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INSECTA Phylum Arthropoda 1. Insecta, “Palaeoptera”, pp. 184-186 Also see indicated ‘Boxes’ on other pages 2. Evolution of wings pp. 208-211 1 Phylum Arthropoda Arthropod Polyphyly? Sidnie Manton & others have argued that the Arthropoda are polyphyletic - i.e. the common ancestor was not an arthropod but rather a worm If so, then the key worm lineages are extinct Monophyly is the default Phylum Arthropoda Arthropod Polyphyly? Monophyly is the default Modern phylogenetics: homology is assumed unless contradicted = parsimony, because homology =1 event and homoplasy = 2 or more events So we assume, e.g. the exoskeleton of Arthropods is homologous in all groups until a more parsimonious result, due to evidence from other characters, contradicts this. Phylogeny of the Hexapoda Error Pterygota one Branch off Fig. 7.2 Fig. 7.2 Entognathous mouthparts Phylogeny of basal Hexapoda Insecta Fig. 7.3 2 Insecta - Ectognathous mouthparts Insecta Apomorphies: 1. Ectognathous mouthparts 2. Antennae of 3 true segments (annulated antennae) 3. Johnston’s organ and others…. Insecta Insecta Antennae of 3 true segments – Scape, Pedicel, Flagellum (w/ flagellomeres) – true segment = with muscle attachment – Antennal segments = antenomeres – Annulated antenna (muscles only in scape & pedicel) Insecta – Segmented antenna (muscles throughout) Non-insect Hexapoda (which are…?) Fig. 2.17 Insecta Insecta Johnston’s Organ -in pedicel -perceives movements in the flagellum -e.g. Calliphora monitor flight speed (fig. of mosquito most are smaller) Characteristics - p. 184 Compound eyes & ocelli in adults Palpi well developed Legs with 6 segments Ancestrally 11 segmented abdomen Gonopore usually on segment 8 in female and segment 9 in male Ancestrally with cerci on posterior Tracheal system with spiracles on thorax & ab. Development epimorphic 3 Mandible: Monocondylar hinge / Dicondylar hinge (with one or two condyles, or points of articulation) Pivotal / Monocondylar mandibles - Archeognatha movement in one plane only Insecta Fig. 7.3 Archeognatha • “Jumping Bristletails” Archeognatha • Abdomen with styli (vestigial limbs [exites]) • Monocondylar mandibles • Compound eyes touch • Possible sister group to Zygentoma • Humped thorax • Detritivores (inc. lichen, algae) • 2 cerci, 1 median caudal filament • Molting continues for life Archeognatha Archeognatha • 500 species, 2 families (20-35 spp in NA) • 6-25 mm long • Nocturnal or crepuscular • Elongate maxillary palpi © Alex Wild 4 Dicondylar mandibles apomorphic of the Dicondylia Key to major Hexapod groups Insecta Fig. 7.3 Dicondylia - Zygentoma Zygentoma • “Silverfish,” “Firebrats” - often with silvery scales • Dorsoventrally flattened (not arched) • Eyes (if present) not contiguous • Dicondylar mandibles • Abdominal styli on segs 7-9 (sometimes 2-9) Zygentoma Zygentoma • Cerci subequal in length to median filament Scales • 400 species, 5 families Anti-predator defense? • 5-30 mm long; detritivores, starches • Nocturnal, don’t jump • Difficult to preserve 5 First insects: Terrestrial or Aquatic? p.208 First insects: Terrestrial or Aquatic? p.208 Tracheal system had to develop in air Fig. 7.2 Key to major Hexapod groups Fig. 7.2 (from Pritchard et. al. 1993 ) Family richness In fossil record Labandeira & Sepkoski 1993 Fossil History Oldest winged insects ~ 325-300 mya (Carboniferous) Ancient proto-Dragonflies 72 cm wingspan Fossil History Wings = “key innovation” Thin outfoldings of body wall w/ network of tracheae & blood vessels largest insect 6 Wings Compare species richness Questions Morphological origin? “Apterygota” - ancestrally wingless <10,000 species Original function? Process of transition to new (flying) function? Pterygota - winged insects (99% of species) Wings Appeared once = monophyletic Pterygota (lost repeatedly) 2 theories on origin of wings: Wings exite theory - fusion of exit & endite lobes - each with tracheation & articulation paranotal theory - thoracic tergal lobes (not from pre-existing limb structures) exite theory - articulated gill / leg appendages Leg exites Fig. 8.4a Leg exites Fig. 8.4b 7 Wings Wings Recent gene expression studies have shown support for homology of gills & wings Protowing non-flight function? Suggests wings evolved from gills present in Crustacean ancestors of insects Exite theory has most support (Box 6.1) protection of legs covers for spiracles thermoregulation sexual display crypsis defense - escape jump-> glide Averoff & Cohen (1997) Nature: 385 Wings Wings Routes to flight Routes to flight p. 210-211 1. Floating - dispersal 2. Paragliding - up->down 3. Running-jumping-flying ground->up 4. Skimming - surface sailing 1. Floating - dispersal 2. Paragliding - up->down 3. Running-jumping-flying ground->up 4. Skimming - surface sailing 1 unlikely, size & friction 3 unlikely, physical constraints (velocity) 2 Aerodynamic theory/ test support 4 Stoneflies (Plecoptera) - some skim Pterygota • Most species rich lineage • Winged, some secondarily apterous (wingless) • Meso & metathorax = pterothorax • No styli (styles) Movie - Odonata flight (Shape of Life) • No adult ecdysis (molting) - except Ephemeroptera 8 “Palaeoptera” • First thought to be monophyletic but now considered paraphyletic (DNA & some morphology) • Orders Odonata & Ephemeroptera (& extinct orders, e.g. Palaeodictyoptera) - extant have aquatic larvae • Wings cannot be folded flat against the body articulation via fused plates Order Ephemeroptera - mayflies • Nymphs (larvae) aquatic & long lived - the feeding stage • Non-functional reduced mouthparts in adult – Short-lived, “ephemeral,” hours to a few days 9 Order Ephemeroptera • 3,000 species Order Ephemeroptera • Penultimate instar = subimago (subadult), fully winged - Apomorphy • Hindwings reduced, sometimes absent • Imagos form mating swarms (larger from standing • Nymphs usually with 3 caudal filaments & 1 tarsal claw per leg Order Odonata - Dragon & Damselflies • 5,500 species, mostly tropical, predacious • Nymphs with extensible pre-hensile labium modified for grasping prey • Male copulatory organs on segments 2&3 but gonopore on segment 9 copulate in unique ‘wheel position’ • 360° vision - aerial hunters Neoptera • Wings can fold back flat over the abdomen due to articulation via separate, movable sclerites water, more species in running water) • Feed on algae, detritus, some predacious species Order Odonata - Dragon & Damselflies • Two suborders hold 99% of species • Dragonflies: Anisoptera – Wings to side, larvae with rectal gills • Damselflies: Zygoptera – Wings vertical, larvae with 3 caudal lamellae (gills) Phylogeny of the Hexapoda • Explosive radiation - difficult phylogenetically Fig. 7.2 10 Phylogeny of the Hexapoda • Monday: Neoptera - 90% of Hexapoda Polyneoptera Paraneoptera - Hemipteroids Endopterygota (Holometabola) • Insecta, Neoptera in part, Polyneoptera in part pp. 184-189 Also see indicated ‘Boxes’ on other pages Fig. 7.2 11