Amphibian Diversity

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.

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

Extant Amphibia • Salamanders have elongate trunks and tails. • Most have 4 limbs, although sometimes they are reduced or lost. • Amphiuma tridactylum

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? Extant Amphibia

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.

S.A. Lepidobatrachus Larvae have huge heads and jaws. Adults have huge heads and jaws. S.A. Ceratophrys Normal Larvae Adults have huge heads and Jaws Anuran Development

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.

Heterotherm Homeotherm Poikilotherm Endotherm Ectotherm “Hot Blooded” “Cold Blooded” Some Basic Terminology

Thermoregulation in Cnemidophorus • Widely foraging. • High BT maintained by behavior: shuttling, basking, conduction, and convection. • Blood shunting?

Amphibian Diversity