The influence of population mixing on newborn shoaling behaviour in the guppy (Poecilia reticulata)

The introduction of non-native populations into new habitats where they can mix with the original inhabitants poses a major thread to the genetic distinctiveness of the native population. Interbreeding between introduced and native individuals can disrupt local adaptations and lead to outbreeding depression in resulting hybrid offspring. In the guppy (Poecilia reticulata), shoaling behaviour plays an important part in avoiding predators and is displayed from birth, but differences in shoaling tendency exist between populations. The populations used for our experiment reflect the ones involved in Haskins' introduction more than 60 years ago, when Guanapo guppies where introduced into the Turure, thereby bringing genetically very distinct populations into secondary contact. This introduction led to an invasive event and subsequent disappearance of the original Turure genotype. Here we show that the mixing of genepools by interbreeding between populations affects adaptive behaviour such as shoaling and creates more variation in the resulting offspring. Furthermore, parental origin has a subtle effect on offspring shoaling behaviour. We found that the shoaling behaviour of hybrid offspring significantly differed from pure-bred offspring of either parental population, but resembled those found in Turure newborns that are likely to be of mixed ancestry as well.