DynamicEnergy Budget Theory - I Tânia Sousa withcontributionsfrom : Tjalling Yager& Bas Kooijman
EnvironmentalApplications • Toxicology • Which is the toxicity of the environmental concentration of a compound? • Which are the toxic effects of a compound? • Climate Change • Will an increase in 1ºC have a drastic impact on the distribution range of a species? • Waste water treatment plant • What are the necessary conditions to mantain an healthy microbian comunity in the biological reactors?
Human-made toxicants • Wide variety of uses • paints, detergents, solvents, pesticides, pharmaceuticals, polymers, … • probably some 100.000 compounds • Chemical industry is BIG business! • production value 2009: 3.4 trillion dollar (3.400.000.000.000 $) • equals the GDP of Germany • All are toxic, some are intended to kill • fungicides, insecticides, herbicides, nematicides, molluscicides, …
Human-made & natural toxicant Dioxins • e.g., 2,3,7,8-TCDD • human: paper and fiber bleaching, incineration of waste, metal smelting, cigarette smoke • natural: incomplete combustion of chlorine-containing things
Human-made vs. natural What is the difference? • Time scale • major increase after second world war • rapid development of new types of molecules • Spatial scale • amounts emitted • landscape and even global instead of local • Since 1970’s, most countries have programmes for environmental protection ...
Ecotoxicology • Daphnia reproduction test OECD guideline 211
Reproduction test wait for 21 days …
EC50 NOEC Dose-response plot total offspring log concentration
If EC50 is the answer … … what was the question? “What is the concentration of chemical X that leads to 50% effect on the total number of offspring of Daphnia magna (Straus) after 21-day constant exposure under standardised laboratory conditions?” • What does this answer tell me about other situations? • (almost) nothing!
Organisms are complex… • Response to stress depends on • organism (species, life stage, sex, …) • endpoint (size, reproduction, development, …) • type of stressor (toxicant, radiation, parasites, …) • exposure scenario (pulsed, multiple stress, …) • environmental conditions (temperature, food, …) • etc., etc.
E.g., effect on reproduction • To understand an effect on reproduction … • need to know how food is used to make offspring • and how chemicals interfere with this process
Why is DEB important for toxicity? • The use of DEB theory allows extrapolation of toxicity test results to other situations and other species • To study the effects of toxicity on life-history traits, DEB follows naturally • food is used to fuel all traits over the life cycle • toxicants affect DEB parameters • should allow extrapolation to untested conditions • it is valuable for environmental risk assessment
Whatis DEB theory? • It captures thequantitativeaspectsofmetabolismatthe individual level for allspecies • Whythehope for generality? • universalityofphysicsandevolution • Entropyproductionis >=0 • widespreadbiologicalempiricalpatterns
A widespreadbiologicalempiricalfact: VonBertalanffygrowth • Growth as a function of time • Depends on length at birth, maximum length and growth rate • It was proposed in 1938 by Von Bertalanffy an austrian biologist
Basic concepts in DEB Theory • Consistencywithotherscientificknowledge (thermodynamics, evolution, etc) • Consistencywithempirical data • Life-cycleapproach: embryo, juvenileandadult • Occam’srazor: the general modelshouldbe as simple as possible (andnot more)
A DEB organism • Metabolism in a DEB individual. • The boundary of the organism • Rectangles are state variables ME- Reserve MV - Structure MH - Maturity
DEB model: theStateVariables • What defines a DEB organism? • Biomass • Mv - Massof Reserve • ME - MassofStructure • Life-Cycleapproach: differentlifestages • MH - LevelofMaturity (itrepresentsneithermassnorenergy) • Whataboutotherpossiblesstatevariablessuch as age?
Not age, but size Trichopsis vittatus These gouramis are from the same nest, they have the same age and lived in the same tankSocial interaction during feeding caused the huge size differenceAge-based models for growth are bound to fail; growth depends on food intake
DEB model: Reserve andStructure • Stronghomeostasis • Reserve & Structurehaveconstantaggregatedchemicalcomposition • Weakhomeostasis • Atconstantfoodorganismstend to constantaggregatedchemicalcomposition • Why more than 1 statevariable to define thebiomass? • Theaggregatedchemicalcompositionoforganismsisnotconstant – itchangeswiththegrowth rate • Whynot use thousandsofchemicalspecies to define theorganism? • Two are sufficient (in animalsandbacteria) to capture thechange in aggregatedchemicalcompositionwiththegrowth rate • Strong & Weakhomeostasis -> highercontrolovermetabolism
DEB model: Maturity • LifeStages (darkblue) andtransitions (light blue) • Essentialswitchpoints for metabolicbehavior • Birth (startoffeeding) • Puberty (startofallocation to reproduction) • Switchpointssometimes in reversedorder (aphids) embryo juvenile adult baby infant weaning fertilization birth death puberty MHb- thresholdofmaturityatbirth MHp- thresholdofmaturityatpuberty
Notation 2 General Indices for compounds Indices for transformations
A DEB organism • Metabolism in a DEB individual. • Rectangles are state variables • Arrows are flows of foodJXA, reserveJEA, JEC, JEM, JET, JEG, JER, JEJor structureJVG. • Circles are processes Feeding ME- Reserve Assimilation MV - Structure MH - Maturity
Feeding & Assimilation • Feeding: theuptakeoffood • Assimilation: conversionofsubstrate (food, nutrients, light) into reserve(s) • Dependsonsubstrateavailability& structuralsurfacearea (e.g. surfaceareaofthegut) - surfacemaximumassimilation rate -yield of reserve onfood • Empiricalpattern: theheatincrementoffeedingsuggeststhatthere are processes onlyassociatedwithfoodprocessing • Stronghomeostasisimposes a fixedconversionefficiency • Consistencywithotherfields: masstransferisproportional to area
Intra-taxon predation: efficient conversionyEX a high yield of reserve on food Hemiphractus fasciatus is a frog-eating frog Beroe sp is a comb jelly-eating comb jelly Solaster papposus is a starfish-eating starfish Chrysaora hysoscella is a jelly fish-eating jelly fish Coluber constrictor is a snake-eating snake Euspira catena is a snail-eating snail
Intra-taxon predation: efficient conversionyEX a high yield of reserve on food Asplanchna girodi is a rotifer-eating rotifer Didinium nasutum is a ciliate-eating ciliate Esox lucius is a fish-eating fish Acinonyx jubatus is a mammal-eating mammal Enallagma carunculatum is a insect-eating insect Falco peregrinus is a bird-eating bird