20. Amphibian and Reptilian Anatomy and Physiology


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  • 20. Amphibian and Reptilian Anatomy and Physiology

    1. 1. Amphibian and Reptilian Anatomy and Physiology
    2. 2. Learning Objectives <ul><li>List the taxonomic orders in the classes Reptilia and Amphibia. </li></ul><ul><li>Define ectothermic and explain how ectothermic animals regulate their body temperatures. </li></ul><ul><li>List the unique features of the reptilian and amphibian integumentary systems. </li></ul><ul><li>Describe the process of ecdysis. </li></ul><ul><li>List the unique features of reptilian and amphibian vision and hearing. </li></ul><ul><li>List the components of the reptilian and amphibian heart and describe the flow of blood through the heart. </li></ul><ul><li>Describe the unique features of the reptilian and amphibian respiratory and gastrointestinal systems. </li></ul><ul><li>Describe the structure of the kidneys of reptiles and amphibians. </li></ul><ul><li>Describe the factors that determine the sex of offspring of reptiles and amphibians. </li></ul><ul><li>List the unique features of the musculoskeletal systems of reptiles and amphibians. </li></ul>
    3. 3. Taxonomy <ul><li>Class Reptilia - four orders: </li></ul><ul><ul><li>Crocodylia (alligators and crocodiles) </li></ul></ul><ul><ul><li>Squamata (snakes and lizards) </li></ul></ul><ul><ul><li>Chelonian (turtles and tortoises) </li></ul></ul><ul><ul><li>Rhyncocephalia (tuataras) </li></ul></ul>
    4. 4. Taxonomy <ul><li>Class Amphibia - three orders: </li></ul><ul><ul><li>Gymnophiona (caecilians) </li></ul></ul><ul><ul><li>Anura (frogs and toads) </li></ul></ul><ul><ul><li>Caudata (salamanders and newts) </li></ul></ul>
    5. 5. Metabolism <ul><li>Ectothermic animals are unable to generate body heat internally. </li></ul><ul><ul><li>Body temperature depends on environmental temperature </li></ul></ul><ul><li>Some reptiles can raise body temperatures via metabolic processes (e.g., muscular contractions) </li></ul><ul><li>Herptiles - maintain body temperatures via behavioral thermoregulation (e.g., postural changes) </li></ul>
    6. 6. Ectothermy <ul><li>Related to energy conservation </li></ul><ul><ul><li>Animal regulates temperature depending on metabolic needs </li></ul></ul><ul><ul><li>Allows many herptiles to survive on very small amounts of food </li></ul></ul><ul><li>Depends on access to temperatures within the preferred optimal temperature zone (POTZ) </li></ul><ul><ul><li>POTZ: range of temperatures in which the animal can perform all necessary metabolic functions </li></ul></ul>
    7. 7. Reptile Integument <ul><li>Keratinized skin </li></ul><ul><ul><li>Alpha keratin - soft, flexible, found in interscalar skin </li></ul></ul><ul><ul><li>Beta keratin - rigid, found in scales </li></ul></ul><ul><li>Limited subcutaneous space </li></ul>
    8. 8. Reptile Integument <ul><li>Dermis - dense connective tissue </li></ul><ul><ul><li>Blood and lymph vessels, nerves, and chromatophores (pigment-containing cells) </li></ul></ul><ul><ul><li>Chromatophores allow some lizards to change skin color and pattern </li></ul></ul><ul><ul><li>Osteoderms: bony plates within dermis of some lizards and crocodilians </li></ul></ul>
    9. 9. Reptile Integument <ul><li>Scales - formed by epidermal folds in most reptiles </li></ul><ul><ul><li>Vary in size and shape </li></ul></ul><ul><ul><li>Brille (spectacle): modified scales that may cover eyes </li></ul></ul><ul><li>Other epidermal structures may be present </li></ul><ul><ul><li>Crests, tubercles, spines, and dewlaps </li></ul></ul>
    10. 10. Reptile Integument <ul><li>Scale and scute nomenclature - aids in species identification and medical recording </li></ul>
    11. 11. Ecdysis <ul><li>Shedding of the skin </li></ul><ul><li>Occurs with growth and in response to skin injury </li></ul><ul><li>Process is controlled by thyroid gland </li></ul><ul><li>Shed in pieces or in one large piece </li></ul><ul><li>Shed skin: exuvia </li></ul>
