Quantifying the Speed of Chromatophore Activity at the Single-Organ Level in Response to a Visual Startle Stimulus in Living, Intact Squid

Abstract

The speed of adaptive body patterning in coleoid cephalopods is unmatched in the natural world. While the literature frequently reports their remarkable ability to change coloration significantly faster than other species, there is limited research on the temporal dynamics of rapid chromatophore coordination underlying body patterning in living, intact animals. In this exploratory pilot study, we aimed to measure chromatophore activity in response to a light flash stimulus in seven squid, Doryteuthis pealeii. We video-recorded the head/arms, mantle, and fin when squid were presented with a light flash startle stimulus. Individual chromatophores were detected and tracked over time using image analysis. We assessed baseline and response chromatophore surface area parameters before and after flash stimulation, respectively. Using change-point analysis, we identified 4,065 chromatophores from 185 trials with significant surface area changes elicited by the flash stimulus. We defined the temporal dynamics of chromatophore activity to flash stimulation as the latency, duration, and magnitude of surface area changes (expansion or retraction) following the flash presentation. Post stimulation, the response’s mean latency was at 50 ms (± 16.67 ms), for expansion and retraction, across all body regions. The response duration ranged from 217 ms (fin, retraction) to 384 ms (heads/arms, expansion). While chromatophore expansions had a mean surface area increase of 155.06%, the retractions only caused a mean reduction of 40.46%. Collectively, the methods and results described contribute to our understanding of how cephalopods can employ thousands of chromatophore organs in milliseconds to achieve rapid, dynamic body patterning.

Squid adjust their body color according to substrate

“…The position of white-squid in the environment during color-changing events is significantly affected by squid swimming orientation (p < 0.0001; Table 1 , Supplementary Table 2 ). The shortest white-squid color-changing event duration recorded by us in this study (0.3 s) corresponds with published single chromatophore expansion/contraction durations in loliginid squids 59 – 61 , but on average, the color-changing events in our study took four times longer. This variable and relatively long duration for the color-changing process which begins and is completed often centimeters from the divider (Supplementary Table 2 ) suggests that although squids anticipate the upcoming background, evidenced by becoming paler or darker before entering the light or dark substrate respectively, the final color is usually fully determined once the divider has been crossed, similarly to cuttlefish 26 , 27 .…”

Cuttlefish color change as an emerging proxy for ecotoxicology

“…Such a tool was recently developed from video recordings of S. officinalis’ skin explants, following the bioassay protocol implemented by Loi and collaborators (1996) for highlighting the pharmacological basis of chromatophore control. It will likely be able to process high-resolution images acquired from motile cuttlefish, as recent works have shown ( Reiter et al, 2018 ; Hadjisolomou et al, 2021 ). Yet, the number of animals needed for ex vivo/in vitro tests is reduced by the potential for high-throughput using of several skin patches from one animal only.…”

What If I Told You Camouflage is a Myth? Animal Coloration is Mainly A-biotic and not Biotic (Camouflage)

“…The ability of coleoid cephalopods to change colour according to their environment, although highly impressive, is not proof of biotic reason-i.e., to avoid the danger of predation or of preparation for predation; and if in place of the word "camouflage" we write "reflection of the colour of the habitat", it is still an impressive ability, with the animals' anatomy having been and still being studied in depth in order to understand this ability [30,31] . Similarly, because the animal has the ability to project the colour of its environment-i.e., a variety of colours, it exploits this ability also for interspecific communication [32] as is known in chameleons (see below).…”