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

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

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

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

Background: Maternally inherited endosymbionts like Wolbachia pipientis 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 Naupactus cervinus, a serious pest of ornamental and fruit plants. Results: Molecular evolution analyses of mitochondrial (COI) and nuclear (ITS1) sequences from 309 individuals of Naupactus cervinus 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 Wolbachia strain, which could have caused a moderate bottleneck in the invaded population which survived the initial infection. Conclusions: Clonal reproduction and Wolbachia infection induce the coevolution of bacterial, mitochondrial and nuclear genomes. The time elapsed since the Wolbachia 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 Wolbachia in all populations of N. cervinus agree with the hypothesis of an ancient infection. Wolbachia probably had great influence in shaping the genetic diversity of N. cervinus. However, it would have not caused the extinction of males, since sexual and asexual infected lineages coexisted until recent times.Facultad de Ciencias Naturales y Muse

Species delimitation in the Andean grasshopper genus <i>Orotettix</i> Ronderos & Carbonell (Orthoptera: Melanoplinae): an integrative approach combining morphological, molecular and biogeographical data

The reciprocal illumination nature of integrative taxonomy through hypothesis testing, corroboration and revision is a powerful tool for species delimitation as more than one source has to support the hypothesis of a new species. In this study, we applied an integrative taxonomy approach combining molecular and morphological data sets with distributional patterns to examine the level of differentiation between and within the grasshopper Orotettix species. Orotettix was described based on five valid species distributed in the Andes of Peru. In our study, initially a molecular-based hypothesis was postulated and tested against morphological data and geographical patterns of distribution. Results from molecular and morphological analyses showed agreement among the species delimitation in Orotettix, and were also consistent with the geographical distribution. The analyses allowed us to delimit five new species for the genus (O. lunatus sp. nov., O.astreptos sp. nov., O. colcaensis sp. nov., O.paucartambensis sp. nov. and O.dichrous sp. nov.) from the Eastern and Western Cordilleras of Peru. We also provide critical knowledge on the phylogenetic relationships and distribution of the genus and conduct a revision of Orotettix.Facultad de Ciencias Naturales y MuseoCentro de Estudios Parasitológicos y de Vectore

Species delimitation in the Andean grasshopper genus <i>Orotettix</i> Ronderos & Carbonell (Orthoptera: Melanoplinae): an integrative approach combining morphological, molecular and biogeographical data

The reciprocal illumination nature of integrative taxonomy through hypothesis testing, corroboration and revision is a powerful tool for species delimitation as more than one source has to support the hypothesis of a new species. In this study, we applied an integrative taxonomy approach combining molecular and morphological data sets with distributional patterns to examine the level of differentiation between and within the grasshopper Orotettix species. Orotettix was described based on five valid species distributed in the Andes of Peru. In our study, initially a molecular-based hypothesis was postulated and tested against morphological data and geographical patterns of distribution. Results from molecular and morphological analyses showed agreement among the species delimitation in Orotettix, and were also consistent with the geographical distribution. The analyses allowed us to delimit five new species for the genus (O. lunatus sp. nov., O.astreptos sp. nov., O. colcaensis sp. nov., O.paucartambensis sp. nov. and O.dichrous sp. nov.) from the Eastern and Western Cordilleras of Peru. We also provide critical knowledge on the phylogenetic relationships and distribution of the genus and conduct a revision of Orotettix.Facultad de Ciencias Naturales y MuseoCentro 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 surviveLa colonización de áreas marginales a menudo requiere que la especie invasora sea capaz de enfrentar características ecológicas diferentes a aquellas que predominan en su área nativa. En los insectos, uno de los factores que afectan la capacidad invasiva figura el sistema reproductivo. La unisexualidad proporciona varias ventajas, entre ellas la capacidad de fundar una nueva población a partir de un único especimen y evitar la ruptura de las combinaciones genéticas que promueven la especialización ecológica, esta última puede limitar el potencial evolutivo para la colonización. A fin de evaluar la importancia del modo reproductivo en la capacidad colonizadora de un grupo de gorgojos nativos de Sudamérica, comparamos dos especies con reproducción partenogenética y una especie bisexual que expandieron su rango geográfico a lo largo de los últimos 200 años. Por un lado, para las especies partenogenéticas pusimos a prueba la hipótesis de reproducción clonal. Además, propusimos áreas centrales y marginales a través de análisis filogeográficos y de modelado ecológico del hábitat e identificamos las rutas de dispersión de cada especie. La especie bisexual Naupactus xanthographus (Germar) (Coleoptera: Curculionidae) expandió su rango hacia el oeste, estableciéndose en áreas con restricciones ambientales similares a las de su área nativa. Por el contrario, las especies partenogenéticas Naupactus leucoloma Boheman y Naupactus cervinus Boheman (ambos Coleoptera: Curculionidae) invadieron otros continentes, donde las predicciones de ocurrencia en base a las condiciones del hábitat son bajas a nulas. Un único clon de N. cervinus consiguió establecerse en áreas con condiciones aparentemente adversas y los clones de N. leucoloma solo expandieron su rango a áreas moderadamente adecuadas. Concluimos que la partenogénesis es un factor fundamental en la colonización exitosa de hábitats marginales de estos gorgojos. Sin embargo, N. cervinus tendría adaptaciones pre-existentes que le habrían permitido el establecimiento en áreas con un potencial aparentemente bajo para la supervivencia.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.Facultad de Ciencias Naturales y Muse