Biology subjects

Vila, R. V.

Publications and source records attributed to Vila, R. V..

2 recordsLinked to original sources

bioRxiv2026

Contrasting modes of dosage compensation on ancestral and neo-Z chromosomes in butterflies

The evolution of sex chromosomes from homologous autosomes generally causes degeneration of the sex-limited chromosome (Y in XY systems and W in ZW systems), leading to altered or disrupted gene regulation. Dosage compensation has evolved repeatedly to mitigate the effects of such unbalanced expression of sex-linked genes. Previous analyses show that X chromosomes often are upregulated in males in XY-systems, while upregulation of the Z chromosome in females is unusual in ZW-systems, but understanding the generality of this pattern requires broader taxonomic sampling. In addition, little is known about how dosage compensation is established when sex chromosomes initially evolve. Here, we narrow this knowledge gap by characterizing dosage compensation in butterflies (Leptidea sp.) that harbor both ancestral, intermediate and recently derived sex chromosomes. Analyses of 120 samples, representing both sexes, different tissues and developmental stages, reveal a mixture of gene expression patterns. We confirm that downregulation in males is the predominant mode on the ancestral Z chromosome, but we find complex patterns of male downregulation and female upregulation for Z chromosomes with different evolutionary histories, as well as between different tissues. Dosage compensation has for example evolved rapidly in regions of the youngest neo-Z where the neo-W gametologs have lost function, but not in regions with functional gene copies on both Z and W. Our results provide novel insights into the complex evolutionary trajectories underlying dosage compensation and show that development of specific mechanisms likely depends on both sex chromosome system and dosage sensitivity of sex chromosome-linked genes.

evolutionary biology↗

bioRxiv2025

The 229 chromosomes of the Atlas blue butterfly reveal rules constraining chromosome evolution in Lepidoptera

Chromosomal arrangements are important for processes including genetic recombination, adaptation, and speciation. Related taxa often possess similar numbers of chromosomes, but some groups show remarkable variation in chromosome numbers. Most Lepidoptera, the butterflies and moths, have 31 or 32 chromosomes, but some species deviate from this norm. We present a chromosome-level genome assembly of a heterogametic female Atlas blue butterfly (Polyommatus atlantica; Lycaenidae), and find it has 227 autosomes and four sex chromosomes, the highest recorded chromosome number in non-polyploid Metazoa. We show that the 227 autosomes, exceptionally small even for Lepidoptera, are derived from extensive fragmentation of the 24 ancestral lycaenid autosomes. We show that autosomal fissions likely largely occurred in euchromatic, lightly-packed regions of chromosomes. We assemble two large Z chromosomes, one of which comprises the ancestral Z fused with an autosome and retains its ancestral length, while the other is a neo-Z, formed from the fusion of an intact ancestral autosome with a fragment of a second. We find two large W chromosomes, derived from copies of the Z-linked, ancestrally autosomal sequences. In contrast to the autosomes, the sex chromosomes have not experienced fission. We observe frequent presence of chromosome-internal arrays of the telomeric repeat motif in P. atlantica. Such arrays are not observed in the genomes of close relatives that have not undergone fission and suggest a possible mechanism for rapid, viable fragmentation. Altogether, our findings in P. atlantica make evident several constraints that govern karyotypic change, a key component of eukaryotic genome evolution.

evolutionary biology↗