Quandennial SI

SI stands for Sharks International, namely the international conference for shark biology, ecology, and conservation held every four years, as listed below.

2010 (1st): June 6–11, 2010 - Cairns, Australia

2014 (2nd): June 2–6, 2014 - Durban, South Africa

2018 (3rd): June 3–8, 2018 - João Pessoa, Brazil

2022 (4th): October 10–14 (Online) & 20–22 (In-person), 2022 - Valencia, Spain

2026 (5th, Upcoming): May 4–8, 2026 - Colombo, Sri Lanka

At the upcoming Sharks International 2026, we introduce an emerging picure of sex chromosome evolution in sharks and rays as well as a versatile molecular toolkit that enables precise sex identification in forensic samples, early embryos, and archived tissues. By bridging the gap between molecular evolution and wildlife forensics, we are providing essential demographic data to bolster the global conservation of threatened shark and ray species. It would be nice to have chances for versatile exchanges with experts in different fields in different areas of the world.

ID: A-0689, May 6 2026, 16:50-17:00 in Hall C

Sex of sharks and rays: evolutionary and genomic investigations

Taiki Niwa1, Yoshinobu Uno2, Shigehiro Kuraku1

1National Institute of Genetics, Japan

2Tokushima University, Japan

The class Chondrichthyes, comprising chimaeras (Holocephali) and elasmobranchs (sharks and rays), exhibits remarkable phenotypic diversity and occupies a wide array of ecological niches, predominantly in marine environments. To explore the molecular basis of their evolutionary diversification, the Squalomix consortium has been organized through collaborations with aquariums and marine stations across Japan, offering a rich repository of DNA sequence data and analytical tools (Hara et al., 2018, Nat. Ecol. Evol.; Nishimura et al., 2025, F1000Res). More recently, we investigated sex chromosome evolution in cartilaginous fishes. We produced chromosome-scale genome assemblies of Scyliorhinus torazame, Chiloscyllium punctatum, and Hemitrygon akajei, and performed comparative analyses of genome sequences and transcriptome profiles across diverse cartilaginous fishes. Sex chromosome identification, supported by cytogenetic experiments, elucidated X chromosome homology between sharks and rays, as well as an extensively degenerated Y chromosome harboring no detectable male-specific genes. Orthologs of known sex-determining genes were identified but were not located on these sex chromosomes. Transcriptomic analyses combined with embryonic gonad histology revealed female-biased expression of X-linked genes indicating incomplete dosage compensation. Sharks and rays share the oldest vertebrate sex chromosomes, dating back approximately 300 million years ago, and employ unique sex determination mechanisms distinct from those of other vertebrates (Niwa et al., 2025, Proc. Natl. Acad. Sci. USA).

Keywords: genome sequencing, sex chromosome, cytogenetics, molecular evolution, sex determination