Data from: Inferring the evolution of reproductive isolation in a lineage of fossil threespine stickleback, Gasterosteus doryssus

Darwin attributed the absence of species transitions in the fossil record
to his hypothesis that speciation occurs within isolated habitat patches
too geographically restricted to be captured by fossil sequences. Mayr’s
peripatric speciation model added that such speciation would be rapid,
further explaining missing evidence of diversification. Indeed, Eldredge
and Gould’s original punctuated equilibrium model combined Darwin’s
conjecture, Mayr’s model, and 124 years of unsuccessfully sampling the
fossil record for transitions. Observing such divergence, however, could
illustrate the tempo and mode of evolution during early speciation. Here,
we investigate peripatric divergence in a Miocene stickleback fish,
Gasterosteus doryssus. This lineage appeared and, over ~8,000 generations,
evolved significant reduction of twelve of sixteen traits related to
armor, swimming, and diet, relative to its ancestral population. This was
greater morphological divergence than we observed between reproductively
isolated, benthic-limnetic ecotypes of extant Gasterosteus aculeatus.
Therefore, we infer that reproductive isolation was evolving. However,
local extinction of low-armoured G. doryssus lineages shows how young
isolate populations often disappear, supporting Darwin’s explanation for
missing evidence and revealing a mechanism behind morphological stasis.
Exctinction may also account for limited sustained divergence within the
stickleback species complex and help reconcile speciation rate variation
observed across time scales.