A difference in timing for the onset of visual and chemosensory systems during embryonic development in two closely related cuttlefish species

Cephalopod Behavior: From Neural Plasticity to Consciousness

It is only in recent decades that subjective experience - or consciousness - has become a legitimate object of scientific inquiry. As such, it represents perhaps the greatest challenge facing neuroscience today. Subsumed within this challenge is the study of subjective experience in non-human animals: a particularly difficult endeavor that becomes even more so, as one crosses the great evolutionary divide between vertebrate and invertebrate phyla. Here, we explore the possibility of consciousness in one group of invertebrates: cephalopod molluscs. We believe such a review is timely, particularly considering cephalopods' impressive learning and memory abilities, rich behavioral repertoire, and the relative complexity of their nervous systems and sensory capabilities. Indeed, in some cephalopods, these abilities are so sophisticated that they are comparable to those of some higher vertebrates. Following the criteria and framework outlined for the identification of hallmarks of consciousness in non-mammalian species, here we propose that cephalopods - particularly the octopus - provide a unique test case among invertebrates for examining the properties and conditions that, at the very least, afford a basal faculty of consciousness. These include, among others: (i) discriminatory and anticipatory behaviors indicating a strong link between perception and memory recall; (ii) the presence of neural substrates representing functional analogs of thalamus and cortex; (iii) the neurophysiological dynamics resembling the functional signatures of conscious states in mammals. We highlight the current lack of evidence as well as potentially informative areas that warrant further investigation to support the view expressed here. Finally, we identify future research directions for the study of consciousness in these tantalizing animals.

Impact of natural and artificial prenatal stimulations on the behavioural profile of Japanese quail

As the sensory systems of vertebrates develop prenatally, embryos perceive many environmental stimuli that can influence the ontogeny of their behaviour. Whether the nature and intensity of prenatal stimuli affect differently this ontogeny remains to be investigated. In this context, this study aimed to analyse the effects of prenatal auditory stimulations (natural stimulations "NS": predator vocalisations, or artificial stimulations "AS": metallic sounds) on the subsequent behaviour of young Japanese quail (Coturnix coturnix japonica). For that, behavioural variables recorded during ethological tests evaluating emotional and social reactivity were analysed using a principal component analysis. This analysis revealed significant differences between the behavioural profile of stimulated chicks and that of non-exposed chicks. Indeed, chicks exposed to NS expressed more intense emotional responses in fearful situations, but less neophobia in the presence of a novel environment or object, whereas chicks exposed to AS appeared more sensitive to social isolation. Our original results show that the acoustic environment of embryos can influence the way young birds subsequently interact with their social and physical environment after hatching, and face challenges in changing living conditions.

Awareness of danger inside the egg: Evidence of innate and learned predator recognition in cuttlefish embryos

Predation can be a very strong selective pressure on prey. Many studies have shown the existence of innate anti-predator responses, mostly in the early developmental stages of juvenile vertebrates. Learning to recognize predators is another possible defensive resource, but such a method involves a high death risk. There is evidence that prenatal learning exists in animals but few studies have explicitly tested for embryonic learning. The aim of this study was to test innate and learned predator recognition in cuttlefish embryos. For this, naïve embryos were exposed to chemical and visual cues emanating from predators, non-predators, and ink. Their response was assessed by measuring their ventilation rate (VR). We first show that VR decreased in response to both visual and chemical predatory cues and ink but not to non-predatory cues. Second, we show that when non-predatory cues (visual or chemical) are paired with predatory cues or ink for several days, embryonic VR significantly decreased. Such a response is likely adaptive, especially in a translucent egg, since it results in reduced movement and hence may lower the risk of detection by visual predators. This freezing-like behavior may also reduce the bioelectric field, thus lessening the predation risk by non-visual foragers. Our results report that cuttlefish embryos had an innate capacity to differentiate between harmless and harmful chemical and visual cues. They were also capable of learning to respond to harmless cues when they were paired with danger (predator or ink) based on conditioning. The combination of these behavioral mechanisms is an example of the early adaptability of cephalopods. Such behavioral plasticity may give the newly hatched cuttlefish a selective advantage when dealing with either known or unfamiliar threats. Nevertheless, more experiments are needed to test the efficiency of the embryos' response faced with known or new predators.