Genetics, Vol. 162, 755-765, October 2002, Copyright © 2002

Spontaneous Mutational Variation for Body Size in Caenorhabditis elegans

Ricardo B. R. Azevedoa, Peter D. Keightleyb, Camilla Laurén-Määttäc, Larissa L. Vassilievad, Michael Lynche, and Armand M. Leroia
a Department of Biology, Imperial College, Berks SL5 7PY, United Kingdom,
b Institute of Cell, Animal and Population Biology, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom,
c Centre for Population Biology, Imperial College, Berks SL5 7PY, United Kingdom,
d Department of Biology, University of Utah, Salt Lake City, Utah 84112
e Department of Biology, Indiana University, Bloomington, Indiana 47405-6801

Corresponding author: Ricardo B. R. Azevedo, University of Houston, Houston, TX 777204., razevedo{at}uh.edu (E-mail)

Communicating editor: T. F. C. MACKAY

We measured the impact of new mutations on genetic variation for body size in two independent sets of C. elegans spontaneous mutation-accumulation (MA) lines, derived from the N2 strain, that had been maintained by selfing for 60 or 152 generations. The two sets of lines gave broadly consistent results. The change of among-line genetic variation between cryopreserved controls and the MA lines implied that broad sense heritability increased by 0.4% per generation. Overall, MA reduced mean body size by ~0.1% per generation. The genome-wide rate for mutations with detectable effects on size was estimated to be ~0.0025 per haploid genome per generation, and their mean effects were ~20%. The proportion of mutations that increase body size was estimated by maximum likelihood to be no more than 20%, suggesting that the amount of mutational variation available for selection for increased size could be quite small. This hypothesis was supported by an artificial selection experiment on adult body size, started from a single highly inbred N2 individual. We observed a strongly asymmetrical response to selection of a magnitude consistent with the input of mutational variance observed in the MA experiment.




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