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Lecture 7

by: Sierra

Lecture 7 FNR 251


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Amphibian Reproduction
Ecology And Systematics Of Amphibians, Reptiles, And Birds
Rod N. Williams
Class Notes
Ecology, amphibians, reptiles, forestry, Natural Resources
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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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