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Functional basis of ecological divergence in sympatric stickleback.

ABSTRACT: BACKGROUND:The evolution of ecological divergence in closely related species is a key component of adaptive radiation. However, in most examples of adaptive radiation the mechanistic basis of ecological divergence remains unclear. A classic example is seen in the young benthic and limnetic stickleback species pairs of British Columbia. In each pair the benthic species feeds on littoral macroinvertebrates whereas the limnetic feeds on pelagic zooplankton. Previous studies indicate that in both short-term feeding trials and long-term enclosure studies, benthics and limnetics exhibit enhanced performance on their own resource but fare more poorly on the other species' resource. We examined the functional basis of ecological divergence in the stickleback species pair from Paxton Lake, BC, using biomechanical models of fish feeding applied to morphological traits. We examined the consequences of morphological differences using high speed video of feeding fish. RESULTS:Benthic stickleback possess morphological traits that predict high suction generation capacity, including greatly hypertrophied epaxial musculature. In contrast, limnetic stickleback possess traits thought to enhance capture of evasive planktonic prey, including greater jaw protrusion than benthics and greater displacement advantage in both the lower jaw-opening lever system and the opercular four-bar linkage. Kinematic data support the expectations from the morphological analysis that limnetic stickleback exhibit faster strikes and greater jaw protrusion than benthic fish, whereas benthics exert greater suction force on attached prey. CONCLUSIONS:We reveal a previously unknown suite of complex morphological traits that affect rapid ecological divergence in sympatric stickleback. These results indicate that postglacial divergence in stickleback involves many functional systems and shows the value of investigating the functional consequences of phenotypic divergence in adaptive radiation.

SUBMITTER: McGee MD

PROVIDER: S-EPMC3890603 | biostudies-other | 2013 Dec

REPOSITORIES: biostudies-other

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Functional basis of ecological divergence in sympatric stickleback.

McGee Matthew D MD Schluter Dolph D Wainwright Peter C PC

BMC evolutionary biology 20131231

<h4>Background</h4>The evolution of ecological divergence in closely related species is a key component of adaptive radiation. However, in most examples of adaptive radiation the mechanistic basis of ecological divergence remains unclear. A classic example is seen in the young benthic and limnetic stickleback species pairs of British Columbia. In each pair the benthic species feeds on littoral macroinvertebrates whereas the limnetic feeds on pelagic zooplankton. Previous studies indicate that in ...[more]

PMID: 24380474

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Project description:BackgroundColor polymorphisms are a conspicuous feature of many species and a way to address broad ecological and evolutionary questions. Three potential major evolutionary fates of color polymorphisms are conceivable over time: maintenance, loss, or speciation. However, the understanding of color polymorphisms and their evolutionary implications is frequently impaired by sex-linkage of coloration, unknown inheritance patterns, difficulties in phenotypic characterization, and a lack of evolutionary replicates. Hence, the role of color polymorphisms in promoting ecological and evolutionary diversification remains poorly understood. In this context, we assessed the ecological and evolutionary consequences of a color polymorphic study system that is not hampered by these restrictions: the repeated adaptive radiations of the gold/dark Midas cichlid fishes (the Amphilophus citrinellus species complex) from the great lakes and crater lakes of Nicaragua, Central America.ResultsWe conducted multi-trait morphological and ecological analyses from ten populations of this young adaptive radiation (<6,000 years old), which revealed sympatric ecological differentiation associated with the conspicuous binary (gold/dark) color polymorphism. Varying degrees of intraspecific ecological divergence were observed across the ten color morph pairs, but most pairs exhibited a consistently parallel ecological and evolutionary trajectory across populations. Specifically, gold Midas cichlids are frequently deeper-bodied, have more robust pharyngeal jaws, and feed at a lower trophic level compared to conspecific, sympatric dark individuals. A common garden experiment suggests there is a genetic correlation of color and eco-morphological traits.ConclusionsWe demonstrate unprecedented ecological and evolutionary consequences of color polymorphism in this adaptive radiation. Across the species complex, sympatric conspecific individuals differed in eco-morphology depending on color morph (gold/dark) and the axis of differentiation tended to be consistent across replicates. The consistent divergence across wild populations and the common garden experiment suggests that color is genetically correlated to ecology. Because Midas cichlids are known to mate color assortatively, the putative genetic correlation of this color polymorphism with an eco-morphological divergence suggests an innate potential to promote ecological and evolutionary divergence across this species complex. However, there are to date no examples of speciation based on color in this radiation, suggesting long-term maintenance of this color polymorphism.

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Functional basis of ecological divergence in sympatric stickleback.

Publications

Functional basis of ecological divergence in sympatric stickleback.

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