Biology subjects

McMillan, W. O.

Publications and source records attributed to McMillan, W. O..

At least 19 recordsLinked to original sources

bioRxiv2026

Parallel phenotypes underpinned by different genes in the visual system of two trans-isthmian coral reef fish species pairs

Understanding the genetic basis of adaptation in natural populations to changing environmental conditions is challenging. The relatively simple genotype-to-phenotype relationship between opsin genes and visual pigments offers a particularly informative model to explore the molecular mechanisms underpinning adaptive phenotypic change in natural populations. Here we leveraged the natural experiment provided by the tectonic closure of the Central American seaway that created allopatric, sister taxa in multiple, independent lineages of marine organisms and exposed them to distinct underwater light environments: either the more turbid Tropical Eastern Pacific (TEP), or the spectrally broader Caribbean Sea. Using two species pairs of planktivorous teleosts, the Azurina multilineata/A. atrilobata damselfish and the Cephalopholis (Paranthias) furcifer/C. colonus groupers, we explore to what extent visual sensitivity converged to similar adaptations in response to similar foraging strategies and shared underwater light in each marine basin. We found that the compression of the underwater light field towards the central portion of the spectrum from Caribbean to TEP waters is reflected in similar shifts towards the centre of the light spectrum in overall single and double cone sensitivities in both families. Both TEP species have single (short-wavelength) cone sensitivities shifted to longer wavelengths and double (long-wavelength) cone sensitivities shifted to shorter wavelengths, compared to their Caribbean counterparts. These parallel shifts in visual sensitivities observed in response to shared underwater light environments are accomplished by different underlying opsin gene toolsets in the two lineages. Similarly, expression changes in pathways associated with the visual system revealed limited parallelism at the molecular level.

evolutionary biology↗

bioRxiv2026

The gene ivory:mir-193 controls scale type differentiation in Heliconius butterflies

The ivory:mir-193 locus is a genetic hotspot underlying melanic wing pattern variation across Lepidoptera, acting as a master regulator of melanic scale fate. This includes the genus Heliconius, where aposematic mimicry is driven by three scale cell types: light Type I, dark-melanic Type II, and red Type III scales. We tested functions of ivory:mir-193 in Heliconius using CRISPR-induced somatic mosaic knockouts of ivory and mir-193 across multiple pattern morphs. Knockouts converted Type II scales to Type I scales. Effects on Type III scales varied among and within individuals, indicating that ivory:mir-193 is permissive for Type III development. Using single-nucleus RNA-seq, we profiled the transcriptional landscape of H. melpomene-{Delta}78k mutants lacking mir-193. Loss of mir-193 produced readthrough transcription, consistent with a model where miR-193 acts as a co-transcriptional terminator. These data show that ivory drives wing pattern variation, while mir-193 mediates downstream diversity in scale fate across Lepidoptera.

evolutionary biology↗

bioRxiv2026

Cognitive robustness in a new insect model of extended longevity

Human life expectancy has jumped by several decades in the last century, but the healthspan has not followed suit. The ageing population has come with an increased prevalence of neurodegenerative disease, and insects have proven to be valuable models of these conditions and their associated cognitive decline. The Heliconius butterfly genus is an emerging system in insect cognition, having recently evolved a significant expansion in neural centres of learning and memory, alongside enhanced stability of visual long-term memory in comparison with their close relatives in the Heliconiini tribe. This is linked to the cognitive demands imposed by Heliconius spatially-faithful foraging behaviour for a protein-rich diet of pollen, and co-occurs with a dramatic lifespan extension in this genus over the other Heliconiini outgroups. Here, we investigate whether the Heliconius cognitive healthspan is similarly discrepant, or if any cognitive decline is instead delayed in accordance with their lifespan extension. We first report evidence that investment in learning and memory circuits co-evolves with Heliconiini lifespan. We then conduct learning and memory assays across the lifespans of a representative longer-lived Heliconius, H. hecale, and the shorter-lived Heliconiini outgroup, Dryas iulia. Across both species, and particularly in H. hecale, we find evidence for cognitive robustness in late life, in contrast to evidence for widespread cognitive declines in insects. Our results add a new taxonomic order to the study of age-related memory impairment, and suggest Heliconius as a valuable model system for mechanistic studies of the maintenance of neurological health in the context of extended life.

animal behavior and cognition↗

bioRxiv2025

Comparative genomic analyses of trans-ithmanian reef fishes reveals different molecular targets of environmental adaptation in different families.

