Metamorphosis What is metamorphosis Metamorphosis refers to the
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What is metamorphosis? • Metamorphosis refers to the way that certain organisms develop, grow, and change form. • Metamorphosis actually means "change".
Two Types of Metamorphosis • INCOMPLETE METAMORPHOSIS - has THREE stages • COMPLETE METAMORPHOSIS has FOUR stages.
INCOMPLETE METAMORPHOSIS • Egg • Nymph • Adult
COMPLETE METAMORPHOSIS • Egg • Larva • Pupa • Adult
Complete and Incomplete Metamorphosis What is metamorphosis? • Metamorphosis means "change". • Metamorphosis refers to the way form changes as certain organisms are born, develop, grow, and change. What’s the difference? Two Types of Metamorphosis • Incomplete Metamorphosis - has THREE stages • Complete Metamorphosis - has FOUR stages.
Incomplete Metamorphosis - 3 Stages • Egg • Nymph • Adult Eggs • A female insect lays eggs. • These eggs are often covered by an egg case which protects the eggs and holds them together.
Incomplete Metamorphosis Nymph • The eggs hatch into nymphs. • Nymphs looks like small adults, but usually don't have wings. • Insect nymphs eat the same food as the adult. • Nymphs shed or molt their exoskeletons (outer casings made up of a hard substance (called chitin) and replace them with larger ones several times as they grow. • Most nymphs molt 4 -8 times.
Incomplete Metamorphosis Adult • The insects stop molting when they reach their adult size. • By this time, they have also grown wings. Insects with Incomplete Metamorphosis… • Praying Mantis • Dragon fly • Water bug • Cockroach • Grasshoppers • Aphids
Complete Metamorphosis 4 Stages • • Eggs Egg Larva Pupa Adult • A female insect lays eggs. • These eggs are often covered by an egg case which protects the eggs and holds them together.
Complete Metamorphosis Larva • Larva hatch from the eggs. • They do not look like adult insects. • They usually have a worm-like shape. • Caterpillars, maggots, and grubs are all just the larval stages of insects. • Larvae molt their skin several times and they grow slightly larger.
Complete Metamorphosis Pupa • Larva make cocoons around themselves. • Pupa don't eat while they're inside their cocoons. • Their bodies develop into an adult shape with wings, legs, internal organs, etc. • This change takes anywhere from 4 days to many months.
Complete Metamorphosis Adult • Inside the cocoon, the pupa change into adults. • After a period of time, the adult breaks out of the cocoon. Insects with Complete Metamorphosis… • Lady bug • Butterfly • Mosquito • Fleas • Wasps • Flies
Complete Metamorphosis Frogs • Frogs undergo a different type of complete metamorphosis. • From the egg emerges a tadpole, which lives in the water, breathes with gills, and has a tail. • As the tadpole grows, lungs and legs form, and the gills and tail are absorbed into the body.
Complete and Incomplete Metamorphosis Quiz What are the two types of metamorphosis? • Complete • Incomplete How many stages are there in incomplete metamorphosis? • Answer: 3 How many stages are there in complete metamorphosis? • Answer: 4 Name the stages in complete metamorphosis. • Egg • Larva • Pupa • Adult
Complete and Incomplete Metamorphosis Quiz Label all the stages.
Complete and Incomplete Metamorphosis
Complete and Incomplete Metamorphosis Quiz Complete or Incomplete Metamorphosis? Answer Complete Metamorphosis?
Complete and Incomplete Metamorphosis Quiz Complete or Incomplete Metamorphosis? Answer Incomplete Metamorphosis?
