Arthropods Flashcards
Where do Arthropods sit in a phylogeny?
A phylum within the super-phylum Ecdysozoa.
Describe water bears/Tardigrada?
Water dwellers.
Can survive extreme temperatures, pressures, space vacuums, radiation, lack of water.
Cryptobiosis (a physiological state in which metabolic activity is reduced to an undetectable level to survive extremely dry conditions).
Describe velvet worms/onychophora?
Convergent, similar to annelids.
Shoot slime from appendages on their heads.
Give birth to live young.
Describe hexapods?
Insects - winged and unwinged.
Beetles, butterflies, moths, ants, wasps and bees, flies.
30 million species
Some undergo metamorphosis
Describe myriapods?
Centipedes and millipedes.
Centipedes have an odd number of leg pairs, poison fanged and nocturnal active hunters.
Millipedes eat rotting vegetation and wood. Secrete noxious chemicals as a defence mechanism.
Describe Chelicerates?
Ticks and mites, Scorpions and spiders.
Named due to their chelicerate appendages.
Independent invasion of land to insects.
Describe Trilobites
They were abundantly and widely distributed in the sea.
Extinction due to competition with crustaceans and predation pressure from early fish.
Describe Crustaceans?
Lobsters, Crabs, Crayfish, Shrimp, Krill, Barnacles, and Woodlice.
Key link between primary producers and higher level consumers in marine ecosystems.
Paraphyletic group as hexapods evolved from a crustacean ancestor. Solved with use of pancrustaceans.
Key anatomy of Arthropods?
Segmentation
Jointed appendages
Exoskeleton
Hemocoel - circulation fluid
Ventral nervous cord
Brains
Segmentation of arthropods?
Common ancestor of arthropods had a series of similar segments.
Segments in extant derived taxa are often fused and/or lost. Some have become specialised - heteronomous.
All arthropods group segments to form a head. Specialised for feeding, sensing and neural integration.
Chelicerates fuse head with thorax to produce a cephalothorax.
Most divide rest of the body into a thorax and abdomen region.
What is tagmosis?
Grouping of segments with similar functions/segments.
Appendages in arthropods?
Arthropod ancestor had an appendage on each segment.
Evolved a wide range of specialised paired appendages:
head: feeding and sensing
others: locomotion, reproduction, respiration, food manipulation
Jointed appendages - joints allow articulation despite hard exoskeleton.
Flexible cuticle at the joint allows bending.
Antagonistic muscles control joint movement.
Exoskeleton in arthropods?
The cuticle provides support, maintains shape, allows joint articulation and provides protection against pathogens and mechanical forces.
Made of chitin - polysaccharide.
Moulting in arthropods?
To permit growth, the cuticle must be periodically moulted - ecdysis.
Stages: 1. Pre moult Detach old cuticle and develop new cuticle 2. Moult Shed old cuticle 3. Post moult Harden new cuticle 4. Inter moult 10% of arthropod life
Which arthropods act as parasites?
Ticks Mites Flies Fleas Lice Crustaceans
Mainly ectoparasites
What body segments do chelicerates have?
Cephalothorax and abdomen.
Arachnid body features?
Fused cephalothorax with carapace
Pedipalps (short at front, used for feeding or inseminating females)
Book lungs
4 pairs of legs
Carnivorous with liquid diet
Spider features?
Silk
Pedicel (waist)
Poison glands
Sperm transfer via pedipalp.
How many times has silk evolved?
23 times
What are the pedipalps?
On all arachnids.
Used for feeding and inseminating females.
Gives out digestive enzymes, sucks in liquid using pumping stomach.
Chelicerae are the only form of teeth, and are hardened with zinc ions to make them harder than other arthropods’ exoskeletons.
Silk in spiders?
Spider silk is stronger than any other known natural/synthetic fiber on Earth.
Ballooning is a behaviour in which spiders and some other invertebrates use airborne dispersal to move between locations. A spider (usually limited to individuals of a small species), or spiderling after hatching, will climb as high as it can, stand on raised legs with its abdomen pointed upwards (“tiptoeing”), and then release several silk threads from its spinnerets into the air. These automatically form a triangular shaped parachute which carries the spider away on updrafts of winds where even the slightest of breezes will disperse the arachnid.