The extent to which selection acts upon the same molecular targets when faced with the same environmental changes has important implications for our understanding of the repeatability and predictability of evolutionary processes. Replicated natural experiments are well positioned to provide insight, however often these involve closely related species or populations of the same species. Given that the similarity of genetic background makes the same molecular change more likely, it is essential to evaluate the extent to which molecular parallelism occurs in more distantly related species. The rise of the Isthmus of Panama presents an ideal natural experiment to investigate the prevalence of parallel molecular changes in distantly related lineages exposed to the same environmental regimes of temperature, salinity and primary productivity in the two newly formed oceans. Here, we generate high-quality reference genomes for two replicate pairs of geminate reef fishes, one in the family Pomacentridae and one in the Serranidae. Comparative analyses of positive selection in protein-coding genes and of gene family evolution revealed multiple signals of potentially adaptive divergence between geminate species in response to environmental regime. Common targets of selection between families included MAPK signalling (MAP3K10), solute transport (SLC46A2) and reproduction (ZPL3L), as well as expansions in immune and MAPK related gene families. Overall, however, we found minimal evidence of parallelism between families either at the gene level or when considering higher functional categories. Our findings suggest that phylogenetic constraints may limit the levels of molecular parallelism in distant lineages even when faced with comparable selective pressures. Significance StatementUnderstanding the extent to which species exposed to similar environmental conditions may adapt using similar genetic solutions has important implications for our understanding of evolutionary processes and how we may expect species to adapt in the future. However, systems where multiple, independent lineages are faced with the same shift in conditions are rare. The rise of the Isthmus of Panama provides a unique, natural experiment where multiple marine species have been divided and exposed to radically different environmental conditions. Here, we generate genomes for separated species in two distantly related families of reef fishes and compare genome-wide patterns of divergence. Our analyses identified signals of selection in protein-coding genes and shifts in gene family size consistent with adaptation to the distinct environments, however the specific genes and pathways involved predominantly differed between the families, revealing that, even under shared selective pressures, molecular mechanisms may differ across more distant lineages.

evolutionary biology↗

bioRxiv2025

Evolution of increased longevity and slowed ageing in a genus of tropical butterfly

Evolution has given rise to lifespans in extant species ranging from days to centuries. Given that mechanisms of ageing are highly conserved, studying long-lived lineages across the animal kingdom could yield insights relevant for healthy ageing in humans. However, typical models of extended lifespan often live for decades, making them impractical for longitudinal studies. Ideal model systems would be organisms that are naturally long-lived compared to their close relatives, but have lifespans on experimentally tractable scales. Here, we present the Neotropical butterfly genus Heliconius as a novel model system for the evolution of extended longevity. We collate data from 27 species across the Heliconiini tribe to reveal a 25-fold variation in lifespan within the group, with our 348-day maximum for Heliconius hewitsoni longer than any butterfly species previously recorded in the scientific literature. While previous work has attributed this lifespan extension to a plastic response to enhanced nutrition, we conduct detailed survival and functional senescence analyses on two species representative of shorter- and longer-lived clades to show evidence of evolved, heritable mechanisms of slowed ageing in Heliconius. Our results add a new case study to the canon of noteworthy agers, and provide valuable insights into the evolution of increased longevity.

evolutionary biology↗

bioRxiv2025

Comparative Genomics of Transisthmian Damselfishes (Abudefduf saxatilis and A. troschelii)

