Higher ploidy is associated with reduced range breadth in the Potentilleae tribe

PREMISE OF THE STUDY: Polyploids are predicted to have greater niche breadth and larger ranges than diploids because of higher ecological tolerances, self-compatibility, and increased genetic variation. However, empirical support for this prediction is mixed, and most studies compare diploids and polyploids, rather than accounting for quantitative variation in ploidy. We test the prediction that species of higher ploidy have greater range breadth and abiotic breadth than those of lower ploidy. METHODS: We estimate range breadth (latitudinal range, attitudinal range, and range size) and abiotic breadth (range in temperature, precipitation, and ultraviolet-B irradiance) for 109 species in the Potentilleae tribe of Rosaceae. We assess the contribution of ploidy to variation in range breadth, while accounting for shared evolutionary history and time of species divergence using phylogenetic comparative methods. KEY RESULTS: Ploidy varied widely among species from 2x to 12x. Phylogenetic relatedness explained little of the variation in ploidy, range breadth, and abiotic breadth. Transitions to higher ploidy were associated with reduced latitudinal and attitudinal ranges, smaller overall range size, and reduced abiotic breadth for temperature and UV-B. CONCLUSIONS: In contrast to predictions, this study shows that transitions to higher ploidy are associated with reduced range size and abiotic breadth. It also highlights the importance of considering continuous variation in ploidy when evaluating ecological correlates with ploidy. We discuss how genome duplication may contribute to the observed negative relationship between ploidy and range breadth.