Climate drives community-wide divergence within species over a limited spatial scale: evidence from an oceanic island

Geographic isolation substantially contributes to species endemism on
oceanic islands when speciation involves the colonisation of a new island.
However, less is understood about the drivers of speciation within
islands. What is lacking is a general understanding of the geographic
scale of gene flow limitation within islands, and thus the geographic
scale and drivers of geographical speciation within insular contexts.
Using a community of beetle species, we show that when dispersal ability
and climate tolerance are restricted, microclimatic variation over
distances of only a few kilometres can maintain strong geographic
isolation and drive incipient speciation. Further to this, we demonstrate
congruent diversification with gene flow across species, mediated by
Quaternary climate oscillations that have facilitated a dynamic of
isolation and secondary contact. The unprecedented scale of parallel
species responses to a common environmental driver for evolutionary change
has profound consequences for understanding past and future species
responses to climate variation.