RESUMEN

We searched for evidence of knockdown resistance (kdr) mutations in the voltage-gated sodium channel gene of Aedes aegypti (Linnaeus) (Diptera: Culicidae) and Aedes albopictus (Skuse) (Diptera: Culicidae) mosquitoes from Panama. Conventional PCR was performed on 469 Ae. aegypti and 349 Ae. albopictus. We did not discover kdr mutations in Ae. albopictus, but 2 nonsynonymous kdr mutations, V1016I (found in 101 mosquitoes) and F1534C (found in 29 of the mosquitoes with the V1016I), were detected in Ae. aegypti. These kdr mutations were present in all specimens that were successfully sequenced for both IIS5-S6 and IIIS6 regions, which included samples collected from 8 of the 10 provinces of Panama. No other kdr mutations were found in Ae. aegypti, including V1016G, which has already been reported in Panama. Findings suggest that the V1016I-F1534C variant is prevalent in Panama, which might be related to the introduction and passive movement of mosquitoes as part of the used-tire trade. However, we cannot rule out the possibility that selection on de novo replacement of kdr mutations also partially explains the widespread distribution pattern of these mutations. These 2 ecological and evolutionary processes are not mutually exclusive, though, as they can occur in tandem. Research in Panama needs to calculate the genotypic and allelic frequencies of kdr alleles in local Ae. aegypti populations and to test whether some combinations confer phenotypic resistance or not. Finally, future studies will have to track the introduction and spreading of new kdr mutations in both Aedes species.

RESUMEN

Among vertebrates, nearly all oviparous animals are considered to have either obligate aquatic or terrestrial oviposition, with eggs that are specialized for developing in those environments. The terrestrial environment has considerably more oxygen but is dry and thus presents both opportunities and challenges for developing embryos, particularly those adapted for aquatic development. Here, we present evidence from field experiments examining egg-laying behavior, egg size, and egg jelly function of 13 species of Central and South American treefrogs in the genus Dendropsophus, which demonstrates that flexible oviposition (individuals laying eggs both in and out of water) and eggs capable of both aquatic and terrestrial development are the likely factors which enable the transition from aquatic to terrestrial reproduction. Nearly half of the species we studied had previously undescribed degrees of flexible oviposition. Species with obligate terrestrial reproduction have larger eggs than species with aquatic reproduction, and species with flexible reproduction have eggs of intermediate sizes. Obligate terrestrial breeding frogs also have egg masses that absorb water more quickly than those with flexible oviposition. We also examined eight populations of a single species, Dendropsophus ebraccatus, and document substantial intraspecific variation in terrestrial oviposition; populations in rainy, stable climates lay fewer eggs in water than those in drier areas. However, no differences in egg size were found, supporting the idea that the behavioral component of oviposition evolves before other adaptations associated with obligate terrestrial reproduction. Collectively, these data demonstrate the key role that behavior can have in facilitating major evolutionary transitions.

Asunto(s)

RESUMEN

Sex chromosomes are evolutionarily labile in many animals and sometimes fuse with autosomes, creating so-called neo-sex chromosomes. Fusions between sex chromosomes and autosomes have been proposed to reduce sexual conflict and to promote adaptation and reproductive isolation among species. Recently, advances in genomics have fuelled the discovery of such fusions across the tree of life. Here, we discovered multiple fusions leading to neo-sex chromosomes in the sapho subclade of the classical adaptive radiation of Heliconius butterflies. Heliconius butterflies generally have 21 chromosomes with very high synteny. However, the five Heliconius species in the sapho subclade show large variation in chromosome number ranging from 21 to 60. We find that the W chromosome is fused with chromosome 4 in all of them. Two sister species pairs show subsequent fusions between the W and chromosomes 9 or 14, respectively. These fusions between autosomes and sex chromosomes make Heliconius butterflies an ideal system for studying the role of neo-sex chromosomes in adaptive radiations and the degeneration of sex chromosomes over time. Our findings emphasize the capability of short-read resequencing to detect genomic signatures of fusion events between sex chromosomes and autosomes even when sex chromosomes are not explicitly assembled.

