Does genome size affect contemporary rates of phenotypic change?

Background/Question/Methods

Populations must continuously respond to environmental changes or they risk extinction. Those responses can be measured as phenotypic rates of change, which can allow us to predict contemporary adaptive responses, some of which are evolutionary. The genome size has been linked to the rate of diversification in different taxa. In particular, the rates of speciation and the increment in genome size are positively correlated across land plants and multiple rounds of whole genome duplication correlate strongly with morphological innovation in vertebrates. Furthermore, larger genome sizes are more prone to mutation. We expect that larger genome sizes are related to larger rates of phenotypic change, due to higher amounts of genetic variance for those species. Here, we update the Phenotypic Rates of Change Evolutionary and Ecological Database (PROCEED), by adding more than 2000 new estimates (bringing it from 7338 estimates of phenotypic change to more than 9500) to assess the relationship between the genome size (C value, pg) and rates of change. We analyzed two evolutionary metrics, ‘haldanes’ and ‘darwins’, as well as the related variability of the traits by applying linear mixed models. The species identity and the specific study systems were included as nested random factors in the analyses.

Results/Conclusions

Preliminary results show that, after controlling for a number of biological and methodological variables known to affect rates of phenotypic change (e.g. the elapsed time, data type, the observational or experimental design, the kind of environmental disturbance driving the change, the taxa and the type of trait measured), the C value has an effect on the different rates of change. On average, each additional pg of DNA increases the rate of change by about 10%, but only in the few first generations. The effect of the genome size on the rate of change depends on the taxa, being positive for all but fishes, and trait type, having a larger effect on phenological traits. However, the analysis of the variability of traits shows a different picture, the relation being negative between the C value and the variance in phenological traits. So, the genome size seems a relevant biological feature underpinning the short term evolvability of populations facing new environmental change but it seems not to be mediated by an increment in the total variability of populations.