    12. 12. Ecdysis <ul><li>Cells replicate new epidermis </li></ul><ul><li>Enzyme-containing lymph secreted between old and new epidermal layers </li></ul><ul><li>Skin color dulls; spectacle opacifies </li></ul><ul><li>Lymph - resorbed prior to ecdysis </li></ul><ul><li>Mechanical rubbing on objects </li></ul>
    13. 13. Amphibian Integument <ul><li>Epidermis - single or few layers of keratinized cells </li></ul><ul><ul><li>Aquatic amphibians - no keratinized cells </li></ul></ul><ul><li>Extremely permeable </li></ul><ul><ul><li>Absorb water directly from environment </li></ul></ul><ul><ul><li>“ Drink patches”: areas of increased permeability on ventral surfaces </li></ul></ul><ul><li>Dermis - chromatophores and glands </li></ul><ul><ul><li>Glands produce secretions which help protect the amphibian’s skin </li></ul></ul>
    14. 14. Amphibian Integument <ul><li>Toxic secretions - produced by some glands within dermis and epidermis </li></ul><ul><ul><li>Defense mechanisms </li></ul></ul><ul><li>Dermis: little subcutaneous space in salamanders and caecilians </li></ul><ul><ul><li>Anurans: looser attachments of dermis (more subcutaneous space) </li></ul></ul><ul><li>Amphibians regularly shed outer layers of epidermis </li></ul>
    15. 15. Vision <ul><li>Reptiles – iris made up of skeletal muscle under voluntary control </li></ul><ul><ul><li>Pupillary light reflex: consensual reflexes usually not seen </li></ul></ul><ul><li>Lower lid usually more mobile than upper </li></ul>
    16. 16. Vision <ul><li>Some species of lizards have thin, transparent lower lids </li></ul><ul><ul><li>Allows for a degree of vision even when lids are closed </li></ul></ul><ul><li>Cartilagenous pads (tarsal pads): found in lids of some reptiles </li></ul><ul><li>Nictitans: well-developed, mobile in many reptiles </li></ul>
    17. 17. Vision <ul><li>Snakes, some lizards - no true eyelids </li></ul><ul><ul><li>Clear, fused scale (spectacle) </li></ul></ul><ul><li>Tear film - between cornea and spectacle in subspectacular space </li></ul><ul><ul><li>Tears drain into mouth through nasolacrimal duct system </li></ul></ul>
    18. 18. <ul><li>Most reptiles - poorly developed extraocular muscles </li></ul><ul><ul><li>Exception - chameleons; eyes move freely and independently of one another </li></ul></ul><ul><li>Chelonians - no nasolacrimal ducts; tears spill over the lid margin </li></ul>Vision
    19. 19. Vision <ul><li>Lacrimal and harderian glands present in most reptiles and amphibians </li></ul><ul><ul><li>Produce secretions that combine to form the tear film </li></ul></ul><ul><li>Eyelids absent in some aquatic species </li></ul><ul><li>Caecilians - eyes covered with skin </li></ul><ul><li>Amphibian eyes - often protrude ventrally into the oral cavity when animal swallowing </li></ul>
    20. 20. Vision <ul><li>Ossicles: scleral bones present in most reptiles (except snakes and crocodilians) </li></ul><ul><li>Lens: more fluid in reptiles than mammals (more rigid in snakes) </li></ul><ul><li>Accommodation </li></ul><ul><ul><li>Chelonians - lens is squeezed through the pupil </li></ul></ul><ul><ul><li>Snakes - lens moves back and forth due to pressure changes within the aqueous and vitreous humors </li></ul></ul>
    21. 21. Vision <ul><li>Reptiles - avascular retinas </li></ul><ul><ul><li>Nutrition and waste removal via choroidal vessels in vitreous </li></ul></ul><ul><ul><li>Conus papillaris: in lizards, extends into vitreous from optic disc </li></ul></ul><ul><ul><ul><li>provides nutrition and waste removal </li></ul></ul></ul><ul><li>Crocodilians have a tapetum </li></ul><ul><li>Parietal eye - found in some reptiles </li></ul><ul><ul><li>Rudimentary retina and cornea, no iris, lids, or musculature </li></ul></ul><ul><ul><li>Exact function unknown </li></ul></ul><ul><ul><li>May play a role in light-cycle-mediated hormone function </li></ul></ul>
