Social influences on embryonic behaviour and the developmental onset of embryonic acquired predator recognition in minnows

Abstract

For oviparous species, the external environment is replete with cues that contain diverse information relevant to developing embryos, including potential predation threats. Information about predators obtained during the egg stage is known to improve survival after hatching by allowing individuals to recognize and respond to potential threats more effectively, but the development and mechanisms by which embryos learn are not well studied. Here, we sought to identify the developmental onset of embryonic learning in a freshwater fish, the fathead minnow, Pimephales promelas, by conditioning embryos to identify a piscivorous predator, the bluegill sunfish, Lepomis macrochirus, and evaluating their behaviour in response to predatory cues each day before hatching. In addition, we manipulated egg number (small or large clutch) and configuration (clustered, isolated) in experimental clutches to determine whether social attributes of the clutch, specifically, group size and embryo proximity, influence the acquisition of learned predator information or the expression of antipredator behaviour. Behavioural evidence of learned predator recognition first emerged among predator-conditioned embryos at 4 days postfertilization, expressed as a reduction in locomotor activity in the presence of predator cues. In addition, we found general effects of both the number and proximity of neighbouring eggs on embryonic activity levels but not on the developmental onset of predator recognition in predator-conditioned embryos or the expression of antipredator behaviour. These findings contribute to a growing body of knowledge on embryonic learning in oviparous aquatic vertebrate species and suggest that aquatic vertebrate embryos may be more sensitive to the social environment of the clutch than is commonly considered.