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Ecological Speciation
Relevant Publications:
Langerhans, Gifford, Joseph. 2007. Evolution
(Featured in Science's Editors' Choice), (Featured in Faculty of 1000), received R.A. Fisher Prize (best dissertation paper in 2007 in Evolution)
Ecological speciation is the evolution of barriers to gene flow resulting from ecologically-based divergent selection. The simplest model of ecological speciation describes adaptation to divergent selective regimes, which incidentally results in reproductive isolation as a by-product.
Theory suggests that divergent natural selection between environments might often result in speciation as a by-product (even before reinforcement can occur), however only a handful of promising examples from nature have so far been revealed. Along with colleagues, I am testing speciation via this by-product mechanism in Gambusia fishes.
So far, we have examined morphological, molecular, and behavioral data to investigate ecology’s role in incipient speciation for a post-Pleistocene radiation of Bahamas mosquitofish (Gambusia hubbsi) inhabiting blue holes (see figures to the right). We found that adaptation to divergent predator regimes is driving ecological speciation as a by-product. Divergence in body shape, coupled with assortative mating for body shape, produces reproductive isolation that is twice as strong between populations inhabiting different predator regimes than between populations that evolved in similar ecological environments. Gathering analogous data on reproductive isolation at the interspecific level in the genus, we have also found that this mechanism of speciation may have been historically prevalent in Gambusia. This suggests that speciation in nature can result as a by-product of divergence in ecologically important traits, producing interspecific patterns that persist long after speciation events have completed. Thus, the microevolutionary processes observed in the blue holes (incipient speciation driven by predator regime) might play a major role in generating broader macroevolutionary trends in the Gambusia genus.
The figure below illustrates morphological divergence between low- and high-predation blue hole populations of Gambusia hubbsi using thin-plate spline transformation grids relative to mean landmark positions (no magnification). Note the larger anterior body/head region and smaller caudal peduncle region in low-predation fish. Circles along the canonical axis represent population means (blue: low-predation, red: high-predation). Representative radiographs of low- and high-predation individuals are provided below the axis. Morphological differences match theoretical predictions based on divergent selection for swimming performance between predator regimes.
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Blue hole on Andros Island, Bahamas.
Two low-predation (top) and two high-predation (bottom) blue holes on Andros Island, Bahamas.
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