研究紹介 海洋高次捕食者、特に板鰓類の 生物学的・生態学的研究 生物資源科学コース 清水校舎 田中 彰 高次捕食者の役割と現状 栄養段階 トップダウン 効果 • 下位段階の過度な生産 を抑制し、安定した生態 系の構築に寄与。 • 漁業活動による高次捕 食者の減少。 • 食物連鎖の単純化。 • 生態系の脆弱化。 高次捕食者の生物学的・ 生態学的知見の充実 研究項目 • 分布・生息場 養育場の保護 • 繁殖 繁殖様式 繁殖価 成熟 • 年齢・成長 成長率 寿命 成熟年齢 • 食性 摂餌物・摂餌量 捕食器官・行動 • 多様性 ある海域の軟骨魚類の種多様性 個体群内の遺伝的多様性 同腹胎仔間の遺伝的多様性 • 分類・系統類縁 形態学的・分子生物学的手法に よる種査定・系統関係 調査海域 駿河湾、八丈島・石垣島周辺海域 研究例 Age, Growth and Genetic Status of White Shark, Carcharodon carcharias, from Kashima-nada, Japan Sho TANAKA*1, Toru KITAMURA*2, Toshihiko MOCHIZUKI*3 and Kazuya KOFUJI*3 *1School of Marine Science and Technology, Tokai University, *2 Environmental Science Laboratory, Japan NUS Co., *3 Ibaraki Prefectural Oarai Aquarium The great white shark is included in the category of “Vulnerable” on the IUCN Red List and in CITES Appendix II. In Japan, the white sharks are rarely caught with coastal fisheries as large set nets or gill nets. Recently, the white sharks around South Africa, Australia, New Zealand and California are studied actively on the movements, habitats and population structure by electric tags and DNA analysis. These reveal that white sharks move large spatial areas; South Africa to Australia, New Zealand to Australia and California to Hawaii. However, their biological and ecological information around Japan are little known (Nakaya, 1993,1994; Uchida et al. 1996). We hypothesized that the life history traits would vary among populations because the conditions of the species’ various habitats are diverse and change through time. The objectives of this study were to: (1) show a simple means of enhancing the visibility of growth bands accumulated in the corpus calcareum of white shark centra, (2) estimate the age and growth rate from the band counts, and (3) examine the relationship between white sharks caught in Japanese waters with other populations in the Indian and Pacific Oceans using genetic techniques. Marine and Freshwater Research;62 (2011) (a) A C B D (b) E (e) (c) (d) Fig.1 X-radiographs of a whole centrum (a) and only half of a corpus calcareum (b-e) in the white shark. (a,b) Male of 442.0 cm TL with 12 bands. (c) Female of 383.2 cm TL with 5 bands. (d) Male of 310.9 cm TL with 4 bands. (e) Male of 231.4 cm TL with 2 bands. Scale bars = 10 mm. 500 500 Female Total length (cm) Male 450 450 400 400 350 350 300 300 250 250 200 200 Symbols with observed TL 150 100 231.4 310.9 353 364.6 323.9 381 406 408 411 426.4 442 150 100 50 50 0 0 0 1 2 3 4 5 6 7 8 9 10 11 12 0 1 2 3 231.8 280.4 320.2 360.0 383.2 398.2 446.3 482.0 4 5 6 Age (years) Fig. 3. Back-calculated lengths at age of individual white sharks using the Fraser-Lee equation . 7 600 Total length (cm) 500 400 300 200 MaleVBG FemaleVBG CA SA 100 0 0 2 4 6 8 10 12 14 16 18 Age (years) Fig. 4. von Bertalanffy growth curves of white sharks from Japan, California (CA) and South Africa (SA). Closed and open circles indicate observed length of males and females, respectively. Table 2. Growth parameter estimates and goodness-of-fit from the von Bertalanffy growth model for male and female white sharks Male Parameter Estimate Female 95% confidence limits Estimate 95% confidence limits k (year-1) 0.196 0.158 0.234 0.159 0.130 0.167 L∞ (cm) 455.0 439.7 472.6 606.7 591.5 635.4 t0 -1.92 -1.64 -2.23 -1.80 -1.63 -1.93 (year) L0 (cm) χ2cal 142.5 2.130 (P=0.546) 150.7 4.259 (P=0.239) von Bertalanffy growth model Lt = L∞(1-EXP(-k(t-t0))) 8000 80 6000 70 60 5000 50 4000 40 3000 30 Maturing female 2000 1000 20 10 0 0 100 150 200 250 300 350 