Mutational Bias for Body Size in Rhabditid Nematodes

¹ University of Florida

^* To whom correspondence should be addressed. E-mail: cbaer{at}zoo.ufl.edu.

Submitted on April 16, 2007
Revised on April 30, 2007
Accepted on 30 April 2007

	Abstract

Mutational bias is a potentially important agent of evolution, but it is difficult to disentangle the effects of mutation from those of natural selection. Mutation accumulation experiments, in which mutations are allowed to accumulate at very small population size, thus minimizing the efficiency of natural selection, are the best way to separate the effects of mutation from those of selection. Body size varies greatly among species of nematode in the family rhabditidae; mutational biases are both a potential cause and consequence of that variation. We report data on the cumulative effects of mutations that affect body size in three species of rhabditid nematode that vary five-fold in adult size. Results are very consistent with previous studies of mutations underlying fitness in the same strains: two strains of Caenorhabditis briggsae decline in body size about twice as fast as two strains of C. elegans, with a concomitant higher point estimate of the genomic mutation rate; the confamilial Oscheius myriophila is intermediate. There is an overall mutational bias, such that mutations reduce size on average, but the bias appears consistent between species. The genetic correlation between mutations that affect size and those underlying fitness is large and positive, on average.

Key Words: Caenorhabditis, mutation accumulation, mutation rate, mutational correlation, mutational variance

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