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Oval squids are polyandrous, with one female mating with multiple males during the spawning season. There are two alternative male mating tactics used by Sepioteuthis lessoniana. Larger males place spermatophores at the opening of the oviduct using a male-parallel mating posture, whereas smaller males attach spermatophores around the female buccal membrane using a male-upturned mating posture. If the route of egg transportation is taken into consideration, male-parallel mating would be expected to result in higher fertilization success than male-upturned mating. Although these male mating tactics are largely dependent on the body size of the male relative to that of the female, it is unclear how female choice affects the male's mating tactics and his mating success. Squids are highly visual animals, and they communicate through dynamic body patterning. In the present study, we observed that smaller male squids in captivity would attempt to mate with a larger female using the male-parallel tactic repeatedly, but they failed to be successful most of the time because of a rejection signal by the female. In contrast, when the males switched to the male-upturned tactic, the mating success rate was increased significantly, with much less female rejection signal. This finding suggests that female squids signal their mating receptivity visually and that male squids alter their mating tactics accordingly. This is the evidence to support the hypothesis that the switch in male mating tactics depends on female choice in oval squids and that this is transmitted via visual communication.

In Sepioteuthis lessoniana, the oval squid, on- togenetic changes in the kinematics of the mantle during escape-jet locomotion imply a decline in the relative mass flux of the escape jet and may affect the peak weight- specific thrust of the escape jet. To examine the relationship between ontogenetic changes in the kinematics of the man- tle and the thrust generated during the escape jet, we simul- taneously measured the peak thrust and the kinematics of the mantle of squid tethered to a force transducer. We tested an ontogenetic series of S. lessoniana that ranged in size from 5 to 40 mm dorsal mantle length (DML). In newly hatched squids, thrust peaked 40 ms after the start of the escape jet and reached a maximum of between 0.10 mN and 0.80 mN. In the largest animals, thrust peaked 70 ms after the start of the escape jet and reached a maximum of between 18 mN and 110 mN. Peak thrust was normalized by the wet weight of the squid and also by the cross-sectional area of the circumferential muscle that provides power for the escape jet. The weight-specific peak thrust of the escape jet averaged 0.36 in newly hatched squid and increased significantly to an average of 1.5 in the largest squids measured (P 0.01). The thrust per unit area of circum- ferential muscle averaged 0.25 mN/mm 2 in hatchlings and increased significantly to an average of 1.4 mN/mm 2 in the largest animals tested ( P 0.01). The impulse of the escape jet was also lowest in newly hatched individuals (1.3 mN s) and increased significantly to 1000 mN si n the largest squids measured (P 0.01). These ontogenetic changes in the mechanics of the escape jet suggest (1) that propulsion efficiency of the exhalant phase of the jet is highest in hatchlings, and (2) that the mechanics of the circumferential muscles of the mantle change during growth.

Animals adopt various forms of hunting according to their ecological, morphological, and cognitive features, and their specific hunting skills are acquired ontogenetically in relation to these features. It is noted that cuttlefish and squid hunt prey through the elongation of tentacles used specifically to capture prey. However, these two cephalopods have different lifestyles, leading to questions such as whether hunting skill is acquired similarly after birth and whether tentacle elongation is behaviorally identical. To address these questions, we observed and compared how captive pharaoh cuttlefish (Sepia pharaonis) and oval squid (Sepioteuthis lessoniana) attack prey during their early life stages. Like the adults, S. pharaonis hatchlings used the tentacular lunge attack, whereas S. lessoniana hatchlings used the arm-opening attack. S. lessoniana began to exhibit the tentacular strike attack after 30 days of age. In addition to timing of the emergence of a specific hunting mode, some differences were observed in the physical aspect of hunting behavior. For cuttlefish, maximum tentacle length and maximum speed of tentacle elongation increased from hatching to 30 days of age and then decreased. In contrast, for squid, maximum tentacle length increased from hatching to 30 days of age and then became constant. The distance to prey was positively correlated with maximum length and speed of tentacle elongation in S. pharaonis and with maximum swimming speed in S. lessoniana. These results show that cuttlefish mainly use an ambush strategy and that squid use a pursuit strategy. Possible causes for the ontogenetic differences in hunting behavior are discussed.

We investigated the kinematics of mantle movement during escape jet behavior in an ontogenetic series of Sepioteuthis lessoniana, the oval squid. Changes in mantle diameter during the jet were measured from digitized S-VHS video fields of tethered animals that ranged in age from hatchlings to 9 weeks. The amplitude of both mantle contraction and mantle hyperinflation (expressed as percent change from the resting mantle diameter) during an escape jet was significantly greater in hatchlings than in older, larger squid (P < 0.05). The maximum amplitude of mantle contraction during the escape jet decreased from an average of -40% in hatchlings to -30% in the largest animals studied. The maximum amplitude of mantle hyper-inflation decreased from an average of 18% in hatchlings to 9% in the largest squid examined. In addition, the maximum rate of mantle contraction decreased significantly during ontogeny (P < 0.05), from a maximum of 8.6 mantle circumference lengths per second (L/s) in hatchlings to 3.8 L/s in the largest animals studied. The ontogenetic changes in the mantle kinematics of the escape jet occurred concomitantly with changes in the organization of collagenous connective tissue fiber networks in the mantle. The alteration in mantle kinematics during growth may result in proportionately greater mass flux during the escape jet in newly hatched squid than in larger animals.

Literature dealing with laboratory studies of live squid usually includes a statement that attempts to rear or maintain squid in aquaria are unsuccessful. When stated, the survival of squid in captivity is most often given for the longest lived individual and predictive survival rates are not specified. A considerable body of current research (principally that dealing with squid "giant axons") depends on a reliable supply and short term maintenance of squid. Several aspects of squid biology lag for want of effective means to carry out lengthy laboratory studies. Preparatory to possible future studies on the maintenance of the squid, Loligo pealei (Lesueur, 1821), we have observed squid survival when subjected to standardized conditions. Quantitative data were obtained in an attempt to specify survivorship for comparison with other reports and for evaluation of certain environmental factors. The most dramatic results of attempts to rear cephalopods were reported by Choe (1966), who succeeded in fostering a few individuals of three species for more than 100 days and one loliginid squid for over 40 days. Edward T. LaRoe (University of Miami, unpublished) has repeatedly reared Sepioteuthis sepioidea to near maturity. Adults of this species have been maintained in floating pens for two months and possibly longer (Arnold, 1965). Immature squid, Loligo vulgaris, were reported to survive captivity for several weeks (Bidder, 1950) and for two months (Tardent, 1962). Tardent (1962) stated that sexually mature L. vulgaris do not normally live more than two weeks in the Naples Aquarium. Bidder (1950) reported that L. vulgaris is less sensitive to handling than Loligo forbesi and quoted a Dr. Sereni in the opinion that L. pealei at Woods Hole is far hardier and more resistant to handling than L. vulgaris at Naples. Roper (1965) reported a female Doryteuthis plei which survived 18 days in an aquarium, laying two egg masses in that time. Arnold (1962) gives the survival of sexually mature L. pealei as about five days and one instance of a male surviving for 17 days. These survival times refer to the longevity of the last remaining individual. In all of the references cited, squid were fed regularly and provided with running seawater. Only references dealing with loliginid squid have been cited because the survival of other families of cephalopods may not be comparable due to differences in life habits and ecological tolerances.