    22. 22. Cardiovascular System <ul><li>Location of the heart varies </li></ul><ul><li>Chelonians - on midline just caudal to thoracic girdle, ventral to the lungs </li></ul><ul><li>Most lizards - within thoracic girdle </li></ul><ul><li>Crocodilians and some lizards - farther back in the coelomic cavity </li></ul><ul><li>Snakes - usually at junction of the first and second third of the body length </li></ul><ul><ul><li>Fairly mobile within the coelomic cavity </li></ul></ul>
    23. 23. Heart <ul><li>Two atria </li></ul><ul><li>One ventricle </li></ul>
    24. 24. Heart <ul><li>Ventricle Regions </li></ul><ul><li>Cavum venosum: paired aortic arches, lead to systemic circulation </li></ul><ul><li>Cavum arteriosum: receives blood from pulmonary veins and directs oxygenated blood to cavum venosum </li></ul><ul><li>Cavum pulmonale: receives blood from right atrium and directs flow into pulmonary circulation </li></ul>
    25. 25. Heart <ul><li>Pressure differences of outflow tracts and muscular ridge that partially separates cavum venosum and cavum pulmonale maintain separation of oxygenated and deoxygenated blood </li></ul>
    26. 26. Heart Rate <ul><li>Depends on species, size, temperature, activity level, and metabolic function </li></ul><ul><li>Heart rate = 33.4 × (Weight in kg -0.25 ) </li></ul><ul><li>Lizards - vasovagal reflex induces drop in heart rate, blood pressure, and a catatonic state </li></ul><ul><ul><li>Triggered by applying gentle pressure to both eyeballs through closed lids </li></ul></ul><ul><ul><li>Lizard recovers with cessation of pressure or mild stimulation </li></ul></ul>
    27. 27. Blood Cells <ul><li>Reptilian red blood cells: oval and nucleated </li></ul><ul><li>RBC life span between 600 and 800 days </li></ul><ul><li>Immature erythrocytes occasionally seen, especially in juveniles and during ecdysis </li></ul>
    28. 28. Blood Cells <ul><li>Heterophils: round with eosinophilic rod-shaped granules and round to oval nuclei </li></ul><ul><ul><li>Analogous to mammalian neutrophils without peroxidase and acid phosphatase </li></ul></ul><ul><ul><li>Reptiles produce caseous pus instead of liquid material </li></ul></ul><ul><li>Eosinophils: similar appearance to heterophils but granules are round </li></ul><ul><li>Basophils: small round cells with deeply basophilic cytoplasmic granules that may obscure the nucleus </li></ul>
    29. 29. Blood Cells <ul><li>Lymphocytes : vary in size; usually round cells with large nuclei, large nuclear-to-cytoplasm ratio, and no cytoplasmic granules </li></ul><ul><li>Monocytes: oval or lobed nuclei, blue-grey cytoplasm, may contain small vacuoles or very fine granules </li></ul><ul><ul><li>Some reptile monocytes have small azurophilic granules (azurophils) </li></ul></ul><ul><li>Thrombocytes: small, oval, nucleated cells; colorless cytoplasm may contain small granules </li></ul>
    30. 30. Respiratory System <ul><li>Reptiles capable of surviving long periods without breathing </li></ul><ul><ul><li>Because of large pulmonary volume, reptiles have efficient anaerobic metabolism and cardiac shunting capabilities. </li></ul></ul><ul><li>Respiration driven by oxygen levels in blood </li></ul>
    31. 31. Respiratory System <ul><li>Glottis of most amphibians and reptiles: rostral portion of oral cavity </li></ul><ul><li>Glottis very mobile in snakes; protrudes from mouth to allow respiration during ingestion of prey </li></ul><ul><li>Paired arytenoid cartilages: border glottal opening; open during respiration </li></ul>
    32. 32. Respiratory System <ul><li>No vocal cords </li></ul><ul><li>Only vocalizations possible are hissing, grunting, bellowing </li></ul><ul><li>Frogs and toads - vocal sacs arise from trachea </li></ul><ul><li>Glottal keel present in some species of snakes </li></ul><ul><ul><li>Increases volume of vocalizations </li></ul></ul>
    33. 33. Pulmonary Tissues <ul><li>Honeycomb appearance </li></ul><ul><li>Openings of honeycomb end at faveoli </li></ul><ul><ul><li>Fixed structures surrounded by capillaries </li></ul></ul><ul><ul><li>Site of gas exchange </li></ul></ul><ul><li>Tracheal rings incomplete (except chelonians) </li></ul>