Asunto(s)

RESUMEN

When populations experience different sensory conditions, natural selection may favor sensory system divergence, affecting peripheral structures and/or downstream neural pathways. We characterized the outer eye morphology of sympatric Heliconius butterflies from different forest types and their first-generation reciprocal hybrids to test for adaptive visual system divergence and hybrid disruption. In Panama, Heliconius cydno occurs in closed forests, whereas Heliconius melpomene resides at the forest edge. Among wild individuals, H. cydno has larger eyes than H. melpomene, and there are heritable, habitat-associated differences in the visual brain structures that exceed neutral divergence expectations. Notably, hybrids have intermediate neural phenotypes, suggesting disruption. To test for similar effects in the visual periphery, we reared both species and their hybrids in common garden conditions. We confirm that H. cydno has larger eyes and provide new evidence that this is driven by selection. Hybrid eye morphology is more H. melpomene-like despite body size being intermediate, contrasting with neural trait intermediacy. Overall, our results suggest that eye morphology differences between H. cydno and H. melpomene are adaptive and that hybrids may suffer fitness costs due to a mismatch between the peripheral visual structures and previously described neural traits that could affect visual performance.

Asunto(s)

RESUMEN

AbstractTropical ectotherms are thought to be especially vulnerable to climate change because they have evolved in temporally stable thermal environments and therefore have decreased tolerance for thermal variability. Thus, they are expected to have narrow thermal tolerance ranges, live close to their upper thermal tolerance limits, and have decreased thermal acclimation capacity. Although models often predict that tropical forest ectotherms are especially vulnerable to rapid environmental shifts, these models rarely include the potential for plasticity of relevant traits. We measured phenotypic plasticity of thermal tolerance and thermal preference as well as multitissue transcriptome plasticity in response to warmer temperatures in a species that previous work has suggested is highly vulnerable to climate warming, the Panamanian slender anole lizard (Anolis apletophallus). We found that many genes, including heat shock proteins, were differentially expressed across tissues in response to short-term warming. Under long-term warming, the voluntary thermal maxima of lizards also increased, although thermal preference exhibited only limited plasticity. Using these data, we modeled changes in the activity time of slender anoles through the end of the century under climate change and found that plasticity should delay declines in activity time by at least two decades. Our results suggest that slender anoles, and possibly other tropical ectotherms, can alter the expression of genes and phenotypes when responding to shifting environmental temperatures and that plasticity should be considered when predicting the future of organisms under a changing climate.

Asunto(s)

RESUMEN

Hybridization allows adaptations to be shared among lineages and may trigger the evolution of new species1,2. However, convincing examples of homoploid hybrid speciation remain rare because it is challenging to demonstrate that hybridization was crucial in generating reproductive isolation3. Here we combine population genomic analysis with quantitative trait locus mapping of species-specific traits to examine a case of hybrid speciation in Heliconius butterflies. We show that Heliconius elevatus is a hybrid species that is sympatric with both parents and has persisted as an independently evolving lineage for at least 180,000 years. This is despite pervasive and ongoing gene flow with one parent, Heliconius pardalinus, which homogenizes 99% of their genomes. The remaining 1% introgressed from the other parent, Heliconius melpomene, and is scattered widely across the H. elevatus genome in islands of divergence from H. pardalinus. These islands contain multiple traits that are under disruptive selection, including colour pattern, wing shape, host plant preference, sex pheromones and mate choice. Collectively, these traits place H. elevatus on its own adaptive peak and permit coexistence with both parents. Our results show that speciation was driven by introgression of ecological traits, and that speciation with gene flow is possible with a multilocus genetic architecture.

