Guava (Psidium guajava) is one of the most aggressive invasive plants in
the Galapagos Islands. Determining its provenance and genetic diversity
could provide valuable information for its control. With this purpose,
we analyzed 11 SSR markers in guava individuals collected from Isabela,
Santa Cruz, San Cristobal and Floreana islands in the Galapagos, as well
as from mainland Ecuador. The mainland guava population appeared
genetically differentiated from the Galapagos populations, with higher
genetic diversity levels found in the former. By using different
approaches for data analysis, we consistently found that the Central
Highlands region of mainland Ecuador is one of the most likely origins
of the Galapagos populations. Moreover, the guavas from Isabela and
Floreana show a potential genetic input from southern mainland Ecuador,
while the population from San Cristobal would be linked to the coastal
mainland regions. Interestingly, the proposed origins for the Galapagos
guava coincide with the first human settlings of the archipelago. By
employing Approximate Bayesian Computation, we propose a model where San
Cristobal was the first island to be colonized by guava from the
mainland, from which it would have spread to Floreana and finally to
Santa Cruz; Isabela would have been seeded from Floreana. An independent
trajectory could also have contributed in the invasion of Floreana and
Isabela. The pathway shown in our model agrees with the human
colonization history of the different islands in the Galapagos. Our
model, in conjunction with the clustering patterns of the guava
individuals (based on genetic distances), suggests that guava
introduction history in the Galapagos archipelago was driven
predominantly by a single event (or events in rapid succession) instead
of several independent introductions. We thus show that genetic analyses
supported by historical sources can be used to answer questions on the
variability and history of guava in the Galapagos Islands.
Human-caused and natural mortality of giant tortoises in the Galapagos Islands during 1995-2004
