Phylogeny of Amphibians

Oldest to most recent

1. Lissamphibia

2. Temnospondyli

3. Gymnophiona, Anura, Caudata (extant amphibians)

Why land?

• unexploted food resources

  • aquatic habitat niches already occupied

• lack of large terrestrial predators

  • largely primitive plants & invertebrates

• low O2 in warm H2O (land O2 unlimited)

Early Tetrapods

• Upper Devonian lobe-finned fish

  • pelvic and pectoral fins slowly transition to paired paddles

    • median fins still present

  • small ribcage

• Carboniferous labyrinthodont amphibian

  • paired paddles slowly turn into limbs

  • larger ribcage to account for organs

More Phylogeny (indivudual spp. discussed further below)

• Era: Paleozoic, Period: Devonian

  • Ichthyostega, Tiktaalik

• Era: end of Paleozoic-beginning of Mesozoic, Period: end of Permian-beginning of Triassic

  • Triadobatrachus

• Era: end of Mesozoic-beginning of Cenozoic, Period: end of Cretaceous-beginning of Tertiary

  • Extant salamanders & frogs

• major evolutionary transitions in last 350 years

• Amphibians were the dominant land animals for ~75 million years

Leposondyli

• very small yet very diverse early amphibians

  • similar to newts, eels, snakes, lizards, etc.

Permian era

• droughty conditions

• reptile & early reptile spp. emerged and evolved

Tiktaalik

• late Devonian (375 MYA)

• discovered in Canada in 2004

• predated Ichthyostega by 5 million years

  • thought to be the oldest up til this point

• 1-2m long

• most notable feature: front pair fins with wrist-like structure

• other features

  • spiracles (primitive nostrils)

  • lungs & gills

• 1st tetrapod with proper neck

  • greater flexibility during short bouts on land

Ichthyostega (“roof fish”)

• late Devonian (370 MYA)

• discovered in Greenland

• 5 ft, 50 lbs

• fish & amphibian features

  • webbed feet

• could breathe air for short periods of time

Eryops

• Permian (270 MYA)

• crocodile-like early amphibian

• aquatic & terrestrial

• had some structural features that would appear in later reptiles

Diplocaulus (“double stalk”)

• middle-late Permian (240-230 MYA)

• 3ft, 5-10 lbs

• wide V-shaped boomerang head

• possibly used to navigate strong currents

• facilitated rapid opening for suction-gape feeding

Frog Evolution Trends

• several modifications for jumping

  • vertebral column short & inflexible

    • reduction in presacral vertebrae

      • found within pelvis (cervical, thoracic, lumbar)

    • increase rigidity, absorption of landing

    • transfer energy directly to hind limbs

    • enlarged pelvic girdle, strengthened & anchored to vertebral column

    • no ribs

    • no tail as adult

    • overall body truncated

  • hind limbs elongated for jumping

  • muscles modified for jumping

Amphibamus (“equal legs”)

• late Carboniferous (300 MYA)

• swamps in Europe & NA

• 6 inches, few ounces

• more salamander-like than frog-like

• 33 presacral vertebrae

  • common characteristic of early amphibs (large amount of presacral vertebrae)

Gerobatrachus (“frogmander”)

• early Permian (290 MYA)

• found in Texas in 2008

• why is it called “frogmander?”

  • 2 fused ankle bones

  • backbone intermediate in length

    • decrease from 33 vertebrae in Amphibamus

  • large tympanum (large, external ear on frogs)

  • wide, frog-like skull

• likely transitional

  • 240-275 MYA splitting frogs & salamanders

Triadobatrachus (“proto frog”)

• early Triassic (250 MYA)

• found in Madagascar

• first fossil frog

• characteristics

  • short, stubby tails

  • 10 cm

  • 13-14 presacral vertebrae

    • 9 in modern frogs

Viraella

• early Jurassic (~200 MYA)

• found in Argentina

• earliest “true” frog

• may belong to Leiopelmatidae (modern family)

• classic frog-like head & large eyes

• legs modified for jumping (explored in next point)

