Historical biogeography of Caribbean Podocarpus does not support the progression rule

Abstract

AbstractAimThe Progression Rule, that older lineages inhabit older islands and colonize newer ones as they emerge, has seldom been tested in the Caribbean due to its geological complexity. Here, we use the conifer genus Podocarpus to explore this hypothesis. We infer the evolutionary history, biogeography, and diversification rates of this genus under a hypothesis testing framework.LocationThe Caribbean archipelago (Antilles).TaxonPodocarpus (Podocarpaceae).MethodsWe present the most comprehensive sampling for Caribbean Podocarpus to date in a Bayesian dated phylogenetic tree using a genotyping by sequencing DNA matrix of 67,589 bp. We inferred ancestral ranges and inter‐island divergence patterns using several models available. We explored diversification rates associated with island colonization, and checked for diversification rate shifts in the phylogeny.ResultsCaribbean Podocarpus is the result of colonization from the Andes during the Eocene to Oligocene (c. 45–31 Ma). Lesser Antillean species originated during the Oligocene from the Andes or the Greater Antilles, depending on the model of choice. Vicariance can explain the divergence of Cuban and Hispaniolan species, with subsequent dispersals into Jamaica. Despite the availability of new habitat opportunities, which might promote cladogenesis, insular Podocarpus did not show higher diversification rates than continental taxa.Main conclusionsThe conditions for progression rule were not met because colonization of younger islands (Lesser Antilles) occurred from the continent, or because suitable habitat in the partially emerged younger islands was likely present at the time older islands (Greater Antilles) were colonized. An improved palaeogeographical knowledge of the Caribbean will allow testing this hypothesis in multiple lineages. Our finding that diversification rates did not increase with island colonization might be common in other Caribbean lineages. Genotyping by sequencing proved promising to reveal complex historical assembly processes of vicariance and dispersal at a fine phylogenetic scale.