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Arthropod Flash Cards
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- 1Phylum Arthropoda, Class Insecta, Order ColeopteraVery successful group in terms of number of individuals / species / biomass / habitats exploited
~ 1 million species described
~ 1018 living at any one time
Insects ~ 72% of all described animal species
Arthropods are typically small but exhibit huge range of size
- Some midges weigh <0.1mg
- Goliath beetle may weigh ~ 100g
- Some mite species are <0.25mm
- This is less than size of the nucleus of
- some large protozoa - 2Arthropod FeaturesHard exoskeleton
- Shed periodically to enable growth
Specialised segments / appendages
- Pinchers
Jointed appendages
Fore- and hindgut lined with cuticle
Specialised respiratory systems
Compound eyes
Haemocoel = primary body cavity
Many undergo complete metamorphosis
- Have an egg, larval, pupal/chrysalis and adult stage - 3ExoskeletonCUTICLE
Secreted by epidermis
Varies in hardness/thickness/composition depending on species and part of body
Stiff regions = sclerites
- Sclerites separate by soft cuticle
- As as to combine strength and flexibility
Mechanical protection
Support for body (Important for terrestrial species. In aquatic species water provides buoyancy)
Attachment sites for muscles
Reduces evaporation (Important for terrestrial species in which high surface area: volume ratio) - 4Exoskeleton ADULT and LARVAEAdult insect
-Tough hard cuticle
-Cannot expand, insect cannot grow in size, does not molt as an adult
Larval insect
-Soft flexible cuticle
-Allows considerable expansion between moults
-Ultimately must be shed
-Number of moults is usually fixed for the species - 5ONE PHYLUM OR SEVERAL PHYLAAlthough the arthropod groups exhibit many similarities, they also exhibit many differences. This has led to two distinct viewpoints.
Monophyly hypothesis:
-The arthropods all evolved from a common ancestor and represent a single phylum.
Polyphyly hypothesis:
- The different groups of arthropods evolved from different ancestors and therefore represent separate phyla - 6MONOPHYLY hypothesis of arthropod evolutionAll arthropods share many common fundamental features such as:
-Their cuticle is composed of chitin and proteins
-They all exhibit segmentation with at least some segments bearing paired articulating limbs
-They all show similar patterns of cephalization (the concentration of sense organs, nervous control etc at the anterior end of the body forming a head and brain both during evolution and in the course of an embryos development) and pre-oral segmentation.
-There is some supporting DNA evidence for the existing arthropod groups - 7POLYPHLY hypothesis of arthropod evolutionArthropods are too different from one another for any conceivable ancestor to be functional unless one goes back to soft-bodied forms.
Although all arthropods have a common basic limb structure there is no other way to design a limb with an exoskeleton. Therefore this is not a useful phylogenetic characteristic
Variations in limb structure between arthropods have been conserved throughout time
Crustacea:
- 2 branches
Insects + myriapods:
- no branches
Chelicerates (marine)
- branched but at a different position to the Crustacea. - 8Evidence for the CLASE ECDYSOZOANucleic acid sequencing indicates a strong relationship between ALL moulting phyla.
The clade Ecdysozoa has been proposed to include all moulting invertebrate phyla.
- This includes the arthropods, nematodes, tardigrades, onychophorans, and priapulids.
There is no DNA support for a close relationship between all segmented animals (e.g. Annelid worms and arthropods) - 9Current Taxonomic ArrangementUncertainty how the various arthropod groups living today relate to one another.
Used to recognize three phyla:
- Chelicerata (scorpions, spiders, and ticks)
- Crustacea (barnacles, lobsters, and crabs)
- Uniramia (centipedes, millipedes = Myriapoda) and insects = Hexapoda).
Molecular evidence indicates Chelicerata is a distinct entity.
BUT the relationship between crustaceans, myriapods, and insects is less certain. - 10Current Taxonomic Arrangement PROBLEMSPhylum Crustacea is not a monophyletic group (i.e. its current members are not derived from a common ancestor).
Insects are more closely related to two obscure groups of Crustacea called the Remipedia and the Cephalocarida than they are to the millipedes and centipedes.
The millipedes, centipedes, and other myriapods are closely related to one another and would probably be best considered as a distinct group within the Arthropoda.
For the purposes of these lectures we will consider three taxonomic divisions:
- Chelicerata
- Crustacea,
- Hexapoda (Insects). - 11The Moulting Process (ECDYSIS)Hard cuticle cannot stretch and soft cuticle can only stretch to a limited extent so it must be shed if growth is to occur.
