Adriana Gava

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.

CHARACTERIZATION OF A HYBRID ZONE BETWEEN CHROMOSOMALLY DIVERGENT POPULATIONS OF CTENOMYS MINUTUS(RODENTIA: CTENOMYIDAE)

Abstract This paper describes a stable chromosomal polymorphism in a species of tuco-tuco (Ctenomys minutus) and examines the dynamics of a narrow hybrid zone between chromosomal races distributed parapatrically on the coastal plain of southeastern Brazil. A cytogenetic survey studied 132 specimens of C. minutus from 22 trapping sites within the contact zone and surrounding areas. Seven polymorphic sites were identified; at all other sites, 2n was fixed for 2n = 46 or 48. A single chromosomal rearrangement is involved in the observed variation, which served as a diallelic Mendelian character in a Hardy–Weinberg analysis. Pooling polymorphic populations revealed that the mating system is random among genotypes (i.e., no mating bias is present or there is no purifying selection). Observed frequency of the metacentric chromosome follows a clinal variation. The hybrid zone is located along an ecotone, which could imply that exogenous selection is important in its maintenance. However, applying static-cline methodologies revealed weak exogenous selection, and it is possible that the hybrid zone could be the result of a relatively recent secondary contact with a width determined primarily by neutral diffusion. A historical scenario for the time, place or origin, and spread of the species and its chromosomal races is also presented.

A new karyotype for the genus Cavia from a southern island of Brazil (Rodentia - Caviidae)

RESUMO A variacao cariotipica nas especies de mamiferos e bastante comum e geralmente causada pela fusao de cromossomos acrocentricos. Foi descrito neste trabalho um novo cariotipo, com 2n = 62 e FN = 112, para o genero Cavia proveniente das ilhas Moleques do Sul, da costa sul do Brasil. Foram analisados os cariotipos de dois machos e quatro femeas que possuiam 24 pares de cromossomos com dois bracos e seis pares de acrocentricos. O par sexual era constituido por um cromossomo X metacentrico grande e um Y acrocentrico. As bandas C estavam localizadas nas regioes centromericas e pericentromericas da maioria dos cromossomos, com excecao de alguns acrocentricos e os cromossomos de dois bracos menores. As regioes organizadoras de nucleolo ocorreram em dois cromossomos com dois bracos e o padrao de bandamento G foi tambem apresentado.

The role of chromosomal rearrangements and geographical barriers in the divergence of lineages in a South American subterranean rodent (Rodentia: Ctenomyidae: Ctenomys minutus )

Identifying factors and the extent of their roles in the differentiation of populations is of great importance for understanding the evolutionary process in which a species is involved. Ctenomys minutus is a highly karyotype–polymorphic subterranean rodent, with diploid numbers ranging from 42 to 50 and autosomal arm numbers (ANs) ranging from 68 to 80, comprising a total of 45 karyotypes described so far. This species inhabits the southern Brazilian coastal plain, which has a complex geological history, with several potential geographical barriers acting on different time scales. We assessed the geographical genetic structure of C. minutus, examining 340 individuals over the entire distributional range and using information from chromosomal rearrangements, mitochondrial DNA (mtDNA) sequences and 14 microsatellite loci. The mtDNA results revealed seven main haplogroups, with the most recent common ancestors dating from the Pleistocene, whereas clustering methods defined 12 populations. Some boundaries of mtDNA haplogroups and population clusters can be associated with potential geographical barriers to gene flow. The isolation-by-distance pattern also has an important role in fine-scale genetic differentiation, which is strengthened by the narrowness of the coastal plain and by common features of subterranean rodents (that is, small fragmented populations and low dispersal rates), which limit gene flow among populations. A step-by-step mechanism of chromosomal evolution can be suggested for this species, mainly associated with the metapopulation structure, genetic drift and the geographical features of the southern Brazilian coastal plain. However, chromosomal variations have no or very little role in the diversification of C. minutus populations.

A new karyotype for Cavia magna (Rodentia: Caviidae) from an estuarine island and C. aperea from adjacent mainland

We describe a new karyotype for Cavia magna Ximenez, 1980 from an estuarine island and the karyotype of Cavia aperea Erxleben, 1777 from an adjacent mainland. The species have differences in diploid number (2n), autosomal fundamental number, quantity, and distribution of heterochromatin as dissimilar distributions of the nucleolus-organizing regions (Ag-NORs). The C. aperea karyotype has a diploid number of 64 as previously reported for C. aperea and most other Cavia species. In contrast, this new C. magna karyotype exhibits a variant diploid number of 2n = 62, considering that previous work reported a karyotype of 2n = 64 for C. magna. The discovery of a distinct diploid number within C. magna represents the first record of intra-specific chromosomal variation in a species of Caviidae. The diploid number of 2n = 62, heterochromatin quantity, Ag-NOR distributions, and inversed X chromosome from this population of C. magna are as seen in the geographically proximate (Cavia intermedia Cherem Olimpio and Ximenez; intermediate Cavy). These data provide further evidence supporting C. magna as the sister species of C. intermedia.

Pequenos mamíferos não-voadores (Didelphimorphia, Rodentia) em dois fragmentos de mata de restinga de Rio Grande, Planície Costeira do Rio Grande do Sul

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.

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.

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.

Mammalia, Chiroptera, Rio Grande, state of Rio Grande do Sul, Brazil

Herein we present a checklist of the bat species recorded in the municipality of Rio Grande, coastal plain of Rio Grande do Sul state. Thirteen species of three families were recorded through field sampling, collection specimen analysis and bibliography compilation. Molossidae and Vespertilionidae, both with five recorded species, were the most representative families, while three species of Phyllostomidae were recorded. Seven species were found in urban areas. In the sampled natural environments, six species were found in riparian systems, being Myotis albescens and Molossus sp. recorded only in these formations. Riparian systems, hence, can represent relevant habitats for chiropteran conservation in coastal areas of southernmost Brazil.

Shape and size variation of Jenynsia lineata (Jenyns 1842) (Cyprinodontiformes: Anablepidae) from different coastal environments

A key question in ecological speciation is to understand the causes and consequences of phenotypic divergence among populations. In this work, we analyzed the body shape and size variation in Jenynsia lineata across different coastal habitats along the Atlantic coast of South America. We hypothesized that J. lineata presents morphological variations to inhabit contrasting environments and that these adaptations are sex specific. We analyzed 13 populations from five coastal habitats, using linear and geometric morphometry, and tested the correlation of body shape variation with environmental variables to understand which environmental factors may influence body shape and size variation. Jenynsia lineata showed differences in body shape and size among populations, and these differences are specific to each sex. While females showed a variation in the caudal peduncle correlated with water current, we did not find such trait variation and correlation in males. Alternatively, individuals from marine rocky pools have a convex body curvature along the dorsal profile and larger body sizes, in both sexes. With these results, we describe the shape and size morphological variation of J. lineata and discuss this uncommon habitat-dependent sexual dimorphism in a Neotropical livebearer fish.