Bryophytes, champions of dispersal

Specialising in island bio-geography, Alain Vanderpoorten’s research unit analyses spore producing plants, and more particularly bryophytes. ‘They were the first plants to have colonised the land. They propagate by producing spores and spread more easily than seed producing plants and animals,’ stresses the scientist. In effect, having a size of no more than a few dozen of micrometres and being very light, spores are easily carried by the wind over large distances. Furthermore, the spores of numerous bryophytes have an unequalled tolerance and resistance to extreme conditions. ‘During their migrations, carried hither and thither by the winds, spores can survive  weather conditions which seeds cannot resist,’ adds Alain Vanderpoorten. Bryophytes thus have a very high dispersal power.

We might thus ask ourselves the following question: does the theory of ‘migratory and evolutionary dead-end islands’ hold for organisms equipped with such potential for dispersal? Within the context of the thesis she worked on within Alain Vanderpoorten’s team, Virginie Hutsemekers has attempted to clear away the undergrowth and reply to this question. To do so, the researchers chose to study the dispersal of the moss Platyhypnidium riparioides between the mid-Atlantic oceanic islands (the Azores, Madeira and the Canary Islands) and the continental lands of southern Europe and North Africa. ‘Plant dispersal is something which is very difficult to study as it cannot be observed directly,’ points out Alain Vanderpoorten. ‘We thus try to estimate it by indirect methods, in studying the genetic structure of various populations. The more populations which are distinct from a geographic point of view have different alleles, the stronger is the genetic structure of these populations. That means that there has been no (or little) dispersion between these two geographical points and that therefore there has been no genetic homogenisation of the populations,’ he continues.