Generation and maintenance of diversity in an island: a history of fragmentation, secondary contact and admixture

Genomic analyses may be able to reveal new insights into within-island
evolution. Here, genotyping-by-sequencing SNP data were used to analyze
genomic variation in the Canary Island gecko Tarentola delalandii from
Tenerife and La Palma. We find that ancient within-island divergence
events appear to explain genomic variation within Tenerife and likely
began some 1.4 – 2.8 Ma ago; considerably more recent than previous
estimates from mtDNA sequence divergence. The applications of a more
robust rate calibration and multispecies coalescent dating appear to
primarily explain these differences. The recent island of La Palma was
colonized from northern Tenerife at least ~1 Ma after it appeared, i.e.,
0.34-0.75 Ma ago, and after populations had diverged within Tenerife.
Admixture analyses revealed that secondary contact (and admixture) among
divergent east coast Tenerife populations likely occurred in the late
Pleistocene. Some fragmentation events coincide well, spatially and
temporally, with ancient mega landslides, such as the Güimar valley
collapse, while others do not. The origins of lineages that are spatially
associated with the Teno and Anaga shield volcanoes to the NW and NE of
the Teide stratovolcano seem to postdate the appearance of these edifices:
extinctions due to volcanic eruptions on the central shield volcano appear
more likely to explain their genesis. The study provides detailed insights
into how biodiversity is generated within a relatively small oceanic
island.