講稿課件16兩棲類

1、Life on land A milestone of the evolutionary history of vertebrates From water to landThe first terrestrial vertebrates: Amphibians Evolutionary force Changes in environmental conditionsIn the Devonian 泥盆紀(jì)（泥盆紀(jì)（3.5-4.2億年前）億年前） Climates: unpredictable Water levels of lakes and rivers: varied periodica

2、lly Oxygen availability in water: reduced due to decay of pteridophyte plants 羊齒植物羊齒植物Forced fishes to crawl in mud from pond to pond Breathing air promoted gill to change into lung Moving on land promoted paired fins to change into limbsWho were the earliest tetrapods ventured onto land? Who are th

3、e ancestors of amphibians?They are the members of subclass Sarcopterygii肉鰭魚亞綱肉鰭魚亞綱Lungfishes or Coelacanths 腔棘魚腔棘魚Which one?Lungfishes which is supported by recent evidence based on molecular biology Freshwater Internal naris 內(nèi)鼻孔內(nèi)鼻孔 Pneumatic sacs 氣囊氣囊: modification of swim bladder, function as lung

4、A duct connecting to the digestive tractSwallowed air enters these sacs and gas exchange occurs across vascular surfaces Bone arrangement of the paired appendages: similar to that of terrestrial vertebratesPelvic girdle 腰帶腰帶 is tied with the vertebral column （1 1）肺魚亞綱）肺魚亞綱特征：特征：體呈紡錘行，硬骨不發(fā)達(dá)，終生有殘存的脊索，

5、體呈紡錘行，硬骨不發(fā)達(dá)，終生有殘存的脊索，體尚未形成；上頜還沒有前頜骨和頜骨；腦顱為體尚未形成；上頜還沒有前頜骨和頜骨；腦顱為單一硬骨整塊單一硬骨整塊水中：用鰓呼吸，旱季：用鰾（肺）呼吸水中：用鰓呼吸，旱季：用鰾（肺）呼吸澳洲肺魚澳洲肺魚非洲肺魚非洲肺魚美洲肺魚美洲肺魚 Coelacanths 腔棘魚腔棘魚 Marine bony fishes, living species 矛尾魚矛尾魚 Internal naris 內(nèi)鼻孔內(nèi)鼻孔 Swim babbler: respiratory organ Muscles at the base of paired fins Bone arrangeme

6、nt of the paired appendages: similar to that of terrestrial vertebratesThe earliest amphibian fossils found in the early Devonian 泥盆紀(jì)泥盆紀(jì)These animals are called Stegocephalia 堅頭類堅頭類The representative: Ichthyostega 魚頭螈魚頭螈 Ancient amphibians: a once-diverse group of animalsThe ancient amphibians gave

7、rise to two lineages:1. Modern amphibians2. Amniote vertebrates 羊膜脊椎動物羊膜脊椎動物reptiles, birds, mammalsWaterLandQuestions animals faceOxygen contentLowHighHow to breath O2 in airBuoyancyHighLowHow to support body weight against the gravityTemperature ConstantVaryingHow to regulate their body temperatur

8、eMoistureHighVaryingHow to prevent water loss from body through evaporationHabitatSimpleDiverseHow to find places safe to predation, bad climates and suitable to reproductionMajor questions animals faced when they moved from water to terrestrial habitatsCharacteristics adaptive for life on land and

9、their insufficiencyThe buoyant support of water disappearedThe pull of gravity required a strengthening of the vertebral column1. Pentadactyl limbs 五趾型附肢五趾型附肢: connecting with vertebral column adapted to terrestrial locomotion Forelimb: through pectoral girdle 肩帶肩帶 Hindlimb: through pelvic girdle 腰帶

10、腰帶Provide powerful supports for the body against gravityHowever, the appendages are relatively weak Unable to lift their bodies far from the ground Unable to move a relatively fast speed2. Respiration Gills larvae Lungs adultHowever, other organs, including the skin and mouth, are required to aid in

