Biology subjects

Bacquet, C. N.

Publications and source records attributed to Bacquet, C. N..

11 recordsLinked to original sources

bioRxiv2026

Adaptation in the eye and brain contributes to species divergence in visual perception in Heliconius butterflies

Sensory systems mediate the interaction between organisms and their environment, but how complex sensory pathways evolve and relate to variation in perception and behavior across ecological contexts, remains poorly understood, especially for terrestrial taxa. Here, we investigate whole-visual-system adaptation in Heliconius erato butterflies. Using continent-wide sampling, we demonstrate that within H. erato, facet count significantly decreased with increasing elevation. Common-garden rearing of low-elevation H. erato populations from Ecuador and their high-elevation sister species, H. himera, showed that eye and brain morphology are heritable, and comparisons to genomic measures of divergence indicates that this variation is due to divergent selection. Parallel comparisons from Colombia involving H. chestertonii (high elevation) and H. erato venus (low elevation) further revealed that eye and brain morphology can evolve as independent, decoupled traits. For both locations, differences in visual acuity correlated with variation in facet count. We also observed parallel evolution of spectral sensitivity, with independent high-elevation populations having fewer red-reflecting lateral filtering pigments. To experimentally link visual system morphology to behavior, we assessed visual acuity in second-generation H. erato cyrbia-H. himera hybrids. Overall, acuity was influenced by facet count, and when analyzed together with brain morphology, by a positive interaction between facet count and optic lobe volume, demonstrating that structural investment in the eye and neural expansion combine to maximize visual perception. This work shows that visual adaptation is a multi-layered process whereby sensory traits can evolve independently under localized ecological pressures, but evolution across the visual pathway contributes to refinements in behavioral performance.

evolutionary biology↗

bioRxiv2025

Sexual dimorphism in pollen foraging and sensory traits in Heliconius butterflies

Sexual dimorphism in foraging behaviour is widespread in insects and may arise from differences in nutritional demands, sensory systems, or cognition. Heliconius pollen-feeding is an evolutionary innovation among butterflies that supports extended lifespans and sustained reproduction. However, how foraging behaviour varies between the sexes and how it relates to sexually dimorphic traits remains poorly understood. We investigated sex-specific foraging strategies in wild Heliconius himera, a highland specialist from southern Ecuador, using field surveys and DNA metabarcoding. Females carried more pollen than males, consistent with higher nutritional demands, yet we observed no differences in plant richness and composition. This indicates that sex differences reflect effort in foraging behaviour rather than shifts in plant choice. Gut samples revealed greater pollen diversity and a more consistent community profile than proboscis samples, suggesting they better capture cumulative foraging history. We also quantified sexually dimorphic sensory traits and found that males had larger eyes and more ommatidia, whereas females had larger mushroom bodies. While the functional significance of these differences remains unclear, these patterns are consistent with sexual dimorphism reported across Heliconius and suggest males and females may be under divergent selective pressures. Our findings highlight how sex-specific foraging differences can arise from differential effort on shared floral resources and co-occur with divergent sensory and neural investment, offering insights into the ecological basis of intraspecific variation in pollen use.

animal behavior and cognition↗

bioRxiv2025

Disentangling local adaptation and phenotypic plasticity in traits associated with altitude and temperature in widespread tropical butterflies

Climatic stratifications, in particular differences in temperature, occur along altitudinal clines. Understanding genetic and phenotypic divergence across these regions can give insight into speciation and diversification, as well as aid in our knowledge of how species may respond to possible climate change scenarios. Most past research has focused on temperate regions, yet it is in the tropics that organisms are thought to be the most vulnerable to rising temperatures. In addition, year-round stable temperatures in the tropics make altitudinal temperature variation more pronounced and increase the likelihood of local adaptation across relatively narrow gradients. Here we investigate how genetics and the environment influence a wide range of traits in two butterfly species, Heliconius erato and Heliconius melpomene, which are widespread across the neotropics and occur along the altitudinal slope of the Andes. Using common garden rearing of over 1,000 offspring from over 70 wild females caught along an altitudinal gradient, as well as rearing of populations from either end of the altitudinal range in their reciprocal temperature environments, we find evidence of genetic, environmental, and in some cases gene-by-environment interaction effects in developmental, morphological, and thermal tolerance traits. We find parallel divergence in wing colour in both species, with wing colour darkening with increasing altitude, consistent with this playing a role in thermoregulation in these species where wing colour has mostly been linked to mimicry and mate choice. We also find evidence for gene-by-environment interactions: In H. erato we found local differences in heat acclimation response, with increased heat knock-out times at higher rearing temperatures found only in low altitude populations, which are exposed to the hottest temperatures. We find evidence for heritable genetic variation in most traits measured, with positive implications for adaptation to climate change, although our results suggest that selection may not act in a straightforward way on these traits.