Metamorphosis in Insects and Amphibians
ENDOCRINE- describing or relating to any gland or other group of cells that synthesizes hormones and secretes them directly into the blood, lymph, or other intercellular fluid Endocrine cells release protein and nonprotein hormones Synthesis of hormones is orchestrated by the CNS Hormones effects are tissue dependent
Metamorphosis in Insects The transformation of an immature insect from a larva to a pupa to an adult
Evolution of Metamorphosis Complete metamorphosis occurs only in higher insects; it evolved only once Early expression of juvenile hormone suppresses the development of adult characteristics Larval and adult forms can occupy different environments and consume different food sources Lack of competition between larva and adult allows species success and diversification Metamorphosis can serve as a model for understanding how shifts in protein production can create different body forms
Hormonal Control of Insect Metamorphosis Temperature, Light, Stress, etc. Prothoracicotropic hormone (PTTH) Brain Corpus Allatum Prothoracic Gland Juvenile Hormone (JH) Larva Ecdysteroid Pupa Adult
Control of Metamorphosis by Internal and External Factors Temperature, Light, Stress, etc. Brain Temperature (day degrees) Critical size matched (availability of food) Light (photoperiod) Chemicals Amount of moisture Stress: mutagens, predators, etc.
Ecdysone: “Molting Hormone” Steroid hormone produced by prothoracic gland (lipid soluble, passes through cell membrane to the nucleus) Activates early response genes (TFs) and then late response genes (may cause differentiation, cell proliferation and migration, structural changes, apoptosis) Primes insect to respond to second hormone, EH Ec. R Ec USP Binding Site Early Response: Transcription Factors Late Response: Transcription initiated by Transcription Factors
Chromosome Puffing in Flies Observed in giant salivary gland chromosomes (no cell division after replication) Can be inhibited by actinomycin Puffing is where transcription is occurring. Ecdysone can be detected by fluorescent antibodies localized to the puffing Early puffs and late puffs seen in larva to pupa and pupa to adult molt
Alternative Splicing of Ecdysone Receptor Prem. RNA Creates Several Forms of the Ec. Receptor Allowing Cell Type Specific Ecdysone Response
Eclosion Hormone Peptide hormone (water soluble and binds cell receptors) Released by tracheal endocrine cells in response to EH Binds cell receptor and results in increase in levels of c. GMP, a secondary messenger Increases cuticle extensibility and prompts ecdysis-specific behavior
Juvenile Hormone Major endocrine factor controlling metamorphosis Released from corpus allata (paired endocrine glands) Methylated to make active form JH can pass through plasma membrane and influence gene expression (like a steroid hormone) Can also act as a peptide hormone by activating second messengers (c. AMP, etc. ) Maintains larval features by repressing adult genes Modifies effects of ecdysone (prevents changes in gene expression)
Regulation of JH Levels Amount of Hormone Juvenile Hormone Ecdysone Larva Pupa Adult Low = larva stage; Medium JH levels = pupa stage; No JH = adult stage Rate of release limited by synthesis Amounts of JH also regulated by protein degradation and methyltransferase levels (can be protected by JH binding proteins, degraded by JH esterase)
Metamorphosis in Action: Remember Imaginal Discs? Adult Insect: - JH Immature Insect: + JH
Hox Gene Expression Determines Leg Segments
Which Stage would You Target?
Insect control by targeting metamorphosis Juvenile hormone mimic: Keep insects in larval stage -- Effective control for insects such as mosquitoes Juvenile hormone antagonist: Cause death of larva or early metamorphosis -- Effective control for crop pests such as hornworm Genes for juvenile hormone binding hormone and JH esterase have been identified
Frogs: Tadpole to Adult
Hormonal Control of Frog Metamorphosis Secretions of two hormones, thyroxine (T 4) and triiodothyronine (T 3) cause metamorphic changes Hormones have different effects depending on location in body Timing of changes regulated by tissue dependent hormone sensitivity Thyroid receptor is transcriptional repressor until thyroid hormone binds causing it to become a transcriptional activator Positive feedback loop is established between thyroid hormone and pituitary gland allowing incremental increases in hormone concentration
Pituitary Metamorphosis Thyroid Hormones (T 3 and T 4 ) Transcriptional Activation
HIGH LOW Number of Receptors in Affected Tissue Amount of Hormone LOW TR T 3 RXR Binding Site HIGH Early Response: Transcription Factors Late Response: Transcription initiated by Transcription Factors
TH does not determine the developmental program, but initiates it • Changing the location of tissue or organ does not alter its response to TH • Transplant eye to tail region o Differentiates & grows into eye in response to TH while tail regresses • Transplant tail to trunk o Tail regresses while limb grows
Species Diversity: Variation in Metamorphosis