Estudios citogenéticos e isoenzimáticos sobre poliforfismos cromosómicos en acrididae sudamericanos (Orthoptera)

El presente trabajo de tesis trata sobrepolimorfismos para cromosomas B e inversionespericéntricas analizados en tres especies de Acrididae (Orthoptera): Cylindrotettix obscurus, C. santarosae y Trinerotropis pallidipennis. Se analizaron los efectos de loscromosomas B sobre la recombinación genética y sobre lafertilidad. Con respecto a esta última, pudo demostrarse unaumento en la producción de las espermátidas anormales en losindividuos portadores de cromosomas supernumerarios de C.obscurus. Esta producción se relacionaría por un lado con unadisminución del valor adaptativo de los individuos potadores alverse afectada posiblemente la fecundidad de los machos,asi como también con mecanismos de eliminación, los cualescobran importancia en lo que respecta a su significado evolutivoya que se relacionan directamente con el mantenimiento de estospolimorfismos en las poblaciones naturales. En cuanto a las condiciones de los quiasmas (carácter esterelacionado directamente con la recombinación genetica), losresultados fueron diferentes, dependiendo estos de la poblaciónen estudio. En Cylindrotettix no se detectaron cambios en lasfrecuencias de los quiasmas de los individuos portadores de Bs. Sin embargo, en tres de las quince poblaciones analizadas de T.pallidipennis se comprobó que cuando disminuye la frecuencia dequiasmas totales existe una tendencia a una redistribución dequiasmas que ocasiona un aumento en la frecuencia de quiasmasintersticiales, los cromosomas B actuarían suprimiendo estafuerte correlación negativa interfiriendo presumiblemente con elcontrol genético sobre las condiciones del entrecruzamiento. Asimismo, en dos poblaciones de esta misma especie también pudodeterminarse una disminución en la frecuencia de quiasmasdistales y proximales en los individuos portadores de B. Ambosefectos de los cromosomas supernumerarios se describen por primera vez en el grupo. Se discute la posibilidad que lasdiferencias interpoblacionales se deberían no tanto adiferencias intrínsecas de los B, sino que podrian explicarse enterminos del acervo genético propio de cada poblacion y/o de diferencias ambientales. En T. pallidipennis se describieron además polimorfismospara diversas inversiones pericéntricas. Estos polimorfimos serelacionan con una distribución proximal y distal de quiasmas entodos los bivalentes. En todas las poblaciones se observó unatendencia a la disminución en la frecuencia de quiasmas totalescuando aumenta el número de bivalentes heteromórficos. En tresde las muestras, como se mencionó previamente, se revierteesta tendencia ya que cuando disminuye la frecuencia de quiasmastotales, a causa de los bivalentes heteromórficos, existe unaredistribución de los mismos ya que aumentan los ubicados enporciones intersticiales. Es posible que el mantenimientoexitoso de los polimorfismos cromosómicos dependa de losrequerimientos de variabilidad genetica. Tales requerimientosserán probablemente especificos para cada especie y más aun,para cada población dentro de una misma especie. Por otro lado se pudieron demostrar correlacionesestadísticamente significativas de las frecuencias de la mayoríade las secuencias cromosómicas de T. pallidipennis con laaltitud. Tres de las inversiones aumentan significativamentecuando aumenta la altitud y otras tres lo hacen a la inversa. Estos patrones de variación cromosómicase repiten en distintosgradientes y también al considerar todas las poblaciones delpaís ubicadas en regiones geográficas muy distintas y a vecesmuy distantes. Otras dos secuencias además se correlacionansignificativamente con la longitud Oeste en forma positiva ynegativa. Por último, otra secuencia presenta aparentemente unaasociación simultánea con la altitud y la latitud. Lareiteración en los patrones de variación cromosómica endistintos gradientes y también al incluir en los analisis atodas las poblaciones se consideraron como una evidenciabastante fuerte de selección natural operando en elmantenimiento de los polimorfismos cromosómicos loscoeficientes de selección no serían pequelos dadas lascaracterísticas de elevada vagilidad y fluctuaciones en losnúmeros poblacionales que presenta la especie. Como reslutado del estudio de sistemas isoenzimáticos entres poblaciones de T. pallidipennis se comprobó un nivelelevado de heterocigosis media poblacional en comparación aotros grupos de insectos. Sin embargo este nivel se repitedentro de los Acrididae en otras especies que coincidentementepresentan una gran incidencia de polimorfismos cromosómicos. Además es congruente con las características ecológicas de laespecie. En concordancia con los resultados cromosómicos sedeterminaron indices de distancia genetica que son superiores alos correspondientes a poblaciones locales, al consideraraquellas ubicadas a altitudes distintas. No ocurrió lo mismoentre las poblaciones próximas geográficamente (y ubicadas aaltitudes similares) las cuales presentaron una identidadgenética elevada. Las poblaciones ubicadas a altitudes distintasmostraron una gran diferenciación cromosómica. Este fenómeno queaparentemente sería mantenido por fuerzas determinísticas podríaoriginar una gran divergencia en las frecuencias génicas deaquellos loci en desequlibrio de ligamiento con las inversionescromosómicas.Fil: Confalonieri, Viviana Andrea. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Mito-nuclear genetic comparison in a Wolbachia infected weevil: insights on reproductive mode, infection age and evolutionary forces shaping genetic variation