The uplift of the Central American Isthmus (CAI) represents a natural laboratory for the study of allopatric speciation in marine organisms. Several geminate species pairs of both vertebrates and invertebrates formed following the uplift of the CAI, including damselfishes of the Pomacentridae family. However, to date no studies have explored the genomic differences among geminate species in the Pacific and Atlantic Oceans. In this study we present genome assemblies for the transisthmian species pair consisting of the Sergeant Major Abudefduf saxatilis (Tropical Atlantic) and the Panamic Sergeant Major Abudefduf troschelii (Tropical Eastern Pacific) derived from PacBio long-read sequencing. The new genomes are near-chromosome level, and among the highest-quality genomes currently available for coral reef fishes. We show that large structural variants distinguish the two species, including a 9 megabase inversion in linkage group (putative chromosome) 6. Additionally, we show through an analysis of demographic history that alleles within the two genomes have different coalescence time distributions, which may be due to different effective population sizes, population structures, and/or selection regimes in the two oceans. Finally, we highlight gene families that were significantly expanded or contracted between A. troschelii and A. saxatilis. Some of these are related to the environmental conditions that differ between the two oceans, such as gamma crystallin M (crygm), which is linked to vision, and vitellogenin (vtg), which is associated with egg provisioning. These genomes set the stage for comparative analyses of genetic structure and selection on the marine organisms that originated with the formation of the CAI. Significance StatementUnderstanding speciation in oceans has represented a historical challenge, given the high rates of dispersal during larval stages for most marine groups. There are few geologic events that have propelled marine biodiversity while completely blocking the genetic exchange during the speciation process. The final closure of the Central American Isthmus (CAI), 2.8 million years ago, is one of these few examples where marine populations from the tropical Pacific and Atlantic oceans have been completely isolated, providing the opportunity to study how genomes diverge in the absence of gene flow. Here, we present the first comparative genomics study of marine organisms separated by the CAI, showing that genomes on the two sides of the CAI differ structurally. We also identify contractions and expansions of various gene families between the two species, which are potentially associated with adaptations to the different environmental conditions in the two oceans. This represents a relevant first step for comparative genomics of geminate species isolated by a major geologic event.

genomics↗

bioRxiv2025

Müllerian mimicry in Neotropical butterflies: One mimicry ring to bring them all, and in the jungle bind them

Understanding the mechanisms underlying species distributions and coexistence is essential to predict and prevent the impacts of global change, particularly in biodiversity hotspots. However, the effects of biotic interactions may be challenging to investigate at large spatial scales. Leveraging well-characterized Mullerian mimetic systems in Neotropical butterflies, we investigated spatial patterns of mutualistic mimetic interactions within and between two tribes of aposematic Nymphalid butterflies: the Heliconiini (Heliconiinae) and the Ithomiini (Danainae). Despite 85 My of independent evolutionary histories, many species share similar warning wing patterns across the Neotropics. In this study we show that both tribes form similar biodiversity hotspots with a high prevalence of rare species and mimetic patterns in the tropical Andes. However, we reveal a higher relative richness of heliconiine butterflies than ithomiines in the Amazon basin contrasting with the Andean concentration of ithomiine diversity. Despite this difference in broadscale diversity patterns, we also document large-scale spatial associations among phenotypically similar species within and between tribes, thereby providing new empirical evidence for Fritz Mullers historical model of mutualistic mimicry at a continental scale. Furthermore, comparative phylogenetic analyses suggest that co-mimetic species within and between tribes have converged towards similar climatic niches as a response to selection favoring co-occurrence. Our findings illustrate the strength of mutualistic interactions in shaping biodiversity patterns at continental scale and in supporting niche convergence even across millions of years of evolution. Critically, it also emphasizes the pervasive vulnerability of mimetic communities, bound by positive interactions, to disassembly induced by climate change. Significance statementMullerian mimicry is a remarkable example of convergent evolution driven by natural selection where coexisting prey species converge in their warning signal advertising their defenses to predators. Heliconiine and ithomiine butterflies found throughout Neotropical rainforests were instrumental in Fritz Mullers historical model, which provided the mechanism for such resemblance. Leveraging decades of fieldwork and museum collections, we show that species with similar color patterns present strikingly similar spatial distributions, regardless of how closely related they are. Such co-occurrence appears reinforced by the evolution of similar climatic requirements among look-alike species. Our findings emphasize the key role of mutualistic interactions in shaping large-scale patterns of biodiversity and supporting convergence in the climatic niches of species spanning across phylogenetically distant clades.

