Species radiations, despite immense phenotypic variation, can be difficult to resolve phylogenetically when genetic change poorly matches the rapidity of diversification. Genomic potential furnished by palaeopolyploidy, and relative roles for adaptation, random drift and hybridisation in the apportionment of genetic variation, remain poorly understood factors. Here, we study these aspects in a model radiation, Syzygium, the most species-rich tree genus worldwide. Genomes of 182 distinct species and 58 unidentified taxa are compared against a chromosome-level reference genome of the sea apple, Syzygium grande. We show that while Syzygium shares an ancient genome doubling event with other Myrtales, little evidence exists for recent polyploidy events. Phylogenomics confirms that Syzygium originated in Australia-New Guinea and diversified in multiple migrations, eastward to the Pacific and westward to India and Africa, in bursts of speciation visible as poorly resolved branches on phylogenies. Furthermore, some sublineages demonstrate genomic clines that recapitulate cladogenetic events, suggesting that stepwise geographic speciation, a neutral process, has been important in Syzygium diversification.
A new species of betel nut palm, Areca unipa, is described and illustrated here for the first time. This is the second species of Areca from New Guinea that is closely related to the widespread, cultivated species A. catechu. A discussion of its morphological characters, distribution, ecology, habitat, uses and conservation status is provided.
Abstract. Fatem SM, Djitmau DA, Ungirwalu A, Wanma AO, Simbiak VI, Benu NMH, Tambing J, Murdjoko A. 2020. Species diversity, composition, and heterospecific associations of trees in three altitudinal gradients in Bird's Head Peninsula, Papua, Indonesia. Biodiversitas 21: 3596-3605. The region of Bird's Head Peninsula, West Papua, Indonesia has a high level of vegetation diversity distributed from coastal to mountain areas. Yet, the information regarding this diversity is limited. We studied species diversity, composition, and heterospecific association of trees in three altitudinal gradients in Bird's Head Peninsula to reveal the biotic phenomenon in the region. Systematic random sampling was applied during data collection in three locations representing lower, middle, and upper altitudes of natural tropical forest. We applied diversity indices to investigate taxonomic diversity, importance value index (IVI) to reveal floristic composition and canonical correspondence analysis (CCA) for heterospecific associations. In total, we recorded 30 families, 44 genera, and 66 species in the three locations. There were 20 families in lower area and each 15 families in middle and upper areas while the genera per site were 29 in lower, 20 in the middle, and 18 in the upper. The number of species found in lower, middle, and upper areas was 35 species, 24 species, and 27 species respectively. The research revealed that the taxonomic diversity of trees generally decreases as the elevation increases in terms of family, genera, and species level. The dominant species was also different across elevation gradients in which the dominant tree had a different pattern in the three locations between understory and upperstory. Moreover, the gradient of elevation has shaped the type of tree communities, suggesting interactions and associations among tree species. Of all species recorded, 26 species were listed in IUCN Red List with two species were under data deficient, 20 species were least concern, three species were near threatened, and one species was vulnerable.
Species radiations have long fascinated biologists, but the contribution of adaptation to observed diversity and speciation is still an open question. Here, we explore this question using the clove genus, Syzygium, the world’s largest genus of tree species comprising approximately 1200 species. We dissect Syzygium diversity through shotgun sequencing of 182 distinct species and 58 additional as-yet unidentified taxa, and assess their genetic diversity against a chromosome-level reference genome of the sea apple, Syzygium grande. We show that Syzygium grande shares a whole genome duplication (WGD) event with other Myrtales. Genomic analyses confirm that Syzygium originated in Sahul (Australia-New Guinea), and later diversified eastward to the Hawaiian Islands and westward in multiple independent migration events. The migrations were associated with bursts of speciation events, visible by poorly resolved branches on phylogenies and networks, some of which were likely confounded by incomplete lineage sorting. Clinal genomic variation in some sublineages follows phylogenetic progression, which coupled with sympatric occurrences of distantly related species suggests that both geographic and ecological speciation have been important in the diversification of Syzygium. Together, these results point to a mixture of both neutral and adaptive drivers having contributed to the radiation of the genus.
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