33 research outputs found

    Karyotypic data of five ant taxa from the Brazilian Atlantic rainforest

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    The Brazilian Atlantic rainforest is an endangered biome and biodiversity hotspot. Ant cytogenetic studies from this biome showed remarkable chromosomal diversity among species, and provided useful insights on phylogeny, chromosomal evolution, and taxonomy. In this study, we karyotyped five ant taxa from the Atlantic rainforest. The karyotypes observed were Pheidole germaini 2n=22, Pheidole sp. flavens group 2n=20, Brachymyrmex admotus 2n=18, Camponotus atriceps 2n=40, and Odontomachus haematodus 2n=44. The data obtained for Pheidole spp. represent the first chromosomal record for the genus in Brazil and provide insights on the chromosomal evolution of P. germaini. Karyotypic information from B. admotus brings the genus back to the cytogenetic scenario after decades of neglect. No karyotype variations were observed among the C. atriceps and O. haematodus from different already studied populations, corroborating their status as good species. This study increased the cytogenetic knowledge of ants from the Brazilian Atlantic rainforest

    Cytogenetic studies in Trachymyrmex holmgreni Wheeler, 1925 (Formicidae: Myrmicinae) by conventional and molecular methods

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    Over the past several decades, ant cytogenetic studies have focused on chromosome number and morphology; however, recently, additional information concerning heterochromatin composition and 45S rDNA location has become accessible. The fungus-growing ants are a peculiar ant group that cultivates fungus for food, and Trachymyrmex is suspected to be the sister group of leafcutter ants. Cytogenetic data are so far available for sixn Trachymyrmex species. The present study aimed to increase the knowledge about Trachymyrmex cytogenetics by the chromosomal characterization of Trachymyrmex holmgreni including the karyotyping, fluorochromes staining, 18S rDNA, and microsatellite (GA)15 fluorescence in situ hybridization (FISH). Karyotyped samples from four ant colonies showed 2n = 20 metacentric chromosomes. Centromeric heterochromatin rich in GC base pairs was detected in all chromosomes. FISH revealed the presence of rDNA clusters on the fourth chromosome pair, and an intense spreading of the microsatellite (GA)15 including exclusively euchromatic areas of the chromosomes. The GC-rich heterochromatin observed in different ant species may have a common origin and, thus, phylogenetic implication that needs to be further investigated. To the best of our knowledge, this study is the first report of the use of chromosomal physical location of repetitive DNA sequences by means of microsatellite probes in Formicidae

    Estimation of Nuclear Genome Size of Three Species of Camponotus (Mayr, 1861) (Hymenoptera: Formicidae: Formicinae) and Their Cytogenetic Relationship

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    The chromosome variability among ant species is remarkable, and the processes generating such variation are still under discussion since polyploidy has been observed in some distinct taxa. The chromosome number of species belonging to the Camponotus, subgenera Myrmothrix and Myrmobrachys, are highly different, whereas, the first subgenus has double the number of chromosomes of the second. In order to test the hypothesis of chromosome number doubling through polyploidy, the genome sizes of Camponotus (Myrmothrix) rufipes, Camponotus (Myrmothrix) renggeri and Camponotus (Myrmobrachys) crassus were estimated by flow cytometry. The chromosome number of specimens from the nests studied was also defined. No significant variation was noted in the genome size among them. The mean haploid genome size value (1C) of workers for the three species was 286.16 Mpb (0.29 pg). The polyploidy hypothesis can be ruled out as an evolutionary step linking the karyotype variations among the three studied species since the genome size of C. crassus with 2n = 20 chromosomes was the same as that of C. rufipes and C. renggeri with 2n = 40. The lack of variation in the amount of DNA between the related species C. rufipes and C. renggeri also demonstrate that flow cytometry is not an adequate approach to distinguish them. Our results highlight the importance of combining distinct methods, DNA quantification, and cytogenetics from the same colony. Understanding the path of chromosome evolution of three species with distinct degrees of relatedness should provide further information in enriching our knowledge about the Minimum Interaction Theory

    Physical chromosomal mapping of major ribosomal genes in 15 ant species with a review of hypotheses regarding evolution of the number and position of NORs in ants