Triadobatrachus vs. Viraella

• Vieraella more truncated overall

  • reduction in presacral vertebrae

  • enlarged & fused pelvic bones in Viraella

  • fused tibiofibula in Viraella

Paleobatrachus (“ancient frog”)

• Cretaceous--Tertiary (130-135 MYA)

• found in Europe

• completely aquatic

  • inhabited swamp basins

  • volcanic gases preserved soft tissue

• resembles present day Xenopus

Amphibians vs. Reptiles

• amphibians

  • clawless

  • scaleless

  • moist skin (respiration)

  • unshelled eggs

• reptiles

  • limbs & muscles

  • increased brain size (cerebrum & cerebellum)

  • more effective jaw

  • skeletal structure improved

  • skin toughened with scales

    • reduced cutaneous respiration

  • well-developed lungs

    • consequence of scales

  • amniote egg

    • no longer relied on water for breeding

  • arose from anthracosaurs (later tetrapods)

Order Caudata (Salamanders)

• characteristics

  • smooth skin

  • long tails

  • long cylindrical bodies

  • most have 2 pairs of very well developed limbs

  • some have nasolabial groove

    • little groove that runs from nose to lips

  • costal grooves

    • body folds found on their sides

  • carniverous & cannibalistic

  • secretive & nocturnal

  • greater diversity in development, respiration, and reproduction than any other vertebrate group

  • nearly all salamander larvae have external gills

    • reabsorbed later

    • Sirenidae keeps external gills (paedomorphic)

• habitat & distribution

  • common throughout U.S.

    • 70% of ~400 spp. of salamander found worldwide are located in Central & NA

  • mostly found in moist woodland habitats

    • hardwood & coniferous forests, grasslands, lowland floodplains

  • highly dependent on precipitation, temperature, & vegetation type

  • Four-toed Salamander requires sphagnum bogs

  • 22 spp. & 2 hybrid forms of the unisexual complex group are found in IN

  • some spp (Wester Lesser Siren) spend summers in estivation by encapsulating themselves in a mucous-lined cocoon

  • some permanently aquatic (ponds, lakes, & streams)

  • some terrestrial (under logs, leaf litter, rocks)

• reproduction

  • ephemeral wetlands

  • breeding season: late winter--early spring

    • few breed in fall

  • courtship practices

    • nudging

    • tail & chin tapping

    • tail fanning

  • majority of salamanders have internal fertilization

    • male salamanders deposit sperm packets (spermatophore) which the females pick up with their cloaca

    • eggs are fertilized as they travel through the oviduct and encounter spermatophore

  • majority of salamander spp. are oviparous (lay unshelled eggs)

    • all IN salamanders are oviparous

    • some give birth to gilled larvae (larviparous)

    • others give birth to fully transformed young (pueriparity)

  • eggs prone to desiccation/drying out

    • must lay eggs either in moist soil or in water

  • most do not provide parental care

    • many do guard eggs

• diet

  • carnivorous; mostly insects, spiders, & earthworms

    • occasional cannablism

Salamander Family Phylogeny

• 10 recognized families

  • 60 genera

  • 400 spp.

• Sirenidae <3 & Cryptobranchidae most primitive

• Polytomy

  • Proteidae

  • Amphiumidae

  • Plethodontidae

  • Rhyacotritonidae

  • ALL RELATED; UNKNOWN WHICH IS MORE DERIVED OR PRIMITIVE

• Salamandridae, Dicamptodontidae, & Ambystomatidae

  • most derived (especially Ambystomatidae)

Sirenidae (“Sirens”) <3

• 100 million years old--oldest extand Salamander families

• 4 spp. & 2 genera

• characteristics

  • eel-like bodies & front limbs

  • has forelimbs; NO HIND LIMBS

  • paedomorphic

    • retain larval characteristics as adults

    • external gills

  • lack eyelids, premaxillary teeth, & hind limbs

  • nocturnal

• distribution

  • fully aquatic

  • heavily vegetated, slow moving water

    • shallow water, swamps, ditches, ponds, etc.

