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36 Cards in this Set
- Front
- Back
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Phylogeny |
The sister group on crustacea sharing a common ancestor (this is the mandibulata hypothesis) Gilbert and Edgecomb 2012 -Sub-phylum is hexapoda |
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Ectognatha |
external jaw - these are the aviant insects |
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Entognathan |
rather obscure soil inhabiting detritivores The earliest fossils of hexapods |
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Fossil record |
The fossil record is patchy but starts in the Early Devonian. The molecular data extrapolated backwards shows that the divergence between ectognathan and entognathan is 474.4Ma in the Ordovician. Supposedly one of the first terrestrial organisms. -The first winged organisms were found in the early carboniferous 345Ma Garrote et al, 2012 The arrival of wings really shows when insects really started to diversify. |
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Bauplan of insect |
Body is composed of 19 segments - divided into 3 tagmata -Cephalon (head) -Thorax (contains wings) -Abdomen ( contains reproductive organs ) |
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Head |
5 segments fused together -compound eye and ocelli(photoreceptive organs) -antennae (smell) -clypeolabrum -mandibles -maxillae |
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Thorax |
3 segments 3 pairs of walking legs. Dorsal appendages form wings
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Abdomen |
11 segments - No developed legs Gas is exchanged from spiracles and tracheae |
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What keeps insects small? |
Chow and Gaston 2010 measured insects -invertebrates and smaller insects are more diverse -titanus giganteus is the heaviest -oxygen levels limit size of organisms. -Not always the case, as oxygen levels rose in the Carboniferous (Palaeozoic), insects size displaced a significant correlation. |
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-Open circulation system |
-> haemolymph carries nutrients, water and hormones but not O2 |
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Spiracles and tracheal system |
Trachea are hollow tubes that carry oxygen to cells with spiracle valves - oxygen enters via diffusion |
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Trachea |
Formed from the invagination of body wall. Air enters via valvelike openings called spiracles -Tracheals go to muscles and every organ. O2 from tracheals dissolves in the liquid of the tracheole and through aqueous diffusion enters the cytoplasm of the adjacent cell. CO2 then diffuses out of the body through the tracheal system. |
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Tracheal system |
Entirely passive and requires no energy to work, therefore making it incredibly efficient. -> works far better when the organism is small and oxygen doesn't have to diffuse as far. insects flex their abdomen, acting as a pump to the tracheal system. |
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Increasing the size |
As size increases and the tracheoles become larger, there are reduced rates of diffusive gas exchange and more investment in the tracheal system to compensate for this. Studies on stick insects and tenebrionids beetles confirm this (Kaiser et al, 2007) |
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Beetle growth |
In beetles, leg diameter and body size increases at a slower rate than tracheal diameter. Mean space for the tracheoles in the legs may limit size |
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Biotic interactions limiting size |
Relationships found between maximum size and O2 levels until the early cretaceous. In the early Cretaceous there as a decoupling of body size from oxygen is observed. This decoupling occurs in at the introduction of Aves and bats. -Statistical model shows the fossil wing span and O2 concentration. Maximum body size drops to a stable level after 130mc and again at 60Ma |
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Extinction event |
Nicholson et al 2014 found that both fossil family organisation and extinction event increased in groups that have wings but not with other key innovations. Insects with complete metamorphism had much lower extinction rates than their sister groups without. |
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Origin |
There's a wide agreement on the signle origin of wings for hexapods -Palaeoptera (direct) are characterised by many veined net-like wings and inability to fold wings over back when at rest. -neoptera (indirect) have reduced venation and diverse modification of fore and hindwings -Wings develop as an invagination of the thoracic integument. Thin circulation membranes form the upper (dorsal) and lower (ventral) surfaces of each wing. -Wing veins contain circulationary haemolymph and eventually open in the body, -Each wing articulates with the notum a dorsolateral pleural process acts as a fulcrum with a hinge confining resilin |
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Direct and Indirect flight |
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Paranotal hypothesis |
this states that the wing originated terrestrially as de novo extension of the thoracic tergum (dorsal plate) or paranotal lobe. Initially, an adaptation to parachuting or gliding before articulation and muscle connections allowed powered flight (Crampton 1916) This hypothesis remains consistent with the flatness and portion of the wing in the tergum-pleuron boundary. -There's a lack of fossil evidence of the wing joint and muscles |
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Limb Branch hypothesis |
wings emerged as a modification of the pre-existing articulated dorsal limb-branch. Protowing branches originally functioned as gills paddles or terrestrial gliding structures. (Averof and Cohen, 1997) -Palaeopteran gill and fossil evidence for dorsal exites -Av n Cohen showes that many arthropods respiratory appendages express orthologues of the drosophila 'wing genes'. -Fossil evidence suggests that winged insects derived terrestrially and later adapted to aquatic lifestyles -However, this requires each of the independent lineages of primitively wingless hexapods to have lost wings in parallel. |
