Polyploidy is thought to be an important driver of plant evolution by facilitating diversification, yet the mechanisms behind the ecological success of individual polyploid species remain poorly understood. Numerous studies have examined broad patterns of species niche overlap and separation between polyploid and diploid plants and many have reported significant niche differentiation. However, few studies have taken trait-based approaches to understand broad-scale niche differentiation between polyploid and diploid progenitor species. Despite the importance of polyploidy in plant evolution, no study has examined if/how broad-scale patterns of niche differentiation are explained by the evolution of novel ecophysiological traits after polyploidization. This work presented here integrates ecophysiology and niche modelling to better understand the evolution of novel traits and their role in driving niche divergence, using species in the North American Polystichum polyploid complex as a model system. Several ecophysiological traits were measured in over 35 populations across the geographic ranges of two parental diploids and their allopolyploid offspring.
Results/Conclusions
Analyses show strong trait by environment relationships in all three species. For example, traits related to gas-exchange, such as mesophyll conductance (gm) and maximum carboxylation rate (Vcmax) were positively correlated with growing season temperatures at the broadest geographic scale. However, multivariate analyses show significant differences in trait combinations among species where at least two species co-occur. Comparative multidimensional analyses of species trait space within shared niche space vs novel niche space occupied only by the polyploid species revealed transgressive changes in hydraulic anatomy in the polyploid species in the driest part if its distribution. Ongoing work will shed more light on how polyploidy may drive the evolution of novel ecophysiological traits conferring competitive advantages and transgressive physiological tolerances in this polyploid fern complex.