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Chapter 25

Chapter 25. The History of Life on Earth. Adaptive Radiations. Adaptive radiation is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities. Worldwide Adaptive Radiations.

abrianna-miles
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Chapter 25

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  1. Chapter 25 The History of Life on Earth

  2. Adaptive Radiations • Adaptive radiationis the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities

  3. Worldwide Adaptive Radiations • Mammals underwent an adaptive radiation after the extinction of terrestrial dinosaurs • The disappearance of dinosaurs (except birds) allowed for the expansion of mammals in diversity and size • Other notable radiations include photosynthetic prokaryotes, large predators in the Cambrian, land plants, insects, and tetrapods

  4. Fig. 25-17 Adaptive Radiation of Mammals Ancestral mammal Monotremes (5 species) ANCESTRAL CYNODONT Marsupials (324 species) Eutherians (placental mammals; 5,010 species) 50 200 250 100 150 0 Millions of years ago

  5. Regional Adaptive Radiations • Adaptive radiations can occur when organisms colonize new environments with little competition • The Hawaiian Islands are one of the world’s great showcases of adaptive radiation

  6. Fig. 25-18 Close North American relative, the tarweed Carlquistia muirii 1.3 million years MOLOKAI KAUAI 5.1 million years Dubautia laxa MAUI OAHU 3.7 million years Argyroxiphiumsandwicense LANAI HAWAII 0.4 million years Dubautia waialealae These plants had a common ancestor 5 million years ago Dubautia scabra Dubautia linearis

  7. Fig. 25-18a 1.3 million years KAUAI 5.1 million years MOLOKAI MAUI OAHU 3.7 million years LANAI Pacific Tectonic plate has been moving to the west, with it the formation of the Hawaiian islands occured causing variation between the islands' topography and weather, causing the formation of different environments and with it different species HAWAII 0.4 million years

  8. Concept 25.5: Major changes in body form can result from changes in the sequences and regulation of developmental genes • Studying genetic mechanisms of change can provide insight into large-scale evolutionary change Evolutionary Effects of Development Genes • Genes that program development control the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult

  9. Changes in Rate and Timing • Heterochronyis an evolutionary change in the rate or timing of developmental events • It can have a significant impact on body shape • The contrasting shapes of human and chimpanzee skulls are the result of small changes in relative growth rates

  10. Fig. 25-19 Heterochrony Arms and legs grow faster than head and trunk parts of body 15 Newborn 5 Adult 2 Age (years) (a) Differential growth rates in a human skuls of human and chimp are similar at the fetus stage, but become much diffe- rent once adults Chimpanzee adult Chimpanzee fetus Human adult Human fetus (b) Comparison of chimpanzee and human skull growth

  11. In paedomorphosis, the rate of reproductive development accelerates compared with somatic development • The sexually mature species may retain body features that were juvenile structures in an ancestral species fish-like tail gills

  12. Changes in Spatial Pattern • Substantial evolutionary change can also result from alterations in genes that control the location/placement and organization of body parts • Homeotic genesdetermine such basic features as where wings and legs will develop on a bird or how a flower’s parts are arranged

  13. Hoxgenes are a class of homeotic genes that provide positional information during development • If Hox genes are expressed in the wrong location, body parts can be produced in the wrong location • For example, in crustaceans, a swimming appendage can be produced instead of a feeding appendage

  14. Evolution of vertebrates from invertebrate animals was associated with alterations in Hox genes • Two duplications of Hox genes have occurred in the vertebrate lineage • These duplications may have been important in the evolution of new vertebrate characteristics

  15. Fig. 25-21 Hypothetical vertebrate ancestor (invertebrate) with a single Hox cluster First Hox duplication Hypothetical early vertebrates (jawless) with two Hox clusters Second Hox duplication Vertebrates (with jaws) with four Hox clusters

  16. The Evolution of Development • The tremendous increase in diversity during the Cambrian explosion is a puzzle • Developmental genes may play an especially important role • Changes in developmental genes can result in new morphological forms

  17. Changes in Genes • New morphological forms likely come from gene duplication events that produce new developmental genes • A possible mechanism for the evolution of six-legged insects from a many-legged crustacean ancestor has been demonstrated in lab experiments • Specific changes in the Ubx gene have been identified that can “turn off” leg development

  18. Fig. 25-22 Hox gene 6 Hox gene 7 Hox gene 8 Ubx About 400 mya Artemia Drosophila

  19. Changes in Gene Regulation • Changes in the form of organisms may be caused more often by changes in the regulation of developmental genes instead of changes in their sequence

  20. Concept 25.6: Evolution is not goal oriented • Evolution is like tinkering—it is a process in which new forms arise by the slight modification of existing forms

  21. Evolutionary Novelties • Most novel biological structures evolve in many stages from previously existing structures • Complex eyes have evolved from simple photosensitive cells independently many times • Exaptations are structures that evolve in one context but become co-opted for a different function • Natural selection can only improve a structure in the context of its current utility

  22. Fig. 25-24 Pigmented cells Pigmented cells (photoreceptors) Epithelium slit shell Limpet www.dkimages.com Nerve fibers Nerve fibers upload.wikimedia.org upload.wikimedia.org (b) Eyecup (a) Patch of pigmented cells Fluid-filled cavity Cellular mass (lens) Cornea Epithelium Nautilus Murex Optic nerve Pigmented layer (retina) Optic nerve (c) Pinhole camera-type eye (d) Eye with primitive lens upload.wikimedia.org Cornea Lens Loligo gahi www.teppitak.com Retina Optic nerve (e) Complex camera-type eye

  23. Evolutionary Trends • Extracting a single evolutionary progression from the fossil record can be misleading • Apparent trends should be examined in a broader context

  24. Fig. 25-25 Recent (11,500 ya) Equus Hippidion and other genera Pleistocene (1.8 mya) Nannippus Pliohippus Pliocene (5.3 mya) Neohipparion Hipparion Megahippus Sinohippus Callippus Archaeohippus Merychippus Miocene (23 mya) Hypohippus Anchitherium Parahippus Miohippus Oligocene (33.9 mya) Mesohippus Paleotherium Epihippus Propalaeotherium Eocene (55.8 mya) Pachynolophus Orohippus Key Grazers Hyracotherium Browsers The End

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