Tjalling Jager

Dept. Theoretical Biology

How to simplify biologyto interpret effects of stressors

Organisms are complex …

Stressing organisms …

… only adds to the complexity

Response to a toxic (and other) stress depends on– organism– endpoint– type of stressor or toxicant– exposure scenario– environmental conditions

Eco(toxico)logical literature is full of descriptions:

“The effect of stressor A on endpoint B of species C (under influence of environmental factor D)”

Practical challenge

Some 100,000 man-made chemicals Wide range of other stressors For animals alone, >1 million species described Complex dynamic exposure situations

“The effect of stressor A on endpoint B of species C (under influence of environmental factor D)”

Complexity

Environmental chemistry …

Idealisation

air

water

sediment

naturalsoil

agricult.soil

industr.soil

emission advection diffusion degradation

Treat each compartment as homogeneous …

Simplifying biology?

At the level of the individual … how much biological detail do we minimally need

…– to explain how organisms grow, develop and

reproduce– to explain effects of stressors on life history– to predict effects for untested cases– without being species- or stressor-specific

Simplifying biology?

At the level of the individual … how much biological detail do we minimally need

…– to explain how organisms grow, develop and

reproduce– to explain effects of stressors on life history– to predict effects for untested cases– without being species- or stressor-specific

One of the few hard laws in biology … all organisms obey conservation of mass and

energy

Effect on reproduction

Effect on reproduction

Effect on reproduction

Effect on reproduction

Effect on reproduction

Energy Budget

To understand effect on reproduction …– we have to consider how food is turned into offspring

Challenge– find the simplest set of rules ...– over the entire life cycle ...– for all organisms (related species follow related rules)

growth

maintenance

maturation

off spring

Quantitative theory for metabolic organisation from ‘first principles’– time, energy and mass balance– consistent with thermodynamics

Life-cycle of the individual– links levels of organisation: molecule

ecosystems

Fundamental; many practical applications– (bio)production, (eco)toxicity, climate

change, evolution …

Kooijman (2000)

Kooijman (2010)

DEB theory

eggs

mobilisation

Standard DEB animal

structurestructure

somatic maintenance

growth

maturity maintenance1-

reproduction

maturitymaturity bufferbuffer

maturation p

food feces

assimilation

reservereserve

b

3-4 states8-12 parameters

system can be scaled to remove dimension ‘energy’

3-4 states8-12 parameters

system can be scaled to remove dimension ‘energy’

Different food densities

Jager et al. (2005)

0 2 4 6 8 10 1220

30

40

50

60

70

80

90

100

time (d)

bo

dy

len

gth

(µ

m)

0 2 4 6 8 10 1220

30

40

50

60

70

80

90

100

time (d)

bo

dy

len

gth

(µ

m)

H

M

L

0 2 4 6 8 10 120

20

40

60

80

100

120

140

160

time (d)

cum

ula

tive

nu

mb

er o

f eg

gs

0 2 4 6 8 10 120

20

40

60

80

100

120

140

160

time (d)

cum

ula

tive

nu

mb

er o

f eg

gs

H

M

L

Toxicant effects in DEB

externalconcentration

(in time)

toxico-kinetics

toxico-kinetics internal

concentrationin time DEB

parametersin time

DEBmodel

DEBmodel

repro

growth

survival

feeding

hatching

…

Kooijman & Bedaux (1996),

Jager et al. (2006, 2010)

over entire life cycle

parasites

environmental stress

Toxicant effects in DEB

externalconcentration

(in time)

toxico-kinetics

toxico-kinetics internal

concentrationin time DEB

parametersin time

DEBmodel

DEBmodel

Affected DEB parameter has specific consequences for life cycle

repro

growth

survival

feeding

hatching

…

Kooijman & Bedaux (1996),

Jager et al. (2006, 2010)

Toxicant case study

Marine polychaete Capitella (Hansen et al, 1999)– exposed to nonylphenol in sediment– body volume and egg production followed– no effect on mortality observed

Jager and Selck (acc.)