11、 respirationThe first major barrier was exposure to increased water loss through evaporation 3. CirculationHearttwo atria + one ventricleDouble circulationsystemic circuit 體循環(huán)體循環(huán) + pulmonary circuit 肺循環(huán)肺循環(huán) However, the circulation is incompleteEctotherm 冷血動物冷血動物Depend on external heat sources to mai

12、ntain body temperature4. Modification of nervous system and sensory organs Two cerebral hemispheres form Archipallium 原腦皮原腦皮 appears in the cerebrum 大腦大腦Evolution of vertebrae brainpalaeopallium 古腦皮古腦皮 archipallium 原腦皮原腦皮 neopallium 新新腦皮腦皮EyeEyelidsGlands: lubricate潤滑潤滑 and wash the eyeEarMiddle ear

13、 first seen in vertebrates5. ReproductionFertilization and larvae development depend on water or moist habitatsBody structures and functionsSkinAmphibian skin is unique among vertebrates Bare lacking any kind of structures such as scales, feathers, or fur Highly permeable滲透性滲透性 water across the skin

14、 primarily through osmosis, less so by diffusion Highly glandular腺體的腺體的 multicelular mucous glands，widespreadto prevent drying Slightly keratinized 角質(zhì)化角質(zhì)化 1-2 layers of cells on the surfacethe nuclear of these cells present Pigment cells/Chromatophores色素細(xì)胞色素細(xì)胞 Specialized cells in the epidermis and

15、dermisResponsible for skin color and color changesThree types (1) Melanophores 黑色素細(xì)胞黑色素細(xì)胞black, brown, or red pigment(2) Iridophores 虹彩細(xì)胞虹彩細(xì)胞white or reflective (3) Xanthophores 黃色素細(xì)胞黃色素細(xì)胞yellow, orange, or red pigmentSkeletonFishes, skeletons function primarily in Protecting internal organs Providi

16、ng points of attachment for muscles Keeping the body from collapsingTerrestrial vertebratesProviding support against gravity Axial skeleton 中軸骨骼中軸骨骼Skull Flattened Smaller Fewer bony elements than the skulls of fishesLightening the skull so it can be supported out of the waterVertebral column Cervic

17、al vertebrae 頸椎頸椎 1 firstly occurs in vertebrates Trunk vertebrae 軀椎軀椎 Sacral vertebrae 薦椎薦椎 1firstly occurs in vertebrates Coccygeal vertebrae 尾椎尾椎The number of cervical vertebrae頸椎頸椎 in vertebratesFishes0Amphibians1Reptiles7-9Birds11-25MammalsMostly 7 Sternums 胸骨胸骨 a character of terrestrial tetra

18、podsAmphibians: lacking ribs, therefore no thoracic cage 胸廓胸廓Appendicular skeleton 附肢骨骼附肢骨骼 a characters of terrestrial tetrapods Pectoral girdle肩胛帶肩胛帶Separate from the skull to allow forelimbs to be more flexible in a larger space Pelvic girdle骨盤帶骨盤帶Tie vertebral column through sacral vertebrae薦椎薦椎

19、 to give hindlimbs a strong supportPelvic girdle consisting of three bones Ilium 髂骨髂骨 Ischium 坐骨坐骨 Pubis 恥骨恥骨They firmly attach the pelvic appendages to the vertebral columnMuscles(1) (1) 原始分節(jié)現(xiàn)象變得不明顯原始分節(jié)現(xiàn)象變得不明顯僅無足目、有尾目依靠軀體收縮擺動運動，僅無足目、有尾目依靠軀體收縮擺動運動，分節(jié)仍明顯分節(jié)仍明顯(2) (2) 軸上肌減少，軸下肌分化明顯軸上肌減少，軸下肌分化明顯肌肉肌肉分層分層

20、(3) (3) 附肢肌發(fā)達(dá)附肢肌發(fā)達(dá)Digestive system Larvae: herbivorous, diverse diets Adults: carnivorous, algae and other plant mattersDigestive tractOral cavity Teeth: unable to chew and only function in holding the food similar to fishes Tongue: on the floor of the mouth, controlled by muscles a true tongue that

