RESUMO
MAIN CONCLUSION: The analysis of meiotic pairing affinities and genomic formulae in species and hybrids of Zea allowed us to speculate an evolutionary model to recreate the ancient polyploidization of maize and allied species. The meiotic pairing affinities and the genomic formulae analysis in Zea species and hybrids obtained in new and previous crosses, together with the molecular data known in the genus, allowed us to speculate an evolutionary model to attempt to recreate the ancient polyploidization process of Zea species. We propose that x = 5 semispecies are the ancestors of all modern species of the genus. The complex evolutionary process that originated the different taxa could be included hybridization between sympatric diploid ancestral semispecies (2n = 10) and recurrent duplication of the hybrid chromosome number, resulting in distinct auto- and allopolyploids. After the merger and doubling of independent genomes would have undergone cytological and genetical diploidization, implying revolutionary changes in genome organization and genic balance processes. Based on the meiotic behaviour of the 2n = 30 hybrids, that showed homoeology between the A subgenomes of all parental species, we propose that this subgenome A would be pivotal in all the species and would have conserved the rDNA sequences and the pairing regulator locus (PrZ). In the hypothetical model postulated here, the ancestral semispecies with the pivotal subgenome A would have had a wide geographic distribution, co-occurring and hybridizing with the semispecies harbouring B subgenomes, thus enabling sympatric speciation.
Assuntos
Poaceae , Zea mays , Zea mays/genética , Poaceae/genética , Poliploidia , Evolução Biológica , Análise Citogenética , Genoma de Planta/genéticaRESUMO
Biogeochemical niche (BN) hypothesis aims to relate species/genotype elemental composition with its niche based on the fact that different elements are involved differentially in distinct plant functions. We here test the BN hypothesis through the analysis of the 10 foliar elemental concentrations and 20 functional-morphological of 60 tree species in a French Guiana tropical forest. We observed strong legacy (phylogenic + species) signals in the species-specific foliar elemental composition (elementome) and, for the first time, provide empirical evidence for a relationship between species-specific foliar elementome and functional traits. Our study thus supports the BN hypothesis and confirms the general niche segregation process through which the species-specific use of bio-elements drives the high levels of α-diversity in this tropical forest. We show that the simple analysis of foliar elementomes may be used to test for BNs of co-occurring species in highly diverse ecosystems, such as tropical rainforests. Although cause and effect mechanisms of leaf functional and morphological traits in species-specific use of bio-elements require confirmation, we posit the hypothesis that divergences in functional-morphological niches and species-specific biogeochemical use are likely to have co-evolved.
Assuntos
Ecossistema , Árvores , Floresta Úmida , Guiana Francesa , Clima Tropical , Folhas de Planta/químicaRESUMO
Many species in the Fusarium fujikuroi Species Complex (FFSC) have an affinity for grass species, with whom they live in an endophytic association or cause disease. We recovered isolates of Fusarium from agriculturally important grasses in Africa and Brazil, and characterized them with morphological markers, mating type, and Amplified Fragment Length Polymorphisms (AFLPs). We also conducted multi-locus phylogenetic analyses based on partial DNA sequences of translation elongation factor-1α (TEF1), ß-tubulin (TUB), and the second largest subunit of RNA polymerase (RPB2) gene regions. Sexual cross fertility was used to test the biological species concept and the sexual stage of F. madaense is described. A novel species within the FFSC, Fusarium mirum, that is different from the other known species in the complex, was formally described. Fusarium mirum, F. madaense, and Fusarium andiyazi are a tightly intertwined species trio that are morphologically identical, but phylogenetically distinguishable, and amongst whom interspecific genetic exchange may still occur. These three species are so close that they cannot be reliably distinguished if only sequences of the TEF1 gene are used. In pathogenicity tests, all tested isolates of F. madaense from sugarcane, sorghum, maize, millet and Brachiaria could induce stalk rot in sorghum, maize and millet, and pokkah boeng in sugarcane. This study increases our understanding of the diversity of species within the FFSC that cause disease in tropical grasses or act as endophytes, and their geographic distributions. The genetically close relationship between F. mirum, F. madaense, and F. andiyazi provides an opportunity to study and identify factors underlying their limited inter-specific cross-fertility and sympatric speciation.
