Assessing ploidy levels and karyotype structure of the fire ant Solenopsis saevissima Smith, 1855 (Hymenoptera, Formicidae, Myrmicinae)

The family Formicidae is composed of ants that organize themselves into castes in which every individual has a joint organizational function. Solenopsis Westwood, 1840 is an ant genus with opportunistic and aggressive characteristics, known for being invasive species and stings that cause burning in humans. This genus is particularly difficult to classify and identify since its morphology provides few indications for species differentiation. For this, a tool that has been useful for evolutionary and taxonomic studies is cytogenetics. Here, we cytogenetically studied Solenopsis saevissima Smith, 1855 from Ouro Preto, Minas Gerais, Brazil. We evaluated the occurrence of polyploid cells in individuals and colonies by conventional cytogenetics. A total of 450 metaphases were analyzed and counted. Chromosome counts of individuals and colonies showed varied numbers of ploidies, from n = 16 to 8n = 128. The karyomorphometrical approach allowed determination of the following karyotypes: n = 10 m + 4 sm + 2 st, 2n = 20 m + 8 sm + 4 st, and 4n = 40 m + 16 sm + 8 st. Polyploidy can be found naturally in individuals and colonies and may represent an adaptative trait related to widespread distribution and invasion ability of new habitats

Geographical distribution patterns and niche modeling of the iconic leafcutter ant Acromyrmex striatus (Hymenoptera: Formicidae).

Ants are considered one of the most successful groups in the planet?s evolutionary history. Among them highlights the fungus-farming ants of the genera Atta and Acromyrmex that occur throughout most of the Americas. Within the Acromyrmex genus, the species A. striatus distinguishes from other Acromyrmex species as its morphology and karyotype differ from its congeners. This species is found in open environments of dry climate in the southern States of Brazil, Argentina, Paraguay and Uruguay; however, little is known about the current distribution of the species. This article aimed to investigate the current distribution of the species by compiling its known distribution and discussing its distributional range. To achieve this, published and unpublished data obtained through a literature search and active collections in various locations were compiled. Published and unpublished data revealed that 386 colonies were recorded, distributed across four countries where its occurrence is known. Environmental factors, such as temperature, humidity, soil type and vegetation, as well as historical geological and climate events that have modified Earth?s surface may have influenced species distribution patterns. In the Neotropics, the environmental factors that most impacted the distribution of species were the glaciation periods that occurred in the Quaternary, leading to a great migratory process. These factors may have contributed to the current geographical distribution of A. striatus

Chromosomal dynamics in space and time : evolutionary history of Mycetophylax ants across past climatic changes in the Brazilian Atlantic coast.

Fungus-farming ants of the genus Mycetophylax exhibit intra and interspecific chromosome variability, which makes them suitable for testing hypotheses about possible chromosomal rearrangements that endure lineage diversification. We combined cytogenetic and molecular data from Mycetophylax populations from coastal environments to trace the evolutionary history of the clade in light of chromosomal changes under a historical and geographic context. Our cytogenetic analyses revealed chromosomal differences within and among species. M. morschi exhibited three distinct karyotypes and considerable variability in the localization of 45S rDNA clusters. The molecular phylogeny was congruent with our cytogenetic findings. Biogeographical and divergence time dating analyses estimated that the most recent common ancestor of Mycetophylax would have originated at about 30?Ma in an area including the Amazon and Southern Grasslands, and several dispersion and vicariance events may have occurred before the colonization of the Brazilian Atlantic coast. Diversification of the psammophilous Mycetophylax first took place in the Middle Miocene (ca. 18?10?Ma) in the South Atlantic coast, while ?M. morschi? lineages diversified during the Pliocene-Pleistocene transition (ca. 3?2?Ma) through founder-event dispersal for the Northern coastal regions. Psammophilous Mycetophylax diversification fits into the major global climatic events that have had a direct impact on the changes in sea level as well as deep ecological impact throughout South America. We assume therefore that putative chromosomal rearrangements correlated with increased ecological stress during the past climatic transitions could have intensified and/or accompanied the divergence of the psammophilous Mycetophylax. We further reiterate that ?M. morschi? comprises a complex of at least three well-defined lineages, and we emphasize the role of this integrative approach for the identification and delimitation of evolutionary lineages

Molecular phylogenetic reconstruction and localization of the (TTAGG)n telomeric repeats in the chromosomes of Acromyrmex striatus (Roger, 1863) suggests a lower ancestral karyotype for leafcutter ants (Hymenoptera).