-Epidermal cells separate from the cuticle and new cuticle is deposited.
-Moulting fluid is released into the space between the old and new cuticle. This fluid contains enzymes that digest the old cuticle but do not harm the new cuticle.
-The arthropod distends its body by contracting its muscles / swallowing air or water / redistributing blood within its body.
-The old cuticle splits and is shed.
-The arthropod emerges. Initially, the new cuticle is soft and pale and the arthropod is very vulnerable to predation / cannibalism / desiccation until it hardens. The old cuticle is often fully or partially eaten - 12Origin of ArthropodsLegs probably evolved prior to the exoskeleton
Primitive arthropods were probably soft, worm-like creatures with unjointed legs + hydrostatic skeleton.
Onychophorans:
-flexible chitinous cuticle
Tardigrades:
-external cuticular plates
Arthropodization
- more cuticular plates produced until whole body covered. This would require articulatory joints between serially repeated plates to enable movement.
This probably occurred during Pre Cambrian era (~605mya) when there was a major radiation in animal diversity
Many arthropod and arthropod-like organisms are known from Cambrian fossils but few of these survived beyond the Cambrian and only 4 outlasted the Devonian (409mya).
The trilobites survived 300 million years but became extinct at the end of the Permian (~290mya). - 13SUB PHYLUM: HEXAPODA AND CLASS: INSECTALargest group of animals
- 750000 species described
Class ENTONATHA
-Primitive insects whos relation to insect is debateable
Class INSECTA
-All winged insects and some primitive wingless insect species - 14Hexapoda FEATURESBody = head + thorax + abdomen
3 pairs of legs on the 3 thoracic segments
Head has 2 pairs of maxillae
-One pair of which has fused to form the labium
Genital openings on terminal/ sub terminal abdominal segments
Median ocelli on head plus lateral ocelli and/or compound eyes either side - 15Class ENTOGNATHAPrimitive
Wingless = Apterygota
Ametamorphic
(i.e. little change in morphology with age apart from change in size and formation of genitalia) - 16Order COLLEMBOLASpringtails
Largest apterygote order
Very common in soil + leaf litter
Found from arctic to equator
All have a ventral tube on first abdominal segment that is involved in maintaining water balance.
Some have a furca
- (jumping organ) on 4th abdominal segment. For escape.
ECOLOGY
-Very important in soil ecology
-May influence the growth of mycorrhizae (important for plant growth)
-Can influence soil structure
•alpine pitch rendzinas are composed of collembola faeces - 17Class INSECTA3 pairs of legs
1 pair of antennae
2 pairs (usually) wings on thorax
1 pair (usually) compound eyes
2 or 3 median ocelli
Base of mouthparts exposed and mouthparts project from the head capsule
Mandibles have 2 points of articulation (except for one primitive order) - 18Class INSECTAECOLOGY
- 75% flowering plants are insect pollinated.
- Insects are essential food for many invertebrates + vertebrates (e.g. bats, birds, lizards)
ECONOMICS
- Some species are pests of food crops + stored productS
HUMAN/VET MEDICINE
- Vectors of disease
(e.g. malaria, bluetongue virus).
-Cause of disease
(e.g. lice, blowfly strike)
BENEFICIAL
Biological control agents
Ladybirds – eat aphids
Part of human diet - 19InsectsInsect wings and evolution of flight
Pterygote insects
-Palaeopterous exopterygotes (e.g. dragonflies)
-Neopterous expoterygotes (e.g. locusts)
- Neopterous endopterygotes (e.g. bees)
Social Behaviour
-Benefits and drawbacks of living in a group
-Simple associations
-Eusocial behaviour
-Honeybee societies - 20WingsCharacteristic feature of insects
Wingless
-2ndry characteristic (e.g. worker termites [male + queen are winged], lice and fleas lost wings completely.
-Never had wings during evolution = apterygotes (Entognatha) - 21Wings EVOLUTIONEvolution uncertain
Assumed began with gliding
Alternative suggestion:
- Some stoneflies use wings as sails to skim across water (cannot fly)
May have evolved from articulated gill plates used by aquatic larval forms
- Some gene sequencing data supports this:
Homologues of genes with wing-specific function found in appendages with osomoregulatory/ respiratory function in Crustacea
(i.e. wings derived from already existing structural features)
All insects share common pattern of wing venation/ articulation.
Suggests common ancestor
BUT
Wings may be used for non-flight locomotion (e.g. certain stoneflies) so it is possible wings arose several times before powered flight attained.
- Hence current similarities may arise through convergent evolution - 22Wings EXOPTERYGOTESWings develop gradually on the outside of the body during development but do not become functional until the adult stage.
