Local differentiation in the defensive morphology of an invasive zooplankton species is not genetically based
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Evolutionary changes in functional traits represent one possible reason why exotic species spread to become invasive, but empirical studies of the mechanisms driving phenotypic differentiation between populations of invasive species are rare. This study tested whether differences in distal spine length among populations of the invasive cladoceran, Bythotrephes longimanus, could be explained by local adaptation or phenotypic plasticity. We collected Bythotrephes from six lakes and found that distal spine lengths and natural selection on distal spine length differed among populations, but were unrelated to the gape-limitation of the dominant fish predator in the lake from which they were collected. A common garden experiment revealed significant genetic and maternal variation for distal spine length, but phenotypic differences among populations were not genetically based. Phenotypic differences among lakes in this ecologically important trait are, therefore, the result of plasticity and not local adaptation, despite spatially variable selection on this heritable trait. The ability of Bythotrephes to plastically adjust distal spine length may explain the success of this species at invading lake ecosystems with diverse biotic environments.
KeywordsBythotrephes longimanus Cladoceran Common garden experiment Invasive species Local adaptation Phenotypic plasticity
We thank Teresa Crease and Beren Robinson for insightful comments, and for providing field and lab equipment. The Dorset Environmental Science Centre (DESC) provided a climate controlled facility. James Rusak (DESC) and Matt Cornish (Hagen Aqualab) assisted with lab set-up. Andrea Miehls helped with Bythotrephes collection and culturing protocols. Guang Zhang assisted with field work. Emily De Freitas, Evan McKenzie, Kaileigh Watson, Katelyn Cross, Kirsten Bradford, Marissa Skinner, Mary Paquet, Meera Navaratnam, Ronena Wolach, and Yu Jin Song assisted with data collection.
This study was funded by an Ontario Ministry of Research and Innovation Early Researcher Award to Andrew McAdam (ER08-05-119), a Natural Sciences and Engineering Research Council Discovery Grant to Andrew McAdam (RGPIN371579-2009), and an Ontario Graduate Scholarship to Giuseppe Fiorino.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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