Assuntos
Fusarium , Fusarium/genética , Filogenia , Poaceae , Zea maysRESUMO
Reproductive isolation is a necessary condition for plant domestication in their domestication centre where crops co-occur with their wild progenitors. However, the identification of reproductive barriers and their relative contribution to reproductive isolation have been overlooked in plants under domestication. We assessed pre- and post-pollination reproductive barriers and their relative contribution to reproductive isolation between wild and domesticated chaya (Cnidoscolus aconitifolius) in its domestication centre. We found that wild and domesticated chaya both exhibit a high degree of reproductive isolation. However, the reproductive isolation barriers exhibited some asymmetry: while pre-pollination barriers (differential pollen production and pollinator specificity) were only detected in wild plants, post-pollination barriers (pollen-pistil incompatibility and/or failure to set fruit) were observed in both wild and domesticated plants. We conclude that complete reproductive isolation has evolved in sympatry in co-occurring domesticated and wild chaya.
Assuntos
Euphorbiaceae , Isolamento Reprodutivo , Simpatria , Euphorbiaceae/fisiologia , Flores , Pólen , PolinizaçãoRESUMO
Sympatric speciation has been debated in evolutionary biology for decades. Although it has gained in acceptance recently, still only a handful of empirical examples are seen as valid (e.g. crater lake cichlids). In this study, we disentangle the role of hypertrophied lips in the repeated adaptive radiations of Nicaraguan crater lake cichlid fish. We assessed the role of disruptive selection and assortative mating during the early stages of divergence and found a functional trade-off in feeding behaviour between thick- and thin-lipped ecotypes, suggesting that this trait is a target of disruptive selection. Thick-lipped fish perform better on nonevasive prey at the cost of a poorer performance on evasive prey. Using enclosures in the wild, we found that thick-lipped fish perform significantly better in rocky than in sandy habitats. We found almost no mixed pairs during two breeding seasons and hence significant assortative mating. Genetic differentiation between ecotypes seems to be related to the time since colonization, being subtle in L. Masaya (1600 generations ago) and absent in the younger L. Apoyeque (<600 generations ago). Genome-wide differentiation between ecotypes was higher in the old source lakes than in the young crater lakes. Our results suggest that hypertrophied lips might be promoting incipient sympatric speciation through divergent selection (ecological divergence in feeding performance) and nonrandom mating (assortative mating) in the young Nicaraguan crater lakes. Nonetheless, further manipulative experiments are needed in order to confirm the role of hypertrophied lips as the main cue for assortative mating.
Assuntos
Ciclídeos/genética , Especiação Genética , Lábio/anatomia & histologia , Seleção Genética , Animais , Ciclídeos/anatomia & histologia , Ecótipo , Feminino , Hipertrofia , Lagos , Masculino , Nicarágua , Comportamento Predatório , Comportamento Sexual Animal , SimpatriaRESUMO
Cichlid fishes are an ideal model system for studying biological diversification because they provide textbook examples of rapid speciation. To date, there has been little focus on the role of gene regulation during cichlid speciation. However, in recent years, gene regulation has been recognized as a powerful force linking diversification in gene function to speciation. Here, we investigated the potential role of miRNA regulation in the diversification of six cichlid species of the Midas cichlid lineage (Amphilophus spp.) inhabiting the Nicaraguan crater lakes. Using several genomic resources, we inferred 236 Midas miRNA genes that were used to predict the miRNA target sites on 8,232 Midas 3'-UTRs. Using population genomic calculations of SNP diversity, we found the miRNA genes to be more conserved than protein coding genes. In contrast to what has been observed in other cichlid fish, but similar to what has been typically found in other groups, we observed genomic signatures of purifying selection on the miRNA targets by comparing these sites with the less conserved nontarget portion of the 3'-UTRs. However, in one species pair that has putatively speciated sympatrically in crater Lake Apoyo, we recovered a different pattern of relaxed purifying selection and high genetic divergence at miRNA targets. Our results suggest that sequence evolution at miRNA binding sites could be a critical genomic mechanism contributing to the rapid phenotypic evolution of Midas cichlids.