21、 first seen in amphibiansFish tongue not controlled by muscles, unable to manipulate food Buccal glands口腔腺口腔腺: excretions contain no enzymesFunction only to wet food to facilitate swallowing fishes have no buccal glandsStomach: obviousCloaca 泄殖腔泄殖腔鯊魚有胃，鯉魚胃分化不明顯鯊魚有胃，鯉魚胃分化不明顯肝臟、胰臟肝臟、胰臟 - 軟骨魚肝臟、胰臟，軟骨魚肝

22、臟、胰臟，硬骨魚肝胰臟硬骨魚肝胰臟Digestive glands Liver PancreasRespiratory systemAdaptation for a life divided between aquatic and terrestrial habitats Larvae and adults of some species external gills Adults lacking thoracic cage胸廓胸廓, buccal pump respiration口咽腔呼吸口咽腔呼吸Vertebrates exhibit two different mechanisms fo

23、r lung ventilation肺通氣肺通氣 Amphibians and some reptiles a positive pressure pumping mechanismpush air into the lungs Most reptiles, all birds and mammals a negative pressure systemRespiratory channel Outer nostril 外鼻孔外鼻孔 Nasal cavity 鼻腔鼻腔 Inner nostril 內(nèi)鼻孔內(nèi)鼻孔 Glottis 喉門喉門 Trachea 氣管氣管: short Lungs 肺肺T

24、he positive pressure pumping mechanismMuscles of the mouth and pharynx creating a positive pressure to force air into the lungs1. Nostril 鼻孔鼻孔 and mouth open, glottis closes, the floor of the mouth lowers air enters the mouth cavity2. contraction of the body wall and elasticity of the lung force air

25、 out of the lungs and out of the mouth cavity through nostril3. nostril and mouth close, the floor of the mouth raises, glottis still opens force air enters the lungs4. Glottis聲門聲門 closes, mouth opens, the floor of the mouth lowers air enters the mouth cavity where some gas exchange occurs (buccopha

26、ryngeal respiration 口咽腔呼吸口咽腔呼吸) The movement is repeated several times before ventilating the lungs again 生生活環(huán)境離不開水，原因活環(huán)境離不開水，原因a a 裸露的皮膚因此不能阻止體內(nèi)水分的蒸發(fā)裸露的皮膚因此不能阻止體內(nèi)水分的蒸發(fā)b b 排泄系統(tǒng)腎小管的亨氏袢短，水分重吸收的能力弱排泄系統(tǒng)腎小管的亨氏袢短，水分重吸收的能力弱Gas exchange: requires a moist surface in all vertebrates drying alters the cell sur

27、faces and prevents diffusion across cell membranesLarvae and a few adult salamanders external gillsThree pairs, project from the outside of the pharyngeal archessalamanders and caecilians 無足目，蚓螈無足目，蚓螈Adults (1) Skin: occurs either in water or on landWhen submerged, all gas exchange through the skin

28、and other moist surfaces The factors that permit the skin to function as a respiratory organ moist rich in capillary beds(2) Mouth and pharynx surfaces Buccopharyngeal respiration 口咽腔呼吸口咽腔呼吸1-7% of total gas exchange(3) Lungsthin-wall sacsLung surface area : skin surface area amphibians: 2:3 mammals

29、: 50-100:1Circulatory systemThree-chambered hearttwo atria + one ventricle incomplete double circulation Vena caval sinus 靜脈竇靜脈竇 right atrium Atrium ventriclePartially divided in urodeles 有尾類有尾類Completely divided in anurans 無尾類無尾類 Single ventricle conus arteriosus 動脈圓錐動脈圓錐No septumIn fact, anuran he

30、arts can keep oxygen-rich and oxygen-poor blood from mixing by special mechanismA spiral valve 螺旋瓣螺旋瓣 within conus arteriosus 動脈圓錐動脈圓錐 or ventral aorta 腹部主動脈弓腹部主動脈弓Help direct blood into pulmonary肺肺 and systemic circuitsExcretion KidneysEither side of the dorsal aorta背主動脈背主動脈 on the dorsal wall of t

