Biology subjects

Silva-Brandao, K. L.

Publications and source records attributed to Silva-Brandao, K. L..

6 recordsLinked to original sources

bioRxiv2026

Contrasting signatures of interspecific gene flow in the Atlantic Forest endemic butterfly Heliconius besckei

Gene flow between diverging species can reshuffle genomic variation and greatly influence the speciation process, sometimes reinforcing, sometimes eroding species boundaries. However, the effect of ecological and historical processes on the patterns of introgression remains poorly understood. Here, we focus on the evolutionary history of Heliconius besckei, a geographically restricted butterfly endemic to the Brazilian Atlantic Forest, together with the mimetic H. melpomene nanna, the sympatric non-mimetic H. ethilla narcaea, and its closely related H. numata robigus. Using whole-genome sequencing, genome-wide tests of introgression, demographic modelling and palaeoclimatic species distribution models, we tested the extent and timing of interspecific gene flow in relation to mimicry, ecological context, and changes in geographic overlap. Despite strong genomic differentiation among the four focal Heliconius species, we detected widespread signatures of interspecific gene flow, greatly influenced by geographical overlap. Demographic models including post-divergence gene flow were better supported than strict-isolation models. In addition, genome-wide introgression analyses showed more numerous and larger candidate introgressed regions between H. besckei and H. ethilla narcaea, consistent with recurrent opportunities for exchange between these currently sympatric species. Species distribution models further recovered repeated expansions of suitable habitat for H. besckei during cold periods, providing a potential geographic context for secondary contact within the Atlantic Forest. Together, our results reveal recurrent gene flow occurring under different temporal, geographic, and potentially selective contexts, and show that the evolutionary history of a geographically restricted lineage can be shaped by repeated genetic exchange while substantial species differentiation is maintained.

evolutionary biology↗

bioRxiv2021

Susceptibility monitoring and the molecular characterization of resistance of Spodoptera frugiperda (Lepidoptera: Noctuidae) to lambda-cyhalothrin and chlorpyrifos

Spodoptera frugiperda (J. E. Smith) is a serious and widespread agricultural pest with several records of resistance to different insecticides and Bt proteins, including the neurotoxic insecticides chlorpyrifos (organophosphate) and lambda-cyhalothrin (pyrethroid). In this study, we (i) characterized and monitored the susceptibility of field populations of S. frugiperda to chlorpyrifos (194 populations) and lambda-cyhalothrin (197 populations) collected from major maize-growing regions of Brazil from 2003 to 2016, and (ii) compared gene expression levels of chlorpyrifos- and lambda-cyhalothrin-resistant strains to a susceptible reference strain (Sf-ss) of S. frugiperda. Laboratory-guided assays to monitor larval susceptibility detected average survival ranging from 29.3% to 36.0% to chlorpyrifos, and 23.1% to 68.0% to lambda-cyhalothrin at diagnostic concentration, based on LC99 of the susceptible reference strain of each insecticide. The resistance ratio of the chlorpyrifos-resistant strain (Clo-rr) was 25.4-fold and of the lambda-cyhalothrin-resistant strain (Lam-rr) was 217-fold. Differential gene expression analyses between resistant vs susceptible strains identified 1,098 differentially expressed genes (DEGs) between Clo-rr and Sf-ss, and 303 DEGs between Lam-rr and Sf-ss. Functional analyses of the DEGs revealed the up-regulation of several detoxification enzymes, mainly cytochrome P450 belonging to the CYP3 and CYP6 clans. Genes associated with regulatory processes, such as the forkhead box O (FoxO) were also up-regulated. Our data points that the resistance mechanisms of Clo-rr and Lam-rr strains of S. frugiperda to chlorpyrifos and lambda-cyhalothrin are mainly mediated by enzyme detoxification.

zoology↗

bioRxiv2021

Supergene formation is associated with a major shift in genome-wide patterns of diversity in a butterfly

Selection shapes genetic diversity around target mutations, yet little is known about how selection on specific loci affects the genetic trajectories of populations, including their genome-wide patterns of diversity and demographic responses. Here we study the patterns of genetic variation and geographic structure in a neotropical butterfly, Heliconius numata, and its closely related allies in the so-called melpomene-silvaniform clade. H. numata is known to have evolved an inversion supergene which controls variation in wing patterns involved in mimicry associations with distinct groups of co-mimics whereas it is associated to disassortative mate preferences and heterozygote advantage at this locus. We contrasted patterns of genetic diversity and structure 1) among extant polymorphic and monomorphic populations of H. numata, 2) between H. numata and its close relatives, and 3) between ancestral lineages. We show that H. numata populations which carry the inversions as a balanced polymorphism show markedly distinct patterns of diversity compared to all other taxa. They show the highest genetic diversity and effective population size estimates in the entire clade, as well as a low level of geographic structure and isolation by distance across the entire Amazon basin. By contrast, monomorphic populations of H. numata as well as its sister species and their ancestral lineages all show lower effective population sizes and genetic diversity, and higher levels of geographical structure across the continent. One hypothesis is that the large effective population size of polymorphic populations could be caused by the shift to a regime of balancing selection due to the genetic load and disassortative preferences associated with inversions. Testing this hypothesis with forward simulations supported the observation of increased diversity in populations with the supergene. Our results are consistent with the hypothesis that the formation of the supergene triggered a change in gene flow, causing a general increase in genetic diversity and the homogenisation of genomes at the continental scale.

