Gene Expression and Population Studies in Daphnia magna:Gene Expression and Population Studies in Daphnia magna:giving biomarkers ecological relevancegiving biomarkers ecological relevance

R Connon,† H L Hooper,† G Orphanides,‡ S Maund,§ T Hutchinson,¶ R M Sibly,† & A Callaghan†

† School of Animal & Microbial Sciences, The University of Reading, Whiteknights PO Box 228, Reading RG6 6AJ, UK.‡Syngenta Central Toxicology Laboratory, Alderley Park, Macclesfield, Cheshire, SK10 4TJ, UK. §Syngenta Jealott’s Hill Research Station, Bracknell, Berks, RG42 6EY, UK. ¶AstraZeneca, Brixham

Environmental Laboratory, Freshwater Quarry, Brixham, Devon, TQ5 8BA, UK.

MethodsInvestigated Stressors:

Selected stressors to be investigated include cadmium,kerosene, lufenuron, salinity, pH and water hardness.

Gene Expression:

Selective Subtractive Hybridisation will be used to generate acDNA library from organisms exposed to stressors.

Population Studies:

A newly developed image analysis system will be used toinvestigate population responses to the above stressors.

ReferencesDepledge M H, et al. (1993), The conceptual basis ofthe biomarker approach. In Biomarkers (eds D.B.Peakall and R.L. Shugart).Forbes V and Calow P (2002) Population growth rateas a basis for ecological risk assessment of toxicchemicals. Philosophical Transactions of the RoyalSociety London B, 357, 1299-1306.Walker C, et al. (2000) Principles of Ecotoxicology,2nd edn. Taylor and Francis, London.

Acknowledgments This project is funded by NERC grant NER/D/S/2002/00413, Syngenta and AstraZeneca.

Fig. 3 Effects of increasing pollutantconcentration on hypothetical expression of genes:As pollution increases above the point at whichhomeostasis is possible (B1), compensatoryresponses are initiated (B2), but with increase inpollution organisms are stressed until responsesbecome costly in terms of energy/nutrients (B3).At higher levels of pollution the organism becomesdamaged, but repair is still possible, (B4). Furtherincreases in pollution lead to acute toxicityresponses and mortality (B5) (After Depledge etal, 1993).

Fig. 1 Daphnia magna(photo by S.P. Hopkin)

Daphnia magna (Fig. 1) are particularlysuited to these studies. Their parthenogeneticmode of reproduction facilitates geneexpression investigations and their rapidreproduction cycle is ideal for populationassessments.

Contact Dr Richard Connon - R.Connon@Reading.ac.uk

IntroductionAs ecotoxicology grows scientifically, it is increasingly realisedthat it needs stronger links on the one hand with populationecology, and on the other with the molecular biology of stressresponses (Walker et al., 2000). Toxic responses are oftenpreceded by alterations in gene expression, thus studies basedon gene expression may offer insights into the overall health ofan organism and thus that of populations and communities.Gene expression studies carried out over short-term exposuresmay sometimes allow the prediction of the chronic effectstoxicants may have on the overall health of an individual, andthis may affect its survival, fecundity and somatic growth andthe overall population (Figs. 2 & 3).

These life history traits together determine effects at thepopulation level, and population growth rate (pgr) provides asuitable measure of population level effects (Forbes and Calow2002). By linking population level effects to changes in geneexpression in Daphnia magna we hope to provide fundamentalunderstanding of the nature of stress responses that will havewide application in ecotoxicology.

This investigation aims to link transcriptional and populationresponses.

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Fig. 2 Gene Expression and Population Analyses