Chromosome counts and karyotype characterization have proved to be important features of a genome. Chromosome changes during the diversification of ants might play an important role, given the diversity and success of Formicidae. Comparative karyotype analyses on ants have enriched and helped ant systematics. Among leafcutter ants, two major chromosome counts have been described, one frequent in Atta Fabricius, 1804 (2n = 22 in all Atta spp. whose karyotype is known) and the other frequent in Acromyrmex Mayr, 1865 (2n = 38 in the majority of species whose karyotype is known). The main exception is Acromyrmex striatus (Roger, 1863), which harbors a diploid chromosome set of 22. Here we describe the use of fluorescence in situ hybridization (FISH) with telomeric probes with (TTAGG)6 repeats to describe the telomere composition of A. striatus and to recover potential interstitial non-telomeric signals that may reflect fusion events during the evolution of leafcutter lineage from 38 to 22 chromosomes. Further, we reconstruct the ancestral chromosome numbers of the leafcutter clade based on a recently proposed molecular phylogenetic hypothesis and phylogenomic tree. Distinct signals have been observed in both extremities on the telomere chromosomes of A. striatus. Non-telomeric signals have not been retrieved in our analysis. It could be supposed that the low-numbered karyotype indeed represents the ancestral chromosome number of leafcutters. The phylogenetic reconstruction also recovered a low chromosome number from the diverse approaches implemented, suggesting that n = 11 is the most likely ancestral karyotype of the leafcutter ants and is a plesiomorphic feature shared between A. striatus and Atta spp

Evolutionary history of species of the genus Mycetophylax Emery, 1913 (Hymenoptera: Formicidae): ants endemic of restinga

As formigas do gênero Mycetophylax pertencem à tribo Attini e são restritas a ecossistemas de dunas da costa do oceano Atlântico. Estas formigas são um grupo taxonômico interessante para o estudo dos efeitos das mudanças climáticas e geológicas do passado sobre a evolução dos habitats abertos costeiros da Mata Atlântica, conhecidos como restinga. Assim, o principal objetivo deste trabalho foi conduzir um estudo sobre a evolução do gênero Mycetophylax por meio de diferentes abordagens, a fim de fornecer informações sobre a diversificação e evolução destes organismos em ambientes abertos de dunas. Para atingir nossos objetivos conduzimos estudos de filogenia molecular, citogenética, e genética de populações, em um contexto evolutivo. As espécies foram caracterizadas citogeneticamente e seus cromossomos foram submetidos às técnicas de bandamento C e coloração por fluorocromos. A integração desses dados a uma hipótese filogenética permitiu a inferida de uma hipótese de evolução cromossômica para o gênero Mycetophylax. A análise filogeográfica de M. simplex permitiu testar o impacto das mudanças paleoambientais sobre a história das populações da costa brasileira sul e sudeste do Atlântico. Além disso, avaliamos como os eventos de regressão e transgressão marinha influenciou a estrutura demográfica desta espécie ao longo de sua área de distribuição. A hipótese filogenética inferida a partir dos genes nucleares wingless e long wave rhodopsin sugerem que o gênero Mycetophylax, em sua atual designação, é monofilético. As espécies M. simplex e M. conformis agruparam em um ramo que é grupo irmão de M. morschi e todas as espécies formam um grupo monofilético com alto suporte estatístico. M. morschi apresentou dois cariótipos, com colônias 2n=26 e 2n=30. M. conformis e M. simplex apresentaram o número diploide de cromossomos igual a 30 e 36, respectivamente. Observou-se que os resultados dos padrões de bandamento cromossômico concordam com a hipótese de filogenia molecular inferida para o gênero. O cariótipo ancestral estimado por meio da abordagem filogenética bayesiana foi n=17. Este resultado sugere que eventos de fusão cromossômica estiveram envolvidos na redução dos cariótipos de M. morschi e M. conformis e fissão cromossômica em M. simplex. A genealogia do gene mitocondrial citocromo oxidase I (COI) de M. simplex sugeriu uma baixa estrutura filogeográfica. Os haplótipos estiveram distribuídos em toda a sua área de distribuição ao longo da costa do Atlântico. Não foram identificadas barreiras evidentes ao fluxo gênico entre as populações de M. simplex e elas parecem ter experimentado um longo período de estabilidade demográfica até expansões populacionais recentes. Estas expansões foram coincidentes com os níveis mais baixos do oceano durante o Quaternário. Esses resultados oferecem evidências adicionais convincentes de que os habitats abertos da costa do Atlântico Sul foram ambientes dinâmicos que influenciaram a diversificação e distribuição das espécies.The ants of the genus Mycetophylax belongs to the tribe Attini and are endemic to sand dune coastal environments of Atlantic Ocean. These ants are an ideal group to examine the impact of geological and climatic changes over the past on the evolution of open habitats associated with Atlantic Forest, known as restinga. The main aim of this thesis is to evaluate the evolution of the genus Mycetophylax by means of different approaches in order to provide insights about the diversification of these ants on the harsh environment of coastal sand dunes. In order to achieve our objectives, the three species of the genus were studied using molecular phylogenetics, cytogenetics and populations genetics, under an evolutionary context. The three species were cytogenetically characterized and the chromosomes were submitted to banding techniques (C-banding and Fluorochrome staining). Using an integrative approach we inferred a chromosome evolution hypothesis for the genus Mycetophylax. A phylogeographic stud was carried out with the species M. simplex to test the relative impact of palaeoenvironmental changes on the population history of south and southeast Brazilian Atlantic Coast. Besides, we tested how the marine regression and introgression had facilitated the gene flow from south to northern distribution of this ant. M. simplex and M. conformis appear as a sister group of M. morschi and the genus are monophyletic, as suggested by published morphological analysis. M. morschi showed a polymorphic number of chromosomes, with colonies showing 2n=26 and colonies 2=30 chromosomes. M. conformis presented a diploid chromosome number of 30 chromosomes, while M. simplex showed 36 chromosomes. The banding patterns were agreement with the molecular phylogenetic hypothesis inferred based on nuclear protein-coding genes. The ancestral haploid chromosome number inferred by Bayesian phylogenetic approach of Mycetophylax genus was 17. These results also claimed that fusions were responsible for the evolutionary reduction in chromosome numbers of M. conformis and M. morschi karyotypes and a fission rearrangement towards M. simplex karyotype. The mitochondrial DNA (mtDNA) gene genealogy of M. simplex suggested a shallow phylogeographic structure with haplotypes distributed throughout their distribution range along the Atlantic Coast. There was no evident genetic break between populations and they seem to have experienced a long period of demographic stability until population expansions that were coincident with the lowest level of the sea during the quaternary. Our findings offer compelling evidences that the coastal open habitats of South Atlantic were an evolutionary dynamic environment underpinning species diversity and distribution.Fundação de Amparo a Pesquisa do Estado de Minas Gerai

