[en] Senecio inaequidens DC. was introduced from South Africa to Europe more than one hundred years ago, in a few precise locations linked to wool industry and extended its distribution throughout Europe. In a context of global warming, the potential evolution in germination and growth during the invasion process was studied in relation to altitude and climate. Seeds were collected along two transects (both altitudinal and climatic) in Belgium and France, going from the sea level to high altitudes (respectively 485 m and 1700 m) through the introduction spots. Respectively four and five climatic zones per transect, two populations per zone and ten randomly selected individuals per population were sampled. Seeds were sorted in order to discard maternal effects. Ten seeds per parent individual were thereafter sown in pots in a common garden experiment in Gembloux (Belgium). Germination was checked every two days. Height and diameter of plants, enabling the calculation of plant volume, were measured every 25 days.
Despite an important variability, linear regression of first germination time (since sowing) vs altitude was significant (p = 0.001) for the French gradient, but not for the Belgian one. No significant difference was found in germination rate between climatic zones. For each of the three measurement times of plant height and diameter, regression of plant volume vs altitude was also significant for the French transect (p varying from 0.025 to 0.000 according to time), but not for the Belgian one. French plants from elevated locations germinated later and grow slowlier.
These preliminary results suggest that contrasted climatic conditions in the French gradient, going from the Mediterranean coast to the Pyrrenean high elevations led to genetic differenciation of Senecio populations during its invasion in southern France. Less contrasted climatic conditions, together with a supposed loss of genetic variability (Lafuma 2003), did not lead to a clear differenciation in Belgium.
References :
Lafuma, L. (2003). L'invasion de Senecio inaequidens (Asteraceae) en Europe: une approche évolutive. PhD thesis, Montpellier University.