Before entering the duct, the silk consists of liquid proteins. When entering the duct, cells raw water away from the silk proteins. Hydrogen is pumped into another part of the duct, creating an acid bath.
The unspun silk transforms from a gel into a final solid fiber as it is pulled through the acidic silk strands (spinnerets).
Spiders usually have 2-8 spinnerets.
Spiders are vibration specialists. Have both air borne and substrate borne vibration sensors present in large numbers on all 8 legs.
Main features of crustaceans?
Mainly marine, but also freshwater and terrestrial.
Large variation in morphology.
Moulting
Body composed of head, thorax and abdomen.
Carapace (hard upper shell).
Gas exchange by gills
Anatomy of crustaceans?
Head:
- eye
- rostrum (protects eyes and brains)
- antennule (senses touch and helps maintain balance)
- antenna (senses touch and taste)
Thorax:
- maxillipeds (hold food)
- walking legs
Abdomen:
- swimmerets (swim, move water over gills)
- telson
- uropods
General crustacean lifecycle?
Mature female gets fertilised by a mature male.
Egg development.
Hatches and becomes free living.
Metamorphosis into final larval stage (megalopa)
Matures into juvenile then mature adult.
Symbiosis in crustaceans?
Shrimp make and maintain a burrow, but are blind.
Goby maintains contact with the shrimp antennae as the fish can see predators and alert the shrimp.
Parasitism in crustaceans?
Cymothoid isopod replaces tongue in the mouth of fish.
Receives food as all the food the fish takes in goes past the tongue.
Parasite also gets a stable home, steady food supply, and can turn energy savings into higher reproduction.
Extreme crustacean habitats?
- Hydrothermal vents
- Kiwa tyleri: Dominant in Southern Ocean vents. Ventral surface covered in setae with filamentous bacteria. Bacteria can only live at a certain distance from vents.
- Rimicaris: Blind so can’t sense light. Sense black smokers, so can position itself right distance for food source - Caves
Lots of crustaceans in caves, have to reduce metabolic rate as not many insects. Hypoxic conditions (lack of oxygen supply). Regressive evolution (troglomorphy) – lack of pigment/eyes, elongated limbs, novel sensory structures - Desert pools
Broad fluctuations in temp, oxygen and pH
Dominated by crustaceans
Rapid hatching (12 hours), fast development, high fecundity
Highly resistant cycts, which can be dormant for decades – up to 6000 years
Only a proportion of cysts hatches each hydration
Define an insect?
A small arthropod animalthat has six legs and generally one or two pairs of wings.
Most successful group of multicellular organisms in terms of
- diversity
- abundance
- longevity of lineage
- ecological predominance
Around for 400 million years.
How have insects become so successful?
- Small size means there are more available micro-environments
- High speciation rates due to short generation time
- Low extinction rates - haven’t been affected by the mass extinction events like other major groups of organisms
- Arthropod exoskeleton
- Evolutionary innovations:
- Appendage specialisation is highly plastic and adapted to any circumstance
- Development of wings
- Holometabolous development
The evolutionary innovations of insects?
- Appendage specialisation:
Legs and mouth parts. Highly plastic and can adapt to any circumstance. The insect leg has 5 segments (podomeres).
Variety of insect mouthparts - 1. chewing (grasshoppers) - siphoning (butterfly)
- lapping (bee)
- piercing and sucking (mosquito)
- sponging (fly)
- Development of wings
Powered flight has only evolved 4 times. Insects took to the sky 100 million years before anything else.
Advantages - increased ability to disperse, find resources, suitable habitat and sexual partners. - Holometabolous development.
Types of holometabolous deveopment?
- Ametaboly:
No metamorphosis. Immature is a miniaturised version of adult. Only 1% of insects. - Hemimetaboly:
Incomplete metamorphosis. Immature (nymph) is a miniaturised, wingless version of adult. 16% of insects. - Holometaboly:
Complete metamorphosis. Immature (larva) is very different from adult. Larva transforms into pupa, from which the winged adult emerges. 83% of insects.
