| Budget Amount *help |
¥3,920,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥420,000)
Fiscal Year 2007: ¥1,820,000 (Direct Cost: ¥1,400,000、Indirect Cost: ¥420,000)
Fiscal Year 2006: ¥2,100,000 (Direct Cost: ¥2,100,000)
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| Research Abstract |
Social interaction might be a selection pressure for animals to enlarge its brain size (Machiavellian Intelligence). The aim of this study is to investigate social system and its evolutionary background in tropical squid, an exceptional invertebrate with large brain, well-developed nervous system and receptor, based on an idea of Machiavellian Intelligence. We observed ontogeny of schooling behavior as social character in oval squid Sepioteuthis lessoniana, a common tropical species that forms organized school, thus is considered as social species. Oval squid emerged schooling around 20 d old after hatching. Sizedependent hierarchy exists in a school of oval squid, in which larger individuals have advantage for feeding occasion. This might be a function to keep school structure of this species. We observed and compare variation of social system and behavior for some tropical cephalopod with special reference to reaction to mirror reflection that is very special behavior in oval squid, a social species. Loliginids and sepiids, social and semi-social group, reacted mirror reflection with active touching behavior to mirror while octopods, solitary group, did not show any attention to mirror reflection. Histological observations on brain of these cephalopod revealed that a brain lobe controlling visual memory and learning is larger in loliginids and sepiids whereas a brain lobe controlling exercise is larger in octopods. This study will add new knowledge for cephalopod social system and comparative cognitive science.
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