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Effects of combined stressors

Effects of combined stressors. From individuals to population using dynamic energy budgets. Tjalling Jager, Bas Kooijman Dept. Theoretical Biology. Introduction. How can we understand and predict effects of combined stressors on populations?. This presentation:

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Effects of combined stressors

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

  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. 100 high food 80 low food EC50 60 total eggs after 15d 40 20 0 0 0.05 0.1 0.15 0.2 0.25 Cd concentration (mg/L) Daphnia reproduction 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. assimilation 5% reproduction maintenance growth Budget components ad libitum

  10. maintenance Energy Budget assimilation limiting reproduction 50% growth

  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. food faeces assimilation reserves somatic maintenance maturity maintenance  1- maturity offspring structure DEB allocation rules

  13. Kooijman (2000)

  14. Embryo development yolk embryo Kooijman (2000)

  15. Food limitation food faeces assimilation reserves somatic maintenance maturity maintenance  1- maturity offspring structure

  16. Food limitation Jager et al. (2005)

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

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

  20. Potential targets food faeces assimilation reserves somatic maintenance maturity maintenance  1- maturity offspring structure

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

  22. Potential targets food faeces assimilation reserves somatic maintenance maturity maintenance  1- maturity offspring structure

  23. Potential targets food faeces assimilation reserves somatic maintenance maturity maintenance  1- maturity offspring structure

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

  25. Potential targets food faeces assimilation reserves somatic maintenance maturity maintenance  1- maturity offspring structure

  26. Potential targets food faeces assimilation reserves somatic maintenance maturity maintenance  1- maturity offspring structure

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

  28. Potential targets food faeces assimilation reserves somatic maintenance maturity maintenance  1- maturity offspring structure

  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 …

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

  34. 0.4 0.3 intrinsic rate (d-1) 0.2 0.1 0 0 0.05 0.1 0.15 0.2 concentration Cd (mg/L) Daphnia and food/Cd

  35. Caenorhabditis elegans • Acrobeloides nanus 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 Alda Álvarez et al. (2005, in press)

  36. C. elegans and cadmium length eggs length survival 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. 1 0.4 0.4 0.4 0.8 0.3 0.3 0.3 0.6 intrinsic rate (d-1) 95% 0.2 0.2 0.2 0.4 90% 0.2 0.1 0.1 0.1 90% 95% 0 0 0 0 0 0 0 2 2 4 4 6 6 8 8 10 10 12 12 0 2 4 6 8 10 12 concentration (mg/L) concentration (mg/L) Intrinsic rate of increase

  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. Body length Cumulative offspring Fraction surviving High food Low food Pulsed exposure • 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. F4 F3 G1 G2 G3 1 2 3 4 P1 P2 P3 P4 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?

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

  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 food Limiting 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. nickel chlorpyrifos Current projects • Mixture toxicity, NoMiracle (Jan Baas) Collaboration with a.o. Animal Ecology (VU, Amsterdam)

  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) • Time-varying exposure, ExxonMobil • Introduce DEBtox to EU regulators, ECB www.bio.vu.nl/thb/deb DEB telecourse 2007

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