How does holometaboly occur?
Internal pockets of ectoderm in the larva form the structures of the adult after the pupal stage.
Advantages of holometaboly/
Larvae and adults don’t compete for same resources
More effective control of development - premature/delayed pupation depending on the environmental conditions.
Good or bad insects?
Good:
- crop pollinators (35% of food crop production relies on animal pollination)
- pest controllers
- models for research
- forensic indicators
Bad:
- pests
- human parasites
- vectors of disease
Cuticle in insects?
Mostly protein (chitin), which is secreted by a single layer of cells in epidermis.
Three layers:
1. Epicuticle
Polymerised lipids and proteins, with waterproofing properties. Outside layer.
2. Exocuticle
High protein cross linking. Very hard. Doesn’t break down, moults
3. Endocuticle
Low protein cross lining. Broken down by enzymes during moulting and reabsorbs.
Moulting cycle in insects?
- Apolysis – retraction of epidermal cells from endocuticle and formation of subcuticular space
- New epicuticle produced – secretion of moulting gel
with inactive enzymes - Procuticle deposition – formation of chitin micro-fibrils. Old endocuticle digested by the activation of enzymes in moulting gel
- Ecdysis – cast skin (epicuticle + exocuticle). Endocuticle reabsorbed and recycled into new procuticle
- Expansion – active growing of the insect. Epicuticle loses its wrinkles
- Darkening and hardening – exocuticle forms
- Endocuticle deposition
Circulatory system in insects?
Functions:
- Transport (of nutrients, hormones, excretion products)
- Hydraulic system (moulting, wing expansion).
- No gas exchange.
- Circulating cells: different types of haemocytes (coagulation, phagocytosis, coating of foreign objects).
Open circulatory system:
Open circulatory systems (evolved in crustaceans, insects, molluscs and other invertebrates) pump blood into a Hemocoel with the blood diffusing back to the circulatory system between cells.
Blood is pumped by a heart into the body cavities, where tissues are surrounded by the blood.
Dorsal vessel = aorta (thorax) + heart (abdomen).
Alary muscles allow entry of haemolymph through ostia. Forward through heart and aorta.
Digestive system in insects?
Foregut:
Salivary glands, crop (food storage) and proventriculus (grinding)
Midgut:
Digestive fluids secretion, nutrient absorption. Gastric caeca increase surface area. Peritrophic membrane provides mechanical protection.
Hindgut: Malpighian tubules (excretion & osmoregulation), ileum, colon rectum (ion & water absorption, fermentation).
Embryonic origin:
Foregut and hindgut have an ectodermal origin, therefore coated by cuticle and they moult. The digestive system is highly variable depending on feeding and ecology.
Excretory and osmo-regulatory function:
Malpighian tubules allow for active transport of ions from haemolymph to tubule lumen (water follows in by osmosis) produce primary urine (uric acid)
Ileum, rectum: ion and water reabsorption from gut lumen to haemolymph leads to concentration of urine and faeces.
Respiratory system in insects?
Tracheal system: gas exchange by a combination of diffusion along a concentration gradient, changes in internal pressure due to haemolymph pumping (linked to circulatory system) and ventilation.
Aquatic respiratory systems; gills (in aquatic nymphs and larvae) and plastron (bubble of air carried under the wings).
Tracheal system:
- Spiracles (openings to the tracheae regulating air exchange)
- Tracheae (shed during moulting)
- Tracheoles (repeatedly divide until their ends penetrate into each body cell, don’t shed)
- Air Sacs (expanded areas of the tracheal system due to their lack of taenidia, air storage, increased ventilation and make the insect lighter for flight).
Ventilation:
Muscular pumping of body parts, typically the abdomen, indirectly ventilate the tracheal system.
Nervous system in insects?
CNS – brain and ventral nerve cord with segmental ganglia
Brain - protocerebrum (eyes, ocelli) + deutocerebrum (antennae) + tritocerebrum (connects to visceral nervous system, labrum)
Periphery nervous system consists of the sensory receptors. They connect to the CNS.
Receptors: mechano-receptors, chemo-receptors, photo-receptors, thermo-receptors.
