Biology 453 Exam 1: Lecture 4

Front 1

LISSAMPHIBIAN SKIN:
Stratum Corneum
presence, type of keratin, other chemicals?

Back 1

* Presence - adults; absent in aquatic larvae
* Type of keratin - alpha only; relatively soft
* Other chemicals - waxes & phospholipids reduce water loss in some species
* Variation
o aquatic adults - thin layer, 1-2 cell layers only, low in waxes
o terrestrial adults
+ thickness increases relative to adaptation to terrestrial/dry environment
+ some (e.g. toads) have more waxes/phospholipids & produce less mucous

Front 2

LISSAMPHIBIAN SKIN:
Special Keratinized Appendages

Back 2

* Keratinized caps - on fingertips, may be "sharp"
o found in aquatic frogs & salamanders that live in fast water streams
o not a true claw
* Tubercles - thick keratinized pads on front thumbs
o used by males for holding females during mating
o common in frogs & salamanders
* Spade - blade-like structure on rear feet for digging - e.g. spadefoot toads

Front 3

LISSAMPHIBIAN SKIN:
Epidermal Mucous Glands: Design, Function?

Back 3

* Chemical Composition - water, mucopolysaccarides
* Design
o unicellular - in larvae only; similar to fish glands
o multicellular - large, abundant, secretion is nearly continuous
+ fewer in the skin of terrestrial adapted amphibians
* Function in Aquatic Taxa
o decrease turbulence & drag during locomotion
* Other Functions
o aestivation - some "drought-adapted" frogs build mucous cocoons
o protect skin from bacteria & parasites
o osmoregulation - help block water flow through skin
o aids cutaneous respiration (it requires a moist skin)

Front 4

LISSAMPHIBIAN SKIN:
Epidermal Granular Glands: What's excreted, Design, Functions?

Back 4

* Chemical Composition - alkaloids & polypeptides
* Design
o unicellular - rare; e.g. giant cells in tadpoles produce alarm substances
o multicellular types - large, common
* Functions
o pheromonal
+ attract mates in some salamanders
+ localized on body - chin, cloaca, tail
o poisonous or sticky
+ deter predators
+ often but not always widespread over body
+ e.g. Parotid gland behind eye has numerous, large poison glands

Front 5

LISSAMPHIBIAN SKIN:
Dermis

Back 5

* Connective Tissue Structure - no special arrangement of fibers
* Dermal "Bony" Scales or Derivatives
o osteoderms are rare & usually small or deep in skin
o caecilians have fibrous scales under the folds of skin along body
o a few tropical toads have large bone plates in back

Front 6

LABYRINTHODONTIA SKIN- FOSSIL AMPHIBIANS, FIRST TETRAPODS
Epidermis, Dermis?

Back 6

A. Epidermis

* Assumed to have s. corneum with keratin
* No Soft Tissues Preserved - we don't know what glands they might have had in skin

B. Dermis

* Dermal "Bony" Scales or Derivatives
o "fish-like" scales numerous in skin are retained from their ancestors the Sarcopterygian fishes
o some of the earliest labyrinthodonts were still very aquatic, in part

Front 7

Sauropsida Skin
(includes turtles, lizards, snakes, alligators, dinosaurs, birds)
Epidermis - Keratinized/Horny Scales or Plates
Design and Chemical Composition?

Back 7

# Design

* dermal papilla stimulates localized outgrowth of epidermis into scales
* specialized stratum corneum that is compact, very thin & very hard
o scales slightly thicker on exposed surface
o hinge of scale is thinner, "ruffled" to allow bending of body
* more heavily keratinized than amphibian skin
* skin is dry, no mucous present

# Chemical Composition

* typically beta keratin + alpha keratin in some combination
* beta keratin is harder than alpha keratin
* added lipids aid water-proofing in some taxa

Front 8

Sauropsida Skin
Variation among taxa

Back 8

* Testudines (Chelonia) - Turtles
o non-overlapping scales cover bony shells - beta keratin
o new keratinized scales are added in layers, wear off slowly
o desert tortoise legs
+ exposed portion - beta keratin
+ hinge region - alpha keratin
o pattern of alpha & beta keratin varies among more aquatic taxa
* Archosauria - alligators & crocodiles
o exposed portion - beta keratin
o hinge region - alpha keratin
o new keratinized scales added in layers; older scales wear off slowly
* Lepidosauria - squamates - snakes & lizards
o several unique, derived design features
o keratin pattern unique
+ exposed portion - 2 layers with top - beta, deeper - alpha
+ hinge region - 2 layers with top - beta, deeper - alpha
o scales are more highly overlapping & thin than other "reptiles"
o old s. corneum shed nearly simultaneously; (a single unit in snakes)

Front 9

Sauropsida Skin
(includes turtles, lizards, snakes, alligators, dinosaurs, birds)
Claws: taxa, design, composition?

