Asexual species change just as often and just as fast as do sexual species when introduced to a new range

Background/Question/Methods

Some of the world’s most economically and environmentally damaging introduced species reproduce asexually. While sexually reproducing introduced herbs have proven capable of rapid evolution, no previous study has quantified morphological changes in obligatory asexually reproducing introduced species, or asked whether their potential for change differs from that of sexual species. We measured herbarium specimens of 8 asexual species introduced to Australia and/or New Zealand.  The herbaria records were sampled to quantify changes in leaf area, leaf shape, leaf mass per area, plant height, and internode length through time since the species’ introduction.

Results/Conclusions

Rates of change and proportion of species showing at least one significant morphological trait change through the study time was compared to the same kind of data for 34 sexual species. Half of the asexual species demonstrated significant change in at least one trait. The observed changes were substantial - up to 561% per 100 years. The proportion of species showing at least one significant morphological change did not differ significantly between sexual and asexual introduced plant species. There was also no significant difference in the rate of morphological change in sexual vs asexual species. Our results challenge the classic assumption that sexuality should enable a faster rate of morphological change and indicate that asexually reproducing plants may be able to adapt to changing conditions better than was previously appreciated.