Exhibit hemimetabolous development:
-Immature stage resembles the adult although they may occupy different ecological niches.
-The resemblance increases with each moult and there is no pupal stage.
Hemimetabolous development
Egg > nymph > adult - 23Wings Exopterygotes PRIMITIVE and ADVANCEDPRIMITVE
- Distinguished by large wings + many cross veins and inability to lay wings flat along back.
Odonata (dragonflies)
Ephemerata (mayflies)
ADVANCED
Can fold wings over the abdomen. Enables insect to hide under crevices etc from predators/ environment.
Orthoptera (locusts)
Plecoptera (stoneflies)
Mantoidea (preying mantids) - 24Social Behaviour Living in a group BENEFITSProtection through collective displays deterring predators
Increased efficiency in detecting + utilizing food
Moderation of adverse environmental factors
Improved defence of limited resources against conspecifics
Improved care of offspring through communal feeding/ protection - 25Social Behaviour Living in a group PROBLEMSCompetition for mates/ food/ nest sites/ limited materials
Risk from contagious diseases
Risk of exploitation of parental care
Risk that conspecifics will kill one progeny - 26Simple GroupsExhibit coordinated movements:
- Migrating butterflies, locust swarms.
-Wooly aphid aggregations produce rhythmic swaying in response to stimulation – gives impression of a single large organism. - 27Temporary AggregationsArise through attraction to common stimuli (e.g. light, temperature) or mutual attraction by pheromones.
- 28Primitive SocietiesRange from simple brood care of offspring by one or both parents to interactions bordering on true social behaviour.
Example:
Spider Theridion sisyphium
Female remains with progeny, provides food, communal feeding/ involvement in prey capture.
Probably enhances growth + survival of young. - 29Eusocial Behaviour CHARACTERISTICSConspecific individuals cooperate in labour force
Division of labour based on reproduction ( one or more sexually active whilst labour force effectively sterile)
At least 2 generations serve on labour force (i.e. offspring assist parents) - 30Eusocial BehaviourCommon in ants, bees, wasps (Hymenoptera) and also termites (Isoptera).
Social interactions in other insect groups probably more complex than previously
thought and something approaching eusociality occurs in some
- Coleoptera, Embioptera and Homoptera.
Members of societies divided on basis of tasks they undertake.
Differences may be exhibited:
- Solely on basis of behaviour
(e.g. many bees + wasps)
On basis of morphology + behaviour
(e.g. soldier castes + worker castes in many ants and termites) - 31Temporal PolyethismTask within the society changes with age.
Example
Honeybee adult starts as a nurse bee within the colony and ends as a forager working primarily outside the colony. - 32Honey Bee Society7 species of honeybee; Apis mellifera is best known
- 33Honey Bee Society COLONYQueen + workers (up to 80k).
All workers are female
Queen lives 3-5 years
Workers ~ 6 weeks - 34Honeybee Society Worker bees: NURSESAdult emerges
2-3 days: just feeds then:
-Wax glands mature = production new comb
-Head glands mature = royal jelly = fed to young larvae
Becomes ‘nurse’: tends young, queen, tidies nest, builds comb, receives food from returning foragers, processes nectar to form honey - 35Honeybee Society Worker bees: FORAGERSStimulus to become a forager not known.
Probably related to success in offloading first load of pollen.
-If rapidly relieved by nurse bees or able to place pollen into storage cell the bee quickly begins another foraging trip. - 36Honey ProductionNectar collected from flowers.
Excess water removed by repeatedly extending the mouthparts.
Nectar transferred to a nurse who continues the process until the nectar thickens and then places it in an empty cell.
Fans the cells to further evaporation
Honey ripens over several days
If no empty cells the nectar is absorbed and this stimulates wax production for the production of more comb. - 37Maintenance of Colony IntregrityDepends on presence of queen + colony size
Behaviour of workers affected by queen substance. This is passed to workers tending the queen and from them to all the other workers.
If no queen substance/ insufficient received in 10 hour period, workers start to rear queens instead of workers – larvae are fed an exclusive diet of royal jelly rather than with pollen.
Workers act aggressively towards the queen and they may attempt to lay eggs.
First queen to emerge kills the others and leaves on a mating flight.
Newly mated queen returns and old queen leaves with a swarm of workers in attendance to found another nest.
Queen honeybees are unable to found a colony by themselves.
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- Animal Diversity and Evolution (Arthropod) Flashcards on Arthropod Flash Cards, created by Sarah Bell on 10/01/2018.
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