Evolutionary dynamics of ZZ/ZW sex chromosomes in Characoidei

• Grant number: 25/28652-9
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: July 01, 2026
• End date: June 30, 2029
• Field of knowledge: Biological Sciences - Genetics - Animal Genetics
• Principal Investigator: Diogo Teruo Hashimoto
• Grantee: Francisco de Menezes Cavalcante Sassi
• Host Institution: Centro de Aquicultura (CAUNESP). Universidade Estadual Paulista (UNESP). Campus de Jaboticabal. Jaboticabal , SP, Brazil
• Associated research grant: 24/03891-8 - Sex chromosomes evolution in Characoidei fishes, AP.TEM

Abstract

Current knowledge about the evolution of sex chromosomes is largely based on model organisms with highly differentiated chromosomes, resulting in an underrepresentation of the vast diversity of sex determination systems existing in nature. Overcoming this gap requires investigating groups that exhibit systems at distinct evolutionary stages. In this context, the fish order Characiformes offers an exceptional model, by displaying a high karyotypic diversity, including homomorphic systems, ZZ/ZW systems at various stages of differentiation, and the occurrence of multiple systems, such as the rare ZW¿W¿. This project aims to investigate the evolutionary dynamics of sex chromosomes in Characiformes through an integrated approach combining state-of-the-art genomics and high-resolution cytogenetics. Specifically, the project aims to: I) generate the first chromosome-level reference genomes for Characiformes species with ZW systems (14 species, covering the whole number of genera known with such system) using PacBio HiFi sequencing and Hi-C data; II) characterize the structural and functional architecture, and evolutionary dynamics of the sex chromosomes, identifying chromosomal rearrangements, divergence strata, accumulation of repetitive elements and conservation or turnover patterns of this system across phylogeny; and III) validate the genomic rearrangements and sex chromosome organization through Oligo-FISH technique, establishing a direct connection between genomic sequences and physical chromosomes. Expected results include the identification of the main genomic processes associated with the origin and differentiation of simple and multiple sex chromosomes in Characiformes, the evaluation of independent or recurrent evolution of these systems between different groups, and the comprehension of the structural and functional mechanisms involved in recombination suppression and in the beginning of sex chromosome differentiation. In addition, the project will establish a robust comparative framework to test classical and alternative theoretical models of sex chromosome evolution in vertebrates, besides creating high-quality novel genomic resources for Neotropical Characiformes, endowing studies in evolution, cytogenetics, and comparative genomics in fish. (AU)