Assuntos
Ciclídeos/genética , Evolução Molecular , Especiação Genética , MicroRNAs/genética , Animais , DNA Mitocondrial , Repetições de Microssatélites/genética , Nicarágua , Filogenia , Polimorfismo de Nucleotídeo Único , Análise de Sequência de DNA , Especificidade da EspécieRESUMO
Sex pheromones produced by females of Rhagoletis conversa Bréthes and Rhagoletis brncici Frías are deposited on the surface of fruits after the eggs are laid. These pheromones repel other females, preventing repeated oviposition on the same fruit. They also attract males, thus assisting mating. Observations were made on wild populations, and cross-species behavioral tests were performed on males. The pheromone released by females was significantly more attractive for males of the same species. The two species showed remarkable differences in mating behavior, in the duration of oviposition, and in the number of circuits made around the fruit after eggs were laid. A morphological analysis of flies collected from their respective host plants indicated great host fidelity and the reproductive isolation of the two species. Possibly, the specific male-arresting effect of this pheromone was important for the sympatric speciation and evolution of these sibling species.
Assuntos
Oviposição , Feromônios , Tephritidae/fisiologia , Animais , Feminino , Frutas , Masculino , ReproduçãoRESUMO
Speciation on islands, and particularly the divergence of species in situ, has long been debated. Here, we present one of the first, complete assessments of the geographic modes of speciation for the flora of a small oceanic island. Cocos Island (Costa Rica) is pristine; it is located 550 km off the Pacific coast of Central America. It harbors 189 native plant species, 33 of which are endemic. Using phylogenetic data from insular and mainland congeneric species, we show that all of the endemic species are derived from independent colonization events rather than in situ speciation. This is in sharp contrast to the results of a study carried out in a comparable system, Lord Howe Island (Australia), where as much as 8.2% of the plant species were the product of sympatric speciation. Differences in physiography and age between the islands may be responsible for the contrasting patterns of speciation observed. Importantly, comparing phylogenetic assessments of the modes of speciation with taxonomy-based measures shows that widely used island biogeography approaches overestimate rates of in situ speciation.
Assuntos
Especiação Genética , Filogeografia , Plantas/classificação , Plantas/genética , Costa Rica , Marcadores Genéticos , Ilhas , Dados de Sequência Molecular , FilogeniaRESUMO
Adaptive radiation is recognized by a rapid burst of phenotypic, ecological and species diversification. However, it is unknown whether different species within an adaptive radiation evolve reproductive isolation at different rates. We compared patterns of genetic differentiation between nascent species within an adaptive radiation of Cyprinodon pupfishes using genotyping by sequencing. Similar to classic adaptive radiations, this clade exhibits rapid morphological diversification rates and two species are novel trophic specialists, a scale-eater and hard-shelled prey specialist (durophage), yet the radiation is <10 000 years old. Both specialists and an abundant generalist species all coexist in the benthic zone of lakes on San Salvador Island, Bahamas. Based on 13 912 single-nucleotide polymorphisms (SNPs), we found consistent differences in genetic differentiation between each specialist species and the generalist across seven lakes. The scale-eater showed the greatest genetic differentiation and clustered by species across lakes, whereas durophage populations often clustered with sympatric generalist populations, consistent with parallel speciation across lakes. However, we found strong evidence of admixture between durophage populations in different lakes, supporting a single origin of this species and genome-wide introgression with sympatric generalist populations. We conclude that the scale-eater is further along the speciation-with-gene-flow continuum than the durophage and suggest that different adaptive landscapes underlying these two niche environments drive variable progress towards speciation within the same habitat. Our previous measurements of fitness surfaces in these lakes support this conclusion: the scale-eating fitness peak may be more distant than the durophage peak on the complex adaptive landscape driving adaptive radiation.
