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.

The development of a model system for study of local adaptation: Scenedesmus

Predator-induced defenceIn 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

Isolation of Scenedesmus communities from ecologically contrasting ponds

Pond 15: clear pond withLarge Daphnia, 52 strains Pond 18: turbid pond with small

Zooplankton, 75 strains

Nature reserve“De Maten”, Genk, Belgium

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.

Molecular methods for species delineation

• 18S-rDNA RFLP

• DGGE of the ITS-2 region

• Sequence analysis of ITS-2

3´-GCGTCGGTTT TTCGACCTGAGC-5´

rDNA ITS2 gene

~ 227 - 264 bp

SSU (18S) large SSUITS 1 ITS 25.8S rDNAsmall (25-28S)

Location of the ITS spacer region on the genome

10

>AJ249506>AJ237956

>AJ400496>AJ400498

>S4>S112

>AJ400493>AJ400494

>S45>S97

>AJ400499>S93>AJ400505>S104>S108>S122>S24>S27>S29>S59>S5>S62>S63>S65>S81>S94>AJ400502>S70

>S100>S101>S105>S107>S118>S16>S20>S22>S23

>S30>S36

>S42>S46>S51>S58>S60>S72>S74>S85>S86>S87>S90

>S68>S69>S96>S99>S50>S18

>S106>S11>S7>S83

>S38>S49

>S71>S9

>AJ400506>S113

>S28>AJ237959>AJ400504>S12>S114>S35>S52>S8>S98

>AJ237960>AJ237961

>AJ400495>AJ400500

>S39>S41

>AJ400503>S110>S129>S19>S33>S40>S61>S66>S6>S82>S84>S92>S95

>S64>S102>S26>S89>S25

>S44>AJ400497

>S135>S21>S37>S75

>AJ400501>AJ400492

>S34>AJ316581

>S67>AJ237958

>S10>AJ237957

>S43>S13

>S111>S47>S88

“D.communis-clade”

“D.armatus-clade”

“D.opoliensis-clade”

“D.bicellularis?-clade”

“D.brasiliensis-clade”

“Desmodesmus sp.”

Desmodesmus opoliensis

Desmodesmus armatus

Typical shape, bristles, difference between ponds

Very variable, present in both ponds

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

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