31、he body cavity A duct leads to the cloaca泄殖腔泄殖腔 Urinary bladder: a ventral outgrowth of the cloaca 泄殖腔腹部分支泄殖腔腹部分支Nitrogenous wastes AmmoniaSpecies spent much time in water its toxic effects are avoided due to rapid diffusion into water Urea: a product from ammonia in liverSpecies spent much time in

32、landSome amphibians excrete ammonia when in water and urea when on landOsmoregulation the biggest problem that amphibians faceWhen in water remove excess water and conserve essential ionsHow do they do? kidneys produce large quantities of hypotonic urine 低滲尿低滲尿 skin and urinary bladder transport Na+

33、 and Cl- and other ions into the blood水中：水中：皮膚裸露，體內(nèi)滲透壓高于體外，水分進(jìn)入體內(nèi)，腎小球泌尿功能強皮膚裸露，體內(nèi)滲透壓高于體外，水分進(jìn)入體內(nèi)，腎小球泌尿功能強When on landEvaporation蒸發(fā)蒸發(fā) the significant source of water loss in terrestrial amphibians陸地：陸地：皮膚裸露，身體失水，但重吸收水的能力弱，因此在潮濕環(huán)境生活皮膚裸露，身體失水，但重吸收水的能力弱，因此在潮濕環(huán)境生活Strategies of conserving waterBehaviorally

34、 reduce exposure to desiccating 干燥干燥conditions Staying in moist habitats Entering into water frequentlyReducing the amount of body surface exposed to air Curling body卷曲卷曲 Living together to reduce overall surface area Hardened skin Forming cocoons on skinReproduction and developmentReproduction and

35、development繁殖方式的多樣性繁殖方式的多樣性體內(nèi)受精、體內(nèi)發(fā)育體內(nèi)受精、體內(nèi)發(fā)育體外排精、體內(nèi)受精、體內(nèi)發(fā)育體外排精、體內(nèi)受精、體內(nèi)發(fā)育體外受精、體外發(fā)育，水環(huán)境是必需的體外受精、體外發(fā)育，水環(huán)境是必需的 Metamorphosis 變態(tài)現(xiàn)象變態(tài)現(xiàn)象A series of abrupt structural, physiological, and behavioral change limbs: develop lungs: develop tail: reabsorption skin: becomes thickNervous system and sensory organs

36、two cerebral hemispheres form archipallium 原腦皮原腦皮 appears in the cerebrum EyeEyelidsGlands: lubricate and wash the eyeEar tympanic membrane 鼓膜鼓膜 middle ear inner ear眼：有可動下眼瞼和淚腺等防干燥裝置眼：有可動下眼瞼和淚腺等防干燥裝置耳：耳：出現(xiàn)中耳出現(xiàn)中耳傳音裝置傳音裝置鼓膜和耳柱骨鼓膜和耳柱骨對陸地生活的初步適應(yīng)及其不完善性對陸地生活的初步適應(yīng)及其不完善性Lateral line responding to low-freque

37、ncy vibrations in the waterPresent in all aquatic larvae, aquatic adult salamanders, and some adult anuransChemoreceptors important for many amphibiansDistribution Skin Mouth lining Tongue Nasal epitheliumClassification of living amphibiansClass Amphibia Order Caudata / Urodela 有尾目有尾目salamanders, ne

38、wts Order Gymnophiona 無足目無足目caecilians Order Anura 無尾目無尾目frogs and toadsOrder Caudata / Urodela 有尾目有尾目 salamanders蜥蜴蜥蜴, newts蠑螈蠑螈 About 350 species, mostly inhabit mountain streams in the Northern Hemisphere Several centimeters to 1.5 m A tail throughout life Two pairs of limbs, or secondarily degenerated External gills Skin is important in gas exchange Most internal fert