Reproduction

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Reproduction life histories

1. Reproductive cycles
2. Modes of Fertilization
3. Asexual reproduction
4. Evolution of parental care
5. Parental care
6. Viviparity

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I. Reproductive cycles

• 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

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• Hypothalamus Pituitary axis
• GnRH
• Gonads
• Annually
• Biennially

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• Oogonia are self-renewing stem cells that persist
  for the life of the frog
• Can generate a new cohort of oocytes each year

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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.
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Reptilian cycles

• Associated
• Dissociated
• Continuous

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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

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II.Fertilization modes of amphibians

• External
• Internal
• Evolved independently several times
• Only a few Anurans, 90 salamanders all
  caecilians
• Salamanders Spermatophore, females able to
  retain
• Mating separate from oviposition

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III. Asexual Reproduction
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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.

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R. lessonae R. ribidunda
R. esculenta
RL, RLL, RRL
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female
male
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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

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• texanum (TT)
• laterale (LL)
• jeffersonianum (JJ)
• Triploid, unisexual females
• LLJ
• LLT
• LJJ
• Hybridogenesis
• LJ
• LT
• JT

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C. Parthenogenesis
C. tigris
C. inornatus

• Occurs in 7 lizard clades 1 snake clade

C. neomexicanus asexual species
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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

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V. Ecology of Anuran Metamorphosis
Dramatic morphological physiological changes

• Density dependent variation
• when growth conditions are poor,
• Plasticity in larval growth

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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

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• In viviparous amphibians, nutrition for embryos is