ecology↗

bioRxiv2025

Genetic parallelism underpins convergent mimicry coloration across Lepidoptera

Convergent evolution, the repeated evolution of similar phenotypes in response to the same selective pressures across multiple lineages, is widespread in nature. The extent to which the same genetic mechanisms contribute to convergent evolution could reveal whether the pathway towards these optimal endpoints is flexible or constrained to follow a particular route. Although mimicry of aposematic colour patterns is well known in Lepidoptera, our knowledge of the genetic basis of these convergent patterns is mostly restricted to a few closely-related species. Here we study the genetic basis of mimicry across seven species of Ithomiini and Heliconius butterflies and a day-flying Chetone moth, representing lineages that diverged between [~]1-120 Mya, each presenting similar colour pattern switches. In all the butterfly species, the genetic variants most strongly associated with convergent colour pattern switches are similarly located in non-coding regions near the genes ivory and optix. Colour pattern variation in the moth is associated with a [~]1 Mb inversion around ivory paralleling the supergene architecture of the co-mimic Heliconius numata. In contrast to previous studies in Heliconius, there is limited evidence of alleles shared by means of hybridization in convergence among closely-related ithomiine species. Repeated parallel evolution of regulatory switches via reuse of the same two genes suggests that convergent colour pattern evolution is highly constrained, even across large evolutionary timescales.

evolutionary biology↗

bioRxiv2023

Quantifying visual acuity in Heliconius butterflies

Heliconius butterflies are well-known for their colourful wing patterns, which advertise distastefulness to potential predators and are used during mate choice. However, the relative importance of different aspects of these signals will depend on the visual abilities of Heliconius and their predators. Previous studies have investigated colour sensitivity and neural anatomy, but visual acuity (the ability to perceive detail) has not been studied in these butterflies. Here, we provide the first estimate of visual acuity in Heliconius: from a behavioural optomotor assay, we found that mean visual acuity = 0.49 cycles-per-degree (cpd), with higher acuity in males than females. We also estimated visual acuity from eye morphology and reported slightly lower values (mean visual acuity = 0.38 cpd), but acuity was still higher in males. Finally, we estimated how visual acuity affects Heliconius visual perception compared to a potential avian predator. Whereas the bird predator maintained high resolving power, Heliconius lost the ability to resolve detail at greater distances, though colours may remain salient. These results will inform future studies of Heliconius wing pattern evolution, as well as other aspects in these highly visual butterflies, which have emerged as an important system in studies of adaptation and speciation.

evolutionary biology↗

bioRxiv2023

Oviposition behaviour is not affected by ultraviolet light in a butterfly with sexually-dimorphic expression of a UV-sensitive opsin

Animal vision is important for mediating multiple complex behaviours. In Heliconius butterflies, vision guides fundamental behaviours such as oviposition, foraging and mate choice. Colour vision in Heliconius involves ultraviolet (UV), blue and long-wavelength sensitive photoreceptors (opsins). Additionally, Heliconius possess a duplicated UV opsin, and its expression varies widely within the genus. In Heliconius erato, opsin expression is sexually dimorphic; only females express both UV-sensitive opsins, enabling UV wavelength discrimination. However, the ecological pressures that have driven these sex-specific differences in visual perception remain unresolved. Heliconius females invest heavily in finding hostplants to lay their eggs, a behaviour heavily reliant on visual cues. We tested whether UV vision is used for oviposition in H. erato and Heliconius himera females by manipulating the availability of UV in behavioural experiments under naturalistic conditions. We found that UV did not influence the number of oviposition attempts or the number of eggs laid. In addition, their hostplant, Passiflora punctata, does not reflect UV wavelengths, and models of H. erato female vision suggest only minimal stimulation of the UV opsins. Overall, these findings suggest that UV wavelengths do not directly affect the ability of Heliconius females to find suitable oviposition sites. Alternatively, UV discrimination could be used in the context of foraging or mate choice, but this remains to be tested.

evolutionary biology↗

bioRxiv2021

Repeated genetic adaptation to high altitude in two tropical butterflies

Repeated evolution can provide insight into the mechanisms that facilitate adaptation to novel or changing environments. Here we study adaptation to high altitude in two divergent tropical butterflies, H. erato and H. melpomene, which have repeatedly and independently adapted to high elevations on either side of the Andean mountains. We sequenced 518 whole genomes from elevational transects and found many regions under selection at high altitude, with repeated genetic differentiation across multiple replicates, including allopatric comparisons. In contrast, there is little molecular parallelism between H. erato and H. melpomene. With a further 85 whole genomes of five close relatives, we find that a large proportion divergent regions have arisen from standing variation and putative adaptive introgression from high-altitude specialist species. Taken together our study supports a key role of standing genetic variation and gene flow from pre-adapted species in promoting parallel genetic local adaptation to the environment.

