Does climate influence genome size diversity? A study of genome size-environment associations across the Madagascar grass flora

Repetitive DNA accumulation and whole genome duplication are common across angiosperm lineages, resulting in some of the largest ever-recorded genomes, yet the majority of angiosperm species have small genomes. This suggests selection may be acting to reduce genome size (GS), and there is growing evidence of environmental factors influencing GS diversity. This paper examines this relationship using a dataset of ecologically diverse Malagasy Poaceae across wide environmental gradients. Flow cytometry was used to estimate 1C-values for 92 grass species, and species mean values for four environmental variables – elevation, annual mean temperature, mean annual precipitation and temperature seasonality - were estimated using calculated alpha hulls. Phylogenetic comparative methods were then used to examine the relationship between GS and each of these variables. Significant linear relationships were found between GS and both elevation and annual mean temperature, while significant non-linear relationships were found between GS and both mean annual precipitation and temperature seasonality. The results also indicate that grass species with large genomes are excluded from extreme environments. Together, these results provide evidence for the Large Genome Constraint Hypothesis, suggesting that the physiological consequences of larger DNA content impact upon survival and growth under different climatic conditions.