Abstract
Cephalopods use dynamic body patterns for camouflage and communication. This complex body patterning also plays an important role in their reproductive behavior. In the oval squid Sepioteuthis lessoniana, males of different body sizes use distinct mating body patterns and postures to interact with females, this results in different spermatophore planting sites and fertilization success. However, little is known about the significance of these body patterns in courtship behavior, and the evolution of these mating postures in reproductive strategy. To study visual communication and reproductive strategy in S. lessoniana, we first characterized body patterns of males and females during courtship (i.e., ethogram of distinct chromatic component expression) at spawning grounds in wild and in captivity. Five behaviors were commonly seen among these reproductively active squids, namely parallel swimming, male guarding, male-male fighting, male-parallel mating, and male-upturn mating. Total of 27 chromatic components were identified in these five reproductive behaviors. By analyzing the dynamic body patterning time series associated with each behavior, the results not only revealed that each behavior is composed of multiple chromatic components, but the findings also showed that each component is often associated with multiple behaviors. The present study thus demonstrates that dynamic body pattering, by expressing unique sets of key components, is an efficient behavioral information in communication among individuals in the oval squid. To assess mating success of different male copulation postures and female choices in the mating behavior, we conducted a captivity experiment in which males displayed alternative mating types and the correlation between male mating success and female choice was examined. We found that male squid changed their adopting mating tactics according to female mate choice. This finding suggests that females use body patterns to show their mating preference visually and that males alter their mating tactics accordingly. In addition, we examined the sperm morphology from different sizes of males to investigate if there is any morphological difference in sperm competition. We found that there was no distinct size dimorphism in relation to either spermatophore size or sperm morphology in oval squids. This suggests that males change mating tactic flexibly according to male-male competition and female choice outcomes, thus morphological specialization is not evolved in this species. This behavioral plasticity may benefit the reproductive success of these males and maintain the dynamic stability of two alternative mating types in this polyandrous species. By studying the body patterning, female choice, male alternative mating types, and diverse reproductive structure in oval squids, this study sheds light on visual communication and reproductive strategy of cephalopods.