    34. 34. Reptile Lungs <ul><li>Unicameral lung </li></ul><ul><ul><li>Simple, saclike </li></ul></ul><ul><ul><li>Cranial portion: site of gas exchange </li></ul></ul><ul><ul><li>Caudal portion: avascular, comparable to avian air sac </li></ul></ul>
    35. 35. Reptile Lungs <ul><li>Multicameral lung </li></ul><ul><ul><li>Many compartments </li></ul></ul><ul><ul><li>Intrapulmonary bronchi </li></ul></ul>
    36. 36. Reptile Lungs <ul><li>Paucicameral Lung </li></ul><ul><ul><li>Characteristics of both unicameral and multicameral lungs </li></ul></ul>
    37. 37. Reptile Respiratory System <ul><li>No true diaphragms </li></ul><ul><li>Action of intercostal muscles and parts of axial musculature used for respiration </li></ul>
    38. 38. Reptile Respiratory System <ul><li>Crocodilians - muscular septum caudal to lungs </li></ul><ul><ul><li>Cranial aspect of liver is attached to septum </li></ul></ul><ul><ul><li>Caudal aspect of liver is attached to pubis by diaphramaticus muscle </li></ul></ul><ul><ul><li>Lung inflation results from contraction of diaphramaticus moving the septum caudally </li></ul></ul>
    39. 39. Amphibian Respiratory System <ul><li>Simple saclike lungs </li></ul><ul><li>Some salamanders have no lungs </li></ul><ul><ul><li>Cutaneous respiration </li></ul></ul><ul><li>Pulmonary ventilation results from pumping of buccal cavity and pharynx </li></ul><ul><ul><li>Gas exchange can also occur across mucous membranes of buccal cavity, pharynx, and cloaca </li></ul></ul>
    40. 40. Hearing <ul><li>Ears - both sides of head, usually caudal to eyes </li></ul><ul><li>Tympanum - may lie in depression and/or be covered by folds of skin (some lizards and crocodilians) </li></ul><ul><li>Columella - single bone in middle ear of reptiles </li></ul><ul><ul><li>Connects to tympanum and quadrate bone </li></ul></ul><ul><ul><li>Transmits vibrations to oval window of cochlea </li></ul></ul><ul><ul><li>Converted to nerve impulses and transmitted to the brain via the vestibulocochlear nerve </li></ul></ul>
    41. 41. Hearing <ul><li>Semicircular canals control balance and equilibrium (reptiles) </li></ul><ul><li>Snakes - no external ears; columella articulates with quadrate bone </li></ul><ul><ul><li>Allows snakes to be very sensitive to ground vibrations transmitted through the mandibles </li></ul></ul><ul><ul><li>Snakes also able to hear aerial sounds </li></ul></ul><ul><li>Salamanders and caecilians - no tympanic membranes; columella may be degenerate </li></ul>
    42. 42. Feeding Strategies <ul><li>Carnivorous, omnivorous and herbivorous reptiles all exist </li></ul><ul><li>Snakes, crocodilians, and adult amphibians are strict carnivores </li></ul><ul><li>Some diets are very specialized </li></ul>
    43. 43. Oral Cavity <ul><li>Snakes and lizards: deeply forked tongues </li></ul><ul><ul><li>Function as particle delivery system for vomeronasal organ (accessory olfactory organ) </li></ul></ul><ul><ul><li>Allow for detection of particle gradients </li></ul></ul>
    44. 44. Oral Cavity <ul><li>Chameleons: specialized projectile tongues designed for capturing prey from long distances </li></ul><ul><ul><li>Sticky end which the prey items stick to </li></ul></ul><ul><li>Turtles and tortoises: typically thick, fleshy, relatively immobile tongues </li></ul>
    45. 45. Oral Cavity <ul><li>Crocodilians: immobile tongue attached to intermandibular space </li></ul><ul><ul><li>Muscular flaps from base of tongue and dorsal pharynx allow for opening of mouth while submerged without ingesting or inhaling water </li></ul></ul>
    46. 46. Oral Cavity <ul><li>Tongue used to capture prey (most amphibians) </li></ul><ul><li>Anurans, most terrestrial </li></ul><ul><li>salamanders: caudodorsal </li></ul><ul><li>aspect of tongue is flipped </li></ul><ul><li>cranioventral to prehend </li></ul><ul><li>food (lingual flipping) </li></ul>
