Behaviour is considered among the most important factors in colonising new habitats. While population divergence in behaviour is well-documented, intraspecific variation in exploratory behaviour in species with populations successfully colonising and adapting to extreme (compared to the ‘typical’) habitats is less understood. Here, by studying surface- vs. cave-adapted populations of water louse (Asellus aquaticus), we tested whether (i) adaptation to the special, ecologically isolated cave habitat includes a decrease in explorativeness and (ii) recent, surface-type cave colonists are more explorative than their surface conspecifics from the source population. We repeatedly tested dispersal related novel area exploration and dispersal speed in both the presence and absence of light. We found that surface populations showed higher behavioural activity in dark than in light, and they were more explorative and dispersed faster than their cave conspecifics. Recent colonists showed a trend of higher dispersal speed compared to their source surface population. We suggest that extreme and isolated habitats like caves might work as ‘dispersal traps’ following successful colonisation, because adaptation to these habitats includes the reduction of explorativeness. Furthermore, we suggest that individuals with higher explorativeness are likely to colonise markedly new environments. Finally, we provide experimental evidence about surface A. aquaticus moving more in dark than in light.
