Abstract
Many aquatic organisms respond phenotypically, through morphological, behavioral, and physiological plasticity, to environmental changes. The small-size cladoceran Bosmina longirostris , a dominant zooplankter in eutrophic waters, displayed reduced growth rates in response to the presence of a toxic cyanobacterium, Microcystis aeruginosa , in their diets. The magnitude of growth reduction differed among 15 clones recently isolated from a single population. A significant interaction between clone and food type indicated a genetic basis for the difference in growth plasticity. The variation in phenotypic plasticity was visualized by plotting reaction norms with two diets. The resistance of each clone to dietary cyanobacteria was measured as the relative change in growth rates on the “poor” diet compared with the “good” diet. The enhanced resistance to M . aeruginosa in B . longirostris was derived from both the reduced slope of reaction norms and the increased mean growth rates with two diets. The large clonal variation within a B . longirostris population may contribute to local adaptation to toxic cyanobacteria and influence ecosystem function via clonal succession.
Highlights
Phenotypic plasticity refers to the phenomenon that a genotype produces distinct phenotypes when living in different environmental conditions [1,2]
This phenomenon has been described as cyclomorphosis, temporal and cyclic morphological changes that occur within a planktonic population [27]
The present study provides strong evidence of the extensive growth variation in response to M. aeruginosa within a single population of B. longirostris
Summary
Phenotypic plasticity refers to the phenomenon that a genotype produces distinct phenotypes when living in different environmental conditions [1,2]. It is clear that phenotypic plasticity is widespread in organisms, and mainly involves ecologically relevant morphological, physiological, behavioral and life-history traits [3]. The changing pattern of a genotype with environment is usually characterized as a reaction norm. For continuous variables such as morphological, physiological, and life history variables, reaction norms are often visualized as a line or curve plotting the phenotypic value with the environmental value [1,2]. The evolution of genotypic plasticity can be visualized as a change in the slope of the reaction norm. Adaptive plasticity allows a genotype to have a broader tolerance to environmental changes. Such plasticity lessens extinction pressure in new environments, and aids populations to move from one adaptive peak to another [2,3]
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