Cuttlefish crypsis: asymmetries in the serotonergic system and visual processing

Abstract : Cuttlefish visually assess a range of background features to blend in with their surroundings. Previous research has shown that cuttlefish respond to conflicting visual cues (i.e. different visual information on their left and right sides) with mixed body patterns. This response to conflicting visual cues may be partially affected by asymmetric visual processing, since cuttlefish exhibit biases when processing visual information (i.e. visual lateralization). We used cuttlefish at different developmental stages (i.e. hatching, one-month, two-months) and tested whether they prioritise information perceived in their left or right visual field for brightness matching, which is a key aspect of crypsis. We also investigated whether the serotonergic system was driving this perceptual asymmetry, as this has been shown in some vertebrates. We found that cuttlefish exhibit perceptual asymmetries during brightness matching; both hatchlings and two-month-old cuttlefish exhibited a right eye preference, as the grey level perceived in the right visual field was predominately used for brightness matching. We also found asymmetries in the serotonergic system within the optic lobes (i.e. brain structures implication in visual processing). The expression of a serotonin receptor was significantly higher in the left optic lobe in the hatchlings. Moreover, the ratio of expression between the left and the right optic lobes was reversed between the hatchlings and the two-month old cuttlefish. Although we found asymmetries in both visual processing during brightness matching and the serotonergic neurotransmission system, the developmental trajectory of these asymmetries were not correlated. This suggests that this asymmetry of the serotonergic system was not driving the perceptual bias observed in our study. As the serotonergic system has been implicated in learning and memory in other cephalopod species, future research should focus on testing whether the asymmetrical expression of this serotonin receptor has a role in different kinds of learning and memory abilities.