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, altitudinal 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 2× to 12×. Phylogenetic relatedness explained little of the variation in ploidy, range breadth, and abiotic breadth. Transitions to higher ploidy were associated with reduced latitudinal and altitudinal 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.