公益財団法人京都大学教育研究振興財団藤洋作会長様令和6年  7月   5日
今回の出張では6月22日から25日までSnake Ecology Group（ウィスコンシン州ウィンター）、27日から30日までSSAR（ミシガン州アナーバー）の学会にそれぞれ参加した。 Snake Ecology Groupはへビ類の生態をテーマにした非常に専門性の高い学会であり、 SSAR は爬虫・両生類学を中心としたより規模の大きい学会であった。Snake Ecology Groupでは、私の博士課程の研究テーマであるリュウキュウアオヘビの頭部形態や捕食行動をテーマに発表した。一方、SSARではサプテーマで行っていたアオダイショウとシマヘビの登攀能力の比較について発表した。発表時間はどちらも一時間程しかなく、ディベイトできる機会は限られていたが、その後の懇親会で多くの研究者と意見交換することができた。英語で相手の質問を聞いたり答えたりすることが難しく、上手く意思疎通できないときもあったが、非常に良い経験ができた。さらに申請者の研究室の共同研究者とも会うことができ、今後の研究方針についても議論することができた。日本ではヘビ類の生態を中心に活動している研究者はほとんどいないが、アメリカにはたくさんのへビ研究者がおり、保全活動なども盛んに行われていることを知った。特にSNSなどを活発に利用して一般市民に情報を公開しつつ寄付を募って保全や研究活動を実施している研究室が多かったのが印象的であった。日本ではヘビ類などのマイナーな生物の保全や基礎研究は遅れているが、それらの重要性を理解してもらうためにも一般市民との情報共有がとても大切だと改めて感じた。また、学会には付属のエクスカーションや博物館見学、オークションなどもあり、他の研究者たちと共にそれらを楽しむことができた。エクスカーションでは学会会場周辺でヘビ類を始めとする生物を探し、大きなカミツキガメやシシバナへビなども見ることがでた。アメリカは世界一爬虫・両生類の研究が盛んな国であるため、多くの爬虫・両生類の行動や形態の機能、系統関係などが明らかになっており、それらを実際に現地で観察できたことは今後研究を進めていく上でも大きな財産になるだろう。博物館見学ではアメリカの種だけでなくアジアやオーストラリアに生息する希少な種の標本も拝見することができ、大きな感銘を受けた。私はこれまでの研究活動で国内の様々な博物館を訪れたが、多くの博物館で標本の管理がずさんであり、状態の悪いものや紛失して見つからないものなどが多々あった。我が国の研究水準を高め、国際的に活躍できる研究者を増やすためにも博物館を充実させていくことは重要であると感じた。オークションでは入手が難しい爬虫両生類の専門書を安価で購入することができた。今後はこれらの本を用いて輪読会を実施し、研究室のメンバーと共に互いに知識を高め合いたいと考えている。
【発表内容】
Snake Ecology Group
The specialization of the head morphology and the feeding behavior in earthworm-eating snakes. Yanagi Hiroaki (Kyoto university)
Introduction
Predators have head morphology and feeding behavior adapted to their feeding habits (Lillywhite, 2014). Snakes are interesting subjects for the study of foraging traits because they have no limbs and swallow their prey whole (Mori and Vincent, 2008). In snakes, earthworm-eating habits have evolved independently many times. However, specialization of feeding traits for earthworms has been poorly studied. Cyclophiops is a group of carthworm-cating snakes. Recent molecular phylogenetic analysis revealed that Cyclophiops is included in Ptyas , a vertebrate-eating group (Figueroa et al., 2016). Earthworm feeding habits probably have evolved multiple times in the Ptyas clade. Therefore, comparison of foraging traits among these species provides a better understanding of their adaption to the earthworm-eating habits. I compared head morphology of Cyclophiops and Ptyas (Fig. 1) and observed feeding behavior of C. semicarinatus in captivity.