Asunto(s)

RESUMEN

Visual preferences are important drivers of mate choice and sexual selection, but little is known of how they evolve at the genetic level. In this study, we took advantage of the diversity of bright warning patterns displayed by Heliconius butterflies, which are also used during mate choice. Combining behavioral, population genomic, and expression analyses, we show that two Heliconius species have evolved the same preferences for red patterns by exchanging genetic material through hybridization. Neural expression of regucalcin1 correlates with visual preference across populations, and disruption of regucalcin1 with CRISPR-Cas9 impairs courtship toward conspecific females, providing a direct link between gene and behavior. Our results support a role for hybridization during behavioral evolution and show how visually guided behaviors contributing to adaptation and speciation are encoded within the genome.

Asunto(s)

RESUMEN

Traits under divergent ecological selection that also function during mating can be important in maintaining species boundaries. Few studies have considered mutual mate choice, where both males and females base mating decisions on the same trait. Wing colouration in Heliconius butterflies evolved as a warning signal but also functions as a mating cue. We investigated the contribution of visual preference to assortative mating in an aposematic butterfly Heliconius cydno in the context of reproductive isolation with its sympatric, visually distinct relative Heliconius melpomene. Heliconius cydno have conspicuous white bands on their forewings, whereas those of H. melpomene are red in colour. We predicted that both sexes of H. cydno contributed to assortative mating by exhibiting visual preference towards conspecific wing colouration. We analysed published and new data from preference experiments, in which males were presented with conspecific and H. melpomene females. We also recorded female responses and mating outcomes in choice experiments, involving conspecific males with either the original white or artificially painted red forewing bands. Both sexes of H. cydno responded more positively towards the conspecific colouration, and males strongly preferred females of its own colours. In contrast, male colouration did not predict mating outcomes in female choice experiments. As courtships are initiated by males in butterflies, our findings suggest that female visual preference might be of secondary importance in H. cydno. Our data also suggest that the contribution of visual preference to reproductive isolation might be unequal between H. cydno and its sympatric relative H. melpomene.

Asunto(s)

RESUMEN

Heliconius butterflies exhibit expanded mushroom bodies, a key brain region for learning and memory in insects, and a novel foraging strategy unique among Lepidoptera - traplining for pollen. We tested visual long-term memory across six Heliconius and outgroup Heliconiini species. Heliconius species exhibited greater fidelity to learned colors after eight days without reinforcement, with further evidence of recall at 13 days. We also measured the plastic response of the mushroom body calyces over this time period, finding substantial post-eclosion expansion and synaptic pruning in the calyx of Heliconius erato, but not in the outgroup Heliconiini Dryas iulia. In Heliconius erato, visual associative learning experience specifically was associated with a greater retention of synapses and recall accuracy was positively correlated with synapse number. These results suggest that increases in the size of specific brain regions and changes in their plastic response to experience may coevolve to support novel behaviors.

RESUMEN

Flight was a key innovation in the adaptive radiation of insects. However, it is a complex trait influenced by a large number of interacting biotic and abiotic factors, making it difficult to unravel the evolutionary drivers. We investigate flight patterns in neotropical heliconiine butterflies, well known for mimicry of their aposematic wing color patterns. We quantify the flight patterns (wing beat frequency and wing angles) of 351 individuals representing 29 heliconiine and 9 ithomiine species belonging to ten color pattern mimicry groupings. For wing beat frequency and up wing angles, we show that heliconiine species group by color pattern mimicry affiliation. Convergence of down wing angles to mimicry groupings is less pronounced, indicating that distinct components of flight are under different selection pressures and constraints. The flight characteristics of the Tiger mimicry group are particularly divergent due to convergence with distantly related ithomiine species. Predator-driven selection for mimicry also explained variation in flight among subspecies, indicating that this convergence can occur over relatively short evolutionary timescales. Our results suggest that the flight convergence is driven by aposematic signaling rather than shared habitat between comimics. We demonstrate that behavioral mimicry can occur between lineages that have separated over evolutionary timescales ranging from <0.5 to 70 My.

