Dominance mechanisms in supergene alleles controlling butterfly wing pattern variation: insights from gene expression in Heliconius numata.

Loci under balancing selection, where multiple alleles are maintained, offer a relevant opportunity to investigate the role of natural selection in shaping genetic dominance: the high frequency of heterozygotes at these loci has been shown to enable the evolution of dominance among alleles. In the butterfly Heliconius numata, mimetic wing color variations are controlled by an inversion polymorphism of a circa 2 Mb genomic region (supergene P), with strong dominance between sympatric alleles. To test how differences in dominance observed on wing patterns correlate with variations in expression levels throughout the supergene region, we sequenced the complete transcriptome of heterozygotes at the prepupal stage and compared it to corresponding homozygotes.

Deep structure, long-distance migration and admixture in the colour polymorphic land snail Cepaea nemoralis.

Although snails of the genus Cepaea have historically been important in studying colour polymorphism, an ongoing issue is that there is a lack of knowledge of the underlying genetics of the polymorphism, as well as an absence of genomic data to put findings in context. We, therefore, used phylogenomic methods to begin to investigate the post-glacial history of Cepaea nemoralis, with a long-term aim to understand the roles that selection and drift have in determining both European-wide and local patterns of colour polymorphism. By combining prior and new mitochondrial DNA data from over 1500 individuals with ddRAD genomic data from representative individuals across Europe, we show that patterns of differentiation are primarily due to multiple deeply diverged populations of snails.

The draft genome sequence of the grove snail Cepaea nemoralis.

Studies on the shell color and banding polymorphism of the grove snail Cepaea nemoralis and the sister taxon Cepaea hortensis have provided compelling evidence for the fundamental role of natural selection in promoting and maintaining intraspecific variation. More recently, Cepaea has been the focus of citizen science projects on shell color evolution in relation to climate change and urbanization. C.

Evo-devo of shell colour in gastropods and bivalves.

Recent technical innovations are revealing surprising patterns in mollusc shell pigmentation, such as an unexpectedly modest role for melanins and rapid divergences in the mix of pigments used to achieve similar colour patterns. The elucidation of the molecular genetic basis of shell pigmentation has been slow, probably because of the high genome complexity of gastropods and bivalves. Recent work within the old field of evolutionary ecology of shell pigmentation allows a greater role for the analysis of large-geographic-scale patterns (sometimes employing citizen-science data), as well as experimental field studies.

Unravelling the genes forming the wing pattern supergene in the polymorphic butterfly .

Background: Unravelling the genetic basis of polymorphic characters is central to our understanding of the origins and diversification of living organisms. Recently, supergenes have been implicated in a wide range of complex polymorphisms, from adaptive colouration in butterflies and fish to reproductive strategies in birds and plants. The concept of a supergene is now a hot topic in biology, and identification of its functional elements is needed to shed light on the evolution of highly divergent adaptive traits.

The gene cortex controls mimicry and crypsis in butterflies and moths.

The wing patterns of butterflies and moths (Lepidoptera) are diverse and striking examples of evolutionary diversification by natural selection. Lepidopteran wing colour patterns are a key innovation, consisting of arrays of coloured scales. We still lack a general understanding of how these patterns are controlled and whether this control shows any commonality across the 160,000 moth and 17,000 butterfly species.

Amelanism in the corn snake is associated with the insertion of an LTR-retrotransposon in the OCA2 gene.

The corn snake (Pantherophis guttatus) is a new model species particularly appropriate for investigating the processes generating colours in reptiles because numerous colour and pattern mutants have been isolated in the last five decades. Using our captive-bred colony of corn snakes, transcriptomic and genomic next-generation sequencing, exome assembly, and genotyping of SNPs in multiple families, we delimit the genomic interval bearing the causal mutation of amelanism, the oldest colour variant observed in that species. Proceeding with sequencing the candidate gene OCA2 in the uncovered genomic interval, we identify that the insertion of an LTR-retrotransposon in its 11(th) intron results in a considerable truncation of the p protein and likely constitutes the causal mutation of amelanism in corn snakes.

