Popular in Ecology And Systematics Of Amphibians, Reptiles, And Birds
Popular in Agriculture and Forestry
This 23 page Class Notes was uploaded by Sierra on Saturday February 6, 2016. The Class Notes belongs to FNR 251 at Purdue University taught by Rod N. Williams in Spring 2016. Since its upload, it has received 24 views. For similar materials see Ecology And Systematics Of Amphibians, Reptiles, And Birds in Agriculture and Forestry at Purdue University.
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Date Created: 02/06/16
LECTURE 6: AMPHIBIAN REPRODUCTION, GROWTH AND DEVELOPMENT I. Reproduction and Life Histories Amphibians have evolved diverse solutions to enhance their reproductive output and offspring survival. For example: a) Amphibians display a spectacular diversity of reproductive modes b) Fertilization can occur inside or outside the body of females c) Development can be direct or indirect II. Gametogenesis and Ovulation In most amphibians, two sexes (♀♂) are needed for reproduction Gametogenesis is a major feature of sexual reproductive preparations: Involves the division and growth within the ovaries (♀) and testes (♂) through hormonal activation II. Gametogenesis and Ovulation Vitellogenesis is a very important process in egg-laying vertebrates: Accumulation of nutrients in the cytoplasm of the developing egg Rapid growth of cotocytes II. Gametogenesis and Ovulation Ovulation occurs when the follicular and ovarian walls rupture As eggs pass through the oviduct, protective membranes are deposited around them Amphibian eggs are anamniotic Eggs are expelled singly, in gelatinous masses, or strings II. Gametogenesis and Ovulation Gelatinous mass of eggs - Wood FrogTiger Salamander egg mass Eggs from an American Toad deposited as long strings III. Fertilization Fertilization is defined as the fusion of male and female gametes to form a zygote During mating, many sperm can reach the egg, but only one will penetrate it and fertilize it (exception are salamanders which have internal fertilization) Two types in amphibians: a) external III. Fertilization 1. External Fertilization: Simultaneous shedding of eggs and sperm into water Most frogs and Crytobranchoid salamanders Constrain where the eggs are laid Frogs: males grasp females in back around legs so that his cloaca is positioned just above female’s cloaca Salamanders: amplexus may occur or males follows females depositing sperm on egg masses III. Fertilization Wood Frogs Tree Frogs Amplexus in Frogs III. Fertilization 2. Internal Fertilization: Few species of frogs, Salamadroid salamanders, and all Caecilians Allows eggs to be laid in spot and at time of choice Frogs: require special intromittent organs (hemipenis) in males for delivering sperm into female’s cloaca Salamanders: male produces sperm which are deposited externally Fertilization occurs in cloaca, but often is delayed with sperm storage in series of tubules on roof of cloaca called spermatheca III. Fertilization Spermatophore in a Salamander IV. Reproduction Without Fertilization Asexual Reproduction: reproduction occurs without the males genetic contribution, and in some taxa, populations are 100% females Two types in amphibians: a) hybridogenesis b) synogenesis IV . Reproduction Without Fertilization Bisexual and Unisexual Reproduction in Amphibians. The “B” in the offspring produced by hydridogenesis and gynogenesis comes from the mother. FNR 251 01/23/2008 IV. Reproduction Without Fertilization • “Unisexual” hybrid Ambystoma complex • ~ 5 million years ago • 5 parental species • Ploidy number varies: – 2n, 3n, 4n, 5n V. Parental Care Definition: Most amphibians show no parental care other than attendance and guarding of eggs Represented by a variety of behaviors: 1. nest egg 2. egg brooding 3. transport 4. feeding of young V . Parental Care Australian Gastric Brooding Frog (female with froglet) Mallorcan Midwife Toad (male carrying eggs on hind legs)Surinam Toad (female with eggs on back) VI. Development Important terms: Exotrophic Metamorphosis Paedomorphosis a) Progenesis b) Neoteny VII. Growth Two growth pulses a) Embryonic b) Juvenile VIII. Age A. Intervals (periodicity and not age) are important: 1. Sexual Maturity 2. Embryogenesis 3. Larval period metamorphosis VIII. Age IX. Dynamics of Reproduction Multitude of patterns geared to the right environment for offspring All temperate species are cyclic Tropical species cyclic or acyclic In temperate salamanders, two patterns: 1. Winter/spring mating and egg deposition (Ambystomatids) 2. Late summer/fall mating and spring egg deposition (Plethodontids) IX. Dynamics of Reproduction Mate attraction and selection Location usually not a problem Reproduction is more efficient within home range Courtship has communication as key Females heavy investment in gametes obligates her to select most fit male Review of Terms: Lecture 6 Gvitellogenin and vitellogenesis, Ovulation, Spermatheca,s, Spermatophore, Polyspermic Fertilization: Amplexus, Fertilization, internal, external, Hemipenis, Paedomorphosis Reproduction without Fertilization: Asexual reproduction, Gynogenesis, Hybridogenesis Development and Growth: Exotrophic, Metamorphosis, Neoteny, Progenesis Parental care
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