    47. 47. Oral Cavity <ul><li>Numerous salivary glands </li></ul><ul><li>Salivary secretions provide lubrication that aids in ingestion of large prey </li></ul><ul><ul><li>Also has enzymatic properties </li></ul></ul><ul><li>Venom glands (some snakes, lizards) - modified salivary gland </li></ul>
    48. 48. Dentition <ul><li>Turtles and tortoises </li></ul><ul><li>No teeth </li></ul><ul><li>Tomia (keratinized beaks) </li></ul><ul><li>Other reptiles: 3 types of dentition </li></ul>
    49. 49. Types of Dentition <ul><li>Thecodont dentition: teeth arise from sockets in skull bones (crocodilians) </li></ul>
    50. 50. <ul><li>Pleurodont dentition: teeth attached to medial aspect of periosteum on mandibles and maxillae (snakes and iguanid lizards) </li></ul>Types of Dentition
    51. 51. Types of Dentition <ul><li>Acrodont dentition: teeth fused to biting edge of mandible and maxillae (some lizards) </li></ul>
    52. 52. Dentition <ul><li>Snakes have 6 rows of teeth: two mandibular, two maxillary, two on palantine/pterygoid bones </li></ul><ul><li>Aglyphous snakes lack fangs </li></ul>
    53. 53. Dentition <ul><li>Venomous snakes - specialized dentition for venom delivery </li></ul><ul><li>Proteroglyphous and opisthoglyphous - fangs are fixed upright </li></ul><ul><li>Solenoglyphous - fangs are folded on roof of mouth when mouth is closed and are erect when snake bites </li></ul>
    54. 54. Dentition <ul><li>Venom-delivering teeth: hollow with an opening near end where venom expelled </li></ul><ul><li>Fangs receive venom through a duct from venom gland at its base </li></ul><ul><li>Contraction of muscles around venom gland forces venom out through the fang </li></ul><ul><li>Snakes can control amount of venom delivered with each bite </li></ul>
    55. 55. Dentition <ul><li>Most amphibians have teeth </li></ul><ul><li>Caecilians and salamanders - both maxillary and mandibular teeth </li></ul><ul><ul><li>Palatal teeth in some species </li></ul></ul><ul><li>Maxillary dentition present in some anuran species </li></ul><ul><li>Odontoid process: cutting plates on rostral mandibles of some frogs </li></ul>
    56. 56. Esophagus <ul><li>Reptile - thin and distensible </li></ul><ul><ul><li>Unique morphology reflects type of prey </li></ul></ul><ul><li>Amphibian esophagus very short and wide, especially in anurans </li></ul>
    57. 57. Stomach <ul><li>Reptile - variable size and shape </li></ul><ul><ul><li>Snakes - highly distensible </li></ul></ul><ul><ul><li>Crocodilians - thick muscle comparable to avian gizzard </li></ul></ul><ul><li>Amphibian - anurans capable of prolapsing stomach through the mouth; gastric prolapse is a terminal event in dying animals </li></ul>
    58. 58. Amphibian Intestinal Tract <ul><li>Indistinct regions </li></ul><ul><li>Liver may contain melanomacrophages involved in immune function </li></ul><ul><li>Pancreas - between stomach and proximal segments of intestine </li></ul>
    59. 59. Reptilian Intestinal Tract <ul><li>Varies according to diet </li></ul><ul><ul><li>Herbivores - longer intestinal tracts than carnivores </li></ul></ul><ul><li>Snakes - relatively straight intestinal tracts </li></ul>
    60. 60. Reptilian Intestinal Tract <ul><li>Colon - large and complex in herbivores </li></ul><ul><ul><li>Hindgut fermentation for digestion </li></ul></ul><ul><li>Cecae - site of hindgut fermentation in herbivorous lizards and chelonians </li></ul><ul><li>Liver - usually large and bi-lobed </li></ul>
    61. 61. Cloaca <ul><li>Common outflow tract for GI and urogenital tracts (all reptiles and amphibians) </li></ul><ul><li>Three chambers: coprodeum, urodeum and proctodeum </li></ul>
    62. 62. Reptile Kidney <ul><li>Usually oblong and smooth-surfaced </li></ul><ul><li>Snakes - kidneys that are lobulated </li></ul><ul><li>Ureters empty into dorsolateral aspects of the urodeum </li></ul><ul><ul><li>Some species do not have urinary bladders </li></ul></ul>
    63. 63. Reptile Kidney <ul><li>No distinct renal pelvis </li></ul><ul><li>Distal collecting tubules join into collecting ducts that merge to form the ureter </li></ul><ul><li>No loop of Henle present </li></ul><ul><li>Not able to concentrate urine as mammals do </li></ul><ul><li>Water can be absorbed from urine through wall of the urinary bladder, rectum, or cloaca </li></ul>