evolutionary biology↗

bioRxiv2025

Convergent molecular evolution associated with repeated transition to gregarious larval behaviour in Heliconiini

Collective behaviour forms the basis for many anti-predator strategies. Within Lepidoptera, larval gregariousness has evolved convergently across many phylogenetically disparate lineages. While the selection pressures shaping variation in larval social behaviours are well investigated, much less is known about the mechanisms that control social attraction and behavioural coordination. Similarly, little is known about how secondary selection pressures associated with social living shape genome evolution. Here, using genomic data for over 60 species from an adaptive radiation of Neotropical butterflies, the Heliconiini, in which gregarious behaviour has evolved repeatedly, we explore the molecular basis of repeated convergent shifts towards gregarious larvae. We focus on three main areas of genomic evolution: differential selection on homologous genes, accelerated rates of evolution on non-coding regions of key genes, and differential gene expression in the brains of solitary and gregarious larvae. We identify strong signatures of convergent molecular evolution, on both coding and non-coding loci, in Heliconiini lineages which evolved gregarious behaviour. Molecular convergence is also detected at the transcriptomic level in larval brains, suggesting convergent shifts in gene regulation in neural tissue. Among loci showing strong signals of convergent evolution in gregarious lineages, we identify several strong candidates linked to neural activity, feeding behaviour, and immune pathways. Our results suggest sociality profoundly changes the selection pressures acting on multiple physiological, immunological and behavioural traits.

evolutionary biology↗

bioRxiv2024

Single-nucleus transcriptomics of wing sexual dimorphism and scale cell specialization in sulphur butterflies

The evolution of sexual secondary characteristics necessitates regulatory factors that confer sexual identity to differentiating tissues and cells. In Colias eurytheme butterflies, males exhibit two specialized wing scale types -- UV-iridescent (UVI) and lanceolate scales -- absent in females and likely integral to male courtship behavior. This study investigates the regulatory mechanisms and single-nucleus transcriptomics underlying these two sexually dimorphic cell types during wing development. We show that Doublesex (Dsx) expression is itself dimorphic and required to repress the UVI cell state in females, while unexpectedly, UVI activation in males is independent from Dsx. In the melanic marginal band, Dsx is required in each sex to enforce the presence of lanceolate scales in males, and their absence in females. Single-nucleus RNAseq reveals that UV-iridescent and lanceolate scale cell precursors each show distinctive gene expression profiles at 40% of pupal development, with marker genes that include regulators of transcription, cell signaling, cytoskeletal patterning, and chitin secretion. Both male-specific cell types share a low expression of the Bric-a-brac (Bab) transcription factor, a key repressor of the UVI fate. Bab ChIP-seq profiling suggests that Bab binds the cis-regulatory regions of gene markers associated to UVI fate, including potential effector genes involved in the regulation of cytoskeletal processes and chitin secretion, and loci showing signatures of recent selective sweeps in an UVI-polymorphic population. These findings open new avenues for exploring wing patterning and scale development, shedding light on the mechanisms driving the specification of sex-specific cell states and the differentiation of specialized cell ultrastructures.

developmental biology↗

bioRxiv2024

Modality specific memory enhancement in Heliconius butterflies

How animals perceive, process and respond to environmental cues is tightly tuned to the species-specific demands, and reflected by the structure of neural systems. In the Neotropical butterflies, Heliconius, the mushroom bodies, insect learning and memory centres, are significantly expanded compared to their closest relatives. This expansion coincided with the evolution of a novel diet, pollen feeding, and a spatial foraging behaviour consistent with trap-lining. Previous research has shown that Heliconius have more accurate visual long-term memory than other Heliconiini. Here, we tested whether this enhanced memory stability is specific to visual cues by conducting a long-term olfactory memory assay in two Heliconius species and two outgroup species. We found no differences in the long-term olfactory memory between Heliconius species and the outgroup species. Combining data from olfactory and visual memory trials confirms a significant shift in performance among sensory modalities between Heliconius and outgroup genera. In contrast, tests of how Heliconiini prioritise olfactory and visual cues when in presented in conflict also show no consistent shift in attentiveness to sensory cues between species. Our data provide a rare case where memory performance has been compared across species and sensory modalities, to identify evidence of a modality specific shift.