400 450 500 Total length (cm) Fig. 5. Relationship of total length with gonad weight and clasper length in white sharks from Japan . Clasper length (cm) 7000 Gonad weight (g) Maturing male Ovary Testis Clasper Table 3. FST estimates for pairwise comparisons among four white shark populations in Indo-Pacific OceansFST values are all significant (P<0.001) Japan California 0.828 California Australia & New Zealand GU002308 CA GU002321 CA GU002310 CA GU002312 CA GU002313 CA GU002314 CA GU002309 CA GU002307 CA ‐ GU002306 CA GU002317 CA GU002305 CA Australia & New Zealand 0.433 0.343 ‐ South Africa 0.938 0.951 0.855 GU002315 CA GU002316 CA GU002303 CA GU002320 CA GU002302 CA GU002304 CA Fig. 6. Genetic relationship of 56 white sharks from 5 locations inferred using the Neighbor-Joining method. GU002311 CA GU002318 CA AY026205 Au カリフォルニア、オーストラリア ニュージーランド AY026204 Au GU002319 CA AY026209 NZ AY026202 Au AY026208 NZ AY026197 Au AY026207 NZ AY026196 Au AY026203 Au AY026210 NZ The bootstrap consensus was inferred from 1000 replicates. The tree is drawn to scale, with branch lengths in the same units as those of the genetic distances used to infer the phylogenetic tree. The genetic distances are in the units of the number of base substitutions per site. There were a total of 403 positions in the final dataset. The bootstrap values are indicated near nodes. AY026200 Au AY026198 Au AY026199 Au D-loop region sequences of mitochondrial DNA AY026201 Au AY026206 Au No 2 Jp No 1 Jp No 3 Jp No 5 Jp No 7 Jp No 4 Jp 日本 No 6 Jp AY026212 SA AY026219 SA AY026213 SA AY026214 SA AY026217 SA AY026222 SA AY026223 SA 南アフリカ AY026220 SA AY026221 SA AY026216 SA AY026224 SA AY026215 SA AY026211 Au Genetic distance AY026218 SA Au: Australia CA: California Jp:Japan NZ: New Zealand SA: South Africa Summary • The von Bertalanffy growth parameters were estimated at L∞=455 cm TL, k=0.196 year-1 and t0=-1.92 years for males and L∞=607 cm TL, k=0.159 year-1 and t0=-1.80 years for females. • The growth rate to maturity was higher than that known for individuals from California and South Africa. • Male sharks matured at 310 cm TL and an age of 4 years, and females began to mature at about 450 cm TL and 7 years. • The D-loop region sequences of mitochondrial DNA extracted from Japanese white sharks and GenBank datasets from sharks of California, Australia, New Zealand and South Africa indicate that Japanese white sharks formed a monophyletic clade, separate from the populations of other regions. • The results suggest that unique life history traits of Japanese white sharks may be caused by genetic differences. 進行中の研究 • Growth of young smooth hammerheads, Sphyrna zygaena, in the inner area of Suruga Bay, Japan. 15th EEA Scientific Conference (2011)で発表、論文作成中。 • Morphological and genetic comparison of the genus Deania between European and Japanese waters. Symposium: Biology of Deep-water Chondrichthyans [Sponsored by AES] August 8 - 14, 2012: Vancouver, BC Canadaで発表予定。 共同研究 • 東海大学医学部 Genetic and family structure in a group of 165 common bottlenose dolphins caught off the Japanese coast. Marine Mammal Science 2012 Sequence analysis and phylogeny of whole mitochondrial genomes from Hexanchiform sharks. BMC Evolutionary Biology 投稿中 • 国立遺伝学研究所 反復配列の変異がもたらすミトコンドリアDNA調節領域の多様性と進化 学会発表予定 • Radboud University Nijmegen SEARCH FOR THE PRESENCE OF THE CL- CHANNEL PHOSPHOLEMMAN IN ORGANS AND TISSUES OF THE FRILLED SHARK CHLAMYDOSELACHUS ANGUINEUS . 投稿準備中
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