Determinants of ant communities in Restinga

O litoral brasileiro apresenta aproximadamente 9.200 quilômetros de extensão, das quais 5.000 km são ocupados por ecossistema de Restinga. Este ecossistema é um conjunto de formações vegetacionais que se desenvolvem em dunas e cordões arenosos do período Quaternário dentro do domínio da Floresta Atlântica. As espécies de plantas que ocorrem em Restinga possuem elevada plasticidade, apresentando adaptações para seu desenvolvimento sob influência de vários fatores abióticos como: estresse hídrico, ventos, topografia e salinidade. Tais fatores condicionam a ocorrência e a distribuição das comunidades vegetais em ambientes de Restinga, e similarmente, devem influenciar a distribuição e a diversidade da fauna animal. O presente estudo teve por objetivo testar o pressuposto de que a riqueza de espécies de formigas aumenta com o aumento da distância em que se encontram em relação ao oceano e as seguintes hipóteses explicativas: (1) a riqueza de espécies de formigas aumenta com a riqueza de espécies de plantas, que por sua vez aumenta com a distância do mar; (2) a riqueza de espécies de formigas é diretamente proporcional a cobertura do solo por plantas e serapilheira; (3) a riqueza de espécies de formigas aumenta com a concentração de matéria orgânica no solo; (4) a riqueza de espécies de formigas diminui com o aumento da concentração de sal no solo; e (5) a riqueza de espécies de formigas responde positivamente à heterogeneidade espacial do ambiente. Além disso, nós testamos um segundo pressuposto de que diferentes fitofisionomias de Restinga possuem composição de espécies de formigas específicas. As coletas de formigas foram realizadas na Restinga herbáceo-arbustiva do Morro dos Conventos, em Araranguá (SC) utilizando armadilhas de solo. Foram instaladas 65 armadilhas distantes 10 metros entre si, em dois transectos do oceano para o continente. Em cada ponto amostral, foram coletadas as seguintes variáveis explicativas: riqueza de espécies de plantas, percentagem de cobertura vegetal e de serapilheira, concentração de matéria orgânica e sal no solo. No total, foram coletadas 71 espécies de formigas. Os resultados obtidos permitiram confirmar nossos dois pressupostos. Observamos que a riqueza de espécies de formigas está positivamente relacionada com a distância em que se encontram do mar, com a riqueza de espécies de plantas, cobertura vegetal e cobertura por serapilheira do solo. Além disso, observamos que diferentes fitofisionomias dentro da Restinga apresentam comunidades de formigas específicas, e que em geral, habitats próximos ou com condições ambientais semelhantes apresentaram maior similaridade quanto à composição de espécies. Esses resultados sugerem que a vegetação e os fatores ambientais condicionados por ela, podem ser os principais fatores determinando a riqueza e composição de espécies de formigas em Restinga.The Brazilian coast presents approximately 9,200 kilometers, which 5.000 km of them are occupied by the Restinga ecosystems. This ecosystem is a set of vegetation formations that develop in sandy plains dating from the Quaternary, within the Atlantic Forest domain. The plant species that occur in Restinga have high plasticity, presenting adaptations for their development under the influence of various biotic and abiotic factors such as drought stress, wind, topography and salinity. These factors influence the occurrence and distribution of plant communities in the Restinga, and similarly, should influence the distribution and diversity of animals. The aim of this dissertation was to test the assumption that the species richness of ants increases with distance from the ocean, as well as the following hypotheses: (1) ant species richness increases with plant species richness, which in turn increases with distance from the sea, (2) ant species richness is proportional to soil cover by plants and litter; (3) ant species richness increases with soil organic matter concentration, (4) ant species richness decreases with soil salinity, and (5) the species richness of ants responds positively to spatial heterogeneity of the environment. Moreover, we tested a second assumption that the distinct Restinga phytophysiognomies have different ant species composition. The ants were sampled in herbaceous and shrubby Restinga of the Morro dos Conventos in Araranguá (SC) using pitfall traps. Sixty-five pitfall traps were placed 10 meters away from each other in transects disposed from the ocean to the continent. At each sampling point, were collected the following explanatory variables: plant species richness, percentage of vegetation cover and litter, concentration of organic matter and salt in soil. In total, we collected 71 species of ants. Our results have confirmed both assumptions. Ant species richness was related to distance from the sea, plant species richness, soil cover by plant and litter. Moreover, we observed that different vegetation types within Restinga have specific communities of ants, where habitats near or with similar environmental conditions had higher similarity among them. These results indicate that the vegetation and environmental factors affected by them are the main factors determining the ant species richness and composition in Restinga.Fundação de Amparo a Pesquisa do Estado de Minas Gerai

