Ecological sorting of zooplankton metapopulations in response to selection from historical and contemporary environmental gradients.
Derry, Alison*,1, Arnott, Shelley1, Boag, Peter1, 1 Queens University, Kingston, ON, Canada
ABSTRACT- As freshwater ecosystems are faced with unprecedented rates of stress from human activities, it is critical to understand processes that may control biological recovery in damaged lakes. This project employed two field transplant experiments to test if zooplankton metapopulations are adaptively segregated among lakes with different acidification histories. For the first experiment, zooplankton communities from local (Killarney, ON) buffered (n=3) and acid-recovering (n=3) lakes, and from more regionally-distant (Dorset, ON) un-acidified lakes (n=3) were stocked in 72 10-L cubitainers that were incubated in acid-recovering Carlyle Lake for one week. This experiment had three factors: acidification history (buffered vs. acid-recovering vs. regionally distant and un-acidified); pH treatment (circum-neutral 6.2 to 7.6 vs. 5.2 vs. 4.7); and water treatment (home lake water vs. lake water from Carlyle Lake). To investigate effects of historical acidification on both direct and indirect contemporary zooplankton response to acidification, a reciprocal transplant experiment was conducted using zooplankton communities from a buffered lake and an acid-recovering lake crossed with a circumneutral (6.2 or 7.0) and low (4.7) pH treatment. This second experiment was conducted with 2000-L mesocosm bags for four weeks (n=3). Although all study lakes are now circum-neutral (>pH 6.2), Leptodiaptomus minutus copepods from lakes with a history of acidification had greater acid tolerance at pH 4.7 than lakes without prior exposure. Experimental populations from the unacidified lakes completely collapsed at pH 4.7 despite that this species has a broad distribution across Canadian Shield lakes, including acidic habitats. Historical differences in selection across environmental gradients can therefore interact with contemporary anthropogenic stressors, such as lake acidification, in the distribution of zooplankton ecotypes on the landscape.
Key words: acidification history, local adaptation, transplant experiments, zooplankton
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