Coexistence with an invasive species in the context of global warming lead to behavioural changes via both hereditary and ontogenetic adjustments to minimise conflict

Global warming and invasive species often act synergistically to threat native communities. The Neotropical Poeciliidae have extensively been introduced to control populations of malaria-transmitting mosquitoes and are now successful invaders around the world. Poecilids introduced to a habitat in the fringe of its thermal tolerance will be increasingly more competitive as temperature increases. This can lead to either local extinction or rapid adaptation of native species. We evaluated if the introduction of two-spot livebearers ( Pseudoxiphophorus bimaculatus ) has led, after approximately 28 years, to hereditary differences between amarillo fish ( Girardinichthys multiradiatus ) from an invaded and a non-invaded adjacent temperate mountain lake. Laboratory-born F1 amarillo from the two lakes were raised in either presence or absence of feeding competition with two-spot livebearers. F1 females from Zempoala foraged for shorter periods and were more frequently aggressive than those from Tonatiahua, whereas Zempoala males were quicker to start foraging, did so for shorter periods, and were less likely to fight with their own, than males from Tonatiahua. Similarly, amongst fish from Zempoala reared in the presence of competition with P. bimaculatus , females were slower to start foraging and foraged for shorter periods, and males had reduced foraging and agonistic behaviour, than those reared facing only conspecific competition. We conclude that temperature-dependent behavioural differences have arisen between populations of a native fish, seemingly linked to foraging in a competitive environment and the tendency to be aggressive towards conspecific and heterospecific fish. These differences are the result of both local adaptation and behavioural flexibility.