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    Recently, hypotheses regarding the evolutionary patterns of ribosomal genes in ant chromosomes have been under discussion. One of these hypotheses proposes a relationship between chromosomal location and the number of rDNA sites, suggesting that terminal locations facilitate the dispersion of rDNA clusters through ectopic recombination during meiosis, while intrachromosomal locations restrict them to a single chromosome pair. Another hypothesis suggests that the multiplication of rDNA sites could be associated with an increase in the chromosome number in Hymenoptera due to chromosomal fissions. In this study, we physically mapped rDNA sites in 15 new ant species and also reviewed data on rDNA available since the revision by Teixeira et al. (2021a). Our objectives were to investigate whether the new data confirm the relationship between chromosomal location and the number of rDNA sites, and whether the increase in the chromosome number is significant in the dispersion of rDNA clusters in ant karyotypes. Combining our new data with all information on ant cytogenetics published after 2021, 40 new species and nine new genera were assembled. Most species exhibited intrachromosomal rDNA sites on a single chromosome pair, while three species showed these genes in terminal regions of multiple chromosome pairs. On one hand, the hypothesis that the chromosomal location of rDNA clusters may facilitate the dispersion of rDNA sites in the ant genome, as previously discussed, was strengthened, but, on the other hand, the hypothesis of chromosomal fission as the main mechanism for dispersion of ribosomal genes in ants is likely to be refuted. Furthermore, in certain genera, the location of rDNA sites remained similar among the species studied, whereas in others, the distribution of these genes showed significant variation between species, suggesting a more dynamic chromosomal evolution

    Pervasive gaps in Amazonian ecological research

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    Pervasive gaps in Amazonian ecological research

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    Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

    Pervasive gaps in Amazonian ecological research

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    Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

    Primeiro relato de hibridização espontânea entre Astyanax giton Baird & Girard 1854 e Oligosarcus argenteus Günther 1864 (Pisces : Characidae): inferências ecológicas e filogenéticas

