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

Durack & Wijffels (2010) J. Climate doi: 10.1175/2010JCLI3377.1

(pss/50-years) freshwater flux (m3 yr-1)

Issues of climate change – 3) CO2 and seawater acidification

‘the other CO2 problem’

Doney et al. (2009) Annual Reviews - Marine Science, 1

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)

3a) bicarbonate buffering…

carbonate dissolution…

Issues of climate change – 3) CO2 and seawater acidification

‘the other CO2 problem’

from Pörtner et al. (2004)

3b) disruption to acid base balance in osmoconformers

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)

Treatment

Control Nom. pH 7.8Nom. pH 7.6

CO

PIE

S m

RN

A.

g t

ota

l RN

A-1

0

2e+6

4e+6

6e+6

hsp70 gene

4.0e+6

2.4e+7

4.4e+7

6.4e+7

gapdh gene

*

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)

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

Issues of climate change – predictions by 2100?

However…

coastal and estuarine environments extremely variable

species which may have evolved strategies to accommodate extreme episodic low pH

Ringwood & Keppler, 2002

Attrill et al., 1999

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

Adult Size 1

Adult Size 2

Adult Size 3

Juvenile

Larval pool

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

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)

Existing approaches – organism physiology models (2)

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™)

Organism life history

Integration of existing models

Organism physiology

Ecosystem model

So what is the issue?

Limitation of DEB and SFG models (1) – a personal view

Ecosystem model

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, immune function

Limitation of DEB and SFG models (1) – a personal view

Ecosystem model

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, immune function 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

Ecosystem model

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?

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