讲稿课件16两栖类

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 泥盆纪（泥盆纪（3.5-4.2亿年前）亿年前） Climates: unpredictable Water levels of lakes and rivers: varied periodica

2、lly Oxygen availability in water: reduced due to decay of pteridophyte plants 羊齿植物羊齿植物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肉鳍鱼亚纲肉鳍鱼亚纲Lungfishes or Coelacanths 腔棘鱼腔棘鱼Which one?Lungfishes which is supported by recent evidence based on molecular biology Freshwater Internal naris 内鼻孔内鼻孔 Pneumatic sacs 气囊气囊: 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 腰带腰带 is tied with the vertebral column （1 1）肺鱼亚纲）肺鱼亚纲特征：特征：体呈纺锤行，硬骨不发达，终生有残存的脊索，

5、体呈纺锤行，硬骨不发达，终生有残存的脊索，体尚未形成；上颌还没有前颌骨和颌骨；脑颅为体尚未形成；上颌还没有前颌骨和颌骨；脑颅为单一硬骨整块单一硬骨整块水中：用鳃呼吸，旱季：用鳔（肺）呼吸水中：用鳃呼吸，旱季：用鳔（肺）呼吸澳洲肺鱼澳洲肺鱼非洲肺鱼非洲肺鱼美洲肺鱼美洲肺鱼 Coelacanths 腔棘鱼腔棘鱼 Marine bony fishes, living species 矛尾鱼矛尾鱼 Internal naris 内鼻孔内鼻孔 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 泥盆纪泥盆纪These animals are called Stegocephalia 坚头类坚头类The representative: Ichthyostega 鱼头螈鱼头螈 Ancient amphibians: a once-diverse group of animalsThe ancient amphibians gave

7、rise to two lineages:1. Modern amphibians2. Amniote vertebrates 羊膜脊椎动物羊膜脊椎动物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 肩带肩带 Hindlimb: through pelvic girdle 腰带

10、腰带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 体循环体循环 + pulmonary circuit 肺循环肺循环 However, the circulation is incompleteEctotherm 冷血动物冷血动物Depend on external heat sources to mai

12、ntain body temperature4. Modification of nervous system and sensory organs Two cerebral hemispheres form Archipallium 原脑皮原脑皮 appears in the cerebrum 大脑大脑Evolution of vertebrae brainpalaeopallium 古脑皮古脑皮 archipallium 原脑皮原脑皮 neopallium 新新脑皮脑皮EyeEyelidsGlands: lubricate润滑润滑 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渗透性渗透性 water across the skin

14、 primarily through osmosis, less so by diffusion Highly glandular腺体的腺体的 multicelular mucous glands，widespreadto prevent drying Slightly keratinized 角质化角质化 1-2 layers of cells on the surfacethe nuclear of these cells present Pigment cells/Chromatophores色素细胞色素细胞 Specialized cells in the epidermis and

15、dermisResponsible for skin color and color changesThree types (1) Melanophores 黑色素细胞黑色素细胞black, brown, or red pigment(2) Iridophores 虹彩细胞虹彩细胞white or reflective (3) Xanthophores 黄色素细胞黄色素细胞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 中轴骨骼中轴骨骼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 颈椎颈椎 1 firstly occurs in vertebrates Trunk vertebrae 躯椎躯椎 Sacral vertebrae 荐椎荐椎 1firstly occurs in vertebrates Coccygeal vertebrae 尾椎尾椎The number of cervical vertebrae颈椎颈椎 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肩胛带肩胛带Separate from the skull to allow forelimbs to be more flexible in a larger space Pelvic girdle骨盘带骨盘带Tie vertebral column through sacral vertebrae荐椎荐椎

19、 to give hindlimbs a strong supportPelvic girdle consisting of three bones Ilium 髂骨髂骨 Ischium 坐骨坐骨 Pubis 耻骨耻骨They firmly attach the pelvic appendages to the vertebral columnMuscles(1) (1) 原始分节现象变得不明显原始分节现象变得不明显仅无足目、有尾目依靠躯体收缩摆动运动，仅无足目、有尾目依靠躯体收缩摆动运动，分节仍明显分节仍明显(2) (2) 轴上肌减少，轴下肌分化明显轴上肌减少，轴下肌分化明显肌肉肌肉分层分层

20、(3) (3) 附肢肌发达附肢肌发达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 泄殖腔泄殖腔鲨鱼有胃，鲤鱼胃分化不明显鲨鱼有胃，鲤鱼胃分化不明显肝脏、胰脏肝脏、胰脏 - 软骨鱼肝脏、胰脏，软骨鱼肝

22、脏、胰脏，硬骨鱼肝胰脏硬骨鱼肝胰脏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肺通气肺通气 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 内鼻孔内鼻孔 Glottis 喉门喉门 Trachea 气管气管: 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声门声门 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 生生活环境离不开水，原因活环境离不开水，原因a a 裸露的皮肤因此不能阻止体内水分的蒸发裸露的皮肤因此不能阻止体内水分的蒸发b b 排泄系统肾小管的亨氏袢短，水分重吸收的能力弱排泄系统肾小管的亨氏袢短，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 无足目，蚓螈无足目，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 静脉窦静脉窦 right atrium Atrium ventriclePartially divided in urodeles 有尾类有尾类Completely divided in anurans 无尾类无尾类 Single ventricle conus arteriosus 动脉圆锥动脉圆锥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 动脉圆锥动脉圆锥 or ventral aorta 腹部主动脉弓腹部主动脉弓Help direct blood into pulmonary肺肺 and systemic circuitsExcretion KidneysEither side of the dorsal aorta背主动脉背主动脉 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 低渗尿低渗尿 skin and urinary bladder transport Na+

33、 and Cl- and other ions into the blood水中：水中：皮肤裸露，体内渗透压高于体外，水分进入体内，肾小球泌尿功能强皮肤裸露，体内渗透压高于体外，水分进入体内，肾小球泌尿功能强When on landEvaporation蒸发蒸发 the significant source of water loss in terrestrial amphibians陆地：陆地：皮肤裸露，身体失水，但重吸收水的能力弱，因此在潮湿环境生活皮肤裸露，身体失水，但重吸收水的能力弱，因此在潮湿环境生活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繁殖方式的多样性繁殖方式的多样性体内受精、体内发育体内受精、体内发育体外排精、体内受精、体内发育体外排精、体内受精、体内发育体外受精、体外发育，水环境是必需的体外受精、体外发育，水环境是必需的 Metamorphosis 变态现象变态现象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 原脑皮原脑皮 appears in the cerebrum EyeEyelidsGlands: lubricate and wash the eyeEar tympanic membrane 鼓膜鼓膜 middle ear inner ear眼：有可动下眼睑和泪腺等防干燥装置眼：有可动下眼睑和泪腺等防干燥装置耳：耳：出现中耳出现中耳传音装置传音装置鼓膜和耳柱骨鼓膜和耳柱骨对陆地生活的初步适应及其不完善性对陆地生活的初步适应及其不完善性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 无足目无足目caecilians Order Anura 无尾目无尾目frogs and toadsOrder Caudata / Urodela 有尾目有尾目 salamanders蜥蜴蜥蜴, newts蝾螈蝾螈 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