Phylogenetic analysis links Xylopia’s pantropical spread to dispersal and habitat shifts

A time-calibrated phylogenetic analysis indicates that the pantropical distribution of the magnoliid genus Xylopia was built through long-distance dispersal among major tropical regions and repeated transitions into drier, inundated and ultramafic environments.

The study analyzed 168 of 191 recognized species, representing 88% of the genus. Researchers combined a species-level phylogeny with curated occurrence records, ancestral-area models, habitat reconstructions, quantitative climatic analyses and spatial measures of phylogenetic diversity and endemism. The analysis covered 51 tropical islands and sampled 36% of the phylogeny’s species as island inhabitants.

The crown age of Xylopia was estimated at 31.8 million years ago, with a 95% confidence interval of 22.6–41.02 million years. Its earliest ancestral area remained equivocal: Africa plus South and Southeast Asia had a model probability of 0.49, while Africa plus Australia and New Guinea had a probability of 0.46. Africa was reconstructed with high support as the ancestral area of the core clade.

Two middle-Miocene movements out of Africa were inferred. One lineage dispersed to South America at about 11.6 million years ago and diversified rapidly into three clades. Another reached the Asia-Pacific region. Six later dispersals from South America to Central America were identified. The timing and absence of relevant land bridges implicated overwater dispersal in the Africa–South America movement, but the study did not establish the specific transport mechanism.

Islands were major destinations for the genus. Forty of 59 island species met the study’s narrow-range endemic criterion, based on an extent-of-occurrence estimate below 20,000 km². Island size was positively associated with total species richness (r = 0.77; 95% CI 0.62–0.86) and endemic species richness (r = 0.57; 95% CI 0.35–0.73), while isolation was not correlated with either measure.

Biogeographic stochastic mapping attributed 89.8% of 167 reconstructed events to in situ speciation within regions, compared with 12% to dispersal and 2.4% to vicariance. Africa was the leading source of between-region dispersal, followed by South America and Australia–New Guinea. Central America, Madagascar and the Pacific were major sinks. The authors interpreted this pattern as evidence that uncommon intercontinental movement combined with repeated within-region diversification shaped the genus’s broad range.

Humid habitat was estimated as the most likely ancestral state, while Xylopia sect. Ancistropetala was reconstructed as subhumid. Of 59 species in subhumid habitats, 42 were Afrotropical, nine Asia-Pacific and eight Neotropical. Climatic reconstructions identified nine shifts toward lower mean annual precipitation and ten toward lower precipitation in the driest quarter. All occurred within the last 14 million years, and most within the last 10 million years.

Transitions onto ultramafic substrates occurred repeatedly during the last 10 million years, chiefly in the Asia-Pacific region but also in Cuba and Madagascar. Three clades radiated after entering these environments, and all ultramafic species occurred on islands. Facultative and obligate ultramafic species were evenly divided between humid and subhumid climatic regimes.

Spatial analyses found high phylogenetic diversity in western and central Africa, Madagascar, Southeast Asia and parts of western South America. Phylogenetic and weighted endemism were highest in Madagascar and Jamaica, with moderate values in several other regions. The authors noted that grid-based metrics may miss narrowly endemic species, while occurrence data remain subject to uneven sampling. Broader sampling within Annonoideae may help resolve the ambiguity surrounding the genus’s earliest ancestral area, but the ancestral reconstruction remains limited by the available data.

Subject of Research: Biogeographic and ecological evolution of the pantropical flowering-plant genus Xylopia

Article Title: Long-distance dispersals and ecological transitions underlie the biogeographic expansion of the pantropical magnoliid genus Xylopia ( Annonaceae )

Article References: Johnson, D. M., Nge, F. J., Stull, G., Murray, N. A., Floyd, K., Streiff, S., Rodrigues-Vaz, C., Soulé, V. R. C., & Couvreur, T. L. P. (2025). Long-distance dispersals and ecological transitions underlie the biogeographic expansion of the pantropical magnoliid genus Xylopia (Annonaceae). Frontiers of Biogeography, 18, Article e159992. https://doi.org/10.21425/fob.18.159992

Image Credits: AI Generated

DOI: 10.21425/fob.18.159992

Keywords: Xylopia, plant biogeography, long-distance dispersal, phylogenetics, ancestral-area reconstruction, habitat transitions, ultramafic ecosystems, island colonization, phylogenetic diversity, Annonaceae, Long-distance, dispersals