The biological importance of measuring individual variation

Abstract

SUMMARY Functional genomics research using Fundulus heteroclitus has focused on variation among individuals because of the evolutionary importance and value of Fundulus in explaining the human condition (why individual humans are different and are affected differently by stress,disease and drugs). Among different populations and species of Fundulus, there are evolutionarily adaptive differences in gene expression. This natural variation in gene expression seems to affect cardiac metabolism because up to 81% of the variation in glucose utilization observed in isolated heart ventricles is related to specific patterns of gene expression. The surprising result from this research is that among different groups of individuals, the expression of mRNA from different metabolic pathways explains substrate-specific metabolism. For example, variation in oxidative phosphorylation mRNAs explains glucose metabolism for one group of individuals but expression of glucose metabolism genes explains this metabolism in a different group of individuals. This variation among individuals has important implications for studies using inbred strains:conclusions based on one individual or one strain will not necessarily reflect a generalized conclusion for a population or species. Finally, there are surprisingly strong positive and negative correlations among metabolic genes,both within and between pathways. These data suggest that measures of mRNA expression are meaningful, yet there is a complexity in how gene expression is related to physiological processes.

Responses to iron limitation in two colonies of Stylophora pistillata exposed to high temperature: Implications for coral bleaching

“…The nubbins were chosen to provide an adequate representation of any regional physiological differences within each colony (Csá szá r et al 2009). This study design is appropriate to assess the physiological responses of individual colonies to iron limitation but cannot fully represent the broader metabolic response in the coral population (Crawford and Oleksiak 2007), which may involve genotypic variation in the defensive responses in S. pistillata. The latter goal would require the testing of multiple coral and endosymbiont genotypes simultaneously, with multiple replicates of each, which was logistically prohibited by the requirements for many closed chambers and extensive space in water baths to contain them for such an experiment.…”

Metabolism in the age of ‘omes’

“…Other researchers are not so pessimistic. For example, variation in mRNA coding for metabolic enzymes explained >80% of variation in the metabolic rates of Fundulus cardiac ventricles in vitro, despite large amounts of variation in both mRNA levels and ventricular metabolic rates across individuals (Crawford and Oleksiak, 2007). However, high throughput screening approaches applied to a wide variety of cell types reveals that positive correlation between mRNA and protein levels can range from as low as 9% to as high as 87% (Gracey, 2007;de Sousa Abreu et al, 2009).…”

Thermal variation, thermal extremes and the physiological performance of individuals

“…However, this focus draws attention away from the fact that contemporary patterns in biochemistry and physiology are products of selection on the variation that existed in the ancestors of present-day organisms. When confronted with changes in their environment, different individuals within a species can be quite variable in their response (Crawford and Oleksiak, 2007;Krebs and Feder, 1997;Nikinmaa and Waser, 2007;Williams, 2008). The sources and consequences of this variation are pivotal to understanding species' potentials to cope with changing environments (Whitehead and Crawford, 2006).…”