Ecdysis and metamorphosis Flashcards
what are the functions of ecdysis
1) to allow the insect to grow
2) to replace the mouthparts
3) to replace/extend the lining of the trachea
4) to restore waterproofing ability
5) to shed pathogens
what are the disadvantages to ecdysis
1) the process is slow = unable to do anything else whilst undergoes ecdysis including feeding
2) dangerous process = leaves the insect vulnerable to predation during the process whilst the cuticle is hardening
3) energetically expensive = cuticle is made mostly from proteins and sclerotised cuticle which cant be reused
what are the steps of ecdysis
1) Apolysis
2) Epicuticle formation
3) New procuticle deposition
4) Ecdysis
5) procuticle expansion
6) Hardening and darkening
7) Endocuticle deposition
= ECDYSIS OCCURS BETWEEN EVERY INSTAR AND PUPA AND TO ADULT AS IT IS THE SHEDDING OF EVERY OLD CUTICLE AS IT GROWA
what is ecdysis
the process of casting off the outer cuticle in insetcs and other arthropods
What is meant by the terms pharate and teneral when describing insects
pharate = the name given to the adult insect prior to its emergence from a pupa or when the insect is actively constructing a new cuticle
teneral = the name given to an insect prior to hardening and darkening of the cuticle when it is still soft and colourless
describe the ecdysis stage known as apolysis
- the epidermal cells sperate from the inner surface of the endocuticle (olf exoskeleton from the epidermis)
- inactive moulting fluid containing chitinases, proteases and lipases are then secreted into the subcuticular space created
= these are the enzymes needed to break down the old cuticle
outline the stage known as epicuticle formation in ecdysis
- a new outer epicuticle is laid down below the moulting fluid and above the epidermis
- a new inner epicuticle is deposited just inside the epicuticle
- both layers are chemically stabilised
- new outer epicuticle protects the epidermal cells and new layers from the moulting fluid enzymes
outline the stage known as activation of moulting fluid and new procuticle deposition during ecdysis
- chitin microfilaments formed beneath the inner cuticle
- moulting fluid begins to digest the original endocuticle
- new procuticle is protected by the new outer epicuticle
outline the stage of ecdysis known as new procuticle deposition
digestion using the moulting fluid is complete and only the exocuticle and epicutile remain
outline the stage ecdysis
the old cuticle splits along ecdysial lines (lines of weakness)
- an exuvicum (refers to cast off outer covering) is fromed from epicuticle and exocuticle
outline the stage of procuticle expansion which starts as part of ecdysis
- muscular contractions develop pressure within the body of 1-30kPa
- some insects support this by swallowing air or water
- the pressure splits the cuticle allong ecdysial lines
- this inflates the body and smoothes out the surface and stretches the procuticle to accomidate a bigger size
what is meant by hardening and darkening during ecdysis
the stabilisation of the new procuticle trough chemical changes
outline the hormonal steps of ecydsis
1) environmental cues trigger neurosecretory cells in the brain causing the secretion of prothoraticicotropic hormone (PTTH)
2) PTTH passes to the corpa cardica for storage and is later released into the ciruclatory system
3) PTTH stimulates the prothoratic glands to secrete ecdyson (prohormone) into the haemolymph and is transported to the epidermis
4) ecdysone is converted to active for 20-hydroxyedcdysone by haem-containing oxidase in mitochondria and microsomes of peripheral tissues
5) 20-HED regulates gene controlling cuticle production, epidermal cell synthesise enzymes for apolysis
6)ecdysis triggering hormone from inka cells intitates pre-ecdysis behaviour which loosen muscle attachments from old cuticle
7) ETH also causes release of eclosion hormone from brain which causes plasticisation of cuticle
what are the hormones involoved in ecydisis
1) Prothoraticicotropic hormone
2) Ecdysone (prohormone, inactive)
3) 20-hydroxyecdysone (active)
4) Ecdysis triggering hormone
5) Eclosion hormone
6)Bursicon
what is the role of prothoraticicotropic hormone
stimulates the prothoratic gland to secrete ecdysone into the haemolymph
what is the role of ecdyson
a prohormone which is converted into 20-hydroxyecodysone by haem-containing oxidases in the mitochondria
what is 20-HED hormone
regulates the gene control of cuticle production
what is the role of ecdysis triggering hormone
produced from inka cells it intitaes pre-ecdysis behaviour which causes the loosening of muscle attachemnts from the old cuticle
= also causes release of eclosion hormone from brain neurosecretory cells
what is the role of eclosion hormone
causes plasticisation of the cuticle
what is the role of bursicon
stored in corpa cardiaca and part of eclosion behaviour but subject to sensory control
= causes cucticle sclerotization and depositon of endocuticle
How has metamorphosis lead to the success of insects
= transformation between larval and adult stages
- life cycle compartmentalisation= larval form and function is optimised for growth and feeding
- no compromise is needed to adaptations of adult for dispersal and reproduction
- allows exploitation of different environmental resources and occupy different habitats
outline the role of juvenile hormone
- normally secreted from the corpora allata prior to each moult
= inhibits genes which cause the development into an adult
BUT
during the last larval instar the corpa allata reduces activity and at the same time there is an increase in the ability to degrade the juvenile hormone
= causes JH levels to drop below threshold and triggers the release of PTTH–> ecdysone–> behavioural changes and moult to pupae development
what does stopping the production of juvenile hormone do
it prevents the inhibition on development of adult structures resulting in the insect moulting into a pupa or adult rather than another instar
what is the role of juvenile hormones in adult insects
- at onset of sexual maturity the brains neurosecretory cells releases a hormone
- this reactivates corporta allata and renewed production of JH stimulated
- JH stimulates yolk production in females or accessory glands to produce proteins for seminal fluid
- adult will remain sexually sterile in the absence of normal JH production
who is Maria Sibylla Merian
- one of tarliest European naturalists who documented evidence of the metamorphic process and the plant hosts
- before her work it was though that insects were born of mud by spontaneous generation
who is Sir vincent brian wigglesworth
- hormonal control of insect metamorphosis was shown by this man who was an eminent insect physiologist
- discovered PTTH
what did Sir Vincent Brian Wigglesworth demonstrate in his work
that the corpora allata produced hormones preventing metamorphosis
if you remove the CA and a 3 rd instar nymph will transform into a small adult at the next moult
if CA from 4th instar implanted in 5th instar moult will produce 6th instar rather than into adults
