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Effects of combined stressors
Tjalling Jager, Bas KooijmanDept. Theoretical Biology
From individuals to population using dynamic energy budgets
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
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Cd concentration (mg/L)
tota
l eg
gs
afte
r 15
d
Daphnia reproduction
high food
low food
EC50
Data Heugens et al. (in press)
Stress affects reproduction
food limitation
Stress affects reproduction
toxicant
Stress affects reproduction
toxicant
Stress affects reproduction
toxicant
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?
Budget components
growth
reproduction
assimilation
maintenance
ad libitum
5%
Energy Budget
growth
reproduction
assimilation
limiting
maintenance
50%
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)
DEB allocation rules
food faeces
reserves
assimilation
structure
somatic maintenance
1-
maturityoffspring
maturity maintenance
Kooijman (2000)
Embryo development
yolk
embryo
Kooijman (2000)
Food limitation
food faeces
reserves
structure maturityoffspring
maturity maintenancesomatic maintenance
assimilation
1-
Food limitation
Jager et al. (2005)
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time (d)
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Food limitation
food faeces
reserves
structure maturityoffspring
maturity maintenancesomatic maintenance
assimilation
1-
X
What determines maximum size?
L2
L3
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
DEB model
DEBtox
internal concentration
allo
catio
n p
aram
eter
NEC
blank value
toler
ance
targetparameter
toxicokinetics
“intrinsic sensitivity”
growth/repro/survival
Potential targets
food faeces
reserves
structure maturityoffspring
maturity maintenancesomatic maintenance
assimilation
1-
Potential targets
time
cum
ula
tive
off
spri
ng
time
bo
dy
len
gth
TPT
Crommentuijn et al. (1997), Jager et al. (2005)
Potential targets
food faeces
reserves
structure maturityoffspring
maturity maintenancesomatic maintenance
assimilation
1-
Potential targets
food faeces
reserves
structure maturityoffspring
maturity maintenancesomatic maintenance
assimilation
1-
Potential targets
time
bo
dy
len
gth
time
cum
ula
tive
off
spri
ng Pentachlorobenzene
Alda Álvarez et al. (2006)
Potential targets
food faeces
reserves
structure maturityoffspring
maturity maintenancesomatic maintenance
assimilation
1-
Potential targets
food faeces
reserves
structure maturityoffspring
maturity maintenancesomatic maintenance
assimilation
1-
Potential targets
time
cum
ula
tive
off
spri
ng
time
bo
dy
len
gth
Chlorpyrifos
Crommentuijn et al. (1997), Jager et al. (in press)
Potential targets
food faeces
reserves
structure maturityoffspring
maturity maintenancesomatic maintenance
assimilation
1-
Potential targets
food faeces
reserves
structure maturityoffspring
maturity maintenancesomatic maintenance
assimilation
1-
trematode infection in snailsGorbushin and Levakin (1999)
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
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)
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 …
DEB individuals to populations
Intrinsic rate of increase Without limitations, populations grow exponentially
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)(),(),(1t
tcre ctRepro ctSurv
from model or data “intrinsic rate of increase”
Daphnia and food/Cd
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concentration Cd (mg/L)
intr
insi
c ra
te (
d-1)
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 elegans Acrobeloides nanus
Alda Álvarez et al. (2005, in press)
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length
length
eggs
survival
C. elegans and cadmium
Mode of action: assimilation
Alda Álvarez et al. (2005)
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A. nanus and cadmium
Mode of action: costs for growth
Alda Álvarez et al. (in press)
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Intrinsic rate of increase
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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)
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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)
Pulsed exposure
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Body length Cumulative offspring Fraction surviving
Hig
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ow
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Mode of action: assimilation One parameter accounts for food effect Intrinsic sensitivity independent of food Chemical effects fully reversibleHow to go to population effects?
Mode of action: assimilation One parameter accounts for food effect Intrinsic sensitivity independent of food Chemical effects fully reversibleHow to go to population effects?
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?
1 2 3 4
F4
F3
G1 G2 G3
P1 P2 P3 P4
Individual-based models
Follow all individuals seperately … Full flexibility; extremely calculation intensive …
Kooijman (2000)
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)
Cohort based (EBT)
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juvenilesadults
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juvenilesadultsjuvenilesadults
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High food Limiting food
Based on fenvalerate data
Pulsed exposure
Pieters et al. (2006)
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 …
Current projects
Mixture toxicity, NoMiracle (Jan Baas)
Collaboration with a.o. Animal Ecology (VU, Amsterdam)
nickel chlorpyrifos
Current projects
Mixture toxicity, NoMiracle (Jan Baas) Food chain effects, ModelKey (Daniel Bontje)
AirAir
Collaboration with a.o. ECT Oekotoxicologie, (Flörsheim, Germany)
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
