Exploratory behaviour divergence between surface populations, cave colonists and a cave population in the water louse, Asellus aquaticus

Abstract

Behaviour is considered among the most important factors in colonising newhabitats. While population divergence in behaviour is well-documented, intraspecificvariation in exploratory behaviour in species with populations successfully colonising andadapting to extreme (compared to the ‘typical’) habitats is less understood. Here, by studyingsurface- vs. cave-adapted populations of water louse (Asellus aquaticus), we tested whether (i)adaptation to the special, ecologically isolated cave habitat includes a decrease inexplorativeness and (ii) recent, surface-type cave colonists are more explorative than theirsurface conspecifics from the source population. We repeatedly tested dispersal related novelarea exploration and dispersal speed in both the presence and absence of light. We found thatsurface populations showed higher behavioural activity in dark than in light, and they weremore explorative and dispersed faster than their cave conspecifics. Recent colonists showed atrend of higher dispersal speed compared to their source surface population. We suggest thatextreme and isolated habitats like caves might work as ‘dispersal traps’ following successfulcolonisation, because adaptation to these habitats includes the reduction of explorativeness.Furthermore, we suggest that individuals with higher explorativeness are likely tocolonise markedly new environments. Finally, we provide experimental evidence aboutsurface A. aquaticus moving more in dark than in light.Significance statementEnvironmental conditions in caves are differing drastically from those of the surface. Consequently, animals colonising subterranean habitats are subject to different selective forces than those experienced by the ancestral surface-living population. Behaviour is believed to be a key factor in successful colonisation to novel habitats; however, intraspecific behavioural variation in species with both surface- and cave-adapted populations is less known. Here, we compared dispersal related novel area exploration and dispersal speed across surface and cave-adapted populations of the freshwater crustacean Asellus aquaticus. Our results show that cave-adapted A. aquaticus are significantly less explorative and disperse slower than surface-type populations, indicating that caves may act as ‘dispersal traps’, where adaptation includes the loss of explorativeness. Also, recent cave colonists show a trend to be faster dispersers than peers from the surface source population, suggesting that individuals with higher explorativeness are likely to colonise markedly different new environments.