Assuntos
Adaptação Fisiológica/genética , Ecossistema , Especiação Genética , Peixes Listrados/classificação , Animais , Bahamas , Análise por Conglomerados , Fluxo Gênico , Genética Populacional , Peixes Listrados/genética , Lagos , Polimorfismo de Nucleotídeo Único , Especificidade da Espécie , SimpatriaRESUMO
Divergent natural selection driven by competition for limited resources can promote speciation, even in the presence of gene flow. Reproductive isolation is more likely to result from divergent selection when the partitioned resource is closely linked to mating. Obligate symbiosis and host fidelity (mating on or near the host) can provide this link, creating ideal conditions for speciation in the absence of physical barriers to dispersal. Symbiotic organisms often experience competition for hosts, and host fidelity ensures that divergent selection for a specific host or host habitat can lead to speciation and strengthen pre-existing reproductive barriers. Here, we present evidence that diversification of a sympatric species complex occurred despite the potential for gene flow and that partitioning of host resources (both by species and by host habitat) has contributed to this diversification. Four species of snapping shrimps (Alpheus armatus, A. immaculatus, A. polystictus and A. roquensis) are distributed mainly sympatrically in the Caribbean, while the fifth species (A. rudolphi) is restricted to Brazil. All five species are obligate commensals of sea anemones with a high degree of fidelity and ecological specificity for host species and habitat. We analysed sequence data from 10 nuclear genes and the mitochondrial COI gene in 11-16 individuals from each of the Caribbean taxa and from the only available specimen of the Brazilian taxon. Phylogenetic analyses support morphology-based species assignments and a well-supported Caribbean clade. The Brazilian A. rudolphi is recovered as an outgroup to the Caribbean taxa. Isolation-migration coalescent analysis provides evidence for historical gene flow among sympatric sister species. Our data suggest that both selection for a novel host and selection for host microhabitat may have promoted diversification of this complex despite gene flow.
Assuntos
Decápodes/classificação , Fluxo Gênico , Especiação Genética , Filogenia , Anêmonas-do-Mar , Animais , Brasil , Região do Caribe , Núcleo Celular/genética , DNA Mitocondrial/genética , Decápodes/genética , Ecossistema , Modelos Genéticos , Dados de Sequência Molecular , Tipagem de Sequências Multilocus , Isolamento Reprodutivo , Seleção Genética , Especificidade da Espécie , SimpatriaRESUMO
The D. flavopilosa group encompasses an ecologically restricted set of species strictly adapted to hosting flowers of Cestrum (Solanaceae). This group presents potential to be used as a model to the study of different questions regarding ecologically restricted species macro and microevolutionary responses, geographical vs. ecological speciation and intra and interspecific competition. This review aims to revisit and reanalyze the patterns and processes that are subjacent to the interesting ecological and evolutionary properties of these species. Biotic and abiotic niche properties of some species were reanalyzed in face of ecological niche modeling approaches in order to get some insights into their ecological evolution. A test of the potential of DNA-Barcoding provided evidences that this technology may be a way of overcoming difficulties related to cryptic species differentiation. The new focus replenishes the scenario with new questions, presenting a case where neither geographical nor ecological speciation may be as yet suggested.
Assuntos
Drosophila/classificação , Filogenia , Animais , Evolução Biológica , Cestrum , Código de Barras de DNA Taxonômico , Drosophila/genética , Feminino , Geografia , Masculino , Especificidade da EspécieRESUMO
The Synthetic Theory of Evolution is the most unifying theory of life science. This theory has dominated scientific thought in explaining the mechanisms involved in speciation. However, there are some omissions that have delayed the understanding of some aspects of the mechanisms of organic evolution, principally: 1) the bridge between somatic and germinal cells, especially in some phylum of invertebrates and vertebrates; 2) horizontal genetic transferences and the importance of viruses in host adaptation and evolution; 3) the role of non-coding DNA and non-transcriptional genes; 4) homeotic evolution and the limitations of gradual evolution; and 5) excessive emphasis on extrinsic barriers to animal speciation. This paper reviews each of these topics in an effort to contribute to a better comprehension of organic evolution. Molecular findings suggest the need for a new evolutionary synthesis.