Tetrapod: four limbs




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楊懿如 第 頁 2016/4/21

Chapter 6 Amphibians

  1. Introduction

(1)Characters

Tetrapod: four limbs

Glandular skin

Gas exchange by lung, gills or skin

Double circulation

Three-chambered heart

Sound-tympanum and columella

Olfactory epithelium

(2)Fig. 6.1 Early tetrapod evolution and the rise of amphibians: middle Devonian

Fig.6.2 Cladogram of tetrapods



  1. Evolution

Ancestor of amphibians: lungfish, lobe-finned rhipidistian, or lobe-finned coelacanth?

(1)400 million years ago osteolepiform:rhipidistians

Fig. 6.3 Eusthenopteron foordi

Fig.6.4,6.5 earliest amphibians

Similar in jaw and vertebrae

Labyrinth tooth

(2)coelacanth: sequence of amino acid in hemoglobin

(3)anatomical and molecular evidence favoring lungfishes

(4)diphyltic: majority(Rhipidistia), salamders(lungfish)

(5)Great climatic fluctuations during Devonian period, ancestral semiamphibious groups onto land to avoid predators or to seek arthropod prey.

Class Amphibia

Subclass Labyrinthodontia

Subclass Lepospondyli

Subclass lissamphibia



  1. Labyrinthodontia

Order Ichthyostegalis Fig.6.6 earliest amphibian

Upper Devonian freshwater in Greenland –Triassic periods

Best known genera

Icthyostega: 65-70cm

Acanthostega:

Order Temnospondyli: two occipital condyles, 245 million years ago to living amphibians

Order Anthracosauria: ancestral to turtle and diapsids, 370 million years ago

Problems to overcome to survive on land



  1. Locomotion: pelvic and pectoral girdles

  2. Dessiccation: stratum corneum, mucous glands

  3. Internal fertilization, direct development, viviparous

  1. Lepospondyli

Small amphibians, Carboniferous and Permian

Vertebral centra were formed by the directly deposition of bone around the notochord



  1. Lissamphibia

Salamanders: order caudate, fossil in the Upper Jurassic of North America and Eurasia, 145 million years ago

Caecilian: order apoda, Jurassic, 145 million years ago

Frogs and toads: Triassic, 200 million years ago in Madagascar, order Proanura

Order anura, 190 million years ago, Jurassic period



  1. Morphology

(1)Integumentary system

(a)permeable to water

water uptake: seat patch

(b)skin: Fig.6.7a epidermis and dermis

Molt

Intermolt



(c)Fig. 6.7b mucous and granular(poison) glands Function of mucous gland: moist and protective

Glanular glands: Fig.6.7c, warts and parotoid glands, Fig.6.7d, dorsolateral ridge

Toxin-secreting

*vasoconstrictors, hemolytic agents, hallucinogen, neurotoxins

*Bacteria-killing antibiotic peptides: disrupt bacterial membranes by punching holes

*Poison-arrow frog: toxic steroidal alkaloids

*Aposematic (warning) coloration

(d)Thermoregulation is accomplished through changes in their position or location

(e)increase the surface area available for gas exchange Fig.6.8 hairy Frog

(f)superciliary processed, cranial crests, and flaps on the heels: concealment

(g)metatarsal tubercle: digging, locomotion

(h)brood pouch; marsupial frogs

(i)glands on various parts of body, pheromone

(j)webbing, Fig.6.10 toe pads, mucus secretions

Fig. 6.11 intercalary bone

(k)color change: melanophores, iridophore, xanthophore, control by meanocyte-stimulating hormone (anterior lobe of pituitary gland)

Bio-Note 6.2 Why frogs are green? Short wavelength is diffracted and refracted back by the iridophores

(2)Skeletal system

Fig.6.12 increased ossification, loss and fusion of elements, extensive modification of the appendicular skeleton

Fig.6.13 Skulls of cacelians and anurans

Jaw is autostylic

Fig. 6.14 Pectoral girdle:

Arciferous : Bufonidae, Discoglssidae, Hylidae, Pelobatidae, Pipidae, and Leptodactylidae