Control growth

Volumetric body length in control– here, assume no contribution reserve to volume …

0 10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5

3

time (days)

vo

lum

etr

ic b

od

y l

en

gth

(m

m)

0

Control growth

Assumption– effective food density depends on body size

0 10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5

3

time (days)

vo

lum

etr

ic b

od

y l

en

gth

(m

m)

0

Control growth

0 10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5

3

time (days)

vo

lum

etr

ic b

od

y l

en

gth

(m

m)

0

Assumption– initial starvation (swimming and metamorphosis)

Control reproduction

Compare to mean reproduction rate from DEB– ignore reproduction buffer …

0 10 20 30 40 50 60 70 800

500

1000

1500

2000

2500

3000

3500

time (days)

cu

mu

lati

ve

off

sp

rin

g p

er

fem

ale

0

NP effects

Compare the control to the first dose

0 10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5

3

time (days)

volu

me

tric

bo

dy

len

gth

(m

m)

014

0 10 20 30 40 50 60 70 800

500

1000

1500

2000

2500

3000

3500

4000

time (days)

cu

mu

lati

ve o

ffsp

rin

g p

er

fem

ale 0

14

“Hormesis”

Requires a mechanistic explanation …– organism must obey conservation of mass and

energy

Potential assumptions– NP is a micro-nutrient– decreased investment elsewhere (e.g., immune

system)– NP relieves a secondary stress (e.g., parasites or

fungi)– NP increases the food availability/quality

NP effects

Assumption– NP increases food density/quality

0 10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5

3

time (days)

volu

me

tric

bo

dy

len

gth

(m

m)

014

0 10 20 30 40 50 60 70 800

500

1000

1500

2000

2500

3000

3500

4000

time (days)

cu

mu

lati

ve o

ffs

pri

ng

pe

r fe

ma

le

014

NP effects

Assumption– NP affects costs for making structure

0 10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5

3

time (days)

volu

me

tric

bo

dy

len

gth

(m

m)

1452174

1452174

0 10 20 30 40 50 60 70 800

500

1000

1500

2000

2500

3000

3500

4000

time (days)

cu

mu

lati

ve o

ffs

pri

ng

pe

r fe

ma

le

1452174

1452174

Standard DEB animal

structurestructure

food feces

maturity maintenancesomatic maintenance

assimilation

1-

growth reproduction

maturitymaturity bufferbuffer

maturation

reservereserve

mobilisation

eggs

NP effects

Assumption– NP also affects costs for maturation and

reproduction

0 10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5

3

time (days)

volu

me

tric

bo

dy

len

gth

(m

m)

0 10 20 30 40 50 60 70 800

500

1000

1500

2000

2500

3000

3500

4000

time (days)

cu

mu

lati

ve o

ffs

pri

ng

pe

r fe

ma

le

1452174

1452174

1452174

1452174

Standard DEB animal

structurestructure

food feces

maturity maintenancesomatic maintenance

assimilation

1-

growth reproduction

maturitymaturity bufferbuffer

maturation

reservereserve

mobilisation

eggs

fit not satisfactory?

fit

Strategy for data analysis

actualDEB model

experimentaldata

additionalexperiments

literature

educatedguesses

mechanistichypothesis

standardDEB model

testablepredictions

Strategy for data analysis

Are we sure we have the correct explanation?

Occam’s razor Accept the simplest explanation … for now

actualDEB model

Concluding remarks

Understanding stressor effects in eco(toxico)logy is served by idealisation of biology

Stressor effects can be treated quantitatively, ensuring:– mass and energy balance– consistent changes in all life-history traits (trade-offs)

Increase understanding of stressors, but also of metabolic organisation

DEB theory offers a platform– simple, not species- or stressor-specific– well tested in many applications

More information

on DEB: http://www.bio.vu.nl/thb

on DEBtox: http://www.debtox.info

Courses– International DEB Tele Course 2013

Symposia– 2nd International DEB Symposium 2013 on Texel

(NL)

growth

maintenance

maturation

off spring