Contrasting Demographic History and Population Structure ofZamia(Cycadales: Zamiaceae) on Six Islands of the Greater Antilles Suggests a Model for Population Diversification in the Caribbean Clade of the Genus

Abstract

Premise of research. After Cuba, the three largest islands of the Greater Antilles are Hispaniola, Jamaica (JAM), and Puerto Rico (PR), all of which are inhabited by the Zamia pumila complex, a monophyletic group of dioecious gymnosperms treated as a single polymorphic or as many as nine species. We sought to test the following hypotheses for Zamia: (i) Dominican Republic (DR) and JAM fit evolutionary models of panmixis and isolation, respectively; (ii) historical gene flow has occurred between PR and DR, and admixture has occurred between the Caymans (CAY) and JAM; and (iii) vegetative morphological characters in common with populations on different islands do not conform to genetic relationships.Methodology. We genotyped a total of 30 populations from CAY, DR, JAM, and PR with 21–28 microsatellite (simple sequence repeat [SSR]) loci and haplotypes from 10 single-copy nuclear genes (SCNGs) and analyzed the data with permuted analysis of molecular variance, Bayesian clustering, approximate Bayesian computation coalescent modeling, and network and gene flow analyses. By using two different sets of molecular markers with very different mutation rates (SSRs and SCNGs), we sought to capture two distinct time slices of evolutionary history in the populations of each island.Pivotal results. Diversification of Caribbean Zamia follows a different path on each island after migration or vicariance from ancestors putatively originating in Cuba. DR and PR evolved from a common ancestral gene pool. DR fits a model of panmixis, while PR fits a vicariance model of semispeciation. Northern and western populations in JAM represent separate introductions to the island. Overall, JAM shows minimal levels of gene flow among populations and apparent admixture with CAY.Conclusions. We conclude that niche adaptation and associated vegetative morphological character states evolve convergently among different islands in response to environmental and other stochastic variables. We present a model of how these dioecious gymnosperms diversified in the Greater Antilles.