Variation in nuclear DNA content across environmental gradients: a quantile regression analysis

The nuclear DNA content of angiosperms varies by several orders of magnitude. previous studies suggest that variation in 2C DNA content (i.e. the amount of DNA in G1 phase nuclei, also referred to as the 2C-value) is Correlated with environmental factors, but there are conflicting reports in the literature concerning the nature of these relationship,. We examined variation in 2C DNA content for 401 species in the ecologically diverse California flora in relation to the mean July maximum temperature, January minimum temperature, and annual precipitation within the geographical ranges of these species. Species with small 2C-values predominate in all environments. Species with large 2C-values occur at intermediate July maximum temperatures, and decline in frequency at both extremes of the July temperature gradient, and with decreasing annual precipitation. Our analysis demonstrates the utility of quantile regression for statistical inference of complex distributions such as these. The method supports our observation that relationships between nuclear DNA content and environmental factors are stronger for species with large 2C-values.