Biology subjects

Kuwalekar, M.

Publications and source records attributed to Kuwalekar, M..

4 recordsLinked to original sources

bioRxiv2024

Evolution of novel mimicry polymorphisms through Haldanes sieve and rare recombination

Origins of phenotypic novelty represent a paradox. Maintenance of distinct, canalized morphs usually requires a complex array of polymorphisms, whose co-retention requires a genetic architecture resistant to recombination, involving inversions and master regulators. Here, we reveal how such a constraining architecture can still accommodate novel morphs in evolving polymorphisms using the classic polymorphic Batesian mimicry in Papilio polytes, whose supergene-like genetic architecture is maintained in a large inversion. We show that rapidly evolving alleles of the conserved gene, doublesex, within this inversion underlie the genetic basis of this polymorphism. Using precisely dated phylogeny and breeding experiments, we show that novel adaptive mimetic morphs and underlying alleles evolved in a sequentially dominant manner, undergoing selective sweeps in the mimetic species as predicted under Haldanes sieve. Furthermore, we discovered that mimetic forms share precise inversion breakpoints, allowing rare exon swaps between the universally dominant and a recessive allele to produce a novel, persistent intermediate phenotype, ultimately facilitating the acquisition of phenotypic novelty. Thus, genetic dominance, selective sweeps, rapid molecular divergence, and rare recombination promote novel forms in this iconic evolving polymorphism, resolving the paradox of phenotypic novelty arising even in highly constrained genetic architectures.

evolutionary biology↗

bioRxiv2022

Duplication and sub-functionalisation characterise diversification of opsin genes in the Lepidoptera

Gene duplication is a vital process for evolutionary innovation. Functional diversification of duplicated genes is best explored in multicopy gene families such as histones, hemoglobin, and opsins. Rhodopsins are photo-sensitive proteins that respond to different wavelengths of light and contribute to diverse visual adaptations across insects. While there are several instances of gene duplications in opsin lineages, the functional diversification of duplicated copies and their ecological significance is properly characterised only in a few insect groups. We examined molecular and structural evolution that underlies diversification and sub-functionalisation of four opsin genes and their duplicated copies across 132 species of the diverse insect order--Lepidoptera. Opsins have largely evolved under purifying selection with few residues showing signs of episodic and pervasive diversifying selection. Although these do not affect overall protein structures of opsins, substitutions in key amino acids in the chromophore-binding pocket of duplicated copies might cause spectral sensitivity shifts leading to sub-functionalisation or neofunctionalisation. Duplicated copies of opsins also exhibit developmental stage-specific expression in Papilio polytes, suggesting functional partitioning during development. Together, altered spectral sensitivities owing to key substitutions and differential expression of duplicated copies across developmental stages might enable enhanced colour perception and improved discrimination across wavelengths in this highly visual insect group.

evolutionary biology↗

bioRxiv2022

Reproductive barriers and genomic hotspots of adaptation during allopatric species divergence

Theory predicts that in allopatric populations, genomic divergence and reproductive barriers will be driven largely by random genetic drift, and thereby evolve slowly in large populations. However, local adaptation and divergence under selection may also play important roles, which remain poorly characterised. Here we address three key questions in young allopatric species: (a) How widespread are genomic signatures of adaptive divergence?, (b) What is the functional space along which young sister species show divergence at the genomic level?, and (c) How quickly might prezygotic and postzygotic reproductive barriers evolve? Analysis of 82 re-sequenced genomes of the Oriental Papilio polytes species group revealed surprisingly widespread hotspots of intense selection and selective sweeps at hundreds of genes unique to each species, and spanning all chromosomes, rather than divergence only in a few genomic islands. These genes perform diverse ecologically important adaptive functions such as wing development, colour patterning, courtship behaviour, mimicry, pheromone synthesis and olfaction, and host plant use and digestion of secondary metabolites, that could contribute to local adaptation and subsequent reproductive isolation. Divergence at such functional genes appeared to have reproductive consequences: behavioural and hybridisation experiments revealed strong assortative mate preference (prezygotic barriers) as well as postzygotic barriers to hybridisation in timespans as short as 1.27 my, indicating that speciation was already complete, rather than incipient. Our study thus demonstrates an underappreciated role of intense selection and potential local adaptation in creating genome-wide hotspots of rapid molecular evolution and divergence, during differentiation and speciation in young allopatric species.

evolutionary biology↗

bioRxiv2020

Molecular evolution and developmental expression of melanin pathway genes in Lepidoptera

Pigmentation is involved in a wide array of biological functions across insect orders, including body patterning, thermoregulation, and immunity. The melanin pathway, in particular, has been characterized in several species. However, molecular evolution of the genes involved in this pathway is poorly characterized, and their roles in pigmentation of early developmental stages are just beginning to be explored in non-model organisms. We traced the molecular evolution of six melanin pathway genes in 53 species of Lepidoptera covering butterflies and moths, and representing over 100 million years of diversification. We compared the rates of synonymous and nonsynonymous substitutions within and between these genes to study signatures of selection at the level of individual sites, genes, and branches of the gene tree. We found that molecular evolution of all six genes was governed by strong purifying selection. Yet, a number of sites showed signs of being under positive selection, including in the highly conserved domain regions of three genes. Further, we traced the expression of these genes across developmental stages, tissues, and sexes in the Papilio polytes butterfly using a developmental transcriptome dataset. We observed that the expression patterns of the genes in P. polytes largely reflected their known tissue-specific function in other species. The expression of sequentially acting genes in the melanin pathway was correlated. Interestingly, four out of six melanin pathway genes (ebony, pale, aaNAT, and DDC) showed a sexually dimorphic pattern of developmental heterochrony; i.e., females showed peak activity much earlier in pupal development compared to that of males. Our evolutionary and developmental analyses suggest that the vast diversity of wing patterning and pigmentation in Lepidoptera may have been aided largely by differential developmental regulation of genes in a highly conserved pathway, in which the sequence evolution of individual genes is highly constrained.

evolutionary biology↗