Understanding organism energy allocations in response to
climate change
– ideas for approaches to ‘systems biology’ modelling?
Chris Hauton
Issues of climate change – 1) CO2, CH4 and temperature
based on: Petit et al. (1999) Nature, 399: 429-436
Issues of climate change – 2) warming and salinity change
(pss/50-years)
freshwater flux (m3 yr-1)
Durack & Wijffels (2010) J. Climate doi: 10.1175/2010JCLI3377.1
Issues of climate change – 3) CO2 and seawater acidification
‘the other CO2 problem’
Doney et al. (2009) Annual
Reviews - Marine Science, 1
3a) bicarbonate buffering…
CO2 (g)  CO2 (aq)
CO2 (aq) + H2O (aq)  HCO3- (aq) + H+ (aq)
CaCO3 (s)  Ca 2+ (aq) + CO3 2- (aq)
H+ (aq) + CO32- (aq)  HCO3- (aq)
carbonate dissolution…
Issues of climate change – 3) CO2 and seawater acidification
‘the other CO2 problem’
3b) disruption to acid base balance in osmoconformers
from Pörtner et al. (2004)
Issues of climate change – 3) CO2 and seawater acidification
‘the other CO2 problem’
3b) disruption to acid base balance in osmoconformers (Hauton et al., 2009)
COPIES mRNA. g total RNA-1
6.4e+7
4.4e+7
*
2.4e+7
gapdh gene
4.0e+6
6e+6
4e+6
2e+6
hsp70 gene
0
Control
Nom. pH 7.8Nom. pH 7.6
Treatment
Issues of climate change – 3) CO2 and seawater acidification
‘the other CO2 problem’
3a) reduced availability of carbonate ions causing a reduction
in calcification (Riebesell, 2000; Sciandra et al., 2003; Gazeau et
al. 2007) but species/experimental differences? (Iglesias-Rodriguez
et al., 2008)
3b) direct impact on the intracellular pH (pHi) of many species
(Seibel & Walsh, 2003), impacting normal protein synthesis (Kwast &
Hand, 1996), respiratory function (Spicer & Taylor, 1994; Pörtner et
al., 2004) and immune function (Bibby et al., 2008)
disruption to the physiology and
performance of marine species (Kurihara et
al., 2004; Berge et al., 2006; Spicer et al., 2007)
Issues of climate change – predictions by 2100?
All estimates are subject to uncertainty; variation with region, latitude
and depth (IPCC Fourth Assessment Report)
–  T of +2 to +4 oC
–  pH of -0.4 to -0.5 units
–  S of -0.05 psu
However…
coastal and estuarine environments extremely
variable
species which may have evolved strategies to
accommodate extreme episodic low pH
Attrill et al., 1999
Ringwood & Keppler, 2002
Requirements for modelling
– stakeholders and policy makers require
predictions
– research efforts must be directed towards
outputs which have stakeholder relevance
– large-scale EU and UK research programmes
have a significant component for integrating
predictive models at different levels of
biological organization
Existing approaches – ecosystem models
European Regional seas
Ecosystem Model
version run by PML
tends to treat organisms as black
boxes
efforts to refine this to reflect the
different performance of different
species
keystone species and ecosystem
engineers
requires inputs from organism life
history models
Existing approaches – life history models
Larval
pool
Juvenile
Adult
Size 1
Adult
Size 2
Adult
Size 3
Losses to the system from: mortality, predation, hydrodynamics, etc
– essentially concerned with reproductive output to predict numbers
– do not consider organism performance as such (e.g. how active is a
bioturbating species?)
– need input from organism physiology models
Existing approaches – organism physiology models (1)
Scope for growth (Bayne & Newell, 1983)
SFG = A - (R + U)
Scope for growth = assimilation – (respiration + excretion)
•
expressed in terms of energy (calories or joules)
•
A = C – [(C x %L/100) + L0 + F]
•
R = O2 consumed (ml O2 consumed. day-1)
•
U= ammonia excretion (ammonia-N in g.l-1)
•
calorific conversions for R and U are available from the literature
Saoud & Anderson, 2004
Litopenaeus setiferus
Existing approaches – organism physiology models (2)
SFG models are regarded as ‘net production models’
– empirically determined sequence for nutrition and resource
allocation based on allometry
– assume that assimilated energy is immediately available for
maintenance, the rest is used for growth or stored as reserves
Dynamic energy budget (DEB) models (Kooijman, 2000)
from Muller et
al. (2010)
DEB models
– assimilated energy is stored in reserves which are then used for
maintenance, growth, development and reproduction
– do not use allometric relationships, feeding rate is proportional to
surface area, maintenance scales to body volume
– ‘aim’ is for a generic theory of energy budgets
Existing approaches – organism physiology models (2)
(DEB) models for the Pacific oyster (Pouvreau et al., 2006)
Existing approaches – organism physiology models (2)
(DEB) models incorporating infection in Manila clams Rudtiapes
philippinarum (Flye-Sainte-Marie et al., 2009)
Existing approaches – organism physiology models (2)
(DEB) models incorporating heavy metal pollution in bivalves
(Muller et al., 2010)
Existing approaches – organism physiology models (2)
(DEB) models (oyster Crassostrea gigas model in STELLA™)
Integration of existing models
Organism
physiology
Organism life
history
Ecosystem
model
So what is the issue?
Limitation of DEB and SFG models (1) – a personal view
1) measurements of the impacts of perturbation in pCO2, temperature
and salinity are revealing sub-lethal changes in processes within ‘somatic
maintenance’
e.g. acid base balance, protein turnover, osmoregulation,
Ecosystem
immune function
model
Limitation of DEB and SFG models (1) – a personal view
1) measurements of the impacts of perturbation in pCO2, temperature
and salinity are revealing sub-lethal changes in processes within ‘somatic
maintenance’
e.g. acid base balance, protein turnover, osmoregulation,
Ecosystem
immune function
model
2) some are (presently) unpredictable or not intuitive, but will have an
impact on an organism performance when additional factors (e.g.
pathogens) are added to the environment
3) current models, despite intentions, appear species or condition
specific – a parsimonious solution is desired which accounts for all
environmental perturbation and which is truly generically applicable
Limitation of DEB and SFG models (2) – a personal view
4) at critical life stages (e.g. larvae, juveniles) or in some species
(polychaetes, small crustaceans or gastropods) only certain types of
physiological measurements are possible
- protein expression, gene expression, enzyme activities, rates of
protein turnover
- there is no convention on converting these to energy
equivalents
- a need to cope with rates and proportions or relative quantities?
Ecosystem
model
Summary
–
an end user need to predict the effects of future scenarios on
marine ecosystems
–
working towards this by developing our understanding of organism
physiology from laboratory studies and small-scale lab and field
mesocosm experiments
–
results indicate non linear and indirect effect of perturbations from
temperature and pCO2, acting in isolation and synergy
–
have yet to incorporate in these experiments issues such as
infection, pollution or salinity as multiplexed drivers
–
reliance on integrated modelling from organism physiology to life
history and thence ecosystem models
–
the challenge of incorporating disparate and high resolution
datasets (which are planned or being collected) into organism level
models (DEB or SFG) or alternatives… (process algebra?)
–
a need to be generic