Abstract. Understanding the utility and limitations of molecular markers for predicting the evolutionary potential of natural populations is important for both evolutionary and conservation genetics. To address this issue, the distribution of genetic variation for quantitative traits and molecular markers is estimated within and among 14 permanent lake populations of Daphnia pulicaria representing two regional groups from Oregon. Estimates of population subdivision for molecular and quantitative traits are concordant, with Q ST generally exceeding G ST . There is no evidence that microsatellites loci are less informative about subdivision for quantitative traits than are allozyme loci. Characterspecific comparison of Q ST and G ST support divergent selection pressures among populations for the majority of lifehistory traits in both coast and mountain regions. The level of within-population variation for molecular markers is uninformative as to the genetic variation maintained for quantitative traits. In D. pulicaria, regional differences in the frequency of sex may contribute to variation in the maintenance of expressed within-population quantitative-genetic variation without substantially impacting diversity at the genic level. These data are compared to an identical dataset for 17 populations of the temporary-pond species, D. pulex.

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Understanding the impact of spontaneous mutations on fitness has many theoretical and practical applications in biology. Although mutational effects on individual morphological or life-history characters have been measured in several classic genetic model systems, there are few estimates of the rate of decline due to mutation for complex fitness traits. Here, we estimate the effects of mutation on competitive ability, an important complex fitness trait, in a model system for ecological and evolutionary genomics, Daphnia. Competition assays were performed to compare fitness between mutation-accumulation (MA) lines and control lines from 8 different genotypes from two populations of D. pulicaria after 30 and 65 generations of mutation accumulation. Our results show a fitness decline among MA lines relative to controls as expected, but highlight the influence of genomic background and genotype on this effect. In addition, in some assays MA lines outperform controls providing insight into the frequency of beneficial mutations.

Understanding how genetic variation is generated and how selection shapes mutation rates over evolutionary time requires knowledge of the factors influencing mutation and its effects on quantitative traits. We explore the impact of two factors, genomic background and generation time, on deleterious mutation in Daphnia pulicaria, a cyclically parthenogenic aquatic microcrustacean, using parallel mutation-accumulation experiments. The deleterious mutational properties of life-history characters for individuals from two different populations, and for individuals maintained at two different generation times, were quantified and compared. Mutational properties varied between populations, especially for clutch size, suggesting that genomic background influences mutational properties for some characters. Generation time was found to have a greater effect on mutational properties, with higher per-generation deleterious mutation rates in lines with longer generation times. These results suggest that differences in genetic architecture among populations and species may be explained in part by demographic features that significantly influence generation time and therefore the rate of mutation.A S the ultimate source of all genetic variation, mutation is an important evolutionary force affecting the ability of natural populations to respond to selective pressures. Most spontaneous mutations are deleterious (Lynch et al. 1999;Eyre-Walker and Keightley 2007), which is thought to explain many evolutionary phenomena, including inbreeding depression, mating system evolution, senescence, and risk of extinction to small populations Lynch et al. 1999). Despite the importance of knowing mutation rates in both theoretical and applied biology, few empirical estimates exist other than those for classic genetic model organisms (Baer et al. 2007), and little is known about the factors influencing the rate of mutation among individuals, populations, and species (Lynch 2010).In addition to direct estimates based on sequencing, estimates of the parameters for mutations affecting fitness [i.e., the genome-wide deleterious mutation rate (U) and the average effect (š)] have now been reported for several species (reviewed in Baer et al. 2007). However, little empirical attention has been given to variability in the phenotypic effects of deleterious mutation [i.e., per-generation rates of change in the mean phenotype (DM) and mutational variance (DV)] or to the associated deleterious mutation parameters that can be inferred from these quantities (U andš) among populations within a species. Recent theoretical treatments of mutation-rate evolution, however, predict individual variation in mutation rates (Lynch 2008;Desai and Fisher 2011) and fitness dependence of mutation rates (Agrawal 2002;Shaw and Baer 2011), highlighting the importance of this variability.The deepest understanding comes from recent mutationaccumulation studies in Drosophila melanogaster that provide evidence for variability in mutation rates among genotypes, using bot...

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