Reproduction & life histories. Reproductive cycles Modes of Fertilization Asexual reproduction Evolution of parental care Parental care Viviparity. I. Reproductive cycles. Environmental stimuli Moisture, temperature, food availability, amount of sunlight, stimulate GnRH
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Reproduction & life histories • Reproductive cycles • Modes of Fertilization • Asexual reproduction • Evolution of parental care • Parental care • Viviparity
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
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 • External • Internal • Evolved independently several times • Only a few Anurans, 90% salamanders & all caecilians • Salamanders: Spermatophore, females able to retain… • Mating separate from oviposition
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
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
texanum (TT) • laterale (LL) • jeffersonianum (JJ) • Triploid, unisexual females: • LLJ • LLT • LJJ • Hybridogenesis: • LJ • LT • JT
C. Parthenogenesis C. tigris C. inornatus • Occurs in 7 lizard clades & 1 snake clade C. neomexicanus asexual species
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