animal behavior and cognition↗

bioRxiv2024

Lepidopteran scale cells derive from sensory organ precursors through a canonical lineage

The success of butterflies and moths is tightly linked to the origin of scales within the group. A long-standing hypothesis postulates that scales are homologous to the well-described mechanosensory bristles found in the fruit fly Drosophila melanogaster, where both derive from an epithelial precursor specified by lateral inhibition that then undergoes multiple rounds of division. Previous histological examination and candidate gene approaches identified parallels in genes involved in scale and bristle development. Here, we provide definitive developmental and transcriptomic evidence that the differentiation of lepidopteran scales derives from the canonical cell lineage, known as the Sensory Organ Precursor (SOP). Live imaging in moth and butterfly pupae shows that SOP cells undergo two rounds of asymmetric divisions that first abrogate the neurogenic lineage, and then lead to a differentiated scale precursor and its associated socket cell. Single-nucleus RNA sequencing across a time-series of early pupal development revealed differential gene expression patterns that mirror canonical lineage development, including Notch-Delta signalling components, cell adhesion molecules, cell cycling factors, and terminal cell differentiation markers, suggesting a shared origin of the SOP developmental program. Additionally, we recovered a novel gene, the POU-domain transcription factor pdm3, involved in the proper differentiation of butterfly wing scales. Altogether, these data open up avenues for understanding scale type specification and development, and illustrate how single-cell transcriptomics provide a powerful platform for understanding the evolution of cell types.

developmental biology↗

bioRxiv2024

Dietary resilience of coral reef fishes to habitat degradation

The ability of consumers to adjust their diet in response to resource shifts is a key mechanism allowing the persistence of populations and underlying species adaptive capacity. Yet on coral reefs, one of the marine habitats most vulnerable to global change, the extent to which species alter their diet remains poorly understood. Here, we integrated DNA-based gut content analyses (metabarcoding), otolith analysis, body condition, and field surveys to test how diet can mediate effects of habitat degradation on two invertivorous fishes: Chaetodon capistratus, a browser, and Hypoplectrus puella, an active predator. Metabarcoding revealed significant dietary variation in both species across a habitat gradient. However, the response was more pronounced in the browser, whose diet was anthozoan-dominated on healthy reefs, whereas annelid-dominated on degraded reefs. We found reduced growth and body condition on degraded reefs in the browser but not the active predator. Our results reveal that dietary versatility can serve as a mechanism to cope with degraded environments, but that species differ as to whether these changes are sufficient to buffer from changes in habitat. We detected intraspecific dietary variation across sites that suggests food webs and energy flow differ at relatively small scales between healthy and degraded reefs.

ecology↗

bioRxiv2023

Adaptive divergence in the eyes of Heliconius butterflies likely contributes to pre- and post mating isolation

When populations experience different sensory conditions, natural selection may favor whole sensory system divergence, from the peripheral structures to the brain. We characterized the outer eye morphology of sympatric Heliconius species 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 in more open areas. Previous work has shown that, 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. Thus, eye morphology differences between H. cydno and H. melpomene are consistent with adaptive divergence, and when combined with previous neuroanatomy data, suggest hybrid visual system disruption due to mismatched patterns of intermediacy and dominance in the visual pathway.

evolutionary biology↗

bioRxiv2023

Divergent warning patterns influence male and female mating behaviours in a tropical butterfly

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. We investigated the contribution of visual preference to assortative mating between an aposematic butterfly Heliconius cydno and its sympatric relative H. melpomene. Wing colouration in Heliconius butterflies evolved as a warning signal but also functions as a mating cue. 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, yet 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 preventing gene flow between H. cydno and H. melpomene.