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Combinatorial hypothesis |
Niwa et al ,2010 examined wingless and vestigial in early development of the dorsal thoraic appendages in extant basal insects. In P. unimaculatus vg-wg associated with stylus and paranotal region. This suggests a dorsal migration of wg-vg dorsal limb branch induction module to location where effect is to produce sheetlike outgrowth (wings) T1 gene transformation indications dorsal and dorsolateral outgrowth that combine to form elytra-like structures. A knockdown of vestigial causes reduction of wings elytra and pronotal structures that are expanded in transformed T1 |
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Summary |
30 orders in incesta earliest are terrestrial and wingless major diversification occurred with the production of wings . Gas exchange by spiracles and trachae, excretion by ectodermally derived malpigian tubules. Major issues such as the evolution of body size and the origin of wings remain unresolved but integrated approaches combing morphometric, palaeontologial, genetic and developmental evidence continue to shed new light. |
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Modes of development in Pterygota |
Pterygota = winged insects -Hemimetabolous nymphs represent the adult but lack fully developed wings and genetalia -external wing buds -holometabolous larvae specialised for feeding -internal wing and genital disk -final moult generates pupa discs evert to generate adult structures -Holometabola phylogeny diversification coincides with angiosperm radiation and development of flowering plants (Weigman et al, 2008) |
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Holometabola |
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Coeloptera |
Beetles -strongly selectorized front wings (elytra) provide protection while retaining powered flight (Hunt et al, 2007). -No strong correlation between herbivory and diversity |
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Diptera |
Fly Cycclorraptian phylogeny is supported by the invagination of the larval head capsules, modifications of the larval mouthparts and pupation within the skin of the last larval instar -Halteres greatly facilitate controlled flight -balance organs |
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Lepidoptera |
Butterflies and moths -Basal butterflies have chewing mandibles -proboscis an adaptation of the maxilla facilitate feeding on herbaceous plants Ditrysia contain 98% of species -Labanderia et al 1984 Date back to the Triassic Scales provide functions such as insulation, thermoregulation, gliding flight and colour patterning for sexual selection (Jaron et al, 2006) |
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Heliconius butterflies |
a longstanding example of mimicry and geographical diversification. -> pattern changes with geographic location ->Colour pattern involved with mate choice and may have arisen through hybridisation ->( Maurez et al, 2006) |
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Imaginal discs |
In Coleoptera and Lepidoptera appendages and genitalia are generated from groups of imaginal cells set aside during embryogenesis that proliferates and event during metamorphosis. In higher diptera, all head thorax and genitalia derived from imaginal disks. The abdomen derived from histoblasts |
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Juvenile Hormone & Ecdysone |
Wigglesworth initially identified JH through parabiosis experiments -topical application of JH analogues maintains immature cuticle(outer layer) pattern. Systematic JH suppress wing and genital development. JH interacts with moulting hormone ecdysone |
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Papilo Xuthus Catapillous |
mimetic in instars 1-4 but cryptic in instar 5. Cryptic morphology is strongly related with a reduction in JH. JH analogue addition maintains mimetic characteristics and suppresses cryptic |
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Juvenile Hormone & Ecdysone genes |
Kr H1 & Br-C are downstream targets for hormones - Up until the penultimate larval stage only Kr-h is expressed. At the final larval stage JH drops, then peaks again before the moult to the pupa. At the final peak, both Kr-h1 and Br-C are expressed. Kr-h1 prevent precocious metamorphosis Br-C specifies the pupal stage. Koponava et al 2011 |
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Strepsiptera |
Females are endoparasites males are free-living Females are vivaporous ( develop in the body of the parents). The embryos develop in female body cavity and first instar larvae emerge from the brood canal. -> find a host and undergo hypermetamorphosis to legless second instar that grow inside the host. --> male larvae form a pupa and emerge from the host on eclossion --->females don't form a pupa but they undergo moult to become neotonous adult |
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Sex |
Weapons are ornaments are evolutionarily liable -> host weapons to fight other males -> females ornaments attract males (Emien et al, 2005) Horns are perhaps a condition dependent, this makes them an honest signal of male fighting ability. -> horn size correlates with body size -> insulin /IGF pathways integrate physiological conditions with growth in multiple taca. If a taxa is hypersensitive to conditions, should also be hypersensitive to insulin. (Emlen et al, 2012) |
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Summary |
Holometabola - monophyletic group from the late carboniferous -> all orders undergo complete metamorphosis ->separation of feeding/growth from dispersal/reduction makes it possible for larvae and adults to respond to selective pressures in different ways, developing independent adaptations and evolve different lifestyles The most successful orders include Coleoptera, Diptera and Lepidoptera. Metamorphosis is achieved in part by senng aside the groups of cells that will form adult-specific organs (wings , genitalia) to form imaginal discs. It is regulated by changes in the levels of JH and its receptors. Sexual selec?on is thought to drive signficant morphological diversifica?on and holometabolous insect species provide powerful model systems for studying this |