Asunto(s)

RESUMEN

Evaluating whether hybrid zones are stable or mobile can provide novel insights for evolution and conservation biology. Butterflies exhibit high sensitivity to environmental changes and represent an important model system for the study of hybrid zone origins and maintenance. Here, we review the literature exploring butterfly hybrid zones, with a special focus on their spatiotemporal dynamics and the potential mechanisms that could lead to their movement or stability. We then compare different lines of evidence used to investigate hybrid zone dynamics and discuss the strengths and weaknesses of each approach. Our goal with this review is to reveal general conditions associated with the stability or mobility of butterfly hybrid zones by synthesizing evidence obtained using different types of data sampled across multiple regions and spatial scales. Finally, we discuss spatiotemporal dynamics in the context of a speciation/divergence continuum, the relevance of hybrid zones for conservation biology, and recommend key topics for future investigation.

Asunto(s)

RESUMEN

Coral reefs rank among the most diverse species assemblages on Earth. A particularly striking aspect of coral reef communities is the variety of colour patterns displayed by reef fishes. Colour pattern is known to play a central role in the ecology and evolution of reef fishes through, for example, signalling or camouflage. Nevertheless, colour pattern is a complex trait in reef fishes-actually a collection of traits-that is difficult to analyse in a quantitative and standardized way. This is the challenge that we address in this study using the hamlets (Hypoplectrus spp., Serranidae) as a model system. Our approach involves a custom underwater camera system to take orientation- and size-standardized photographs in situ, colour correction, alignment of the fish images with a combination of landmarks and Bézier curves, and principal component analysis on the colour value of each pixel of each aligned fish. This approach identifies the major colour pattern elements that contribute to phenotypic variation in the group. Furthermore, we complement the image analysis with whole-genome sequencing to run a multivariate genome-wide association study for colour pattern variation. This second layer of analysis reveals sharp association peaks along the hamlet genome for each colour pattern element and allows to characterize the phenotypic effect of the single nucleotide polymorphisms that are most strongly associated with colour pattern variation at each association peak. Our results suggest that the diversity of colour patterns displayed by the hamlets is generated by a modular genomic and phenotypic architecture.

Asunto(s)

RESUMEN

Among butterflies, Heliconius have a unique behavioural profile, being the sole genus to actively feed on pollen. Heliconius learn the location of pollen resources, and have enhanced visual memories and expanded mushroom bodies, an insect learning and memory centre, relative to related genera. These structures also show extensive post-eclosion growth and developmental sensitivity to environmental conditions. However, whether this reflects plasticity in neurite growth, or an extension of neurogenesis into the adult stage, is unknown. Adult neurogenesis has been described in some Lepidoptera, and could provide one route to the increased neuron number observed in Heliconius. Here, we compare volumetric changes in the mushroom bodies of freshly eclosed and aged Heliconius erato and Dryas iulia, and estimate the number of intrinsic mushroom body neurons using a new and validated automated method to count nuclei. Despite extensive volumetric variation associated with age, our data show that neuron number is remarkably constant in both species, suggesting a lack of adult neurogenesis in the mushroom bodies. We support this conclusion with assays of mitotic cells, which reveal very low levels of post-eclosion cell division. Our analyses provide an insight into the evolution of neural plasticity, and can serve as a basis for continued exploration of the potential mechanisms behind brain development and maturation.

RESUMEN

The slender anole, Anolis apletophallus, is a small arboreal lizard of the rainforest understory of central and eastern Panama. This species has been the subject of numerous ecological and evolutionary studies over the past 60 years as a result of attributes that make it especially amenable to field and laboratory science. Slender anoles are highly abundant, short-lived (nearly 100% annual turnover), easy to manipulate in both the lab and field, and are ubiquitous in the forests surrounding the Smithsonian Tropical Research Institute in Panama, where researchers have access to high-quality laboratory facilities. Here, we present a high-quality genome for the slender anole, which is an important new resource for studying this model species. We assembled and annotated the slender anole genome by combining 3 technologies: Oxford Nanopore, 10× Genomics Linked-Reads, and Dovetail Omni-C. We compared this genome with the recently published brown anole (Anolis sagrei) and the canonical green anole (Anolis carolinensis) genomes. Our genome is the first assembled for an Anolis lizard from mainland Central or South America, the regions that host the majority of diversity in the genus. This new reference genome is one of the most complete genomes of any anole assembled to date and should facilitate deeper studies of slender anole evolution, as well as broader scale comparative genomic studies of both mainland and island species. In turn, such studies will further our understanding of the well-known adaptive radiation of Anolis lizards.

