Preprint: Ulva green algae hybridise bidirectionally with evidence for paternal chloroplast inheritance

A preprint deposited on bioRxiv (22 July 2026) by researchers studying the Yellow Sea green tides reports new evidence on hybridisation dynamics between Ulva prolifera and Ulva linza, two closely related green macroalgae whose blooms create large-scale coastal ecological events in East Asia.

Previous work had suggested only asymmetric gamete compatibility — specifically that only one crossing direction was viable — but the new study uses sex-linked genetic markers to identify hybrid diploids reliably and demonstrates bidirectional compatibility: hybrids form when either species contributes the maternal or paternal gamete. The authors also document evidence for paternal chloroplast inheritance in the hybrids, a departure from the maternal chloroplast inheritance typical of most green algae and plants.

The findings carry implications for species delimitation between U. prolifera and U. linza, for understanding interspecific gene flow, and for interpreting the ecological genetics of green tide events. Paternal organelle inheritance, when confirmed, is also of interest to evolutionary geneticists studying the mechanisms and drivers of organelle inheritance modes across eukaryotes.

This work is a preprint and has not yet been peer-reviewed. Findings should be treated as preliminary until independent review and, where appropriate, replication.