evolutionary biology↗

bioRxiv2020

Genomics of altitude-associated wing shape in two tropical butterflies

Understanding how organisms adapt to their local environment is central to evolution. With new whole-genome sequencing technologies and the explosion of data, deciphering the genomic basis of complex traits that are ecologically relevant is becoming increasingly feasible. Here we study the genomic basis of wing shape in two Neotropical butterflies that inhabit large geographical ranges. Heliconius butterflies at high elevations have been shown to generally have rounder wings than those in the lowlands. We reared over 1100 butterflies from 71 broods of H. erato and H. melpomene in common-garden conditions and show that wing aspect ratio, i.e. elongatedness, is highly heritable in both species and elevation-associated wing shape differences are maintained. Genome-wide associations with a published dataset of 666 whole genomes from across a hybrid zone, uncovered a highly polygenic basis to wing shape variation in the wild. We identify several genes that have roles in wing morphogenesis or wing shape variation in Drosophila flies, making them promising candidates for future studies. There was little evidence for molecular parallelism in the two species, with only one shared candidate gene, nor for a role of the four known colour pattern loci, except for optix in H. erato. Thus, we present the first insights into the heritability and genomic basis of within-species wing shape in two Heliconius species, adding to a growing body of evidence that polygenic adaptation may underlie many ecologically relevant traits.

evolutionary biology↗

bioRxiv2020

Selection and gene flow define polygenic barriers between incipient butterfly species

Characterizing the genetic architecture of species boundaries remains a difficult task. Hybridizing species provide a powerful system to identify the factors that shape genomic variation and, ultimately, identify the regions of the genome that maintain species boundaries. Unfortunately, complex histories of isolation, admixture and selection can generate heterogenous genomic landscapes of divergence which make inferences about the regions that are responsible for species boundaries problematic. However, as the signal of admixture and selection on genomic loci varies with recombination rate, their relationship can be used to infer their relative importance during speciation. Here, we explore patterns of genomic divergence, admixture and recombination rate among hybridizing lineages across the Heliconius erato radiation. We focus on the incipient species, H. erato and H. himera, and distinguish the processes that drive genomic divergence across three contact zones where they frequently hybridize. Using demographic modeling and simulations, we infer that periods of isolation and selection have been major causes of genome-wide correlation patterns between recombination rate and divergence between these incipient species. Upon secondary contact, we found surprisingly highly asymmetrical introgression between the species pair, with a paucity of H. erato alleles introgressing into the H. himera genomes. We suggest that this signal may result from a current polygenic species boundary between the hybridizing lineages. These results contribute to a growing appreciation for the importance of polygenic architectures of species boundaries and pervasive genome-wide selection during the early stages of speciation with gene flow.

evolutionary biology↗

bioRxiv2019

Microclimate buffering and thermal tolerance across elevations in a tropical butterfly

Microclimatic variability in tropical forests plays a key role in shaping species distributions and their ability to cope with environmental change, especially for ectotherms. Yet, currently available climatic datasets lack data from the forest interior and our knowledge of thermal tolerance among tropical ectotherms is limited. To tackle this, we studied natural variation in the microclimate experienced by a tropical genus of butterflies (Heliconius sp.) along their Andean range across a single year. We found that the forest strongly buffers temperature and humidity in the understory, especially in the lowlands where temperatures are more extreme. There were systematic differences between our yearly records and macroclimate databases (WorldClim2), with lower interpolated minimum temperatures and maximum temperatures higher than expected. We then assessed thermal tolerance of ten Heliconius butterfly species in the wild and showed that populations at high elevations had significantly lower heat tolerance than those at lower elevations. However, when we reared populations of the widespread H. erato from high and low elevations in a common-garden environment, the difference in heat tolerance across elevations was reduced, indicating plasticity in this trait. Microclimate buffering is not currently captured in publicly available datasets but could be crucial for enabling upland shifting of species sensitive to heat such as highland Heliconius. Plasticity in thermal tolerance may alleviate the effects of global warming on some widespread ectotherm species, but more research is needed to understand the long-term consequences of plasticity on populations and species. Summary statementTropical forests along the Andes were found to greatly buffer climate. The butterflies inhabiting high elevations were less thermally tolerant but not when reared in common-garden conditions, indicating plasticity.

ecology↗

bioRxiv2019

Altitude and life-history shape the evolution of Heliconius wings

Phenotypic divergence between closely related species has long interested biologists. Taxa that inhabit a range of environments and have known and diverse, natural histories, can help understand how different selection pressures shape diverging traits. In butterflies, wing colour patterns have been extensively studied, whereas wing shape diversity is less well understood despite its importance for flight. Here we study a measure of wing shape, aspect ratio, and wing size in a large dataset of over 3200 individuals, representing 13 Heliconius species, from across the Neotropics. We assess the relative importance of phylogenetic relatedness, natural history and habitat in determining wing shape and size. We find that both larval and adult behavioural ecology affect patterns of adult size dimorphisms. On one hand, species with solitary larvae have larger adult males, in contrast to gregarious Heliconius species, and indeed most Lepidoptera. On the other hand, species in the pupal-mating clade are smaller overall than those in the adult-mating clade. Interestingly, while controlling for phylogeny, sex ratios and allometry, we find that species inhabiting higher altitudes have rounder wings and, in one of the two major Heliconius clades, are also bigger in size than their lowland relatives. Thus, we reveal novel adaptive wing morphological divergence among Heliconius species beyond that imposed by natural selection on aposematic wing colouration. Our study highlights the value of phylogenetic comparative methods in study systems that have diverse and well-studied natural histories to disentangle the selection pressures shaping adaptive phenotypes.

evolutionary biology↗