Asunto(s)

RESUMEN

Heliconius butterflies, a speciose genus of Müllerian mimics, represent a classic example of an adaptive radiation that includes a range of derived dietary, life history, physiological and neural traits. However, key lineages within the genus, and across the broader Heliconiini tribe, lack genomic resources, limiting our understanding of how adaptive and neutral processes shaped genome evolution during their radiation. Here, we generate highly contiguous genome assemblies for nine Heliconiini, 29 additional reference-assembled genomes, and improve 10 existing assemblies. Altogether, we provide a dataset of annotated genomes for a total of 63 species, including 58 species within the Heliconiini tribe. We use this extensive dataset to generate a robust and dated heliconiine phylogeny, describe major patterns of introgression, explore the evolution of genome architecture, and the genomic basis of key innovations in this enigmatic group, including an assessment of the evolution of putative regulatory regions at the Heliconius stem. Our work illustrates how the increased resolution provided by such dense genomic sampling improves our power to generate and test gene-phenotype hypotheses, and precisely characterize how genomes evolve.

Asunto(s)

RESUMEN

Butterfly color patterns provide visible and biodiverse phenotypic readouts of the patterning processes. Although the secreted ligand WntA has been shown to instruct the color pattern formation in butterflies, its mode of reception remains elusive. Butterfly genomes encode four homologs of the Frizzled-family of Wnt receptors. Here, we show that CRISPR mosaic knockouts of frizzled2 (fz2) phenocopy the color pattern effects of WntA loss of function in multiple nymphalids. Whereas WntA mosaic clones result in intermediate patterns of reduced size, fz2 clones are cell-autonomous, consistent with a morphogen function. Shifts in expression of WntA and fz2 in WntA crispant pupae show that they are under positive and negative feedback, respectively. Fz1 is required for Wnt-independent planar cell polarity in the wing epithelium. Fz3 and Fz4 show phenotypes consistent with Wnt competitive-antagonist functions in vein formation (Fz3 and Fz4), wing margin specification (Fz3), and color patterning in the Discalis and Marginal Band Systems (Fz4). Overall, these data show that the WntA/Frizzled2 morphogen-receptor pair forms a signaling axis that instructs butterfly color patterning and shed light on the functional diversity of insect Frizzled receptors.

Asunto(s)

RESUMEN

Quantifying gene flow between lineages at different stages of the speciation continuum is central to understanding speciation. Heliconius butterflies have undergone an adaptive radiation in wing color patterns driven partly by natural selection for local mimicry. Color patterns are also known to be used as assortative mating cues. Therefore, wing pattern divergence is considered to play a role in speciation. A corollary is that mimicry between closely related species may be associated with hybridization and interfere with reproductive isolation. Here, we take a multifaceted approach to explore speciation history, species boundaries, and traits involved in species differentiation between the two closely related species, Heliconius hecale and Heliconius ismenius. We focus on geographic regions where the two species mimic each other and contrast this with geographic regions where they do not mimic each other. To examine population history and patterns of gene flow, we tested and compared a four-population model accounting for linked selection. This model suggests that the two species have remained isolated for a large part of their history, yet with a small amount of gene exchange. Accordingly, signatures of genomic introgression were small except at a major wing pattern allele and chemosensing genes and stronger in the mimetic populations compared with nonmimetic populations. Behavioral assays confirm that visual confusion exists but that short-range cues determine strong sexual isolation. Tests for chemical differentiation between species identified major differences in putative pheromones which likely mediate mate choice and the maintenance of species differences.