<p>Abstract</p> <p>Background</p> <p>Maternally inherited endosymbionts like <it>Wolbachia pipientis </it>are in linkage disequilibrium with the mtDNA of their hosts. Therefore, they can induce selective sweeps, decreasing genetic diversity over many generations. This sex ratio distorter, that is involved in the origin of parthenogenesis and other reproductive alterations, infects the parthenogenetic weevil <it>Naupactus cervinus</it>, a serious pest of ornamental and fruit plants.</p> <p>Results</p> <p>Molecular evolution analyses of mitochondrial (<it>COI</it>) and nuclear (<it>ITS1</it>) sequences from 309 individuals of <it>Naupactus cervinus </it>sampled over a broad range of its geographical distribution were carried out. Our results demonstrate lack of recombination in the nuclear fragment, non-random association between nuclear and mitochondrial genomes and the consequent coevolution of both genomes, being an indirect evidence of apomixis. This weevil is infected by a single <it>Wolbachia </it>strain, which could have caused a moderate bottleneck in the invaded population which survived the initial infection.</p> <p>Conclusions</p> <p>Clonal reproduction and <it>Wolbachia </it>infection induce the coevolution of bacterial, mitochondrial and nuclear genomes. The time elapsed since the <it>Wolbachia </it>invasion would have erased the traces of the demographic crash in the mtDNA, being the nuclear genome the only one that retained the signal of the bottleneck. The amount of genetic change accumulated in the mtDNA and the high prevalence of <it>Wolbachia </it>in all populations of <it>N. cervinus </it>agree with the hypothesis of an ancient infection. <it>Wolbachia </it>probably had great influence in shaping the genetic diversity of <it>N. cervinus</it>. However, it would have not caused the extinction of males, since sexual and asexual infected lineages coexisted until recent times.</p

Unraveling the diversification history of grasshoppers belonging to the <i>"Trimerotropis pallidipennis"</i> (Oedipodinae: Acrididae) species group : A hotspot of biodiversity in the Central Andes

The Andean Mountain range has been recognized as one of the biodiversity hotspotsof the world. The proposed mechanisms for such species diversification, among others, are due to the elevation processes occurring during the Miocene and the intensiveglacial action during the Pleistocene. In this study we investigated the diversificationhistory of the grasshopper Trimerotropis pallidipennis species complex which showsa particularly wide latitudinal and altitudinal distribution range across the northern, central and southern Andes in South America. Many genetic lineages of this complexhave been so far discovered, making it an excellent model to investigate the role of thecentral Andes Mountains together with climatic fluctuations as drivers of speciation. Phylogenetics, biogeographic and molecular clock analyses using a multi-locus datasetrevealed that in Peru there are at least two, and possibly four genetic lineages. Twodifferent stocks originated from a common ancestor from North/Central Americawould have dispersed toward southern latitudes favored by the closure of the PanamaIsthmus giving rise to two lineages, the coastal and mountain lineages, which still coexistin Peru (i.e., T. pallidipennis and T. andeana). Subsequent vicariant and dispersalevents continued the differentiation process, giving rise to three to six genetic lineages(i.e., clades) detected in this study, which were geographically restricted to locationsdispersed over the central Andes Mountains in South America. Our results provideanother interesting example of ``island diversification" motored by the topographyplus unstable climatic conditions during the Pleistocene, pointing out the presence ofa hotspot of diversification in the Andean region of Peru.Centro de Estudios Parasitológicos y de Vectore

The Effect of Reproductive System on Invasiveness: Lessons from South American Weevils

