Raw allelic matrix and supplementary materials: Origin and dispersion pathways of guava in the Galapagos Islands inferred through genetics and historical records

Guava (Psidium guajava) is an aggressive invasive plant in the Galapagos
Islands. Determining its provenance and genetic diversity could explain
its adaptability and spread, and how this relates to past human
activities. With this purpose, we analyzed 11 SSR markers in guava
individuals 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. 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. Through Approximate Bayesian Computation, we propose a
model where San Cristobal was the first island to be colonized by guava
from the mainland, then 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 individuals (based on
genetic distances), suggests that guava introduction history in the
Galapagos archipelago was driven by either a single event or a series of
introduction events in rapid succession. We thus show that genetic
analyses supported by historical sources can be used to track the arrival
and spread of invasive species in novel habitats and the potential role of
human activities in such processes.