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Lecture 15

Lecture 15 - Anthropod Diversity.docx

7 Pages

Biology (Sci)
Course Code
BIOL 111
Suzanne Gray

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th October 25 , 2011 Anthropod Diversity 4 major groups with phylogeny currently in revision:  Myriapods (e.g. millipedes, centipedes)  Chelicerates (e.g. spiders, mites and scorpions)  Crustacenas (dominant in marine environment)  Hexapods (includes insects; dominant in terrestrial environment) Myriapods:  “Countless feet”  Two regions: head and trunk  Centipedes (Chilopoda) o 1 pair of appendages per segment o Carnivores o ~3000 species (less diverse)  Millipedes (Diplopoda) o 2 pairs of appendages per segment o Detritivores, herbivores o ~11,000 species (more diverse) ~ Both tend to be small but can grow up to 30 cm in length Chelicerates:  Horseshoe crabs  Pycnogonids (sea spiders)  Arachnids (spiders, mites and scorpions)  No jaws (mandibles)  2 body regions: o Cephalothorax – appendages o Abdomen – no appendages  Pairs of appendages: o #1 (chelicerae) – fangs o #2 (pedipalps) – copulatory organs, pincers o #3,4,5,6 – walking legs (4 pairs of walking legs) Crustaceans:  Crabs, daphnia, barnacles, shrimp, crayfish, isopods  Dominant marine arthropod, but also in freshwater and terrestrial environments  Head and thorax (cephalothorax) and abdomen  Appendages off each segment  Compose “zooplankton” o Example: Daphnia; move on their own but cannot fight the water current  Spiny tail as a defense mechanism; makes it difficult for small fish to eat them Hexapods:  Insects + other groups  Abundant in fw and terrestrial environment, but few marine  Example: springtails are not insects (internal mouthparts) but are considered to be a hexapod  3 body regions: o Head: antennae, mouthparts (i.e. mandibles) o Thorax: 3 pairs of walking legs, may have wings o Abdomen: no appendages •Uniqque to insects: external moutparts •herbivores, detritivores, fluid-drinkers, predators, scavengers, parasites th October 25 , 2011 Anthropod Diversity Diversity in Insects: mouthparts adapted  An abundant and diverse group that includes fleas, bees, termitfor different feeding grasshoppers and butterflies modes  Unique to insects: external mouthparts o Herbivores, detritivores, fluid-drinkers, predators, scavengers and parasites o Diversity in mouthparts adapted for different feeding moods Wings evolved ~ 320mya  A pair of wings and a pair of gliders to help them fly  Beetles have two wings; Used in harder outer wing for gas protection exchange  Clicker Question: Which is not correct? A hormone cannot have an autocrine function. Wings have been secondarily lost by some insect species. Clicker Question: The wing of an insect and the gill of a crayfish are? Homologous Respiratory System: 4  Insects and most Myriapods: holes (spiracles) open into tubular trachea which branch to finer tubes – carrying oxygen to body cells  Crustaceans: gills  Chelicerates: some have spiracles and tracheae, book gills or book lungs  Example: book gills are found in the abdomen, very exposed to the environment (i.e. horseshoe crabs) and book lungs are held internally (i.e. spiders, scorpions) o Book lungs: for land animals  need to protect their structure for gas exchange, gas exchange happens easier over a wet surface, internal surface protects from defecating Circulatory system:  Open system  Dorsal tubular heart (1 chamber) with pores (ostia); drives blood into hemocoel spaces  One- way valves Sexual Reproduction:  Most species are dioecous  Most species lay eggs  Example: scorpion eggs rest on the females back, and stay there until molting occurs  On Land: internal fertilization October 25 , 2011 Anthropod Diversity o Some use spermatophores (= waterproof packets of sperm) when fertilization not completely internal o Male will hold onto the female until shell hardens; to ensure that the sperm is in fact his  In Water: internal (crabs) or external (barnacles) Insects: responding to environment and making nearly faithful copies of themselves  When they molt, they loose their digestive tract and mouths. All they need to do is mate, no eating. Daphnia Life Cycle: 1. Mostly parthenogenic Diploid female produces diploid daughter without fertilization 2. Under stress, partenogenetic males and haploid eggs are produced (e.g. decreased food, light decreases, temperature decreases) 3. Sexual reproduction results in diapause eggs – ephippia, which hatches under favorable env. Conditions Daphnia lifecycle 1. Mostly parthenogenic Diploid female produces diploid daughter without fertilization 2. Understres, partenogenetic males and haploid eggs are produced (e.g. decreased food, light decreases, temperature decreases) Metamorphosis 3. Sexual reproduction •ephippia, whiche eggs hatches under favorable Insects cease molting as adults. env. conditions •mmeetamoorphose to adultform:: •incomplete metamorphosis or complete metamorphosis Crustaceans continue Metamorphosis mooltng as adults.  Molting enables changes in morphology  Example: each instar (larva) produces a new exoskeleton  At each molt, modification is possible
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