Biotic and abiotic factors shaping ant (Hymenoptera: Formicidae) assemblages in brazilian coastal sand dunes: the case of Restinga in Santa Catarina

Species inhabiting Brazilian coastal sand dunes (restingas) may feature a number of adaptations in their development and survival in these physical stressful environments. The present study determined the effect of biotic and abiotic factors on the assemblage of grounddwelling ants in a sand dune ecosystem of the Santa Catarina coastal plain in Brazil. Both linear and quadratic models were significant, but the quadratic model fitted the obtained data better. Furthermore, we also found a relationship between plant species richness and distance from the ocean only by using the quadratic model. Ant species richness was correlated with plant species richness, litter and vegetation coverage. Different environmental factors associated with plant species richness may have influenced the ant species richness by increasing the diversity and amount of available resources. The vegetation may also offer protection from higher temperatures by providing shade, a humid microclimate and a source of water, which is a limiting factor in sand dune environments. Our results showed the importance of plant species richness, and soil cover by litter and plants as local characteristics determining ant species richness in sand dunes. Further studies should explore additional habitat components, such as biotic interactions, as determinants of ant species richness.Espécies que habitam a restinga apresentam adaptações para seu desenvolvimento e sobrevivência sob inúmeros fatores ambientais estressantes. A seleção de um habitat particular deve depender destes diversos componentes do ambiente físico, associado às interações biológicas. O presente estudo foi realizado na restinga herbáceo- arbustiva do Morro dos Conventos para determinar a influência da distância do oceano, fatores bióticos e abióticos sobre a comunidade de formigas de solo. Foram instaladas 65 armadilhas de solo em dois transectos arbitrários de 650 metros a partir do oceano em direção ao continente. Um total de 71 espécies de formigas foi amostrado. Os gêneros Pheidole, Solenopsis e Camponotus foram os gêneros mais representativos. Foi encontrada uma relação positiva entre distância do oceano e riqueza de espécies de formigas, bem como entre distância do oceano e riqueza de espécies de plantas. Das hipóteses testadas, apenas as que estavam relacionadas com a vegetação foram aceitas. A riqueza de espécies de formigas esteve relacionada com a riqueza de espécies de plantas e cobertura do solo. A riqueza de espécies de plantas pode ter influenciado o aumento da riqueza de espécies de formigas pelo aumento da variedade de recursos para consumo e nidificação. Além disso, a vegetação pode alterar as condições microclimáticas, com o aumento da umidade e diminuição da temperatura, fatores extremamente importantes em ambientes com alta incidência de radiação solar e altas taxas e evapotranspiração como a restinga. Esses resultados permitem sugerir a importância da vegetação, e os componentes ligados a ela, como fatores locais determinantes da riqueza de espécies de formigas em Restinga