Abstract
Keywords: Thermal reaction norm, phenotypic plasticity, enzyme kinetics, temperature, development rate, growth rate, body size, Drosophila, anura, thermal adaptation, thermal tolerance limits, reversible temperature inactivation, cell cycle, Sharpe – Schoolfield equation, degreeday summation, tradeoff.
This thesis investigates to what extent the thermodynamics of biological rates constrains the thermal adaptation of developing ectotherms. The biophysical Sharpe – Schoolfield model is applied to explain the temperature dependence of body size in ectotherms, to predict the temperature tolerance limits in developing ectotherms and to predict patterns of thermal adaptation within and among species. If the Sharpe – Schoolfield equation is applied to model the temperature dependence of growth and differentiation rate separately, then the temperature dependence of size at maturity follows from the interaction between these processes. Recent studies have shown that this approach provides an explanatory framework for all ectotherms, which obey the Temperature – size Rule, the observation that ectotherms at high temperatures grow and develop faster to a smaller size at maturity compared to low temperatures, but also to the exceptions of this rule.
The Sharpe – Schoolfield equation basically consist of two parts: the numerator, which is formed by the Eyring equation, models the exponential increase of reaction rates with temperature based on reaction kinetics, and the denominator, which describes the reversible temperatureinduced inactivation of enzymes. If the denominator is applied to a genetic control system of the cell cycle, it can be shown that the temperature tolerance limits are accurately predicted in a range of insect species. It is argued that reversible temperatureinduced inactivation of regulatory components of the cell cycle mimics the dosage change during the cell cycle. The Eyring equation is also successfully applied to crossspecies comparisons of thermal adaptation in a large group of related frogs and toads. The recently developed model of Universal Temperature Dependence is critically discussed and it is argued that the predictions are partly based on incorrect assumptions and biased use of literature data. Furthermore, the supposed invariant biophysical parameters may vary in response to thermal adaptation.
When ectotherms adapt to lower temperatures (horizontal shift) a correlated response occurs of a wider thermal range (specialist – generalist shift), a smaller slope (sensitivity shift) and lower activity (vertical shift). This correlated response is mainly determined by the Eyring equation. The enzyme activity – stability tradeoff is the most important thermodynamic constraint and limits the viable development of most ectotherms to a relative small thermal tolerance range of approximately 20 °C. It is argued that this correlated response does not limit evolution within thermal environments, but instead may be one of the drivers of evolution and consequently biodiversity. The overall conclusion is that the biophysical Sharpe – Schoolfield equation is an excellent model to study thermal adaptation in ectotherms.
This thesis investigates to what extent the thermodynamics of biological rates constrains the thermal adaptation of developing ectotherms. The biophysical Sharpe – Schoolfield model is applied to explain the temperature dependence of body size in ectotherms, to predict the temperature tolerance limits in developing ectotherms and to predict patterns of thermal adaptation within and among species. If the Sharpe – Schoolfield equation is applied to model the temperature dependence of growth and differentiation rate separately, then the temperature dependence of size at maturity follows from the interaction between these processes. Recent studies have shown that this approach provides an explanatory framework for all ectotherms, which obey the Temperature – size Rule, the observation that ectotherms at high temperatures grow and develop faster to a smaller size at maturity compared to low temperatures, but also to the exceptions of this rule.
The Sharpe – Schoolfield equation basically consist of two parts: the numerator, which is formed by the Eyring equation, models the exponential increase of reaction rates with temperature based on reaction kinetics, and the denominator, which describes the reversible temperatureinduced inactivation of enzymes. If the denominator is applied to a genetic control system of the cell cycle, it can be shown that the temperature tolerance limits are accurately predicted in a range of insect species. It is argued that reversible temperatureinduced inactivation of regulatory components of the cell cycle mimics the dosage change during the cell cycle. The Eyring equation is also successfully applied to crossspecies comparisons of thermal adaptation in a large group of related frogs and toads. The recently developed model of Universal Temperature Dependence is critically discussed and it is argued that the predictions are partly based on incorrect assumptions and biased use of literature data. Furthermore, the supposed invariant biophysical parameters may vary in response to thermal adaptation.
When ectotherms adapt to lower temperatures (horizontal shift) a correlated response occurs of a wider thermal range (specialist – generalist shift), a smaller slope (sensitivity shift) and lower activity (vertical shift). This correlated response is mainly determined by the Eyring equation. The enzyme activity – stability tradeoff is the most important thermodynamic constraint and limits the viable development of most ectotherms to a relative small thermal tolerance range of approximately 20 °C. It is argued that this correlated response does not limit evolution within thermal environments, but instead may be one of the drivers of evolution and consequently biodiversity. The overall conclusion is that the biophysical Sharpe – Schoolfield equation is an excellent model to study thermal adaptation in ectotherms.
Original language  English 

Qualification  Doctor of Philosophy 
Awarding Institution 

Supervisors/Advisors 

Award date  8 Jan 2008 
Place of Publication  Wageningen 
Publisher  
Print ISBNs  9789085047483 
Publication status  Published  2008 
Keywords
 temperature
 heat adaptation
 body temperature
 body temperature regulation
 phenotypes
 biological development
 growth rate
 heat tolerance
 cell cycle
 simulation models
 anura
 drosophila