  • found primarily in southeastern NA (not really common in IN)

• reproduction

  • breeding season: early spring

  • 200-700 eggs deposited to base of aquatic vegetation

  • may have external fertilization

• special concern; may eventually become endangered :(

Cryptobranchidae (“giant salamanders”)

• 3 spp. & 2 genera

  • Eastern Hellbender (smallest)

    • found only in northeastern USA

  • Japanese Giant Salamander

  • Chinese Giant Salamander (largest)

    • 1.5m & ~100 lbs

• characteristics

  • paedomorphic

  • flattened body & head

  • skin folds for respiration

• distribution

  • fully aquatic

    • cold, fast moving streams

  • cool shallow areas where rocks not embedded in substrate

  • essentially nocturnal

• diet

  • primary: crawfish

  • fish, aquatic insects

• reproduction

  • external fertilization

  • multiple females may lay eggs in one male’s nest (which are defended)

  • male fertilizes eggs; chases away female

  • eggs hatch in ~55-75 days

  • young remain in larval stage for 2 years

  • juveniles require an additional 3-4 years to reach sexual maturity

Proteidae (“mudpuppies”)

• 6 spp. & 2 genera

• characteristics

  • similar to sirens, but have hind limbs

  • large, bushy external gills (paedomorphic)

  • caudal fins

  • 4 toes

• diet

  • insects & fish

• distribution

  • fully aquatic

    • lakes, ponds, rivers, & streams

  • rarely seen in depths less than 1 meter

    • commonly found 20 meters below surface

  • found in central & eastern USA, southern Europe

• reproduction

  • internal fertilization

  • males & females guard eggs

• why “mudpuppy?”

  • stems from the erroneous belief that members of this family smit barking sounds when disturbed

• special concern; may become endangered

Ambystomatidae (“mole salamanders”)

• 30 spp.

• characteristics

  • stout bodies

  • thick, robust limbs

  • thick tails

  • short, blunt head

  • functional lungs

• reproduction

  • breeding season: spring

    1. males & females migrate in the hundreds to ephemeral ponds

    2. lay eggs in water

    3. stay in aquatic salamander larvae form for 4-6 months

    4. metamorphose (indirect development)

    5. leave aquatic environment

    6. spend life on land

• why “mole salamanders?”

  • comes from their habit of staying underground & in burrows of other creatures except when breeding

Plethodontidae (“lungless salamanders”)

• 2/3 of all salamander spp. belong here

• characteristics

  • primarily breathe through moist skin

  • thin, elongated bodies

  • prominent coastal grooves

  • ONLY family with nasolabial groove

  • autotomize tail when attacked

• distribution

  • diverse habitats

    • fully/semi/not aquatic

• reproduction

  • internal fertilization

    • eggs hatch into mini adults (direct development)

• diet

  • typically feed at night

  • insects, millipedes, worms, spiders, snails, & mites

Salamandridae (“newts”)

• characteristics

  • thick, granular skin

    • granules due to numerous toxic glands

    • aposematic

      • bright coloration usually to deter predators

  • unken reflex

    • posturing areas laden with high toxicity

    • tetrodotoxin

      • neurotoxin used for chemical defense

• distribution

  • live in forests

• reproduction

  1. lay eggs in water

  2. eggs --> gilled larvae

  3. partial transformation into red efts (2-3 years)

     1. really bright skin

     2. only terrestrial stage of newt

     3. only found in this family

  4. reach sexual maturity and spend life in water

• distribution

  • found in eastern & western NA, Europe, Africa, & Asia

• diet

  • eat invertebrates, amphibian, & fish eggs

Anuran Diversity (Anura = “without tail”)

• currently 45 recognized families

• ~5,500 spp.

