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Local and regional factors determine community and population structures

Local and regional factors determine community and population structures. Local community structure: result of the interplay of local and regional factors. Local adaptation/population differentiation: enhanced by contrasting local conditions, prevented by ongoing gene flow.

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Local and regional factors determine community and population structures

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  1. Local and regional factors determine community and population structures • Local community structure: result of the interplay of local and regional factors. • Local adaptation/population differentiation: enhanced by contrasting local conditions, prevented by ongoing gene flow. • Model system: Nature reserve “De Maten”, Genk, with its system of overflows and identical abiotic but contrasting biotic background.

  2. The development of a model system for study of local adaptation: Scenedesmus • Predator-induced defence • In Scenedesmus-species • colony formation • Genetic variation present Hypothesis: Scenedesmus genotypes from a clear pond with high grazing pressure will be bigger and show a Stronger response to infochemicals

  3. Isolation of Scenedesmus communities from ecologically contrasting ponds Pond 15: clear pond with Large Daphnia, 52 strains Pond 18: turbid pond with small Zooplankton, 75 strains Nature reserve“De Maten”, Genk, Belgium

  4. Problems associated with species identification • Description of each morphotype as distinct taxon: monograph by Hegewald & Silva lists over 1300 taxa • Phenotypic plasticity: each genotype produces a variety of morphotypes • Recent changes using molecular methods, 18S and ITS-region.

  5. Molecular methods for species delineation • 18S-rDNA RFLP • DGGE of the ITS-2 region • Sequence analysis of ITS-2

  6. small SSU (18S) ITS 1 5.8S rDNA ITS 2 large SSU (25-28S) rDNA ITS2 gene 3´-GCGTCGGTTT TTCGACCTGAGC-5´ ~ 227 - 264 bp Location of the ITS spacer region on the genome

  7. “Desmodesmus sp.” “D.armatus-clade” “D.opoliensis-clade” “D.brasiliensis-clade” “D.communis-clade” “D.bicellularis?-clade”

  8. Desmodesmus opoliensis Typical shape, bristles, difference between ponds Desmodesmus armatus Very variable, present in both ponds

  9. Desmodesmus communis Present in both ponds, outer cell wall layer Desmodesmus brasiliensis Distinctive ribs, short spines Desmodesmus bicellularis? Very small, no spines, Morphologically heterogenous, only in turbid pond

  10. Conclusions • Agreement of morphological and molecular methods. • Shifts in species composition though the most abundant species are present in both ponds. • Further work at the intraspecific level in progress

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