Polyploidization as driver for plant invasions into mountains

Background/Question/Methods

Polyploidization may result in changes e.g. in morphological or physiological plant traits within short time periods. Thus, it may be one mechanism favoring a species to become invasive outside its native range. Polyploids are supposed to have a broader ecological tolerance, e.g. an increased cold tolerance, and thus colonize a wider range of environmental conditions. Patterns along latitudinal gradients show a positive correlation of polyploidy with latitude. This goes in line with the assumption that stressful conditions in marginal habitats favor spontaneous polyploidization. However, such a correlation could not been shown for elevation patterns. Plant invasions in mountains are mainly shaped by a lowland introduction filter; i.e. alien species are introduced at low elevations and spread from there to higher elevations. First, they mostly spread along roads which are the main introduction pathway, but later some species spread from these ruderal sites into more natural habitats. With survey data recorded along an elevation gradient on the island of Tenerife we test the hypotheses that (1) polyploid alien plant species reach higher elevations and occupy a wider elevation range than diploid species, and that (2) polyploids spread more frequently and further away from roadsides.

Results/Conclusions

Along the elevation gradient we found 58 alien plant species that fitted in our target group of annual herbs. Thirteen of them were polyploid, 45 were diploid. We classified species as old and recent introductions to account for a possible effect of residence time on species distribution patterns. Within polyploid species we had seven old and six recently introduced species, while these were 27 and 18, respectively, for diploid species. Polyploids had a significantly wider elevation range than diploid species. Although not significant, they seem to expand their elevation range over time, while the diploid’s ranges remained constant. Polyploids also tended to invade natural habitats more frequently than diploids, i.e. from the species occurring at the roadsides a higher proportion of polyploids spread away from the road. Our results suggest that a higher ploidy level supports alien plant invasions in mountains and also enables species to invade native communities. This might be related to a broader environmental tolerance or a higher adaptation potential due to an increased genetic variability. Additionally, polyploids may benefit from genome downsizing which can favor a species’ “weedy” behavior.