Amphibian Diversity
Some observations on the origins and
diversity of the Amphibia
Extant Amphibia
• There are 3
groups of
extant
amphibians:
Urodeles,
Anurans, and
Gymnophiona.
• (Ambystoma
maculatum)
Amphibia
• Modern amphibians constitute the
Lissamphibia. ‘Liss’ means smooth,
without scales.
• Amphibians do not ‘drink.’ They have H20
transport via the integument.
• H20 absorbs and evaporates across the skin:
this has implications for spatial and
temporal distributions.
Extant Amphibia
• Anurans and
Caecilians are
highly derived.
Perhaps, the
caudata are less
derived.
• (Rana
sylvatica)
Extant Amphibia
• Caecilians
are also
highly
derived. Can
you speculate
on their
ecology?
• (Ichthyphis
glutinosus).
Extant Amphibia
• About 4,600 species of Lissamphibia.
• There is still some controversy about the
monophyly of the Lissamphibia.
• The earliest amphibians appeared in the
Devonian, and there is a significant gap
between these organisims and the modern
forms. The gap includes the end-Permian
mass extinction (95% of all species lost).
Extant Amphibia
• The first amphibian adaptive radiation
produced large forms.
• The second radiation produced what we
have today.
• Modern forms are not ‘primitive.’ They are
highly derived, and in the case of anurans
and gymnophiona, highly specialized.
Extant Amphibia
• They are tied to water
for respiration and
reproduction.
• Lungs are simple, and
bucal cavities, gills,
and skin are used for
gas exchange.
• What consequence
does this have for
circulation?
• Anurans and urodeles
have external
fertilization. What
consequence does this
have for their life
histories?
• Epidermal layer is
small, skin contains
many dermal glands.
Why?
Extant Amphibia
• Salamanders
have elongate
trunks and tails.
• Most have 4
limbs, although
sometimes they
are reduced or
lost.
• Amphiuma
tridactylum
Extant Amphibia
• Many salamanders
(plethodontids) have
lost lungs entirely.
• Consider SA/V ratios.
Where would you
expect to find large
forms? Where would
you expect to find
small forms?
• Many salamanders are
paedomorphic (show
larval characteristics
as adults). Contrast
this with neoteny.
• What environmental
features might select
these traits?
Plethodontids
• They have lost their lungs.
• The hyoid aparatus is pirated for tongue
projection - it no longer serves to ventilate
the lungs.
• In bilitoglossines, the tongue can be
extended longer than the H&B length to
capture insects.
Neoteny or Paedomorphosis?
Extant Amphibia
• Paedomorphosis is an example of
heterochrony - a change in the timing of
developmental events. Another good
example of heterochrony is development of
human head size (relative to chimps), and
the development of patagia in flying
squirrels, scaly tailed squirrels, and gliding
phalangers.
Extant Amphibia
• About 4000 species
of anurans.
• Extreme functional /
morphological
diversity within a
restricted body plan:
hoppers, jumpers,
walkers, gliders,
burrowers.
Anuran Morphology
Extant Amphibia
• All anurans except Ascaphus truei lack a
tail.
• Anura is 2 greek words and means: without
tail.
Extant Amphibia
• Development can be
direct, viviparous, or
include aquatic
larvae.
• Consider the
complicated
selective regime
faced by anurans:
ecologies of tadpoles
and adults are very
different.
Anuran Development
• S.A. Lepidobatrachus
• S.A. Ceratophrys
• Larvae have huge
heads and jaws.
• Adults have huge
heads and jaws.
• Normal Larvae
• Adults have huge
heads and Jaws
Anuran Development
• The 2 forms have different evolutionary
trajectories.
• Their common ancestor had filter-feeding
larvae
• Both larval forms prey on other tadpoles.
• Both adult forms prey on other frogs.
• Is this a result of heterochrony?
Extant Amphibia
• Caecilians have
internal
fertilization.
• They are fossorial
• Limited in
distribution to
tropics.
• Least known of all
amphibians.
• Gymnophis
Caecillians
• Most spend their entire lives under ground.
• Exotic reproductive specializations include
embryonic development within the female embryos feed with fetal teeth and scrape off
walls of the oviducts.
Why are Amphibians and Reptiles
covered in the same course?
• They are monophyletic groups, just like
mammals and fishes (that is, if we consider
birds to be reptiles).
• Answer: Linneaus did not see the
difference.
Why are Reptiles and Amphibians
covered together?
• With the exception of crocodillians, they
share a pleisiomorphic character: a ventricle
without a septum. Thus, there is a potential
for mixing of O2 rich and O2 poor blood. In
reality, there is very little mixing.
• A big plus is that they can use an
intracardiac shunt to promote heating and
cooling. (Crocs do this differently).
How are they similar?
• Both groups are for the most part
ectothermic. This is true of most fish as
well.
• Ectothermy means the organisms use
external sources to generate their body heat.
Endotherms use internal sources (shivering
thermogenesis etc.).
Advantages of Ectothermy
• Ectothermic organisms require about 5% as
much food as endotherms! Because they
rely on solar energy instead of internal
thermogenesis, they are significantly more
efficient than endotherms at converting food
energy to new biomass.
Some Basic Terminology
•
•
•
•
•
Heterotherm
Homeotherm
Poikilotherm
Endotherm
Ectotherm
• “Hot Blooded”
• “Cold Blooded”
Thermoregulation in
Cnemidophorus
• Widely foraging.
• High BT
maintained by
behavior:
shuttling,
basking,
conduction, and
convection.
• Blood shunting?