animal behavior and cognition↗

bioRxiv2023

Adaptive introgression of a visual preference gene

Visual preferences are important drivers of mate choice and sexual selection, but little is known of how they evolve at the genetic level. Here we take advantage of the diversity of bright warning patterns displayed by Heliconius butterflies, which are also used during mate choice. We show that two Heliconius species have evolved the same visual mating preferences for females with red patterns by exchanging genetic material through hybridization. Extensive behavioral experiments reveal that male preferences are associated with a genomic region of increased admixture between these two species. Variation in neural expression of regucalcin1, located within this introgressed region, correlates with visual preference across populations, and disruption of regucalcin1 with CRISPR/Cas9 impairs courtship towards conspecific females, proving 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.

evolutionary biology↗

bioRxiv2023

Enhanced long-term memory and increased mushroom body plasticity in Heliconius butterflies

As highly labile structures on both individual and evolutionary time-scales, the mushroom bodies, a key site of learning and memory in insects, are an excellent model for investigating the evolution of cognitive variation. We explored the behavioural consequences of mushroom body expansion in Heliconius butterflies, which possess greatly expanded mushroom bodies relative to their closest outgroups. We conducted long-term visual memory assays across three Heliconius and three other Heliconiini species using trained food-colour associations. We confirm robust differences between clades, with Heliconius exhibiting greater fidelity to the trained colour after 8 days without reinforcement compared to other Heliconiini, with further evidence of stable preferences at 13 days. We extended this analysis to consider the plastic response of the mushroom body calyces over this time period, measuring the volume of the mushroom body calyx, and the number of neurons and synapses it contains. We find substantial post-eclosion expansion and synaptic pruning in calyx of Heliconius erato, but not in Dryas iulia. In Heliconius erato, visual associative learning experience specifically is associated with a greater retention of calyceal synapses. At an individual level, fidelity to the trained colour in Heliconius erato was also positively correlated with synapse number. These results point to an enhanced visual long-term memory across Heliconius, facilitated not only by phylogenetic expansion of the mushroom body, but also changes in its developmental response to learning experience. The co-evolution of mushroom body expansion, plasticity and specific behaviours provides an important case study in the evolution of cognition. Significance StatementHow are cognitive differences between species supported by evolutionary changes in the brain? We investigated this question using Heliconius butterflies which have expanded mushroom bodies, a region of the insect brain involved in learning and memory. We show that Heliconius have more stable visual long-term memories and exhibit more substantial age- and experience-related plasticity than a closely related genus with smaller mushroom bodies. Recall accuracy was also predicted by synapse number in Heliconius erato, but not Dryas iulia, suggesting functional importance. These results suggest that increases in the size of specific brain regions and changes in their plastic response to experience may co-evolve to shape the evolution of cognition.

animal behavior and cognition↗

bioRxiv2023

Frizzled2 receives the WntA morphogen during butterfly wing pattern formation

Butterfly color patterns provide visible and biodiverse phenotypic readouts of the patterning processes that occur in a developing epithelium. While the secreted ligand WntA was shown to instruct the color pattern formation in butterflies, its modes of reception and signal transduction remain elusive. Butterfly genomes encode four homologues of the Frizzled-family of Wnt receptors. Here we show that CRISPR mosaic knock-outs of frizzled2 (fz2) phenocopy the color pattern effects of WntA loss-of-function in multiple nymphalids. While WntA mosaic clones result in intermediate patterns of reduced size, consistently with a morphogen function, fz2 clones are cell-autonomous. Shifts in pupal expression in WntA crispants show that WntA and fz2 are under positive and negative feedback, respectively. Fz1 is required for Wnt-independent planar cell polarity (PCP) 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.

developmental biology↗

bioRxiv2023

Patterns of host plant use do not explain mushroom body expansion in Heliconiini butterflies

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 three to four times larger than their Heliconiini, 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 recognising and learning the 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.

animal behavior and cognition↗