1. Effects of combined stressors Tjalling Jager, Bas Kooijman Dept. Theoretical Biology From individuals to population using dynamic energy budgets

2. Introduction How can we understand and predict effects of combined stressors on populations? This presentation:  start from physiology of the individual  Dynamic Energy Budget (DEB) theory  focus: food and toxicants  from DEB individuals to populations

3. 0 20 40 60 80 100 00.050.10.150.20.25 Cd concentration (mg/L) total eggs after 15d Daphnia reproduction high food low food EC50 Data Heugens et al. (in press)

4. Stress affects reproduction food limitation

5. Stress affects reproduction toxicant

6. Stress affects reproduction toxicant

7. Stress affects reproduction toxicant

8. Energy Budget Stressors affect the individual’s energy budget  Look closer at metabolic organisation how is food turned into offspring?  How do stressors interact? why does food limitation increase Cd toxicity?

9. Budget components growth reproduction assimilation maintenance ad libitum 5%

10. Energy Budget growth reproduction assimilation limiting maintenance 50%

11. DEB theory Quantitative theory; “first principles” time, energy and mass balance Life-cycle of the individual links levels of organisation: molecule  ecosystems Comparison of species body-size scaling relationships; e.g., metabolic rate Fundamental to biology; many practical applications (bio)production, (eco)toxicity, climate change, … Kooijman (2000)

12. DEB allocation rules foodfaeces reserves assimilation structure somatic maintenance  1-  maturity offspring maturity maintenance

13. Kooijman (2000)

14. Embryo development yolk embryo Kooijman (2000)

15. Food limitation foodfaeces reserves structure maturity offspring maturity maintenancesomatic maintenance assimilation  1- 

16. Food limitation Jager et al. (2005)

17. Food limitation foodfaeces reserves structure maturity offspring maturity maintenance somatic maintenance assimilation  1-  X What determines maximum size? L2L2 L3L3

18. Toxicants  Toxicants affect resource allocation just like other stresses!  Large variety mechanisms of action many opportunities to test theory  Practical benefits improving chemical RA: DEBtox

19. DEB model DEBtox internal concentration allocation parameter NEC blank value tolerance target parameter toxicokinetics “intrinsic sensitivity” growth/repro/survival

20. Potential targets foodfaeces reserves structure maturity offspring maturity maintenancesomatic maintenance assimilation  1- 

21. Potential targets time cumulative offspring time body length TPT Crommentuijn et al. (1997), Jager et al. (2005)

22. Potential targets foodfaeces reserves structure maturity offspring maturity maintenancesomatic maintenance assimilation  1- 

23. Potential targets foodfaeces reserves structure maturity offspring maturity maintenancesomatic maintenance assimilation  1- 

24. Potential targets time body length time cumulative offspring Pentachlorobenzene Alda Álvarez et al. (2006)

25. Potential targets foodfaeces reserves structure maturity offspring maturity maintenancesomatic maintenance assimilation  1- 

26. Potential targets foodfaeces reserves structure maturity offspring maturity maintenancesomatic maintenance assimilation  1- 

27. Potential targets time cumulative offspring time body length Chlorpyrifos Crommentuijn et al. (1997), Jager et al. (in press)

28. Potential targets foodfaeces reserves structure maturity offspring maturity maintenancesomatic maintenance assimilation  1- 

29. Potential targets trematode infection in snails Gorbushin and Levakin (1999)

30. Modes of action … Based on resource allocation contrasts common use (‘narcosis’, ‘uncoupling’) different MoA’s have specific effects patterns Model is based on processes extrapolations to time-varying exposure, temperature, etc. easy to combine stressors easy to combine data sets

31. Combined stressors/data Modified Daphnia reproduction test 15-day partial life cycle toxicant cadmium, three food levels determine repro and survival daily body residue and size at end test Data in Heugens et al. (in press)

32.  Mode of action: assimilation  One parameter accounts for food effect  Intrinsic sensitivity independent of food  BCF depends on food …  Mode of action: assimilation  One parameter accounts for food effect  Intrinsic sensitivity independent of food  BCF depends on food …

