Data from: Evidence for ecotone speciation across an African rainforest-savanna gradient

Accelerating climate change and habitat loss make it imperative that plans
to conserve biodiversity consider species' ability to adapt to
changing environments. However, in biomes where biodiversity is highest,
the evolutionary mechanisms responsible for generating adaptative
variation and, ultimately, new species are frequently poorly understood.
African rainforests represent one such biome, as decadal debates continue
concerning the mechanisms generating African rainforest biodiversity.
These debates hinge on the relative importance of geographic isolation
versus divergent natural selection across environmental gradients.
Hindering progress is a lack of robust tests of these competing
hypotheses. Because African rainforests are severely at-risk due to
climate change and other anthropogenic activities, addressing this
long-standing debate is critical for making informed conservation
decisions. We use demographic inference and allele frequency-environment
relationships to investigate mechanisms of diversification in an African
rainforest skink, Trachylepis affinis, a species inhabiting the gradient
between rainforest and rainforest-savanna mosaic (ecotone). We provide
compelling evidence of ecotone speciation, in which gene flow has all but
ceased between rainforest and ecotone populations, at a level consistent
with infrequent hybridization between sister species. Parallel patterns of
genomic, morphological, and physiological divergence across this
environmental gradient and pronounced allele frequency-environment
correlation indicate speciation is mostly likely driven by ecological
divergence, supporting a central role for divergent natural selection. Our
results provide strong evidence for the importance of ecological gradients
in African rainforest speciation and inform conservation strategies that
preserve the processes that produce and maintain biodiversity.