Biology subjects

Mallet, J.

Publications and source records attributed to Mallet, J..

3 recordsLinked to original sources

bioRxiv2017

Supergene evolution triggered by the introgression of a chromosomal inversion

Supergenes are groups of tightly linked loci whose variation is inherited as a single Mendelian locus and are a common genetic architecture for complex traits under balancing selection1. Supergene alleles are long-range haplotypes with numerous mutations underlying distinct adaptive strategies, often maintained in linkage disequilibrium through the suppression of recombination by chromosomal rearrangements2-5. However, the mechanism governing the formation of supergenes is not well understood, and poses the paradox of establishing divergent functional haplotypes in face of recombination1,6. Here, we show that the formation of the supergene alleles encoding mimicry polymorphism in the butterfly Heliconius numata is associated with the introgression of a divergent, inverted chromosomal segment. Haplotype divergence and linkage disequilibrium indicate that supergene alleles, each allowing precise wing-pattern resemblance to distinct butterfly models, originate from over a million years of independent chromosomal evolution in separate lineages. These \"superalleles\" have evolved from a chromosomal inversion captured by introgression and maintained in balanced polymorphism, triggering supergene inheritance. This mode of evolution is likely to be a common feature of complex structural polymorphisms associated with the coexistence of distinct adaptive syndromes, and shows that the reticulation of genealogies may have a powerful influence on the evolution of genetic architectures in nature.

evolutionary biology↗

bioRxiv2017

Melanism patches up the defective cuticular morphological traits through promoting the up-regulation of cuticular protein-coding genes in Bombyx mori

Melanin and cuticular proteins are important cuticle components in insect. Cuticle defects caused by mutations in cuticular protein-encoding genes can hinder melanin deposition. However, the effects of melanin variation on cuticular protein-encoding genes and the corresponding morphological traits associated with these genes are remain largely unknown. Using Bombyx mori as a model, we showed that the melanism levels during larval cuticle pigmentation correlated positively with the expression of cuticular protein-encoding genes. This correlation stemmed from the simultaneous induction of these genes by the melanin precursors. More importantly, the effect of the melanism background on the cuticles induced the up-regulation of other functionally redundant cuticular protein-encoding genes to rescue the morphological and adaptive defects caused by the dysfunction of some mutated cuticular proteins, and the restorative ability increased with increasing melanism levels, which gives a novel evidence that melanism enhances insect adaptability. These findings deepen our understanding of the interactions among cuticle components, as well as their importance in the stabilizing of the normal morphology and function of the cuticle.

genetics↗

bioRxiv2017

North Andean origin and diversification of the largest ithomiine butterfly genus

The Neotropics harbour the most diverse flora and fauna on Earth. The Andes are a major centre of diversification and source of diversity for adjacent areas in plants and vertebrates, but studies on insects remain scarce, even though they constitute the largest fraction of terrestrial biodiversity. Here, we combine molecular and morphological characters to generate a dated phylogeny of the butterfly genus Pteronymia (Nymphalidae: Danainae), which we use to infer spatial, elevational and temporal diversification patterns. We first propose six taxonomic changes that raise the generic species total to 53, making Pteronymia the most diverse genus of the tribe Ithomiini. Our biogeographic reconstruction shows that Pteronymia originated in the Northern Andes, where it diversified extensively. Some lineages colonized lowlands and adjacent montane areas, but diversification here remained scarce. The recent colonization of lowland areas was reflected by an increase in the rate of evolution of species elevational ranges towards present. By contrast, speciation rate decelerated with time, with no extinction. The geological history of the Andes and adjacent regions have likely contributed to Pteronymia diversification by providing compartmentalized habitats and an array of biotic and abiotic conditions, and by limiting dispersal between some areas while promoting interchange across others.

evolutionary biology↗