Photonic crystals cause active colour change in chameleons.

Many chameleons, and panther chameleons in particular, have the remarkable ability to exhibit complex and rapid colour changes during social interactions such as male contests or courtship. It is generally interpreted that these changes are due to dispersion/aggregation of pigment-containing organelles within dermal chromatophores. Here, combining microscopy, photometric videography and photonic band-gap modelling, we show that chameleons shift colour through active tuning of a lattice of guanine nanocrystals within a superficial thick layer of dermal iridophores.

Precise colocalization of interacting structural and pigmentary elements generates extensive color pattern variation in Phelsuma lizards.

Background: Color traits in animals play crucial roles in thermoregulation, photoprotection, camouflage, and visual communication, and are amenable to objective quantification and modeling. However, the extensive variation in non-melanic pigments and structural colors in squamate reptiles has been largely disregarded. Here, we used an integrated approach to investigate the morphological basis and physical mechanisms generating variation in color traits in tropical day geckos of the genus Phelsuma.

Evolutionary history of the recruitment of conserved developmental genes in association to the formation and diversification of a novel trait.

Background: The origin and modification of novel traits are important aspects of biological diversification. Studies combining concepts and approaches of developmental genetics and evolutionary biology have uncovered many examples of the recruitment, or co-option, of genes conserved across lineages for the formation of novel, lineage-restricted traits. However, little is known about the evolutionary history of the recruitment of those genes, and of the relationship between them -for example, whether the co-option involves whole or parts of existing networks, or whether it occurs by redeployment of individual genes with de novo rewiring.

Involvement of the conserved Hox gene Antennapedia in the development and evolution of a novel trait.

Background: Hox proteins specify segment identity during embryogenesis and have typical associated expression patterns. Changes in embryonic expression and activity of Hox genes were crucial in the evolution of animal body plans, but their role in the post-embryonic development of lineage-specific traits remains largely unexplored. Here, we focus on the insect Hox genes Ultrabithorax (Ubx) and Antennapedia (Antp), and implicate the latter in the formation and diversification of novel, butterfly-specific wing patterns.

Single locus affects embryonic segment polarity and multiple aspects of an adult evolutionary novelty.

Background: The characterization of the molecular changes that underlie the origin and diversification of morphological novelties is a key challenge in evolutionary developmental biology. The evolution of such traits is thought to rely largely on co-option of a toolkit of conserved developmental genes that typically perform multiple functions. Mutations that affect both a universal developmental process and the formation of a novelty might shed light onto the genetics of traits not represented in model systems.

Development of a wingless morph in the ladybird beetle, Adalia bipunctata.

Many taxa of winged insects have independently lost the ability to fly and often possess reduced wings. Species exhibiting natural variation in wing morphology provide opportunities to investigate the genetics and developmental processes underlying the evolution of alternative wing morphs. Although many wing dimorphic species of beetles are known, the underlying mechanisms of variation are not well understood in this insect order.

A gene-based linkage map for Bicyclus anynana butterflies allows for a comprehensive analysis of synteny with the lepidopteran reference genome.

Lepidopterans (butterflies and moths) are a rich and diverse order of insects, which, despite their economic impact and unusual biological properties, are relatively underrepresented in terms of genomic resources. The genome of the silkworm Bombyx mori has been fully sequenced, but comparative lepidopteran genomics has been hampered by the scarcity of information for other species. This is especially striking for butterflies, even though they have diverse and derived phenotypes (such as color vision and wing color patterns) and are considered prime models for the evolutionary and developmental analysis of ecologically relevant, complex traits.

Conserved developmental processes and the formation of evolutionary novelties: examples from butterfly wings.

The origin and diversification of evolutionary novelties-lineage-specific traits of new adaptive value-is one of the key issues in evolutionary developmental biology. However, comparative analysis of the genetic and developmental bases of such traits can be difficult when they have no obvious homologue in model organisms. The finding that the evolution of morphological novelties often involves the recruitment of pre-existing genes and/or gene networks offers the potential to overcome this challenge.