Successful invasion of a species into novel, marginal areas often requires the ability to face different ecological characteristics than those prevailing in its native environment. In insects, one of the factors that affect invasiveness is the reproductive system. Unisexuality provides advantages because a single specimen can initiate a new population. Unisexual reproduction precludes breakup of genetic combinations that promote ecological specialization, although it may limit evolutionary potential for colonization. In order to assess the importance of the reproductive mode in the colonization ability of the weevils that are native to South America, we compared 1 bisexual and 2 parthenogenetic species that expanded their ranges in the last 2 centuries. First, for parthenogenetic species we tested clonality of the sample. Second, we proposed central and marginal areas through phylogeographic and habitat modeling analyses, and identified the pathways of dispersal for each species. Bisexual Naupactus xanthographus (Germar) (Coleoptera: Curculionidae) expanded its range westward to areas with similar environmental constraints than in its native ecosystem. Conversely, parthenogenetic Naupactus leucoloma Boheman and Naupactus cervinus Boheman (both Coleoptera: Curculionidae) invaded other continents where they had low to null predicted habitat suitability. While a single clone of N. cervinus successfully established around the world in areas with apparently adverse conditions, clones of N. leucoloma expanded their range to areas only moderately suitable. We conclude that parthenogenesis is a driver in these particular species for colonization of marginal habitats. However, N. cervinus also would have pre-existing adaptations that allowed it to establish in areas with apparently low potential to survive.Fil: Rodriguero, Marcela Silvina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Guzman, Noelia Veronica. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Lanteri, Analia Alicia. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Confalonieri, Viviana Andrea. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución. Grupo de Investigación en Filogeografía y Filogenias Moleculares; Argentin

Colonization ability of two invasive weevils with different reproductive modes

The flightless weevils Naupactus leucoloma and Naupactu xanthographus (Coleoptera: Curculionidae: Naupactini), which are native to and partially co-distributed in South America, apparently have asexual and bisexual reproductive modes, respectively. We used two different molecular markers to elucidate the effects of these reproductive modes on the colonization ability and genetic variability of both species. First, we investigated the occurrence of clonal reproduction in the putative parthenogenetic species (i.e. significant bias in sex ratio) and second, whether parthenogenesis was associated with higher colonization ability and low levels of genetic variability in marginal environments compared with those of the bisexual species. We assessed the central and marginal areas of distribution of these species with ecological niche modeling that includes environmental variables and with landscape interpolation of molecular variability. Our results support the idea that parthenogenetic species are more successful than bisexual ones in colonizing new environments. N. leucoloma is most probably apomictic, and would have recently experienced significant population growth concomitant with an important geographic range expansion to distant areas with moderately suitable environmental conditions. On the other hand, the populations of the bisexual species, N. xanthographus, seem to have maintained fairly constant sizes, expanding its geographic distribution to locations close to the proposed ancestral area.Facultad de Ciencias Naturales y Muse

Population structure of the boll weevil in cotton fields and subtropical forests of South America: a bayesian approach

The main goal of this contribution is to investigate the genetic structure of boll weevil populations from South America (Argentina and Brazil) and to make further comparisons with a putative source population from USA. Samples were collected in a Paranaense forest under reserve protection, cotton fields and non-cultivated areas. Data from anonymous molecular markers were analysed using both traditional methods of population genetics and Bayesian approaches. Results help to support a previous hypothesis on the presence of two lineages of boll weevil populations in South America: one with characteristics of recent invaders and the other with characteristics of ancient populations. The sample from Urugua-i Provincial Park (Misiones, Argentina) shows the highest percentage of polymorphic loci, the highest values of mean heterozigosity, and the largest number of population-specific alleles, all being typical features of ancient populations. Furthermore, the Urugua-i sample shows two gene pools occurring in sympatry, probably as a consequence of a secondary contact. The remaining samples reveal not only lower percentages of polymorphic loci and heterozygosity values, but also an almost negligible presence of specific alleles. Bayesian methods also suggest the occasional migration of some individuals of ancient lineages from their natural habitats in fragments of the Paranaense forest into cotton fields, and vice versa.Facultad de Ciencias Naturales y Muse

Are flightless Galapaganus weevils older than the Galapagos islands they inhabit?

The 15 species in the weevil genus Galapaganus Lanteri 1992 (Entiminae: Curculionidae: Coleoptera) are distributed on coastal Peril and Ecuador and include 10 flightless species endemic to the Galapagos islands. These beetles thus provide a promising system through which to investigate the patterns and processes of evolution on Darwin's archipelago. Sequences of the mtDNA locus encoding cytochrome oxidase subunit I (COI) were obtained from samples of seven species occurring in different ecological zones of the oldest south-eastern islands: San Cristobal, Espanola and Floreana, and the central island Santa Cruz. The single most parsimonious tree obtained shows two well-supported clades that correspond to the species groups previously defined by morphological characters. Based on a mtDNA clock calibrated for arthropods, the initial speciation separating the oldest species, G. galapagoensis (Linell) on the oldest island, San Cristobal, from the remaining species in the Galapagos occurred about 7.2 Ma. This estimate exceeds geological ages of the extant emerged islands, although it agrees well with molecular dating of endemic Galapagos iguanas, geckos and lizards. An apparent explanation for the disagreement between geological and molecular time-frames is that about 7 Ma there were emerged islands which subsequently disappeared under ocean waters. This hypothesis has gained support from the recent findings of 11 -Myr-old submarine seamounts (sunken islands), south-east of the present location of the archipelago. Some species within the darwini group may have differentiated on the extant islands, 1-5 Ma.Facultad de Ciencias Naturales y Muse

