reproductive modes and terrestriality Flashcards
how does water still pose as a constraint to terrestrial animals
reproduction = Reproductive modes are the different approaches to reproduction and have enabled more or less independence from water for terrestrial animals.
what are the three major clades of amphibians
caecilians (3% of all amphibians), caudates (9%) and frogs (88%)
less diverse than other tetrapods but very diverse in physiological eclogy and reproduction
why are amphibians at greater risk of desiccation and what does this mean
highly permeable skin
constrained to habitats and activity periods which reduces chances of dehydration e.g. high humidity enviro, in or around water, less active during the day
outline some morphological adaptations amphibians have evolved to live life on land with permeable skin
Texture, sculpturing and thicker skin = increases water absorption
pevlic/water patch = thin area of skin which sits to the floor so if find puddle or humid patch = increases ease of absorbing water
- veins in this pelvic patch are abundant so water can be quickly channelled
outline some behavioural adaptations of amphibians to live life on land with permable skin
body postures which minimise surface area exposed to air = less evaporation
live in burrows under ground where humidity is higher = australian bull frog
secretion and active anoitinbg of skin with specialised wax which reduces water loss rates by 95% = Phyllomedusa sauvagii
how have amniotes evloved there skin to avoid water loss
non-permable skin formed from layers of a protien called keratin
- strands wind round each other and overlap to impart strength, flexibility and a tight barrier to water
how has the evolution of the amniotic egg reduced dependence on water by terrestrial animals
the amniotic egg was a key development that enabled amniotes to greatly reduce their dependence on standing water for reproduction (albeit by making their own miniature water bodies for the embryos to develop in, a key function of the amniotic sac).
how have amphibians relaxed their constraints imposed by terrestriality
via their diversity of reproductive modes
1) Aquatic eggs and development in water
2) terrestrial eggs and development in water
3) aquatic eggs and direct development
4) terrestrial eggs and direct development
give an example of a species which have evolved lifecycles which limit the duration that water is needed
natterjack toads use ephemeral scrapes (shallow pools) to breed and have a much higher rate of decelopment than sympatric species = allows for decreased competition and breed without the need for permanent waterbodies
outline some examples of amphibians which have reduced the dependance of water bodies using various forms of parental care
many frogs build ‘foam nests’ from secretions during mating, and the eggs are laid in the foam nest (keeping them in the semi-aquatic foam state) which is left on vegetation or the ground near water bodies. Upon hatching, the tadpoles either wriggle out of the foam nests to drop from vegetation into water bodies below or the parent may dig a channel between the water body and the foam nest left on the ground to allow the tadpoles to swim into the water and resume their development