• constantly changing taxonomy

  • spp. discoveries

  • genetic technologies

• FROGS ARE LEAPERS; TOADS ARE HOPPERS

• found on all continents except Antarctica

• reproduction

  • metamorphose (indirect development)

    • only 4 spp. have tails as adults

    • usually external fertilization

• diet

  • tadpole: herbivorous

  • adults: carnivorous

Scaphiopodidae (“Nearctic Spadefoot Toads”)

• characteristics

  • circular/sickle-shaped hardened keratinous structure on hindfoot, forming a spade

  • transitional spp.; somewhat warty and smooth

  • vertical pupils

  • don’t have prominent paratid glands

    • glands that secrete toxic substance

• distribution

  • found on tropical forest floors

  • NA, Europe, Asia, Africa

• reproduction

  • breed in temporary ponds; highly accelerated development

• diet

  • eat many insects

• special concern

Hylidae (“Treefrogs”)

• 800 spp. & 45 genera

• characteristics

  • smooth & somewhat warty

  • mostly well camouflaged (has flash colors though)

  • can have large or small toepads depending on habitat

• distribution

  • most boreal, some aquatic or fossorial

  • NA, SA, Europe, Asia, Australia

• reproduction

  • all return to water to breed

  • external fertilization

• diet

  • carnivorous insectivores

Bufonidae (“Toads”)

• ~500 spp.

• characteristics

  • thick, granular, warty skin

  • Bidder’s organ

    • vestigal ovary on larval testes

  • prominent parotid gland that secretes toxic substance

  • diurnal during spring & fall; mostly active at night in hot & humid weather

• distribution

  • most are terrestrial or fossorial

• reproduction

  • all return to water to breed

  • external fertilization

Ranidae (“True frogs”)

• ~300 spp.

• characteristics

  • slim-waisted with long legs, smooth skin, & prominent tympanums

  • dorsal lateral skin folds on back or around tympanum

  • extensive hind feet webbing

  • aquatic & nocturnal

    • some fossorial, arboreal, or terrestrial

• reproduction

  1. eggs deposited in shallow pond or creek

  2. tadpoles

  3. froglets

  4. frogs

• diet

  • tadpoles: herbivorous

  • juveniles & adults: insectivorous

    • some can eat other frogs, turtles, small mammals/birds, etc.

Phylogeny of Reptiles

• diverged from amphibians in Carboniferous era, Permian period (arid transition)

• better fossil record

• focus on

  • synapsids (archosaurians)

  • diapsids (archosaurians, lepidosaurs)

  • anapsids

Synapsids (“archosaurians”)

• branched early on from amphibian line

• completely terrestrial

• shelled & amniotic egg

• modern day mammal

Diapsids (“archosaurians, lepidosaurs”)

• archosaurs

  • gave rise to modern birds & crocodilians

  • largely responsible for dinos

• lepidosaurs

  • modern snakes & lizards (Jurassic)

Anapsids (“turtles”)

• Triassic

  • basic body plan (stayed the same for millions of years)

  • Odontochelys

    • late Triassic (220 MYA)

    • discovered in 2008, predates Proganochelys by 10M years

    • “toothed shell”

    • found in E. Asia, shallow marine waters near shore

  • Proganochelys

    • late Triassic (210 MYA)

    • most well-known

    • “early turtle”

    • 3ft, 75 lbs

    • possess few teeth

      • modern turtles lack teeth entirely

• Jurassic

  • Eileanchelys

    • late Jurassic (165-160 MYA)

    • found in W. Europe (Scotland)

    • earliest pond turtle

    • discovered in 2008

• Cretaceous

  • Archelon (marine turtles <3)

    • late Cretaceous (75-65 MYA)

    • found in oceans of NA

    • “Ruling Turtle”; 12 ft, 2 tons

    • large, flipper-like arms & legs

    • closest living relative: leatherback

Early Reptiles: Amniotes

• Casineria: Early Carbnoiferous (340 MYA)

  • salamander-like early tetrapod

  • 5 digits with claws

  • 1st amniote

• amniotes

  • eggs survive out of water

  • disperse onto drier land

1st Lizards, Hylonomus

• Carboniferous (315 MYA)

• discovered in Canada

• characteristics

  • earliest known reptile

  • among first amniotes, anapsid

  • small, lizard-like (8-12 in)

  • fossil with distinct toe & scales

  • numerous sharp teeth (insectivores)

Mesozoic (“Age of Reptiles”)

• explosive radiation of reptiles

  • most numerous & largest

• dominant terrestrial & aerial animals

  • formidable marine predators

Archosauromorphs

• “Ruling Reptiles” of Mesozoic

  • early diapsid amniotes

• ancestral to crocodilians, birds, & turtles

Crocodilians

• surviving archosaurs

• early ancestors (Jurassic-mid Cretaceous)

