Evolutionary ecology of polyploids: understanding species coexistence at the contact zones

The polyploid Aster amellus

Polyploidy has long been recognized as a major mechanism in plant speciation and evolution, occurring in up to 70% of the flowering plants and being distributed in numerous plant lineages. As new evolutionary entities can arise in a single genetic event, polyploidy has been proposed as an important mechanism of sympatric speciation. Facing the potential of polyploidy for sympatric speciation, several studies have addressed the ecological and genetic conditions governing the interactions between diploid and polyploids in mixed populations. The theories preview that under random mating, the establishment of a new cytotype will be subjected to strong frequency-dependent selection (minority cytotype exclusion) and new cytotype establishment and maintenance in mixed populations will occur only if a set of breeding barriers and/or ecological features promote assortative mating.

Figure 1. A. Flower of Aster amellus being visited by a Diptera. B. Experimental crosses between cytotypes being performed under controlled conditions at the experimental garden.

In this frame work, we are studying the breeding barriers involve in the maintenance of a diploid-hexaploid contact zone of the polyploidy Aster amellus (Figure 1A). Data on cytotype distribution, habitat and temporal segregation, pollinator behaviour and preferences, ability to cross (Figure 1B) and viability of the offspring is being investigated. This project is being developed by Sílvia Castro and Zuzana Münzbergová at the Department of Botany of the Charles University in Prague (Czech Republic).