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    A complexa famĂ­lia Characidae Ă© parte da fauna ictiolĂłgica neotropical e conta com várias espĂ©cies e gĂŞneros em condição de Incertae Sedis. Os gĂŞneros Astyanax e Oligosarcus, considerados muito aparentados, estĂŁo incluĂ­dos nesta famĂ­lia e abrangem espĂ©cies de pequeno tamanho e expressiva abundância em muitos rios e cĂłrregos da AmĂ©rica do sul. Na bacia do rio Doce, no sudeste brasileiro, uma análise morfolĂłgica preliminar permitiu a identificação de cinco peixes “semelhantes Ă  Astyanax” que continham no seu osso maxilar de 8 a 13 dentes. Esses cinco peixes, chamados no presente trabalho de dentuços, foram coletados em simpatria com as espĂ©cies Astyanax bimaculatus (Linneaus, 1758), Astyanax giton (Eigenmann, 1908) e Oligosarcus argenteus GĂĽnther, 1864. De modo a determinar a natureza biolĂłgica dos dentuços, foi realizado um estudo multidisciplinar envolvendo dados morfolĂłgicos citogenĂ©ticos e moleculares. Os dentuços apresentaram configurações intermediárias entre as espĂ©cies A. giton e O. argenteus no que diz respeito ao nĂşmero de escamas na linha lateral e ao nĂşmero de dentes no osso maxilar. As análises citogenĂ©ticas, feitas atravĂ©s das tĂ©cnicas de Giemsa, bandeamento NOR, bandeamento-C, fluorocromos, e FISH, indicaram que todas as espĂ©cies de caracĂ­deos contaram com nĂşmero diploide 2n=50 cromossomos diferindo, porĂ©m, em vários caracteres de sua morfologia cromossĂ´mica. Os dentuços caracterizaram-se por apresentar altos Ă­ndices de variação cromossĂ´mica tanto intra- como inter-individual. AlĂ©m do mais, eles contaram com vários cromossomos nĂŁo pareáveis assim como cromossomos de tamanho diminuto que nĂŁo sĂŁo observados em nenhuma daquelas espĂ©cies simpátricas de Characidae. TrĂŞs espĂ©cimes dos dentuços apresentaram seu fragmento de DNA do gene mitocondrial citocromo b (475 pb) idĂŞntico aquele de O. argenteus e, contudo, todos os dentuços compartilhavam mais alelos ISSR com os espĂ©cimes de A. giton do que com os espĂ©cimes de O. argenteus. Por outro lado, uma espĂ©cie de dentuço conta com o gene cyt. b idĂŞntico aquele das espĂ©cies de A. giton estudadas. A análise de fragmentos ITS-1 (1123 pb) mostrou que os dentuços tĂŞm sequencias mais relacionadas Ă  Oligosarcus argenteus. Os dados, desse modo, sugeriram que os dentuços sĂŁo hĂ­bridos entre as espĂ©cies A. giton e O. argenteus representando assim o primeiro caso de hibridismo espontâneo entre dois gĂŞneros de peixes neotropicais. A relevância de tal descoberta para a biologia da conservação e para as investigações filogenĂ©ticas foram discutidas.Conselho Nacional de Desenvolvimento CientĂ­fico e TecnolĂłgicoWithin the Neotropical fish fauna, the taxonomically complex family Characidae has many species and genera in Incertae Sedis condition. Within this family, the closely related genera Astyanax and Oligosarcus are represented by small sized fishes that are an expressive proportion of the freshwater biodiversity in many rivers of South America. In the Doce River Basin, Southeastern Brazil, a preliminary morphologic analysis indicated the presence of 5 Astyanax-like fish with unusually high numbers (8-13) of maxillary teeth which are referred as “toothed morphs”. These fishes were collected in sympatry with Astyanax bimaculatus (Linneaus, 1758), Astyanax giton (Eigenmann, 1908), and Oligosarcus argenteus GĂĽnther, 1864. To determine the biological status of them a comparative multidisciplinary approach involving morphologic, cytogenetic and molecular data was conducted, with the toothed morphs and their sympatric species. The toothed morphs showed an intermediate position in lateral line scale numbers and maxillary teeth number between A. giton and O. argenteus. Cytogenetic analyses (Giemsa, NOR, C-banding, fluorochromes and FISH) indicated that all sympatric characids were 2n=50, although they differed from each other in many other karyotypic characters. The toothed morphs were characterized by high levels of intra and inter-individual chromosomal variation including several unpairable chromosomes and tiny chromosomes that were not observed in either of the other sympatric species. Three toothed morphs specimens had their cytochrome b DNA fragment (475 bp) identical to O. argenteus, with one exception which its cyt. b DNA sequence was identical to A. giton. Moreover, all toothed morphs ITS-1 DNA sequences were characterized by their similitude to those sequences of Oligosarcus argenteus. On the other hand, all toothed morphs shared more ISSR alleles with A. giton. The data suggested that the toothed morphs were hybrids between A. giton and O. argenteus, representing the first evidence for spontaneous hybridization between two Neotropical fish genera. The relevance of such findings in conservation biology and phylogeny assessment were discussed

    Cytogenetics of Strumigenys louisianae Roger, 1863 (Formicidae: Myrmicinae) from North-eastern Amazonia shed light on a difficult species complex

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    International audienceCytogenetic techniques provide powerful insights on species-rich taxa–such as ants–allowing better understanding of their biodiversity. Some hints on evolutionary paths can be observed through comparative populational cytogenetics among different ant groups. In this study, the karyotype of Strumigenys louisianae Roger from the Amazon rainforest is described and showed diploid chromosome number of 26 chromosomes. This configuration intriguingly contrasts with the already described karyotype for this species from the Atlantic rainforest with only 2n = 4 chromosomes. 18S rDNA site were detected on the pericentromeric region of the long arm of a metacentric pair and co-localizing with GC-rich chromatin. Recurrent synonymizations of S. louisianae may not reflect the species status of this taxon. The karyotypic differences and the observable morphological variation between the populations of both localities corroborates the idea of a species complex within S. louisianae. The morphology of S. louisianae from the Amazonian region is similar to that from the United States, the type locality. On the other hand, specimens from the Atlantic rainforest are more similar to the junior synonym Strumigenys unidentata Mayr. This study reinforces the need of taxonomical revision in S. louisianae by means of integrative taxonomy approaches
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