amphibian life-history startegies

Question 1

life-history strategies

Answer 1

patterns of resource acquisition and allocation exhibited by organisms during their lives

they have evolved through natural selectio to maximise individual fitness

Question 2

components of life-history

Answer 2

• growth
• development
• maintanence
• survival
• reproduction
• factors that influence fitness

Question 3

allocation and trade-off

Answer 3

allocation - resources (energy, nutrients, time) must be allocated to growth, maintenance and reproduction

trade-off - enrgy is limited, so enery allocated to one function is not available for another

Question 4

generation time

Answer 4

average time between two consecutive generations in the lineages of a population

Question 5

modes of reproduction

Answer 5

• asexual and sexual reproduction
• seerate sexes, simultanious hermaphrodites and sequential hermaphrodites
• reproductive maturation time
• semelparous and iteroparous
• number of offspring

Question 6

semelparous

Answer 6

A species is considered semelparous if it is characterized by a single reproductive episode before death

Question 7

iteriparous

Answer 7

reproductive strategy characterized by multiple reproductive cycles over the course of a lifetime

Question 8

amphibian life history

Answer 8

• most lay eggs which are exterannly fertillised in water and then hatch into aquatic larvae; these metamorphose into terrestrial adults
• but amphibians display a remarkable diversity of modes of reproduction and parental care

Question 9

caecilians

Answer 9

• all have internal fertilisation
• males have intromittent organ, the phallodeum, which is inserted into the females cloaca
• some species lay eggs which the females may protect till they hatch
• about 75% of species are viviparous

Question 10

diversity of caecillian life-history strategy

Answer 10

• rhinatrematidae - terrestrial with aquatic larvae ( 13 species )
• ichthyophidae - terrestrial with aquatic larvae ( 57 species )
• chikilidae - terrestrial, lay eggs but have larval stage ( 4 species )
scolecomorphidae - terrestrial and vivaparous ( 6 species )
• caeciliidae - terrestrial and aquatic with oviparous and vivaparous species ( 44 species )

Question 11

vivipary in caecillians

Answer 11

• at birth caecillians are 30-60% of their mothers body length
• initial growth supported by yolk
• embryos feed by scraping the oviduct walls with specialised embyronic teeth
• the epithelium of the oviduct produces a creamy substance
• large energetic investment from female

Question 12

salamanders

Answer 12

• most have interanl fertilisation
• they do not have an intromittent organ
• males lay spermatophores and has to entice the female, during a mating dance, to collect them directly into her cloaca
• 10% retain external fertilisation
• courtship patterns important for species recognition
• they show elaborate secondary sexual characters and species-spefic pheromones

Question 13

kleptogenesis in Ambystoma

Answer 13

• hybrid all-female populations
• no males for 5 mil years
• females use sperm from a related species to fertilize their eggs:
  •sperm genome usually discarded and egg
  develop asexually
  •occasionaly incorportate the sperms DNA
  resuting in hybrid offspring
• genome from up to 5 species

Question 14

salamanders

Answer 14

• most lay eggs in water. gilled aquatic larvae transform into terrestrial adults
• some species ( e.g salamandra salamandra ) are ovoviviparous; giving birth to small larvae taht fed on their own egg yolk
• salamandra atra show aplacental viviparity, giving birth to 2 live young (one from each uterus), nourished first by egg yolk, then finally by uterine secretions absorbed through their gut

Question 15

paedomorphosis

Answer 15

is the retention of juvenille traits in adult organisms

common in some families and characterises most cave dwelling salamanders

occurs as a variant in the life-history of some species ( e.g tiger salamander ) which normally metamorphose, when terrestrial conditions are poor

Question 16

anurans

Answer 16

(tailess amphibians : frog or toad
- fertilisation is usually external
- internal fertilisation in a few species
• may be widespread in species which mate
on land
- only 6 species of frog are viviparous and have internal fertilisation
- 20% have no tadpole stage

Question 17

anuran parental care

Answer 17

- large yolky eggs to nourish larvae 
  •1 to 20,000 eggs laid 
- many arboreal frogs lay their eggs on leaves or in
  foam nests 
- adults may guard eggs

Question 18

dart poison frogs : parental care

Answer 18

• adluts may guard the eggs and transport the tadpoles

- females provide food for the tadpoles by laying unferilised eggs

Question 19

pygmy marsupial frog : parental care