Facultative brightness-change in an invasive gecko entering a novel background environment

Abstract Background matching is a common form of crypsis in animals, resulting from selective pressures imposed by visual systems of predators and/or prey. Therefore, it could be expected that novel backgrounds would pose a barrier to the establishment of invasive species, due to a lack of crypsis. Behavioural flexibility in crypsis—through facultative crypsis and/or choice of matching backgrounds—has been suggested as a trait that may facilitate invasiveness. We assessed background-matching and facultative brightness-change in an Australian population of the invasive Asian House Gecko ( Hemidactylus frenatus ). This species is currently expanding from urban environments into surrounding tropical woodland, and demonstrates great variability in colour and pattern among individuals. We quantified wild background-matching in terms of both colour and brightness. We then experimentally tested whether geckos facultatively change brightness in the direction expected for a given background. Hemidactylus frenatus consistently brightness-matched across the backgrounds on which they were found, more than would be expected by chance. Experiments showed that H. frenatus rapidly changed in their dorsal brightness, in the direction expected given their background, suggesting that brightness-matching observed in wild geckos is due to facultative brightness-change. Successful invasion may benefit from facultative crypsis; however, it remains to be demonstrated how facultative brightness-change in H. frenatus is linked to predation and invasion success. We outline how recognition of facultative colour-pattern change in invasive species may be important for early detection and management actions.