evolutionary biology↗

bioRxiv2020

There is more than chitin synthase in insect resistance to benzoylureas: Molecular markers associated with teflubenzuron resistance in Spodoptera frugiperda

Chitin synthesis inhibitors are successfully used in pest control and are an excellent option for use in integrated pest management programs due to their low non-target effects. Reports on field-evolved resistance of lepidopteran pests to chitin synthesis inhibitors and the selection of laboratory resistant strains to these products require a detailed investigation on the resistance mechanisms and on the identification of molecular markers to support the implementation of efficient monitoring and resistance management programs. Teflubenzuron is a chitin synthesis inhibitor highly effective in controlling lepidopteran pests, including nowadays the world widely distributed fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae). We report the selection of a laboratory strain of S. frugiperda resistant to teflubenzuron, and its use for the characterization of the inheritance of resistance, evaluation of cross-resistance to other chitin-synthesis inhibitors and the identification of a set of single nucleotide polymorphisms (SNPs) for use as candidate molecular markers for monitoring the evolution of resistance of S. frugiperda to teflubenzuron. The resistance of the selected strain of S. frugiperda to teflubenzuron was characterized as polygenic, autosomal, and incompletely recessive. The resistance ratio observed was nearly 1,365-fold. Teflubenzuron-resistant strain showed some cross-resistance to lufenuron and novaluron but not to chlorfluazuron. We also detected a set of 72 SNPs that could support monitoring of the resistance frequency to teflubenzuron in field populations. Our data contribute to the understanding of the resistance mechanisms and the inheritance of polygenic resistance of S. frugiperda to benzoylureas. We also contribute with candidate markers as tools for monitoring the emergence and spread of teflubenzuron resistance in S. frugiperda.

evolutionary biology↗

bioRxiv2020

The latitudinal diversity gradient in brush-footed butterflies (Nymphalidae): conserved ancestral tropical niche but different continental histories.

The latitudinal diversity gradient (LDG) is arguably one of the most striking patterns in nature. The global increase in species richness toward the tropics across continents and taxonomic groups stimulated the formulation of many hypotheses to explain the underlying mechanisms of this pattern. We evaluated several of these hypotheses to explain spatial diversity patterns in the butterfly family, Nymphalidae, by assessing the contributions of speciation, extinction, and dispersal to the LDG, and also the extent to which these processes differ among regions at the same latitude. We generated a new, time-calibrated phylogeny of Nymphalidae based on 10 gene fragments and containing ca. 2,800 species ([~]45% of extant diversity). Neither speciation nor extinction rate variations consistently explain the LDG among regions because temporal diversification dynamics differ greatly across longitude. For example, we found that Neotropical nymphalid diversity results from low extinction rates, not high speciation rates, and that biotic interchanges with other regions were rare. Southeast Asia was also characterized by a low speciation rate but, unlike the Neotropics, was the main source of dispersal events through time. Our results suggest that global climate change throughout the Cenozoic, particularly during the Eocene-Oligocene transition, combined with the conserved ancestral tropical niches, played a major role in generating the modern LDG of butterflies.

ecology↗

bioRxiv2017

North Andean origin and diversification of the largest ithomiine butterfly genus

The Neotropics harbour the most diverse flora and fauna on Earth. The Andes are a major centre of diversification and source of diversity for adjacent areas in plants and vertebrates, but studies on insects remain scarce, even though they constitute the largest fraction of terrestrial biodiversity. Here, we combine molecular and morphological characters to generate a dated phylogeny of the butterfly genus Pteronymia (Nymphalidae: Danainae), which we use to infer spatial, elevational and temporal diversification patterns. We first propose six taxonomic changes that raise the generic species total to 53, making Pteronymia the most diverse genus of the tribe Ithomiini. Our biogeographic reconstruction shows that Pteronymia originated in the Northern Andes, where it diversified extensively. Some lineages colonized lowlands and adjacent montane areas, but diversification here remained scarce. The recent colonization of lowland areas was reflected by an increase in the rate of evolution of species elevational ranges towards present. By contrast, speciation rate decelerated with time, with no extinction. The geological history of the Andes and adjacent regions have likely contributed to Pteronymia diversification by providing compartmentalized habitats and an array of biotic and abiotic conditions, and by limiting dispersal between some areas while promoting interchange across others.

evolutionary biology↗