• Stomatosuchus

  • ~36 ft

  • swamps, N. Africa

• Sarcosuchus

  • “flesh crocodile”

  • ~40 ft

  • “Super Croc”

Lepidosauromorphs

• 2nd major Diapsid lineage

  • ancestral to squamates (lizards, snakes), tuataras

• first appeared late Permian

Tuatara (Sphenodontia)

• living fossils; Triassic

  • extant; New Zealand

• descended from beak-headed reptiles (Rhinocephalia)

Order Testudines (or Chelonia), Turtles

• shells helped them persist for 200 MYS

• 400 spp.

• distribution

  • aquatic, semi-aquatic, terrestrial

• reproduction

  • oviparous (all lay eggs)

• diet

  • most adults are omnivorous; some completely herbivorous/carnivorous

  • all turles lack teeth,

• distribution

  • tropic & temperate

Testudines, Chelydridae (“snapping turtles”)

• 2 genera; Macroclemys & Chelydra

  • each with 1 spp.

• characteristics

  • large, long tails

  • muscular legs

  • massive head

  • greatly reduced plastrons

  • nocturnal, fully aquatic

    • eggs on land

• distribution

  • NA, SA, SEA

Testudines, Kinosternidae (“mud & musk turtles”)

• 4 genera, 23 spp.

• characteristics

  • <6 in

  • glands on side produce musky odor

  • domed carapace & plastron (hinged)

• distribution

  • semi-terrestrial

  • poor swimmers; walks along bottom of streams & ponds

  • prefer sandy or muddy dwellings

• reproduction

  • lay several small clutches throughout year (4-5/clutch)

  • all but one spp. in IN have TDS (temperature dependent sex)

    • warm = male (depending on spp.)

• diet

  • omnivorous, but prefer insects, tadpoles, & fish

Testudines, Emydidae (“basking, marsh, & box turtles”)

• 42 spp.

• relatively long-lived

  • eastern box turtle can live up to 80-100+ years

• distribution

  • aquatic, semi-aquatic, some terrestrial

• low reproductive rates

  • countered by longevity

• diet

  • adult: omnivorous; some herbivorous

  • juvenlie: carnivorous

Testudines, Trionychidae (“soft-shelled turtles”)

• GENETIC SEX DETERMINATION; NOT TSD

• characteristics

  • long, tubular nose

  • fully webbed feet (good swimmers)

• distribution

  • almost fully aquatic

    • pharyngeal respiration

      • special throat lining that absorbs O2 from water

• reproduction

  • females lay clutches along sand bars/gravel banks

Ectothermy: Amphibians & Reptiles

• primary heat source external

• heat not always available (winter)

• more economical (behavioural changes to be warm)

Endothermic: Birds & Mammals

• primary heat source internal

• better in cold environments

  • more range than ectothermy

• more expensive

Thermal Interactions & Heat Exchange in Ectotherms

• heat exchange with environment occurs via

  • radiation

  • convection (smaller = faster temp change)

  • conduction (smaller = faster temp change)

  • color also a factor (dark absorbs more heat)

Body Temp Trends

• max & min voluntary can be highly variable

• tropical mean temps is higher than temp

• snakes & lizards tend to have highest body temps

• warmest to coolest

  1. lizards

  2. snakes

  3. turtles

  4. frogs

  5. salamanders

Temp Ranges & Tolerances

• Active Body Temperature (ATR) varies depending on

  • taxa

  • habitat

  • season

  • genetics

• for most, range is between 27C -- 35C

  • few reptiles have ATRs <20C

Regulation of Body Temps

• due largely to behavioural changes (change posture/position, etc.)

