Lecture 14 Flashcards
Other modes of reproduction
-Parthenogenesis- nonfertilized eggs Three types: Thelytoky(female), Arrhentoky(male), Deuterotoky(male and female) -Paedogenesis (larval and pupal) -Hermaphrodism: ovatestis -Endosymbionts: Wolbachia
Parthenogenesis
- Sexual reproduction involves 1n+1n to 2n(sperm+egg=diploid zygote)
- Can also reproduce asexually, without mating, and this is partenogenesis
- These species have females producing offspring without sperm/males
- Advantage in stable environment and abundant food resource
Arrgenotoky
- MALES
- Type of parthenogenesis where all members of order (hymenoptera: ants, bees, wasps) and some thrips and scale insects
- Females are diploid 2n and males are haploids 1n. Females can control release of sperm and can lay a fertilized egg(female) or a unfertilized eggs (male)
- This regulation of sex is important for structure and social ants, bees, wasps
Thelytoky
- FEMALES
- found in aphids, scale insects and cockroaches, and stick insects, and weevils
- These insects have females producing 2n eggs that are exactly like the mother
- Clones herself through parthenogenesis, large amount of offspring in short time
- Advantage of parthenogenesis species live in stable environment and exploits food source
Pseudo-arrhenotoky
- Known as PGE
- Males develop from fertilized eggs but parental gene lost in somatic cells and not passed to offspring
- Beetles, mealy bugs, and scale insects
- equivalent to haploiddiploids arrhenotoky where males are haploid and develop from unfertilized eggs and certain diploid arrhenotoky where males fail to pass half of chromosome from mom
Polyembrony
- Condition where 2 or more embryos devlop from one egg, TWINS
- Hymenoptera; Copidosoma, has parasite of a cutworm laying an egg which turns to 200 individuals
- Fall into two classes, hymenoptera nd strepsiptera
- From one egg, thousands of offspring can be made
Paedogenesis
- Form of reproduction by larvae, without fertilzation
- Distinct from neotenic reproduction (no fertilization) and eventual maturation or metamorphosis of parent organism in adult form
Parental Care
- Not common in insect world, but giant waterbug female glues eggs to male’s back
- Female taking care of eggs, young, earwig good example
Metamorphosis
Each molt= a bit larger
It can also change physically depending on type of metamorphosis (3 types)
Ametabolous
- Insects have little to no structural change as they grow. Immatures are called young, physically similar to adults except size and sexual maturity
- No external manifestation of age or reproductive state
- egg—>nymph—>adult; the same execept size
- NO WINGS
- ex. silverfish
- Also known as no metamorphosis
- Same habitats and habits
Hemimetabolous
- Gradual changes, immatures called nymphs or naiads
- Maturation of wings, sex organs, and other adult structures occur in small steps from molt to molt
- Wings completely absent in first instar, then 2nd-3rd instar they are little stub, and grow until full developed
- Changes are usually visible externally, adults retain same features though
- INCOMPLETE metamorphosis
- Terrestrial insects have nymphs resembling the adults except the adults have wings. Similar habits and habitats
- Aquatic insects will have naiads distinct from adults, closely related but differ in habitats. Feed on different things
- Egg—-> nymph/naiad—–> adult (there is stage between young and adult, SUBIMAGO, may look fully developed but is sexually immature)
Holometabolous
- Insects have immature forms (larva) very different from adults
- Larvae are feeding machines just so they can grow
- Larger in size each molt but don’t develop adult characteristics
- Fully grown larvae molt to immobile pupa stage so they can go under complete transition
- All unneeded parts digested and replaced with adult structures. Adults usually have wings (dispersal and reproduction)
- Egg—>larva—>pupa—> adult
- larvae do not look like adults
- DO NOT have similar habitats or habits
- COMPLETE metamorphosis
Advantage to Complete Metamorphosis
- Reduced competition between immatures and adults
- Adults feed on new source of food
- Adults have different habitats
3 forms of larvae
- Polypod larvae: (many leg)- 3 pair of thoracic legs and 5 pairs of abdominal legs (caterpillar)
- Oligo larvae: well developed thoracic legs, no abdominal legs (beetles)
- Apod larvae: (no leg)- no legs mostly flies, maggot
Pupal types of holometabolous insects
- Obtect: Known as Chrysalis, enclosed with silken cocoon. Appendages held tightly like a shell. Examples are butterflies and moths
- Exarate: All the appendages are free in this type, and very visable. Examples are beetles and lacewings
- Coarctate: Known as puparium. Body is encased in hard exoskeleton of the next to last larval instar. Examples are flies.
Steps to molting
- Molting is the most important aspect of metmorphosis
1) Increase activity of epidermal cells
2) These cells seperate from old cuticle (APOLYSIS)
3) Epidermal cells now secrete molting fluid but its inactive
4) Now cells will secrete new epicuticle. Seperates the cells from molting fluid
5) Now that is sepearte, the fluid is active and it will break down the old endocuticle
6) Old endocuticle is absorbed by epidermal cells. 90% recycled for new endocuticle
7) Exocuticle and epucuticle not broken down by fluid
8) New cuticle is wrinkled under the old one and the insect must expand
9) The exdysial sutures form where there is no exocuticle. When endocuticle is dissolved, it weakens these sutures
10) Insect now takes in air or pumps blood to blow up. This splits old cuticle from sutures and the insect can emerge from old skin (Ecdysis)
11) After exdysis, insect is light and soft, over time it will darken and harden
12) Eats left over cuticle for nutrients
Summary of Molting
1) Apolysis- seperation of old exoskelton from epidermis
2) Secretion of inactive molting fluid
3) Cuticulin later produced for new exoskeleton
4) Activation of molting fluid
5) Digest/Absorb old endocuticle
6) Epidermis secretes new procuticle
7) Ecdysis occurs, where old exoskeleton is shed and epicuticle
8) Expansion of new integument
9) Tanning occurs of new exocuticle
What causes this molting process?
There are hormones
What is PTTH?
Prothoracicotrophic hormone is a brain hormone that stimulates that production of ecdysone(molting hormone) by prothoracic glands in insect larvae
Summary of types of hormones
- Neurosecretory cells produce neurosecretion
- Prothoracic glands produce ecdysone
- Corpora allata produce juvenile hormones
- Corpo cardiaca produce Adipokinetic hormones and stores/release brain hormones
- Midgut endocrine cells produce peptides
- Epitracheal glands produce ecdysis triggering hormone (Eclosion) in lepidoptera
WHOLE PROCESS (picture)
First the brain sends message to the prothoracic gland, sends hormone(PPTH) to stimulate the production of Ecdysone. That way the prothoracic gland will produce ecdysone (molting hormone). There is another part, corpus allatum, that makes the juvenile hormone which is important for immature stages. Pictures shows how the juvenile hormones contribute to the larval-larval molting stages and larval-pupa molting stage. Ecdysteriod is important for every molting stage.
What are the two crucial hormones for molting/development?
Ecdysone and juvenile hormones
What are instar and stadium?
- Instar is the form between the molt
- Stadium is the time between the molts
Voltanism
- # Generations per year
- univoltine: 1 generation
- bivoltine: 2 generations
- multivoltine: many generations