Asunto(s)

RESUMEN

The selective pressures leading to the elaboration of downstream, integrative processing centres, such as the mammalian neocortex or insect mushroom bodies, are often unclear. In Heliconius butterflies, the mushroom bodies are two to four times larger than those of their Heliconiini relatives, and the largest known in Lepidoptera. Heliconiini lay almost exclusively on Passiflora, which exhibit a remarkable diversity of leaf shape, and it has been suggested that the mushroom body expansion of Heliconius may have been driven by the cognitive demands of recognizing and learning leaf shapes of local host plants. We test this hypothesis using two complementary methods: (i) phylogenetic comparative analyses to test whether variation in mushroom body size is associated with the morphological diversity of host plants exploited across the Heliconiini; and (ii) shape-learning experiments using six Heliconiini species. We found that variation in the range of leaf morphologies used by Heliconiini was not associated with mushroom body volume. Similarly, we find interspecific differences in shape-learning ability, but Heliconius are not overall better shape learners than other Heliconiini. Together these results suggest that the visual recognition and learning of host plants was not a main factor driving the diversity of mushroom body size in this tribe.

Asunto(s)

RESUMEN

Changes in the abundance and diversity of neural cell types, and their connectivity, shape brain composition and provide the substrate for behavioral evolution. Although investment in sensory brain regions is understood to be largely driven by the relative ecological importance of particular sensory modalities, how selective pressures impact the elaboration of integrative brain centers has been more difficult to pinpoint. Here, we provide evidence of extensive, mosaic expansion of an integration brain center among closely related species, which is not explained by changes in sites of primary sensory input. By building new datasets of neural traits among a tribe of diverse Neotropical butterflies, the Heliconiini, we detected several major evolutionary expansions of the mushroom bodies, central brain structures pivotal for insect learning and memory. The genus Heliconius, which exhibits a unique dietary innovation, pollen-feeding, and derived foraging behaviors reliant on spatial memory, shows the most extreme enlargement. This expansion is primarily associated with increased visual processing areas and coincides with increased precision of visual processing, and enhanced long term memory. These results demonstrate that selection for behavioral innovation and enhanced cognitive ability occurred through expansion and localized specialization in integrative brain centers.

Asunto(s)

RESUMEN

Changes in ecological preference, often driven by spatial and temporal variation in resource distribution, can expose populations to environments with divergent information content. This can lead to adaptive changes in the degree to which individuals invest in sensory systems and downstream processes, to optimize behavioural performance in different contexts. At the same time, environmental conditions can produce plastic responses in nervous system development and maturation, providing an alternative route to integrating neural and ecological variation. Here, we explore how these two processes play out across a community of Heliconius butterflies. Heliconius communities exhibit multiple Mullerian mimicry rings, associated with habitat partitioning across environmental gradients. These environmental differences have previously been linked to heritable divergence in brain morphology in parapatric species pairs. They also exhibit a unique dietary adaptation, known as pollen feeding, that relies heavily on learning foraging routes, or trap-lines, between resources, which implies an important environmental influence on behavioural development. By comparing brain morphology across 133 wild-caught and insectary-reared individuals from seven Heliconius species, we find strong evidence for interspecific variation in patterns of neural investment. These largely fall into two distinct patterns of variation; first, we find consistent patterns of divergence in the size of visual brain components across both wild and insectary-reared individuals, suggesting genetically encoded divergence in the visual pathway. Second, we find interspecific differences in mushroom body size, a central component of learning and memory systems, but only among wild caught individuals. The lack of this effect in common-garden individuals suggests an extensive role for developmental plasticity in interspecific variation in the wild. Finally, we illustrate the impact of relatively small-scale spatial effects on mushroom body plasticity by performing experiments altering the cage size and structure experienced by individual H. hecale. Our data provide a comprehensive survey of community level variation in brain structure, and demonstrate that genetic effects and developmental plasticity contribute to different axes of interspecific neural variation.

Asunto(s)