    64. 64. Amphibian Kidney <ul><li>Nephrostomes - connect the coelomic cavity to the renal tubules; filter blood and coelomic fluid </li></ul><ul><li>Kidneys usually lobulated and in caudodorsal coelomic cavity </li></ul>
    65. 65. Amphibian Kidney <ul><li>Some amphibians excrete ammonia as a nitrogenous waste product; others excrete urea, some excrete uric acid </li></ul><ul><li>No ability to concentrate urine </li></ul><ul><li>Urinary bladders and cloacal anatomy similar to reptiles </li></ul>
    66. 66. Reptile Reproductive System <ul><li>Males have internal testes located in dorsal coelomic cavity </li></ul><ul><li>Ductus deferens leads from testes to dorsal wall of the urodeum </li></ul><ul><li>Most also have a sexual portion to the kidney tubules </li></ul><ul><ul><li>Develops in response to high levels of circulating sex hormones </li></ul></ul><ul><ul><li>Probably provide secretions that contribute to the seminal fluid </li></ul></ul>
    67. 67. Reptile Reproductive System <ul><li>Copulatory organs vary in structure </li></ul><ul><ul><li>Crocodilians and chelonians - phallus of erectile tissue rising from </li></ul></ul><ul><ul><li>floor of cloaca </li></ul></ul><ul><ul><li>Snakes and lizards - paired hemipenes everted from the tail base through the vent </li></ul></ul>
    68. 68. Reptile Reproductive System <ul><li>Females - paired ovaries in dorsal coelomic cavity </li></ul><ul><li>Paired oviducts lead to cloaca and end at genital papillae in dorsal wall of the urodeum </li></ul>
    69. 69. Reptile Reproductive System <ul><li>Oviducts - 5 regions: infundibulum, magnum, isthmus, uterus, and vagina </li></ul><ul><li>Albumin and shell - in oviparous species, added to ova in the oviduct prior to egg laying </li></ul><ul><li>In viviparous species, fetuses are retained in uterine portion of oviduct </li></ul>
    70. 70. Reptile Reproductive Cycle <ul><li>Vitellogenesis - development and maturation of the follicles </li></ul><ul><ul><li>Triggered by environmental cues that stimulate release of FSH and estrogen </li></ul></ul><ul><li>Vitellogenin - lipid substance added to yolk within developing follicle </li></ul><ul><ul><li>Large amounts of calcium are also added </li></ul></ul><ul><li>In viviparous reptiles - some support of fetus </li></ul><ul><ul><li>Some lizards have true placentas </li></ul></ul>
    71. 71. Reptile Reproductive Cycle <ul><li>Oviposition - many reptiles dig nests to lay eggs </li></ul><ul><ul><li>Without suitable nesting material, female may experience dystocia </li></ul></ul><ul><li>Chelonians and lizard species may excavate deep holes to deposit eggs </li></ul>
    72. 72. Reptile Reproductive Cycle <ul><li>After oviposition or parturition, reptiles not involved with care of eggs or offspring </li></ul><ul><ul><li>Exceptions - crocodilians protect their nests and young for a period of time following hatching </li></ul></ul><ul><ul><li>Pythons and cobras - protect their nests until hatching </li></ul></ul>
    73. 73. Egg Incubation <ul><li>Development and hatching requires proper temperature, humidity, and gas composition of nest </li></ul><ul><li>Incubation time and temperature varies </li></ul><ul><li>Reptile eggs should not be rotated during incubation </li></ul>
    74. 74. Sex Determination in Reptiles <ul><li>Determined by genotype or temperature at which eggs are incubated </li></ul><ul><li>Sex chromosomes: </li></ul><ul><ul><li>Females are heterozygous (ZW) and males are homozygous (ZZ) </li></ul></ul>
    75. 75. Sex Determination in Reptiles <ul><li>Some species do not have sex chromosomes </li></ul><ul><ul><li>Higher incubation temperatures produce males in crocodilians and lizards </li></ul></ul><ul><ul><li>Opposite occurs in chelonians </li></ul></ul><ul><ul><li>Temperature range within the nest allows for production of a mixed clutch of hatchlings </li></ul></ul>