Are flightless Galapaganus weevils older than the Galapagos islands they inhabit?

The 15 species in the weevil genus Galapaganus Lanteri 1992 (Entiminae: Curculionidae: Coleoptera) are distributed on coastal Peril and Ecuador and include 10 flightless species endemic to the Galapagos islands. These beetles thus provide a promising system through which to investigate the patterns and processes of evolution on Darwin's archipelago. Sequences of the mtDNA locus encoding cytochrome oxidase subunit I (COI) were obtained from samples of seven species occurring in different ecological zones of the oldest south-eastern islands: San Cristobal, Espanola and Floreana, and the central island Santa Cruz. The single most parsimonious tree obtained shows two well-supported clades that correspond to the species groups previously defined by morphological characters. Based on a mtDNA clock calibrated for arthropods, the initial speciation separating the oldest species, G. galapagoensis (Linell) on the oldest island, San Cristobal, from the remaining species in the Galapagos occurred about 7.2 Ma. This estimate exceeds geological ages of the extant emerged islands, although it agrees well with molecular dating of endemic Galapagos iguanas, geckos and lizards. An apparent explanation for the disagreement between geological and molecular time-frames is that about 7 Ma there were emerged islands which subsequently disappeared under ocean waters. This hypothesis has gained support from the recent findings of 11 -Myr-old submarine seamounts (sunken islands), south-east of the present location of the archipelago. Some species within the darwini group may have differentiated on the extant islands, 1-5 Ma.Facultad de Ciencias Naturales y Muse

A tale of swinger insects: Signatures of past sexuality between divergent lineages of a parthenogenetic weevil revealed by ribosomal intraindividual variation

Naupactus cervinus (Boheman) (Curculionidae, Naupactini) is a parthenogenetic weevil native to the Paranaense Forest which displays high levels of genetic variation. Two divergent clades were identified, one ranging in forest areas (Forest clade), and the other in open vegetation areas (Grassland clade). Both of them have individuals with high levels of heterozygosity in ribosomal sequences. Investigation of intraindividual variation in ITS1 sequences through cloning and posterior sequencing suggested that mating between both groups most likely occurred in the Paranaense Forest after a secondary contact, which led to fixed heterozygotes as a consequence of parthenogenesis. Otherwise, sexual segregation would have disrupted multilocus genotypes. Only a small number of heterozygous genotypes of all the possible combinations are found in nature. We propose the occurrence of a hybrid zone in the Paranaense Forest. The fact that it is one of the most important biodiversity hotspots of the world, together with its key role for investigating evolutionary processes, makes it worthy of conservation. This is the first genetic evidence of bisexuality in N. cervinus.Fil: Rodriguero, Marcela Silvina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Wirth, Sonia Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Alberghina, Josefina Silvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Lanteri, Analía Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Entomología; ArgentinaFil: Confalonieri, Viviana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin

Dispersal of the Cotton Boll Weevil (Coleoptera: Curculionidae) in South America : Evidence of RAPD Analysis

RAPD technique provides useful information on the geographic origin and dispersal of the boll weevil Anthonomus grandis in South America. Nine populations from Argentina, Brazil, Paraguay, Mexico and USA were analyzed. Weevils were captured on native plants (Misiones province, Argentina) and on cotton cultures, except the sample from the United States (USDA laboratory-reared colony). A sample of the 'Peruvian square weevil', A. vestitus, from Ecuador, was included in the analysis in order to compare interspecific variation. The four primers used in the analysis revealed 41 'anonymous loci'. The neighbor-joining tree based on Nei's distances and values of Nm (migrants per generation), indicate that genetic similarity between samples from Tecoman (Mexico) and Puerto Iguazu (Argentina), is higher than among remaining South American populations. This result supports an hypothesis of natural occurrence of the boll weevil in South America, prior to extensive cotton cultivation. Population outbreaks of the species would be associated with increase of agricultural lands.Facultad de Ciencias Naturales y Muse