The ecology and genetics of fitness in Chlamydomonas. I. Genotype-by-environment interaction among pure strains

  • Bell G
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Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Strains of Chlamydomonas were cultured in different macroenvironments created by manipulating levels of nitrate, phosphate and bicarbonate in liquid growth media. Cell density, measured by optical transmittance, increased in a density-regulated manner, permitting the logistic par-ameters r and K to be estimated for each genotype-environment combi-nation. The main empirical results of a factorial experiment were as follows. (i) A large proportion of the overall genotypic variance in fitness measures was attributable to genotype-by-environment (G x E) interac-tion: 65 % for r and 50 % for K. Variance components for r and K were uncorrelated, but components of the interaction variance may have been correlated with corresponding components of the environmental variance, such that the relative fitness of genotypes was most strongly affected by environmental factors that have the greatest effect on average fitness. Higher-order interactions were as large as lower-order inter-actions, so that relative fitness was sensitive to particular combinations of environmental factors as well as to their main effects. The covariance of r with K also showed strong G x E interaction, being negative in some macroenvironments and zero in others. (ii) An 'environmental' decomposition of the G x E interaction vari-ance separates 'inconsistency', due to lack of complete correlation between genotypes over macroenvironments, from 'responsiveness', due to differences between environmental variances among genotypes. Incon-sistency was much the larger component for both r and K, showing that the greater part of the interaction variance was created by changes in the ranking of genotypes with respect to fitness between macroenvironments. When reaction norms were defined as the linear regressions of genotypic value on mean environmental value, substantial variance among reaction norms was detected: nonlinear effects were also large. (ii) A 'genetic' decomposition of the G xE interaction variance

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  • G. Bell

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