    76. 76. Secondary Sex Characteristics <ul><li>Snakes - no real sexual dimorphism </li></ul><ul><li>In some species, pelvic spurs can be larger in males </li></ul><ul><ul><li>Pelvic spurs: remnants of pelvic limbs; provide tactile stimulation to females </li></ul></ul>
    77. 77. Secondary Sex Characteristics <ul><li>Male chelonians may have concave plastron and more distally located vent </li></ul><ul><ul><li>Allows closer apposition of the cloacas when the male mounts the female </li></ul></ul><ul><li>Some lizards show obvious dimorphism </li></ul><ul><ul><li>Example: male Jackson’s chameleon has three well-developed horns on its face </li></ul></ul>
    78. 78. Amphibian Reproduction <ul><li>Sexual dimorphism in some species </li></ul><ul><ul><li>Poison dart frog males have enlarged toe pads </li></ul></ul><ul><ul><li>Large tympanic membranes in some male anurans </li></ul></ul><ul><ul><li>Prominent cloacal glands in male salamanders </li></ul></ul>
    79. 79. Amphibian Reproduction <ul><li>Paired gonads in dorsocaudal coelomic cavity </li></ul><ul><li>Bidder’s organs - ovarian remnants near testes in male toads </li></ul><ul><li>Most caecilians are viviparous </li></ul><ul><li>Most anurans and salamanders are oviparous </li></ul><ul><li>Amplexus - Male frogs and toads fertilize eggs as they are laid while grasping the female </li></ul>
    80. 80. Amphibian Reproduction <ul><li>Phallodeum - portion of cloaca in caecilians that is everted to deposit semen into female’s cloaca </li></ul><ul><li>Spermatophores - packets of sperm deposited onto substrate by male salamanders </li></ul><ul><ul><li>Picked up by the female salamander’s cloaca </li></ul></ul><ul><ul><li>Spermatotheca - pocket in cloaca of female salamanders where sperm can be stored </li></ul></ul>
    81. 81. Amphibian Reproduction <ul><li>Eggs are usually deposited in or near water </li></ul><ul><li>Some parental care of eggs and/or young in anurans and most salamanders </li></ul><ul><li>Larval anurans (tadpoles) have completely aquatic lives prior to metamorphosis </li></ul><ul><li>Tadpole metamorphosis - usually complete within 90 days </li></ul><ul><ul><li>Metamorphosis is stimulated by thyroid hormones </li></ul></ul>
    82. 82. Endocrine System <ul><li>Single thyroid gland (except lizard) </li></ul><ul><ul><li>Crocodilians - bilobed thyroid has a thin isthmus between lobes </li></ul></ul><ul><li>Size of thyroid gland varies according to season and metabolic state </li></ul><ul><li>Parathyroid glands and ultimobrachial bodies in cervical region </li></ul>
    83. 83. Endocrine System <ul><li>Adrenal glands - usually within the ligaments that suspend the gonads </li></ul><ul><li>Produce epinephrine, norepinephrine, aldosterone, and corticosterone </li></ul><ul><li>No distinct separation of adrenal cortex and medulla </li></ul><ul><li>Exact location of endocrine organs in amphibians varies </li></ul>
    84. 84. Reptile Nervous System <ul><li>Three major divisions of reptilian brain </li></ul><ul><ul><li>Forebrain - olfactory lobes, cerebral hemispheres, diencephalon </li></ul></ul><ul><ul><li>Midbrain - optic lobes, cerebral peduncles, nerve fibers connecting forebrain and hindbrain </li></ul></ul><ul><ul><li>Hindbrain - cerebellum, medulla oblongata </li></ul></ul><ul><li>No surface gyri or sulci on the brain </li></ul>
    85. 85. Reptile Nervous System <ul><li>Brain meninges: pia-arachnoid layer and dura mater </li></ul><ul><li>12 cranial nerves </li></ul><ul><li>Depend on spinal segmental reflexes and locomotor centers for control of movement </li></ul>
    86. 86. Amphibian Nervous System <ul><li>Brain - well developed for basic functions (sight, olfaction, and movement) </li></ul><ul><li>10 cranial nerves </li></ul><ul><li>Spinal cord extends to the tip of the tail in amphibians and caecilians; ends in lumbar region in frogs and toads </li></ul><ul><li>Animal dependent upon spinal segmental reflexes to control movement </li></ul>
