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Biodiversity Notes

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Western University
Biology 3484A/B
Nina Zitani

Biodiversity – Oct. 22/12 - These are six-footed animals with three pairs of walking legs. - Hexapod/insect is a monophyletic group within the arthropoda. A hexapod (insect) is an arthropod with 3 body regions – head, thorax, and abdomen (synapomorphy). The head is sensory and it has compound eyes, one pair of antennae, and mouthparts. The thorax has three segments and is used for locomotion. There are three pairs of legs (synapomorphy), with one pair attached to each segment of the thorax. The thorax also has two pairs of wings (this is a synapomorphy for derived insects). The first pair of wings is attached to the second segment of the thorax and the second pair of wings is attached to the third segment of the thorax. The abdomen contains the major internal organs and is involved in reproduction. - Animalia (metazoan) evolution major events: Eukaryotic cells were present 2BYA (Proterozoic). Animal fossils were present 630MYA and they are relatives of today’s jellyfish and sea anemone. Green algae and probably fungi were present (late Proterozoic). During the Cambrian period (began 550MYA), the Cambrian explosion saw a relatively rapid appearance of most major phyla (fossil record) in oceans (early Paleozoic). Arthropod fossils from Trilobites are present from this time. Ordovician period (began 480MYA) saw animal diversification with vertebrates in oceans and invertebrate animals (ex. arthropods) colonizing land (along with plants and fungi). Silurian period (began 440MYA) – On land, invertebrate animals diversified (along with plants and fungi). Insects were undoubtedly present on land (indirect evidence, not fossil evidence). Devonian period (began 420MYA) – There was continued diversification on land, fins evolved into four limbs, amphibians were the first land vertebrates but they were dependent on water for reproduction. The oldest definitive insect fossils are present from this time. Carboniferous period (began 360MYA) – The amniotic egg and amniota developed, allowing land vertebrates to become totally adapted to life on dry land. Permian period (began 300MYA) – The End-Permian mass extinction resulted in 95% of life going extinct. This was mostly marine invertebrates and insects, and species and higher taxa, but not phyla (ex. arthropoda). Trilobites went extinct. Mesozoic period (began 250MYA) – There was animal diversification in oceans and on land, and coevolution with angiosperms (flowering plants). Insects were especially involved in coevolution with angiosperms. - Insects today: Today insects are not only the dominant arthropods on land, they are the dominant group of organisms on land in terms of numbers of species and biomass. Biomass is the mass of living biological organisms per area, There are nearly 1 million described species of insects (hyperdiverse). Insects are found in all terrestrial habitats, they are freshwater aquatic, and very few are marine. There is incredible diversity of morphological form in insects – body parts come in a variety of forms. - Basal/primitive insects are wingless. Silverfish are 1 inch long. Collembola are 1-2mm in length. - Derived/advanced insects are adapted to life in the air. All derived insects (which are the majority of insects) have wings and can fly in the adult stage. Some higher taxa have secondarily lost their wings (ex. lice, fleas) and some species within higher taxa have secondarily lost wings (ex. some cockroaches). Most insects are nocturnal and fly only at night. True powered flight has convergently evolved in only three extant groups of organisms – bats, birds, and insects. - Insect characteristics – compound eyes: Insects have two compound eyes. The eyes of dragonflies meet at the top of their head. The surface of the eye is comprised of many cells and is a light- gathering surface. Photoreceptors are located here. Inside the eye are neurons that transmit information to the brain. The bigger the eye, the better the insect can see. The eyes are used in hunting and escape from predators. The eye is also part of the exoskeleton. - Insect characteristics – chemoreception: Sensing chemicals are involved in olfaction/smelling. Chemoreceptors, though concentrated in the antennae, are found on other body parts as well. Antennae are segmented. Some types of antennae are related to phylogeny. Some of the com
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