Firmisternal: Ranidae, Rhacophoridae, microhylidae

Frog’s leap

(3) Muscular system

lateral undulations for swimming: axial musculature

land-dwelling: limbs

Hindlimb muscles of frogs

Bio-Note 6.3 Forward motion in Caecilians

(4)Cardiovascular system

Fig. 6.15 two atria and a single ventricle

Fig.6.16 Frog’s heart: Ventricualr trabeculae: to keep oxygenated and deoxygenated blood separated in the ventricle

Fig.6.17 aortic arches

Cutaneous gas exchange

(5)Respiratory System

modifications: skin, lung, blood

Fig. 6.18 Oral cavity of toad

Glottis-larynx-trachea

Vocal cord, vocal sac

Ears act as loudspeakers

Pacific giant salamander

Fig. 6.19 breathing in frogs

Gas exchange: cutaneous, buccopharyngeal, branchial, and pulmonary

Plethodontidae: lungless

Larval amphibians: gills, spiracle

Fig. 6.20 larval gill of salamander

(6)Digestive system

the tongue is poorly developed in aquatic form

a projectile tongue

Fig. 6.21 flipping feeding

Homodont dentition

Larval form: herbivorous, longer intestines

Cloca


Bio-Note 6.6 Right forelimb dominance in toads

(7)Nervous system Fig. 6.22

(8)Sense organ

(a)Neuromast organs: larval and aquatic adult, lateral-line canals

(b)ear Fig.6.23 outer ear, middle ear, inner ear

tympanic membrane(tympanum)

Fig. 6.24 male>female

Tadpole: developing lungs as eardrums

Fig.6.23 scapula-opercularis muscle-operculum route


  1. eyes: large and well developed

color vision

movable eyelids and orbital glands Fig.6.25nictitating membrane

Fig. 6.26 blind salamander


  1. nose

Fig.6.27 nasolabial groove and vomeronasal organs: pheromones

(9)Endocrine system

estrogens and progesterone control in females

Fig.6.28 androgen control in male

(10)Urogenital system

pronephric kidney

Bio-Note 6.7 Using bladders to store water

(11) Female reproductive system Fig. 6.29 c, d

ovisac, spermatheca

(12)Male reproductive system

Fig. 6.29 a, b

Fig. 6.30 tailed frog, intromittent organ

Family Bufonidae: bidder’s organ, sex reversal

4.Reproduction

(1)Aquatic development

(2)Semiterrestrial development

(3)Terrestrial development

precipitation and temperature are major climatic factors affect breeding in amphibians

annual cycling

grow continuous- indeterminate growth: 1-2 years to mature

paecomorphosis

species recognition by visual and olfactory (salamanders): Fig. 6.31 sexual dimorphism

tactile interaction, specific postural displays, and species-specific calls in anurans

amplexus: Fig.6.32

swollen glandular thumb

auditory cues

Female choice:


    1. good territory

    2. large body size

90%salamanders are internal fertilization Fig. 6.33 spermatophores

all cacilians are internal fertilization

5.Growth and development

(1)Oviparous

salamanders:

Fig.6.34 eggs in water

In moist site on land

Anurans have a variety of larval development than any other group of amphibians Fig.6.34c,d, Table 6.1 foam nest, dorsal pouches, attached to the back etc.

800 species direct development

rhinodermatid frog: vocal pouch egg-young

gastric brooding frog Fig.6.35

(2)Viviparous

Four African toads, and one frog

(3)Duration of embryonic development

Fig.6.36 temperature-dependent

Table 6.2 salamanders 13-275 days

Table 6.3 frogs 1-40days

(4)Hatching and birth

frontal gland: hatching enzymes

Eleutherodactylus : egg tooth

(5)Parental care

extended parental care is more common in salamander Fig. 6.37

guarding eggs against predator

moistening or aerating eggs

transporting eggs and larvae

5-6weeks to 275 days

(6)Growth and Metamorphosis

Fig.6.38


Neoteny

paedogenesis

(7)Attainment and sexual maturity

Table 6.4 different at different geographic sites



Bullfrog: 1-3 year tadpole


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