    87. 87. Reptile Musculoskeletal System <ul><li>Types of skulls </li></ul><ul><li>Anapsid: no temporal openings; chelonians </li></ul><ul><li>Diapsid: temporal openings in the skull </li></ul>
    88. 88. Reptile Musculoskeletal System <ul><li>Snake skulls -extremely mobile </li></ul><ul><li>Mandibular symphysis is connected by ligaments that allow jaws to move independently of each other </li></ul>
    89. 89. Snake Skulls <ul><li>Mandibular symphysis connected by ligaments allows jaws to move independently </li></ul><ul><li>Quadrate bones - allow wider opening of mouth </li></ul><ul><li>Moveable bones of maxillae and palate </li></ul>
    90. 90. Reptile Musculoskeletal System <ul><li>Spine - extremely flexible; presacral, sacral, and caudal-vertebral regions </li></ul><ul><li>Single occipital condyle forms the articulation between skull and spine </li></ul><ul><li>Well-developed ribs </li></ul><ul><ul><li>Exceptions: chelonians’ spine and ribs are fused to the bony shell </li></ul></ul>
    91. 91. Amphibian Musculoskeletal System <ul><li>Skulls of anurans - broad and fenestrated </li></ul><ul><li>Parts of the skull involved with olfaction and hearing are well developed </li></ul><ul><li>Palate - poorly developed with reduced dentition </li></ul><ul><li>Caecilians - compact, well-ossified skulls with well-developed dentition </li></ul>
    92. 92. Amphibian Musculoskeletal System <ul><li>Highly variable number of vertebrae </li></ul><ul><li>Vertebrae - no distinctions of regions </li></ul><ul><ul><li>Salamanders and anurans also possess sacral vertebrae </li></ul></ul><ul><li>Anurans’ vertebrae are fused </li></ul><ul><ul><li>Urostyle - last caudal vertebra </li></ul></ul><ul><li>Caecilians lack a sternum </li></ul><ul><li>Sternum is a small cartilaginous plate in salamanders </li></ul>
    93. 93. Axial Skeleton <ul><li>Tail autonomy - defensive mechanism </li></ul><ul><ul><li>Some lizards and salamanders </li></ul></ul><ul><ul><li>Discarded tail usually continues to wiggle and distract predator </li></ul></ul><ul><li>The species capable of tail autonomy have “fracture planes” along which tails break </li></ul><ul><ul><li>Little to no blood loss </li></ul></ul><ul><li>Lost tail can regenerate; regenerated tail stiff and cartilaginous </li></ul>
    94. 94. Reptile Appendicular Skeleton <ul><li>Pectoral girdle - scapula and coracoid bone with muscular attachments to the body </li></ul><ul><li>Pectoral limbs - humerus, radius, ulna, carpal bones, metacarpal bones, and phalanges </li></ul><ul><li>Pelvic limb - femur, tibia, tarsal and metatarsal bones, and the phalanges </li></ul><ul><ul><li>Usually five digits on both front and rear feet </li></ul></ul>
    95. 95. Reptile Appendicular Skeleton <ul><li>Spurs - vestigial pelvic limbs of some snake species </li></ul><ul><ul><li>Found on either side of the vent </li></ul></ul><ul><ul><li>Used in courtship behavior </li></ul></ul><ul><li>Some lizards have very reduced limbs </li></ul><ul><ul><li>“ Legless lizards” retain vestigial thoracic and pelvic limb structures </li></ul></ul>
    96. 96. Amphibian Appendicular Skeleton <ul><li>Pectoral girdle - primarily cartilaginous; consists of precoracoid, coracoid and scapula </li></ul><ul><ul><li>Exception - anurans’ pectoral girdle is completely ossified and consists of scapula, clavicle, and coracoid </li></ul></ul><ul><li>Pectoral limb - similar to reptile, except for radioulna (fused radius and ulna in anurans) </li></ul><ul><ul><li>Four toes usually present on the pectoral limbs </li></ul></ul><ul><li>Pelvic girdle - ilium, ischium and pubis </li></ul>
    97. 97. Amphibian Appendicular Skeleton <ul><li>Pelvic limb - elongated and well developed for swimming and jumping </li></ul><ul><ul><li>Elongated metatarsal bones in anurans </li></ul></ul><ul><ul><li>Usually five toes are present </li></ul></ul>
    98. 98. Muscular Structure <ul><li>In four-limbed amphibians and reptiles, musculature is somewhat analogous to that of mammals. </li></ul><ul><li>Snakes: epaxial muscles and segmental muscles </li></ul>