Genomic insights into rapid speciation within the world's largest tree genus Syzygium

<p><span>Species r</span><span>adiations, despite immense phenotypic variation, can be difficult to resolve phylogenetically when genetic </span><span>change</span><span> poorly matches the rapidity of diversification. Genomic potential furnished by </span><span>palaeopolyploidy,</span><span> and relative roles for </span><span>adaptation, random drift and hybridisation in the </span><span>apportionment of genetic</span><span> variation, remain poorly understood factors.</span><span> Here, we study these aspects in a model radiation, </span><em><span>Syzygium</span></em><span>, the most species-rich tree genus worldwide. </span><span>G</span><span>enomes of 182 distinct species and 58 unidentified taxa are compared against a chromosome-level reference genome of the sea apple, <em>Syzygium</em> <em>grande</em>. We show that while <em>Syzygium</em> shares an ancient genome doubling event with other Myrtales, little evidence exists for recent polyploidy events. </span><span>Phylogenomics confirms that</span><span> <em>Syzygium</em> originated in Australia-New Guinea and diversified in </span><span>multiple migrations</span><span>, eastward to the Pacific and westward to India and Africa</span><span>,</span><span> in </span><span>bursts of speciation </span><span>visible as poorly resolved </span><span>branches</span> <span>on phylogenies. </span><span>Furthermore, </span><span>some sublineages demonstrate genomic clines that recapitulate cladogenetic events, suggesting</span><span> that stepwise geographic speciation, a neutral process, has been important in </span><em><span>Syzygium</span></em><span> diversification</span><span>.</span></p>