Polyploidy associated with altered and broader ecological niches in the Claytonia perfoliata (Portulacaceae) species complex

Abstract

Premise of the study: Polyploids are often hypothesized to have distinct and broader niches than their diploid progenitors. Differences in geographic distributions between diploid and polyploids are frequently used to infer niche differentiation and increased breadth, but they are seldom used to test these hypotheses explicitly.

Methods: Niche overlap and breadth were compared for diploids, tetraploids, and hexaploids of three taxa in the Claytonia perfoliata complex (C. parviflora, C. perfoliata, and C. rubra) with the use of species distribution models. Resampling and randomization approaches were used to test hypotheses of niche differentiation, breadth, and conservatism.

Key results: Niche differentiation was detected between polyploid and diploid cytotypes assigned to the same taxon (e.g., C. parviflora 2× vs. 4×) but not between hexaploids and tetraploids within a taxon (e.g., C. parviflora 4× vs. 6×). Individual hexaploid cytotypes had broader ecological niches than individual diploid cytotypes. However, as a group the three hexaploid taxa did not exceed the combined niche breadth of the three diploids, suggesting that polyploidy does not result in transgressive niche breadth for this group. Niche overlap was lowest among diploids and was highest among the three hexaploid cytotypes, consistent with introgression associated with polyploidy resulting in greater ecological similarity. Although cytotypes possessed nonidentical niches, after accounting for environmental differences among ranges, cytotypes were more similar than expected, suggesting niche conservatism and similar responses to environmental characteristics.

Conclusions: These results suggest that polyploids occupy distinct and broader niches relative to diploids but that cytotypes also share fundamentally similar responses to environmental variation across ploidy levels.