Resumen:
Repeated evolution can provide insight into the mechanisms that facilitate
adaptation to novel or changing environments. Here we study adaptation to
altitude in two tropical butterflies, Heliconius erato and H. melpomene, which
have repeatedly and independently adapted to montane habitats on either
side of the Andes. We sequenced 518 whole genomes from altitudinal transects
and found many regions differentiated between highland (~ 1200 m) and
lowland (~ 200 m) populations. We show repeated genetic differentiation
across replicate populations within species, including allopatric comparisons.
In contrast, there is little molecular parallelism between the two species. By
sampling five close relatives, we find that a large proportion of divergent
regions identified within species have arisen from standing variation and
putative adaptive introgression from high-altitude specialist species. Taken
together our study supports a role for both standing genetic variation and
gene flow from independently adapted species in promoting parallel local
adaptation to the environment.