Back 9

* Taxa - all amniotes
* Design - special unguis & subunguis growth zones
* Chemical Composition - keratinized with calcium salts added for strength
* Functions - aid locomotion on land, grasp prey, defense....

Front 10

Sauropsida Skin
(includes turtles, lizards, snakes, alligators, dinosaurs, birds)
Epidermal Glands: Design, Loation, Function?

Back 10

# Granular Glands
# Design - multicellular
# Locations

* often very localized; only a few on body
* femoral pores are the exit ducts for the glands on many lizards
* chin or cloacal glands in crocodilians, turtles, snakes

# Functions

* Mating
o produce sticky substance that helps male hold onto female
o pheromonal - scent to attract or excite mates
* Defensive
o snakes have unique cloacal glands
o secrete a stinky, sticky material to deter predators; e.g. garter snakes

Front 11

Sauropsida Skin
(includes turtles, lizards, snakes, alligators, dinosaurs, birds)
Dermis - "Bony" Scale Derivatives: Taxa, Location, Functions?

Back 11

Osteoderms

* Taxa - some Archosaurs, e.g. crocodilians, some dinosaurs, some lizards (Lepidosauria), turtles (Chelonia/Testudines) & a few others
* Location - underneath epidermis - on head, shoulder, pelvis
* Functions - some additional protection to underlying tissues
* Turtle Specialization
o key part of bony shell (carapace & plastron) joined with ribs, vertebrae
o ancestors showed gradual increase in size & # osteoderms
o bone plates covered by epidermal scales (horny/keratinized scutes)

Front 12

Bird Skin: Epidermis - Keratinized Specialization
Stratum Corneum

Back 12

* underneath feathers is thin & contains only alpha keratin
* epidermis is very lipogenic - cells produce lots of lipids without specialized glands (lipokeratinocytes)

Front 13

Bird Skin:
Keratinized/Horny Scales

Back 13

* Locations - legs, feet, face
* Type of Keratin
o same arrangement as Archosaurs
o beta on exposed areas, alpha in hinge or joint region of scale

Front 14

Feathers: Composition, Development, Functional Types?

Back 14

* Type of Keratin - theta; extremely tough unique to birds
* Development
o dermal papilla stimulates overlying epidermis to thicken
o epidermis initially grows upward,
o development thus appears to be homologous to an amniote epidermal scale
o dermal papillae & epidermal collar eventually sinks deep into dermis to form feather
o as feather grows out, the dermal papilla tissues dies & leaves a hollow core, making feathers light weight

Functional Types

* Contour - cover surface, aid flight; down - insulation
* Filoplume - sensory information on contour feather position, shaft with small barbs at tip
* Bristle - on face, around mouth & eyes - sensory; shaft with small barbs at base
* Down - insulation beneath contour feathers - lack shaft & lacks hooks on barbules

Front 15

Feathers: Evolutionary origin and Selective pressures

Back 15

#

*

# Hypothesized Evolutionary Origin

* evolved from & homologous to amniote scales
* Coelurosaurs - derived theropod dinosaurs - # fossil taxa found in China show plume-like or filamentous type feathers

# Hypothesized Selective Pressures

* sexual selection - attractiveness
* insulation - for endothermy
* parental care

Front 16

Bird Epidermal Glands - Uropygial (Oil) Glands: Composition, Design, Functions

Back 16

Functions

* water-proofing, lubricate & protect feathers
o largest in aquatic species
o absent from some flightless species like ostriches, but also absent in parrots
* deter bacterial & fungal growth
* foul-smell - a few (e.g. hoopoes) produce foul-smelling odor to deter predators
* pheromonal - some species use scent in mate attraction - e.g. petrels (nocturnally active seabirds)

Front 17

Bird Dermis: Structure

Back 17

Structure

* generalized; thinnest of all terrestrial species. underneath feathers
* dermal papillae control formation of feathers & scales