Study of head morphology
Materials and methods Two juveniles of P. dhumnades, two juveniles of C. semicarinatus and a juvenile of C. herminae were
. Compared the head morphology by geometric morphometrics and principal component analysis.
Results
The two species of Cyclophiops and P. dhumnades were clearly discriminated by PC1 (Fig. 2c). PC1 was primarily associated with variations in the position of the nasal tip and the width of the head. Cyclophiops has a long nose and thin head. On the other hand, Ptyas has short nose and wide head. Discussion Cyclophiops searches for earthworms by thrusting the head beneath the leaf litter layer. The elongated head shape is considered to be adaptive for this foraging behavior. However, the shape likely restricts the gape size, limiting to swallow large prey whole. In the future, I will increase the sample size and use CT scan to compare the skull morphology.
Study of feeding behavior
Materials and methods Recorded 20 predation by five adults of C. semicarinatus in captivity Analyzed first bite position, swallowing time and swallowing direction Breeding environment: 23-28 °C, 60 cm × 30 cm
Results
The bite position when captured would be random (Fig. 3; p=0.522). Swallowing time would correlate with the relative prey size. Cyclophiops semicarinatus is able to swallow earthworms very quickly (Fig. 4). In the typical swallowing style of snakes, they use reciprocating, unilateral cycles of protraction and retraction of the palatomaxillary arches to rachet themselves forward over their prey (pterygoid walk) (Kley and Brainerd, 2002). During swallowing, C. semicarinatus dose not move the palatomaxillary arches much and shakes the head with opening mouth (Mov. 1). Discussion Because an earthworm has little ability to escape and resist, C. semicarinatus would not need to hold it tightly during swallowing. I predict that C, semicarinatus glide forward over the earthworm in the neck region by not holding. Acknowledgemente: I would lase to thank The Kyoto University Pourdation for providing the travel funding that enable re to attend this conference Is the climbing ability related to the different dietary patterns between two bird-eating snakes? Yanagi Hiroaki (Kyoto University)
Introduction
Predators are necessary to have an appropriate locomotion ability for foraging habit. The difference of locomotion ability would affect dietary patterns. Two bird eating snakes are present in the main islands of Japan: Elaphe climacophora and E. quadrivirgata. The former is a specialist that feeds on endotherms and preys on various birds. On the other hand, the latter is a generalist that feeds on ectotherms and endotherms, including birds, but only those nest on the ground (Hamanaka et al., 2014). I hypothesized that E. climacophora has superior climbing ability than E. quadrivirgata. Experiment 1: Adult snakes were allowed to climb the corner of the laboratory walls (210 cm) and their maximum heights they reached were measured. Eight individuals of E. climacophora and seven individuals of E. quadriviryaa were used. The comer of the wall was made at an inside angle of 60 degrees and sandpoper was installed to prevent slipping. Experiment 2: Adult snakes were allowed to climb the tree trunk ( Cedrus libani ) and their climbing speed was measured. • Five individuals were used for each species. • The speed was calculated based on the time it took to climb one meter. Experiment 3: Hatchling snakes were allowed to climb the comer of the laboratory walls (40 cm) and their maximum heights they reached were measured. Nine individuals were used for each species. The corner of the wall was mode at an inside angle of 90 degrees and sandpaper was installed to prevent slipping.
Discussion
The results indicate that E. climacophora has the superior climbing ability than E. quadrivirgata. Because the differences were also observed in hatchlings, the superior climbing ability of E. climacophora would be an innate trait. In morphological aspects, the well-developed lateral ridge keels on the ventral scales (Matsui and Mori, 2021), which E. quadrivirgata does not have, would cause the difference of the climbing ability between the two snake species. Because E. quadrivirgata is not adept at climbing, the snake probably would not be able to access to bird eggs and nestlings on trees and thus exploits only birds that nest on or near the ground. Acknowledgements: I would like to find The Kyeto University Foundation for providing the travel funding that ensible me to artend