Science Focus (issue 022)

23 The Cephalopods “Szechuan pepper. Salt. Chinese five spice. Grind. Seasoning into a bowl. Corn flour. Squid. Score. It helps to tenderize the squid. Cut. Tentacles halved and go straight into the seasoning. Now, we are ready to cook.” While Mr. Gordon Ramsay was demonstrating how to prepare the delicious cuisine of crispy salt and pepper squid, did you know that cephalopods like squids have been favored by scientists not only as food, but as research objects? “Cephalo-pod,” literally means “head-foot” in Greek, and these animals are characterized by the presence of tentacles attached to their head. This class includes squids, octopuses, cuttlefishes and nauti luses. They are highly regarded, given titles such as “the smartest invertebrates” and “the alien intelligence,” and have been useful for understanding advanced cognitive evolution. Their complex behavior never ceases to amaze us in the field or in the laboratory. Observation suggests that octopuses can learn spatial cues from the surroundings to help with their navigation, gaining spatial memory that prevents them from repeatedly scrounging the same areas for resources [1]. Cuttlefish can exert self-control and delay their actions in favor of immediate gratification (footnote 1), displaying a sign of decision-making [2]. Squids react to threats in a rapid manner and escape with their highly propulsive jets [3]. On top of their abilities to go on a furious fight of pushing and biting among the males in pursuit of a mate, cuttlefishes can also deploy tactics where they sneak around and mate with the hiding female without other males noticing [1]. As ide f rom thei r impress ive behavior, thei r sophisticated skin, with color, pattern and texture changing features, is certainly one of their most extraordinary abilities. For camouflage, they first n e e d t o o b s e r v e t h e surroundings. After analyzing t he v i s ua l i n fo r ma t i on , the brai n wi l l f i re neu ral signals to mi l l ions of colorchanging cel ls to create the camouflage pattern. Octopuses and cuttlefishes can further enhance the mimicry by morphing their skin into the 3D texture of the background, such as a sandy seafloor [1]. It takes literally the blink of an eye, about 200 milliseconds, to change their appearance [1]. This fascinating property has enabled them to survive with brilliant camouf lage, crawl ing around wi thout being detected. Commonly Used Model Organisms Our relationship with cephalopods is not limited to the appreciation of their external appearance and behavior. Groundbreaking discoveries have come from laboratory studies of their nervous system. Led by Sir Alan Hodgkin, Sir Andrew Huxley and Sir Bernard Katz, squid were used in the early days of neuroscience as a system for experimenting with neuronal functions, including the nerve impulse. Certain squid neurons have remarkably long and thick (up to 1 mm in diameter) axons, the long projections that extend from neurons. These giant axons offer us a great flexibility for experiments, such as the insertion of electrodes for voltage and current measurement [4, 5]. Based on past observations that the intracellular sodium concentration inside the squid axon was lower than that of the sea water (external fluid), Hodgkin and Huxley conducted pivotal exper iments and obtained results that suggest an influx of sodium ions during the transmission of electrical signals (footnote 2) [6] . T h i s d i scove r y The Amazing Cephalopods 地球上的「外星智慧生物」: 頭足類動物 By Sirius Lee 李揚