Lauric Reynes, our former thesis student, now a young researcher at the University of Hawaii, will be giving a seminar on Monday 26 January 2026 from 13h00 - Oceanomed Amphitheatre, on the theme : Evolution of Reproductive Isolation in the Hawaiian Red Alga Amansia glomerata (Lauric Reynes, James T. Fumo, Alison R. Sherwood - School of Life Sciences, University of Hawai'i, Honolulu, Hawai'i 96822, United States).
Abstract
Speciation in marine environments is inherently complex, and the mechanisms underlying the evolution of reproductive isolation remain a fundamental yet understudied challenge in macroalgae. This study examines two genetically divergent lineages of the marine red alga Amansia glomerata around the island of O'ahu, Hawai'i, to understand processes leading to speciation in this system. We tested the hypothesis that strong reproductive isolation has shaped the genomic landscape through divergence during extended periods of allopatry. Using genome sequencing (ddRAD), fine-scale spatial transects, and demographic inference, we characterized lineage spatial structure and patterns of genomic divergence. Results showed that the two lineages remained strongly differentiated across the genome, even where they were spatially intermixed across extensive areas of sympatry. Demographic analyses supported a scenario of allopatric divergence followed by secondary contact, likely driven by Pleistocene sea-level fluctuations. The absence of recombinant hybrids, along with numerous loci that act as barriers to gene flow, was consistent with the development of strong postzygotic isolation. However, signatures of introgression across a subset of loci showed that gene flow during secondary contact was geographically structured and heterogeneous across the genome. While our results support allopatric divergence and intrinsic reproductive barriers, the role of ecological differentiation remains to be explored. Overall, this study offers pioneering insights into the genomics of speciation in Hawaiian seaweeds and underscores their potential as a model system for marine speciation.
