Communication in cuttlefish includes rapid changes in skin coloration and texture, body posture and movements, and potentially polarized signals. The dynamic displays are fundamental for mate choice and agonistic behavior. We analyzed the reproductive behavior of the mourning cuttlefish Sepia plangon in the laboratory. Mate preference was analyzed via choice assays ( n = 33) under three sex ratios, 1 male (M): 1 female (F), 2M:1F, and 1M:2F. We evaluated the effect of modifying polarized light from the arms stripes and ambient light with polarized and unpolarized barriers between the cuttlefish. Additionally, to assess whether a particular trait was a determinant for mating, we used 3D printed cuttlefish dummies. The dummies had different sets of visual signals: two sizes (60 or 90 mm mantle length), raised or dropped arms, high or low contrast body coloration, and polarized or unpolarized filters to simulate the arms stripes. Frequency and duration (s) of courtship displays, mating, and agonistic behaviors were analyzed with GLM and ANOVAs. The behaviors, body patterns, and their components were integrated into an ethogram to describe the reproductive behavior of S. plangon . We identified 18 body patterns, 57 body patterns components, and three reproductive behaviors (mating, courtship, and mate guarding). Only sex ratio had a significant effect on courtship frequency, and the male courtship success rate was 80%. Five small (ML < 80 mm) males showed the dual-lateral display to access mates while avoiding fights with large males; this behavior is characteristic of male “sneaker” cuttlefish. Winner males showed up to 17 body patterns and 33 components, whereas loser males only showed 12 patterns and 24 components. We identified 32 combinations of body patterns and components that tended to occur in a specific order and were relevant for mating success in males. Cuttlefish were visually aware of the 3D-printed dummies; however, they did not start mating or agonistic behavior toward the dummies. Our findings suggest that in S. plangon , the dynamic courtship displays with specific sequences of visual signals, and the sex ratio are critical for mate choice and mating success.

Cuttlefishes, like their octopus cousins, are masters of camouflage by control of body pattern and skin texture to blend in with their surroundings for prey ambush and threat avoidance. Aside from significant progress on the cuttlefish visual perception and communication, a growing number of studies have focused on their behavioural neurobiology and the remarkably rapid and apparently cognitively complex reactions to novel challenges such as spatial learning to solve maze tasks and vertebrate-like cognitive capabilities (e.g. object recognition, number sense and episodic-like memory). Despite intense interest of cuttlefish, much of our knowledge of its neuroanatomy and links to behaviour and ecology comes from one temperate species, the European common cuttlefish, Sepia officinalis. Here we present the first detailed comparison of neuroanatomical features between the tropical cuttlefish and squid and describe differences in basic brain and wiring anatomy using MRI-based techniques and conventional histology. Furthermore, comparisons amongst nocturnal and diurnal cuttlefish species suggest that the characteristic neuroanatomical features infer interspecific variation in visual capabilities, the importance of vision relative to the less utilised chemosensory system and clear links with life modes (e.g. diurnal vs nocturnal), ecological factors (e.g. living depth and ambient light condition) as well as to an extent, phylogeny. These findings link brain heterogeneity to ecological niches and lifestyle, feeding hypotheses around evolutionary history and provide a timely, new technology update to older literature.

Animals communicate in response to different tasks, including alarm calls, allocation of food, courtship, and mating. Different types of signals are used by animals to communicate, such as chemical signals, vocalisations, colour patterns, and movements. Animal colouration and visual communication have fascinated researchers for decades. Behavioural, anatomical and functional studies are commonly used to study visual communication in both vertebrates and invertebrates. Cuttlefish are well known for possessing intricate body patterns. Cuttlefish use these colourful and dynamic displays to communicate with mates, camouflage, and pursue prey. The cuttlefish central nervous system processes all the visual stimuli and coordinates the expression of postures, body movements, skin textures and colourations that form a body pattern. Interestingly, many species of cuttlefish are colour blind but possess polarisation vision and polarisation patterns in their bodies, which are potentially used for communication with conspecifics. The objective of this thesis is to analyse the mechanisms influencing visual communication and colour patterns in a small coastal cuttlefish Sepia plangon. The mourning cuttlefish S. plangon is a small species with a mantle length (ML) < 140 mm. This species inhabits coastal waters and prefers to forage in seaweed and seagrass environments. It is located to a maximum depth of 85 meters and is active during the day. After introducing the topic of this thesis in detail in chapter 1, we analysed the ontogenetic changes of S. plangon body patterns from embryos to adults in chapter 2. The first description of S. plangon eggs and embryos is included in this chapter. However, because the eggs were collected from their natural environment, only late embryonic development was described. The number and complexity of the body patterns of S. plangon changed throughout the lifespan, transitioning from three body patterns in embryos to a maximum of 18 in males. Seven patterns were exclusive to males and used only during reproductive behaviour. Therefore, in chapter 3, we analysed courtship, mating, and agonistic competition of S. plangon. Three sex ratios were used to study mate choice: 1Male(M):1F(F), 2M:1F, and 1M:2F. Polarised and unpolarised filters were placed between the animals to test the effect of modifying polarised stimuli in the reproductive behaviour of S. plangon. 3D printed cuttlefish models were used to manipulate specific traits (two body sizes, two postures, four body patterns) and determine which factor was crucial to successful mating. The components of the body patterns, reproductive behaviours and visual signals were analysed. We found that only sex ratio had a significant effect on male courtship frequency. Agonistic competition between males included visual signals, and most males avoided fighting. Small males (ML < 80 mm) used a deceptive display to mimic female patterns, avoid male competitions, and mate with females. The dynamic changes in body patterns were the most crucial element for ...