Is the evolution of carnivory connected with genome size reduction?

Premise: As repeatedly shown, the remarkable variation in the genome size of angiosperms can be shaped by extrinsic selective pressures, including nutrient availability. Carnivory has evolved independently in 10 angiosperm clades, but all carnivorous plants share a common affinity to nutrient-poor habitats. As such, carnivory and genome reduction could be responses to the same environmental pressure. Indeed, the smallest genomes among flowering plants are found in the carnivorous family Lentibulariaceae, where a unique mutation in cytochrome c oxidase (COX) is suspected to promote genome miniaturization. Despite these hypotheses, a phylogenetically informed test of genome size and nutrient availability across carnivorous clades has so far been missing.

Methods: Using linear mixed models, we compared genome sizes of 127 carnivorous plants from 7 diverse angiosperm clades with 1072 of their noncarnivorous relatives. We also tested whether genome size in Lentibulariaceae reflects the presence of the COX mutation.

Results: The genome sizes of carnivorous plants do not differ significantly from those of their noncarnivorous relatives. Based on available data, no significant association between the COX mutation and genome miniaturization could be confirmed, not even when considering polyploidy.

Conclusions: Carnivory alone does not seem to significantly affect genome size decrease. Plausibly, it might actually counterbalance the effect of nutrient limitation on genome size evolution. The role of the COX mutation in genome miniaturization needs to be evaluated by analysis of a broader data set because current knowledge of its presence across Lentibulariaceae covers less than 10% of the species diversity in this family.