Reproductive system in insects?
Normally sexual reproduction (haploid egg + haploid sperm = diploid zygote), by internal fertilisation, resulting in oviparity.
Male sexual organs:
Testes produce spermatozoa’s. Accessory glands produce secretions for sperm viability and packing. Aedeagus is the sclerotized terminal portion of the male genital tract that is inserted into the female during insemination. Males also have grasping structures which stops other males interrupting the egg laying process.
Female sexual organs:
Ovaries made of ovarioles. Each ovariole produces eggs (oogenesis). Spermathecae stores sperm after mating and until fertilisation. Accessory glands make substance to preserve sperm, and pack and lay eggs.
However, asexual reproduction (parthenogenesis), external fertilisation and viviparity occur.
Protective adaptations in insects?
Based on morphological traits but supported by specialised behaviours. Some can be used aggressively by predators.
Mimicry:
Resemblance to a species with few enemies. Caterpillar looks/moves like a snake. Can also perform self-mimicry (deceives a predator into attacking non-vital parts of the insect, for example fake heads).
Camouflage:
Special resemblance in leaf stick insect. Trash carrying green lacewing larva.
Chemical defence:
Entangles, deters, etc.
Autotomy:
A calculated sacrifice. Casting off appendages to escape predation. Typically found in stick insects and mantises. Appendages are cast off through predetermined spots. Lost appendages are regenerated in subsequent moults.
Define solitary insects?
adults live independent of one another and do not provide brood care
Define subsocial insects?
adults care for their young for some period of time
Define communal insects?
adults share nest but without cooperation in brood care
Define quasisocial insects?
adults share nest and show cooperation in brood care
Define semisocial insects?
adults nest together, show cooperation in brood care and have some reproductive division of labour
Define eusocial insects?
overlapping generations of adults nest together, show cooperative brood care and only reproductives reproduce (workers are sterile).
E.g.: termites, ants and honeybees.
Advantages are a division of labour and group response. Both of these increase the ability of keeping conditions in the nest stable regardless of environmental fluctuations (homeostatic regulation).
Ant and honeybee lifestyle?
Eusocial. Castes are workers (all female, sterile) and reproductives (female princesses and queens, male drones).
Females develop from fertilised eggs and are diploid, males develop from unfertilised eggs and are haploid.
Chemical based communication (pheromones secreted by multiple glands).
Also communicate by direct contact, and movement.
-Workers:
All female and sterile. Roles include food provisioning, brood care, nest/hive construction, farming and colony defence. Transfer food mouth to mouth, storage in a social stomach. Some species have bigger worker casts usually specialised in defence.
-Reproductives:
Princesses are virgin female reproductives. Mate with drones out of the nest.
Queens are fertilised princesses that find a new colony after mating. Most shed their wings. They can stay fertilised for many years laying millions of eggs (store sperm). Record for longest living insects – up to 30 years.
Drones are male reproductives. Only males in the colony and are made from unfertilised eggs. Only purpose is to fly out of the nest and mate. Die once mated.
Define apterygota?
Insects with no wings
Define pterygota?
Insects with wings
Features of hymenoptera?
Sawflies, wasps, ants and bees.
150,000 species, 0.15mm-12cm. Generally mandibulate. Some are parasitoids (development of larvae kills the host).
Neuropterida: Lacewings, snakeflies and their kin
Strepsiptera: Twisted wing parasites
Features of coleoptera?
Beetles.
Most diverse insect order – 400,000 species worldwide (25% of all animals). Usually mandibulate, diverse feeding habits. Hardened forewings that protect the usually functional hind wings. Very important group.
Mecoptera: Scorpionflies
Siphonaptera: Fleas
Features of diptera?
Flies and mosquitos.
125,000 species worldwide with diverse feeding habits. 1-80mm. Only one pair of forewings. Hind wings are transformed in flight control. Important group ecologically and economically.
Trichoptera: Caddisflies
Features of lepidoptera?
Moths and butterflies
180,000 species worldwide. Feed on nectar. 4mm-30cm. Scales cover the wings. Important ecologically and economically.
