RESUMO
Hybridization between exotic and native species is of great interest to evolutionary biologists and ecologists because it usually shows a quick evolution of species and invasiveness. It has been reported that such hybridization frequently increases the adaptation and aggressiveness of the new hybrids. A hybrid between invasive Sphagneticola trilobata and its native congener S. calendulacea was recently found in subtropical China. S. calendulacea has a significantly higher tolerance to low temperature and weak light stress than S. trilobata, and its range includes both tropical and temperate regions. This study examined how the tolerance of the new hybrid to low temperature and weak light conditions (LTWL), expanded its geographical range. All changes of phenotype, gas exchange parameters, chlorophyll fluorescence parameters, contents of malonaldehyde (MDA) and activity of superoxide dismutase (SOD) and peroxidase (POD) indicated that hybridization slightly catalyzed the tolerance of the hybrid to LTWL condition and the responses of the hybrid were more similar with their invasive parent. The results demonstrate that the current hybrid populations may not expand their geographical distribution ranges in a short period, but the distribution of the backcrossed generations is still uncertain. The threat of the hybrid to its native parent in subtropical region should be concerned.
