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Island ontogeny and phylogeography in the Mascarene radiation of Hibiscus sect. Lilibiscus

Mashburn, Brock1; Linan, Alexander G.1; Le Péchon, Timothée2; Sevathian, Jean Claude; Olsen, Kenneth M.3; Edwards, Christine E.1

Published Jan 22, 2026 on Dryad. https://doi.org/10.5061/dryad.hmgqnk9wd

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Abstract

This study tests evolutionary predictions of the General Dynamic Model (GDM) of oceanic island biogeography using genomic data from a six-species radiation of Hibiscus endemic to the Mascarene Islands (Réunion, Mauritius, and Rodrigues). The GDM proposes that as islands age, the dominant evolutionary processes shaping biodiversity shift from ecological divergence on young islands, to drift on middle-aged islands, and ultimately to extinction on older islands. To evaluate these predictions, we analyzed phylogenetic and population genetic structure within and among Hibiscus species across the three islands. We generated genome-wide SNP data for 128 individuals using 2b-RAD sequencing. Raw reads were filtered and assembled de novo into uniformly 36 bp loci using ipyrad. Raw sequence data are archived in GenBank under BioProject accession PRJNA1271673. Phylogenetic relationships were inferred using a maximum-likelihood tree in IQ-TREE and a species tree in TETRAD. Patristic distances from the ML tree were used to assess interspecific divergence, with differences tested using pairwise Wilcoxon rank-sum tests with Bonferroni correction. Genetic structure was evaluated using principal component analysis (PCA), uniform manifold approximation and projection (UMAP), and model-based clustering in STRUCTURE. To test for gene flow versus incomplete lineage sorting, we conducted ABBA-BABA (D-statistic) tests using Dsuite. To evaluate alternative divergence scenarios and estimate relative divergence times, we used Approximate Bayesian Computation with Random Forests in DIYABC-RF. Our results support the shifting-process predictions of the GDM: ecological differentiation and high intraspecific gene flow were evident on the youngest island (Réunion), genetic drift dominated on the middle-aged island (Mauritius), and deep divergence patterns consistent with extinction were observed on the oldest island (Rodrigues). Altogether, our dataset and analytical framework provide a replicable approach for testing shifting evolutionary process predictions of the GDM using population-level genomic data.