Bis2CF10.Lecture%2034

Bis2CF10.Lecture%2034 - Fall 2010 Lecture 34. Hexapod...

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Fall 2010 Lecture 34. Hexapod Arthropods & Introduction to Deuterostomes A brief discussion of hexapods, reminder on deuterostome characters, phylum Echinodermata. Students should be able to: explain the basic function of the water vascular system recognize among 4 of the 5 major sub-groups of echinoderms discuss the relative ratios of skin to endoskeleton among the classes of echinoderms
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Subphylum Hexapoda • Class Insecta and Class Entognatha 3 tagmata (head, thorax, abdomen) and 6 legs (hence subphylum name) They form the most species-rich group on earth, occupying almost every habitat and lifestyle. 1 million +species head thorax abdomen
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If you are interested in how segments develop and are distinguished, read about Hox genes.
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Hexapoda – insects and allies three tagmata: head, thorax and abdomen one pair of antennae (two pairs in other crustaceans) three pairs of legs (located on the thorax) respiration by tracheae (system of air tubes extending into body) spiracle
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The first great insect radiation is associated with the evolution of wings and took place in the Carboniferous about 345 million years ago. Insects had the air to themselves until pterosaurs evolved (280 mya); birds did not evolve until 150 mya. Comparative gene expression studies suggest that wings arose from dorsal appendages at the base of the legs. In crustaceans the dorsal appendages are used for respiration .
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How did insect wings evolve? For insects, two related questions: 1)From what structures did insect wings evolve? 2)What was the function of proto-wings?
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The second great radiation follows the evolution of flowering plants about 65 to 70 mya. You already know about the coevolution between plants and their pollinators, but many herbivorous insects depend on plants for food or habitat. Australian green ants
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Mouthparts are very diverse
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Two major types of life cycles : • Hemimetabolous life cycles: egg juvenile stages adults develop wings and sex organs after the last molt Examples are crickets and cockroaches
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• Holometabolous life cycles with distinct stages: egg larva pupa adult Examples are butterflies, mosquitos and bot flies
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Bot fly life cycle Imagine having this larva in the skin over your skull! The bot fly is 12 to 18 mm long, blue-black in colour and lives for 8 or 9 days. The female bot fly captures an insect, often a mosquito, and deposits its eggs on the abdomen. When the insect bites a vertebrate host, the larva within the egg senses the change of temperature, hatches and falls off the insect onto the new host. It penetrates the skin via the puncture mark or through a hair follicle. Once within the subcutaneous tissue, the larva respires and excretes waste via a tube which passes to the skin
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This note was uploaded on 04/19/2011 for the course BIOLOGY BIS 2C taught by Professor Doyle during the Fall '10 term at UC Davis.

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Bis2CF10.Lecture%2034 - Fall 2010 Lecture 34. Hexapod...

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