Origin, elevation, and evolutionary success of hybrids and polyploids in British Columbia, Canada

Although it is well established that many clades have polyploidization in their evolutionary history, the question of whether polyploidization is actually adaptive is far from resolved. It has been hypothesized that the evolutionary advantages of polyploidy are context-dependent, although we have yet to clearly identify the geographical or ecological contexts in which polyploids are more common. One reason why polyploidy may be displaying idiosyncratic ecological patterns is that previous comparative studies have often not separated polyploids into allopolyploids and autopolyploids, and we posit that there may be important differences in the origin and evolutionary success between the two types. Here, we examine the distribution of allopolyploid, autopolyploid, and diploid hybrid species along an elevation gradient from sea level to -4500 m within British Columbia, Canada, and find that polyploids (especially those of hybrid origin) are disproportionately present at high elevations. These processes of hybridization and polyploidization may contribute to species richness patterns observed in British Columbia. We discuss whether the associations are more likely to be the result of differential ecological tolerance or differential origination rates of allopolyploids at higher elevations. These findings highlight the importance of studying both hybridization and polyploidy when considering the diversification process in plants. Key words: polyploidization, elevation gradients, allopolyploidy, autopolyploidy, hybridization. Bien qu'il soit bien etabli que plusieurs clades possedent de la polyploidisation dans leur histoire evolutive, la question a savoir si la polyploidisation est reellement adaptative demeure entiere. On a forme l'hypothese que les avantages evolutifs de la polyploidie dependent du contexte dans lequel les polyploides sont les plus communs. Une raison pour laquelle la polyploidie montrerait des patrons ecologiques idiosyncrasiques est que les etudes comparatives anterieures n'ont souvent pas separe les polyploides en allopolyploides et autopolyploides; les auteurs soumettent qu'il pourrait y avoir des differences importantes dans l'origine et le succes evolutif entre les deux types. Ils examinent ici la distribution des allopolyploides, autopolyploides et diploides par espece, le long d'un gradient d'elevation allant du niveau de la mer jusqu'a -4500 m en Colombie Canadienne, au Canada, et constatent que les polyploides (surtout d'origine hybride) montrent une presence disproportionnee aux hautes altitudes. Ces processus d'hybridation et de polyploidisation pourraient contribuer aux patrons de richesse observes en Colombie Canadienne. Les auteurs discutent a savoir si les associations sont plus susceptibles de resulter de tolerances ecologiques differentielles ou de taux d'origine differentiels des alloplolyploides aux hautes altitudes. Ces constatations soulignent l'importance d'etudier a la fois l'hybridation et la polpyploidie lorsque l'on considere le processus de diversification chez les vegetaux. Mots-cles: polyploidisation, gradients d'elevation, allopolyploidie, autopolyploidie, hybridation.
Introduction Polyploidy and interspecific hybridization occur frequently in plants and can affect genetic diversity, adaptation, and diversification. For instance, polyploid speciation is recently estimated to have been involved in at [...]