Reproduction & life histories I.Reproductive cycles II.Modes of Fertilization III.Asexual reproduction IV.Evolution of parental care V.Parental care VI.Viviparity.

Reproduction & life histories

I. Reproductive cycles

II. Modes of Fertilization

III. Asexual reproduction

IV. Evolution of parental care

V. Parental care

VI. Viviparity

I. Reproductive cycles

A. Environmental stimuli Moisture, temperature, food availability,

amount of sunlight, stimulate GnRH– Amphibians = rain & temperature– Reptiles = temperature

• In temperate climates - Soil temperatures and insolation only high enough to allow rapid embryonic development in summer

B. Hypothalamus – Pituitary axis

– GnRH• Gonads

Annually Biennially

• Oogonia are self-renewing stem cells that persist for the life of the frog

• Can generate a new cohort of oocytes each year

Growth of oocytes in the frog. During the first 3 years of life, three cohorts of oocytes are produced. The drawings follow the growth of the first-generation oocytes.

Reptilian cycles

• Associated

• Dissociated

• Continuous

C. Breeding behavior• Location & stimulation of potential mates, primarily

associated with males. In most amphibians, males compete among themselves for mating opportunities – females do the choosing– Ova more costly than sperm, thus female output is limited by

resource availability and time constraints – not mate availability

• Salamanders • Anurans• Reptiles

II.Fertilization modes of amphibians

A. External

B. Internal– Evolved independently several times– Only a few Anurans, 90% salamanders & all caecilians

• Salamanders: Spermatophore, females able to retain…– Mating separate from oviposition

III. Asexual Reproduction

A. Hybridogenesis When females produced via hybridization between 2 closely related

species produce only female offspring (all genetically identical to the mother)

This mode marks hybrids between two parental species (A,B) who are able to reproduce by backcrossing with one of the parents.

These hybrid normally contain two chromosome sets (AB, one from each parent species) in their body cells, but in the gonads the chromosome set of one parent is lost, so that only one set remains (A or B), with A in their gonads, hybrids can backcross with B and vice versa.

R. lessonae R. ribidunda

R. esculenta

RL, RLL, RRL

female

male

B. Gynogenesis

• Egg development activated by a spermatozoon, but to which the male gamete contributes no genetic material

• Ambystoma laterale-jeffersonianum complex: females use sperm from a sympatric, diploid male to initiate the development of the eggs without incorporating the male genome

A. texanum (TT) laterale (LL)

jeffersonianum (JJ)

Triploid, unisexual females:

LLJLLTLJJ

Hybridogenesis:LJLTJT

C. Parthenogenesis

• Occurs in 7 lizard clades & 1 snake clade

C. neomexicanusasexual species

C. inornatus C. tigris

IV. Evolution of parental care

• Parental investment in offspring after the eggs have been deposited or young have been born– Amphibian:

– Reptile:

• Mom vs. Dad

V. Ecology of Anuran Metamorphosis

Dramatic morphological & physiological changes

Density dependent variation when growth conditions are poor,

Plasticity in larval growth

VI. Vivparity

• Viviparity – derived condition, specializations for embryonic development in uterus

• In reptiles - Associated w/ colder climates, female can regulate her body temp. behaviorally

•In reptiles - Associated only w/squamates•In amphibians – Caecilians & a few Anurans

• In viviparous amphibians, nutrition for embryos is