• amphibians (terrestrial) handle regulation differently because of moist skin

  • low resistance to water loss

• Tb (body temp) largely tracks Te (environment temp)

  • couple of degrees cooler due to evaporation

• reptiles can be exposed to sun without excessive water loss (scales)

Dormancy

• response to temp extremes & environmental cues

• can occur in 3 different forms

  1. hibernation

  2. freeze tolerance

  3. estivation

• Scaphiopus: active 1 month/year in Arizona

• Thamnophis: active 4 months/year in Manitoba

• dormancy forms explained

  1. hibernation

     1. Tb largely allowed to track Te, except that metabolic activities slowed even more than “normal” for a given temp

     2. animals tend to move during hibernation (brumation)

     3. aquatic hibernators sink to bottom

  2. freezing tolerance

     1. ice crystals destroy cells & extracellular fluid freezes & dehydrates cells

     2. few spp. can do this (Pseudacris crucifer <3)

        1. use cryoprotectants (glycerol or glucose); replace water in cells with antifreeze

  3. estivation

     1. animals inhabiting desert & semidesert environments

     2. physiology not well-known

     3. animals flee to deep burrows with high humidity & moist soils & reduce their metabolisms

     eastern spadefoot, Scaphiopodidae

Order Squamata (“Lizards”) [snakes will start later]

• 8,000 spp.; 5,000 are lizard spp.

• most abundant & diverse reptilian group that exists today

• lizards will autotomize (lose) tails as defense mechanism

• reproduction

  • extremely diverse, but all have internal fertilization

  • some oviparous (lay eggs outside of body)

  • some viviparous (live birth)

  • some ovoviparous (eggs hatched within body)

  • some have significant courtships (lizards)

  • lay flexible or hard eggs

  • little parental care

• diet

  • carnivorous

• distribution

  • occur in all tropical & temperate regions

Phrynosomatidae (“spiny lizards”)

• 125 spp.

• many morphological differences

• distribution

  • Sceloporus: arboreal, terrestrial, rock-dwelling

• reproduction

  • most oviparous

  • some viviparous

Anguidae (“glass or alligator lizards”) LEGLESS

• 120 spp.

• characteristics

  • has all characteristics of lizard (moveable eyelids, external ear)

  • long & have shiny scales underlined with bony plates (osteoderms)

  • autotomize their tails (which are ~2/3--3/4 of whole body)

  • highly terrestrial & semi-fossorial

• reproduction

  • mostly oviparous

  • some ovoviviparous

  • few viviparous

• diet

  • carniverous

• distribution

  • NA, SA, Europe, Asia

Teridae (“whiptails & racerunners”)

• 110 spp

• characteristics

  • long, slender bodies with well-developed limbs & very long tail

  • often have yellow stripes on body

  • males have blue/green chest during breeding

• distribution

  • only found in NA & SA

  • terrestrial; sandy prairie

• reproduction

  • oviparous

  • some spp. are parthenogenic

    • populations are all female, so all eggs laid are unfertilized & clones of the mother

    • six-lined racerunner is NOT PARTHENOGENIC

Scincidae (“skinks”)

• largest of all lizard families (1200 spp.)

• characteristics

  • osteoderms give them stiff & shiny bodies

  • autotomize tails

• distribution

  • highly varied

    • terrestrial, semi-fossorial, diurnal, etc.

  • everywhere except Antarctica

• reproduction

  • oviparous, ovoviviparous, viviparous

• diet

  • insectivorous

Order Squamata (“snakes”)

• 3000 spp.

• characteristics

  • immovable eyelids

  • legless

  • no external ears

  • Jacobson’s organ (tongue-flicking)

  • left lung either entirely absent or highly degenerate

• distribution

  • highly varied habitats (terrestrial, arboreal, etc.)

• reproduction

  • mostly oviparous, but can be other two

Viperidae (“vipers”)

• 215 spp.

• characteristics

  • long hinged fangs with a hemotoxin (swelling & hemorraging)

    • cobras have a neurotoxin (central nervous system)

  • broad heads & stocky bodies

  • Loreal pit organ senses heat

• habitat

  • terrestrial with wide variety of habitats

  • NA, SA, Europe, Africa, Asia

• reproduction

  • viviparous

• diet

  • carniverous

Colubridae (“snakes”)

• was 2000, but now 650 spp.

• characteristics

  • can be 7in -- 12ft

• distribution

  • terrestrial & aquatic

• reproduction

  • oviparous

  • ovoviviparous

Natricidae (“snakes”)

• 200 spp.

