR) using a 10 μ L radiolabelled reaction containing 50–100 ng of template DNA, 12 pmol of each primer, 0.5 units of Taq DNA polymerase (Promega), 200 μ m of dCTP, dGTP, and dTTP, 20 μ m of dATP, 2 m m MgCl 2 , 10 m m Tris-HCl (pH 8.3), 50 m m KCl, 0.1% Triton X-100 and 0.05 μ L [ α 33 P] dATP at 1000 Ci/mmol overlaid with mineral oil. PCR amplifications were performed in an MJ Research PTC100 thermocycler starting with 94 ° C for 3 min, followed by a ‘touchdown’ (32 cycles at 94 ° C/20 s, annealing/45 s and 72 ° C/60 s), and a final step of 72 ° C for 4 min. The annealing temperature of the ‘touchdown’ PCRs decreased two degrees per cycle until reaching the fifth cycle (Table 1). PCR products were separated by 6% polyacrylamide gel electrophoresis and visualized by autoradiography following Taylor et al. (1994). Twelve loci were successfully amplified and showed high levels of polymorphism and heterozygosity (Table 1). Number of alleles per locus ranged from 6 to 33 and expected heterozygosities from 0.42 to 0.94. An ongoing screening shows that loci with short and less variable repeats (e.g. Odont16) better differentiate between marine and freshwater lineages, while loci with long repeats and higher polymorphism (e.g. Odont07) are useful to reveal fine-scale population structures (L. Beheregaray, unpublished). Marine populations have shown a significant larger number of alleles at all loci than freshwater populations (202 and 120 alleles, respectively, P after a Wilcoxon rank test = 0.002). This difference in genetic variability was expected due to the relatively reduced subpopulation sizes of freshwater fish (Ward et al . 1994). All primer sets were also tested without extra optimization in several Odontesthes species (including the commercially important O. bonariensis ) and in the diverged Basilichthys semotilus, a silverside endemic to freshwater environments west of the Andes Mountains. Amplification and polymorphism was extensive (Table 2), indicating that these markers are potentially useful for a wide range of population studies of wild and captive South American silverside species.