33. DEB individuals to populations Intrinsic rate of increase  Without limitations, populations grow exponentially from model or data “intrinsic rate of increase”

34. Daphnia and food/Cd 00.050.10.150.2 0 0.1 0.2 0.3 0.4 concentration Cd (mg/L) intrinsic rate (d -1 )

35. Predictions based on MoA Life-cycle experiment –two species nematodes –exposed to cadmium in agar –body size, eggs and survival determined –simultaneous analysis of all endpoints Caenorhabditis elegansAcrobeloides nanus Alda Álvarez et al. (2005, in press)

36. length eggs survival C. elegans and cadmium Mode of action: assimilation Alda Álvarez et al. (2005)

37. A. nanus and cadmium Mode of action: costs for growth Alda Álvarez et al. (in press)

38. 246810120 0 0.2 0.4 0.6 0.8 1 concentration (mg/L) 24681012 concentration (mg/L) 0 0 0.1 0.2 0.3 0.4 246810120 0 0.1 0.2 0.3 0.4 0 0 0.1 0.2 0.3 0.4 intrinsic rate (d -1 ) Intrinsic rate of increase 95% 90% 95% 90%

39. Intrinsic rate  Integrates endpoints, ecologically relevant  Limitations only for unlimited growth in constant environment not for populations growing to carrying capacity not for periodic events (e.g. pesticide application)

40. Pulsed exposure Modified 21-day reproduction test Daphnia magna at two (limiting) food levels 24-hour pulse of fenvalerate follow reproduction and survival (daily) measure body size (weekly) Data by Pieters et al. (2005) DEBtox analysis Pieters et al. (in press)

41. Pulsed exposure Body length Cumulative offspring Fraction surviving High food Low food  Mode of action: assimilation  One parameter accounts for food effect  Intrinsic sensitivity independent of food  Chemical effects fully reversible How to go to population effects?  Mode of action: assimilation  One parameter accounts for food effect  Intrinsic sensitivity independent of food  Chemical effects fully reversible How to go to population effects?

42. Matrix models  In combination with DEB(tox) Klok & De Roos (1996), Lopes et al. (2005), Klanjscek et al. (2006), Smit et al. (2006), Liao et al. (2006)  Errors from discretisation …  Only one state variable (size or age) for organism … dynamics of internal concentrations and reserves? 1234 F4F4 F3F3 G1G1 G2G2 G3G3 P1P1 P2P2 P3P3 P4P4

43. Individual-based models  Follow all individuals seperately …  Full flexibility; extremely calculation intensive … Kooijman (2000)

44. Cohort based (EBT) Within a cohort, all individuals are equal from t → t+Δt each cohort followed in continuous time reproduction over Δt collected in separate cohort at t+Δt newborn cohort is closed, gets average chars. cohorts are renumbered De Roos et al. (1992)

45. Cohort based (EBT) High foodLimiting food Based on fenvalerate data

46. Pulsed exposure Pieters et al. (2006)

47. Concluding remarks  Many stressors affect energy budgets food limitation, toxicants, parasites …  DEB theory provides handles for extrapolation and combining stressors  Effects on individual budgets forms basis for population response best method depends on purpose …

48. Current projects  Mixture toxicity, NoMiracle (Jan Baas) Collaboration with a.o. Animal Ecology (VU, Amsterdam) nickelchlorpyrifos

49. Current projects  Mixture toxicity, NoMiracle (Jan Baas)  Food chain effects, ModelKey (Daniel Bontje) Collaboration with a.o. ECT Oekotoxicologie, (Flörsheim, Germany)

50. Current projects  Mixture toxicity, NoMiracle (Jan Baas)  Food chain effects, ModelKey (Daniel Bontje) www.bio.vu.nl/thb/deb DEB telecourse 2007  Time-varying exposure, ExxonMobil  Introduce DEBtox to EU regulators, ECB