• distribution

  • mostly tied to aquatic environments

• reproduction

  • viviparous

  • ovoviviparous

• diet

  • carnivorous

Dipsadidae (“snakes”)

• 700 spp.

• characteristics

  • small-medium

  • from New World

• distribution

  • secretive; hides under cover

• reproduction

  • oviparous

• diet

  • diverse (invertebrates, amphibians, etc.)

Reproduction & Life Histories

• fertilization can happen inside/outside of female

• development can be direct/indirect

Gametogenesis & Ovulation

• most amphibians, 2 sexes required

• reproductive timing has internal controls

  • ultimately coordinated by environment (temp & photoperiod change)

• Gametogensis

  • division & growth of gametes within ovaries & testes through hormonal activation

• Vitellogensis

  • accumulation of nutrients in cytoplasm of developing egg

  • rapid growth of oocytes (egg 10-100x size)

• Ovulation

  • occurs when follicular & ovarian walls rupture

  • releases ova into oviduct

    • as eggs pass through oviduct, protective membrane are deposited around them

      • number of layers is spp. specific

  • amphibian eggs are anamniotic

  • eggs expelled in gelatinous masses or strings

Fertilization

• penetration of sperm & fusion of male & female pronuclei

• many sperm can reach the egg, but only one will penetrate it

  • salamanders have polyspermic fertilization

  • sperm heads (acrosomes) digest eggs membranes, making tiny hole

    • sperm pronuclei moves into ova cytoplasm; fusion

• 2 types

  1. external

     1. normal for Sirenidae & Cryptobranchidae, and most Anurans

  2. internal

     1. found in other salamander families

• external

  • simultaneous shedding of eggs & sperm into water

  • constrain where eggs are laid

  • frogs: males grasp female in amplexus so their cloacas align

  • salamanders: either amplexus or male follows female to deposit

  • inguinal amplexus

    • male has front legs around female’s upper waist (under arms)

  • cephalic amplexus

    • male’s hind legs wraps around female’s head

• internal

  • few frog spp. (Pacific NW), Salamandroidea salamanders, all caecilians

  • allows eggs to be laid in spot & time of choice

  • frogs: hemipenis delivers sperm to female cloaca

  • salamander: spermatophores deposited externally

    • proteinaceous pedicel capped by sperm packet

  • spermatheca

    • sperm storage in series of tubules on cloaca’s roof

Reproduction without Fertilization

• asexual reproduction

  • without male contributions

    • 100% female populations in some taxa

  • 2 types

    1. Hybridogenesis: progeny only transmits female chromosome; all female populations

    2. Gynogenesis: diploid/triploid egg only activated by sperm; no male chromosomes incorproated into embry

       1. only female offspring

       2. fathers from 5 specific spp.

          1. Jefferson salamander, blue spotted salamander, tiger salamander, smallmouth salamander, streamside salamander

Gynogenesis

• “unisexual” hybrid Ambystoma complex

• 5 MYA

• ploidy # varies

• 17 different combos

  • e.g. 2n, 3n, 4n, 5n (n = copies of genetic contribution)

    • if 4n with 4 blue spotted salamander & 1 Jefferson, will look more like blue spotted

Parental Care

• any form of post-egg laying parental behaviour that increases offspring survival at some expense of parent

• most amphibs show no parental care aside from nest construction

• represented by a variety of behaviours

  1. nest, egg, or young attendance/guarding

  2. egg brooding

  3. egg, larval, or hatchling transport

  4. feeding of young

Development

• Exotrophic

  • limited amount of yolk; allows females to lay more, but smaller eggs (quantity > quality)

  • larvae hatch quickly, but must feed themselves

• Metamorphosis

  • shift from embryonic & larval stage to mature terrestrial stage

  • initiated hormonally, but environment also plays a role (crowding, predation, food availability, etc.)

