Genetic population differentiation due to environmental stress is a widespread and well studied phenomenon. Yet, despite extensive theoretical and empirical research, its evolutionary consequences remain largely unknown. One of the key questions is whether local adaptation to environmental stress may trigger reproductive isolation and may subsequently lead to speciation. Prezygotic reproductive isolation is believed to involve different non-exclusive processes, i.e.

1. sexual selection resulting in assortative mating;
2. direct or indirect differentiation of secondary sexual characteristics due to natural selection or genetic drift;
3. condition-dependence of male mating signals (i.e. males that are maladapted to the stressor bear a fitness cost); and
4. energetic constraints rendering mating more costly under stress.

Postzygotic mechanisms, too, may cause reproductive isolation, whether or not in combination with prezygotic ones. Research at the intraspecific level offers an excellent opportunity to investigate speciation processes at the root and in action.

The main aim of this study is to determine whether reproductive isolation occurs between populations originating from stressed versus unstressed habitat, and if so, what are the underlying mechanisms. This question is addressed through a combination of field experiments, controlled laboratory experiments and genetic analysis on populations of wolf spiders (Pirata piraticus and Pardosa saltans). They originate from heavy-metal polluted sites along the Schelde, former zinc quarries in the province of Luik and reference sites in the same regions. Previous research already uncovered the existence of life history trait differentiation between populations of P. piraticus.