Evolutionary history of the endangered shrub snapdragon (Galvezia leucantha) of the Galápagos Islands

Abstract

AbstractAimThe endangered Galápagos shrub snapdragon (Galvezia leucantha, Antirrhineae, Plantaginaceae) is restricted to small populations on four islands. In this study, we appraised results from taxonomy, genetics, phylogenetics, phylogeography and pollination ecology to reconstruct the evolutionary history of the genus Galvezia.LocationPeru, continental Ecuador and Galápagos.MethodsWe sequenced the nuclear ribosomal ITS and two plastid regions, ndhF and ndhF‐rpL32, to infer the origin of Galvezia and patterns of colonization to and across the Galápagos archipelago, based on Bayesian inference and statistical parsimony analyses. To investigate genetic diversity and differentiation within G. leucantha, we screened the genome of six populations and obtained 194 AFLP fingerprints. Autogamy tests and pollination network analyses were performed to evaluate the colonization potential and to investigate the structure of the pollinators’ assemblage of Galvezia.ResultsRelationships of seven nucleotide‐substitution haplotypes and 11 nucleotide‐substitution ribotypes of Galvezia revealed monophyly for the Galapagos species. Dating estimates indicated divergence of the insular Galvezia lineage in the Middle‐Upper Pleistocene (0.66–0.09 Ma). In addition, distribution of genotypes (seven haplotypes, eight ribotypes) across the three continental species showed geographical differentiation, while low differentiation and distribution of G. leucantha. AFLP genetic diversity is relatively high (HT = 0.109), but a low proportion of the total allelic variance is attributed to variation among subspecies/islands (Hb = 0.035, hierarchical AMOVA: 3.77% of total variance). The endemic bee (Xylocopa darwinii) accounted for 87.30% of the floral visits to G. leucantha.Main conclusionsWe inferred a single origin for an insular lineage that colonized the Galápagos Islands from northern Peru in the Pleistocene. Recent colonization of the archipelago, Pleistocene land bridges between islands and active gene flow promoted by X. darwinii may account for the low‐moderate genetic differentiation of G. leucantha subspecies. An unusual pollination shift from ornithophily (hummingbirds on the continent) to entomophily (Xylocopa in the Galápagos Islands) is supported.