• Paedomorphosis

  • retention of juvenile characteristics as adults

  • two types

    1. progenesis: accelerated sexual maturity relative to stomatic growth

    2. neoteny: slowing of stomatic growth with onset to sexual maturity

Growth

• addition of enw tissue in excess oif what was lost in damaged tissue

• two types

  1. embryonic

     1. increase when high quality food is in abundance

     2. influenced by temp (higher = faster development; not too extreme though)

  2. juvenile

     1. much slower because of unpredictable food & environment

• GROWTH IN AMPHIBIANS IS INDETERMINATE/NEVER-ENDING

Age

• intervals (periodicity & not age) are important

  1. sexual maturity (4 months -- 7 years)

  2. Embryogenesis (can be truncated in Scaphiopodidae)

  3. larval period → metamorphosis

Dynamics of Reptilian Reproduction

• multitude of patterns geared to the right environment for offspring

• all temperate spp. are cyclic

• tropical spp. cyclic or acyclic

• 2 patterns (temperate salamanders)

  • winter/spring mating & egg disposition (Ambystomatids)

  • late summer/fall mating & spring egg disposition (Plethodontids)

• mate attraction & selection

  • location usually not a problem

  • reproduction more efficient within home range (sometimes movement is necessary)

  • courtship is key

  • female-heavy investment in gametes = most fit mate

Reproduction & Life Histories of Reptiles

• major difference in reptilian reproduction compared to amphibians

  • all have internal fertilization

  • direct development

  • amniotic egg

    • development can occur on much drier land

Gametogenesis & Ovulation

• Vitellogenesis very important in egg-laying vertebrates

  • accumulation of nutrients → yolk

• vitellogenin selectively absorbed by oocytes & enzymatically converted to yolk proteins (pinocytosis)

Cleidoic (shelled) egg

• prevents desiccation & contamination by environmental pathogens

• creates own aquatic environment

• by folding & curling, reptile embryo can be very long

• 3 extraembryonic membranes are formed (no need to know function)

  1. Allantois

  2. Chorion

  3. Amnion

Fertilization & Copulation

• copulatory organs

  • turtle & crocodilians: a penis of spongy connective tissue erects & retracts via vascular pressure (similar to mammals)

  • tuataras don’t have copulatory organs

  • squamates: penis lost & later replaced by hemipenis

• sperm storage

  • delayed fertilization → females can mate with more than one male → multiple progeny

  • sperm storage tubules on upper-mid section of oviducts

  • mechanism for expelling sperm from these tubules is unknown

Reproduction without Fertilization (reptiles)

• Asexual

  • 1 type in reptiles

    1. parthenogenesis

       1. females reproduce without sperm

       2. inheritance is clonal

Parental Care

1. pre-depositional

   1. involves quantity & size of egg components (egg components = eggshell, protein, lipids, yolk [oviparous reptiles])

   2. hatchling turtles & crocodilians have 50-70% more lipids than required

2. post-depositional

   1. selection of best sites

3. live-bearing

   1. 20% of all lizards & snakes

   2. ovoviviparous

      1. holds eggs much longer than oviparous spp.

      2. embryos can be supported entirely by egg yolk

      3. embryos can absorb some nutrients through oviducts

   3. viviparous

      1. placenta-like structure transfers nutrients to developing embryo

Embryo Development

• direct development in all reptiles

• clutch & egg size msy be proportional to body size

  • larger female = larger eggs & clutch

• reptilians that develop from terrestrial egg

  • humidity (more important for leather eggs)

  • temperature (ATR)

• temperature-dependent sex determination (TSD)

  • widespread in reptiles

    • found in all crocodilians, tuataras, & 11 spp. of turtles & squamates

  • average temp during 2nd trimester

    • crocs & lizards: male at high temps

    • turtles: females at high temps

Growth

• 2 growth pulses

  1. embryonic

     1. increases when yolk is available & decreases with lower Te

  2. juvenile

     1. much slower due to unpredictable food & environment

Age

• similar to amphibians (periodicity > age)

  • conception → hatcling/birth

  • sexual maturity

  • reproductive senility

• reproductive periodicity very important

• longevity can be great for some reptiles

Dynamics of Reproduction

• mate attraction & selection

  • most fit male >>>

  • territory more important because of reduced need to breed

  • courtship:

    • visual signals are important, but also tactile & chemosensory receptors involved