Chapter 25 continued

Homework 1. Lab write up extended for Friday 2. Read and outline pp 521 (beginning with Mass Extinctions) to 530 Chapter 25 outline will be checked for completion grade tomorrow 3. Quiz tomorrow on Chapter 25 on: Hypotheses for origin of life on Earth, the sequence of stages for life on earth, adaptive radiation, and section 25.5

Concept 25.1: Conditions on early Earth made the origin of life possible Hypothesis: Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages: 1. Abiotic synthesis of small organic molecules 2. Joining of these small molecules into macromolecules 3. Packaging of molecules into protocells 4. Origin of self-replicating molecules

Meso- Cenozoic zoic Paleozoic Humans Colonization of land Figure 25.7-3 Meso- zoic Cenozoic Humans Paleozoic Colonization of land Origin of solar system and Earth Animals Multicellular eukaryotes 1 4 Figure 25.7 Clock analogy for some key events in Earth’s history. Proterozoic Archaean B o i l g l i a o n s s a r 2 of y e 3 Prokaryotes Single-celled eukaryotes Atmospheric oxygen

How Rocks and Fossils Are Dated Sedimentary strata reveal the relative ages of fossils The absolute ages of fossils can be determined by radiometric dating A “parent” isotope decays to a “daughter” isotope at a constant rate Each isotope has a known half-life, the time required for half the parent isotope to decay https://www.youtube.com/watch?v=phZeE7Att_s

25.4 Mass Extinctions The fossil record shows that most species that have ever lived are now extinct caused by changes to a species’ environment At times, the rate of extinction has increased dramatically and caused a mass extinction The result of disruptive global environmental changes

The “Big Five” Mass Extinction Events Five mass extinctions documented in fossil records over the past 500 million years In each of the five mass extinction events, more than 50% of Earth’s species became extinct

(families per million years): Figure 25.15 1,100 25 1,000 900 20 800 700 15 600 (families per million years): Total extinction rate Number of families: 500 10 400 300 5 200 Figure 25.15 Mass extinction and the diversity of life. 100 Era Paleozoic Mesozoic Cenozoic Q Period E O S D C P Tr J C P N 542 488 444 416 359 299 251 200 145 65.5 Permian Cretaceous

The Permian mass extinction occurred in less than 5 million years and caused the extinction of about 96% of marine animal species

A number of factors might have contributed to these extinctions Intense volcanism in what is now Siberia Global warming resulting from the emission of large amounts of CO2 from the volcanoes Reduced temperature gradient from equator to poles Oceanic anoxia from reduced mixing of ocean waters

The Cretaceous mass extinction 65 The Cretaceous mass extinction 65.5 million years ago separates the Mesozoic from the Cenozoic Organisms that went extinct include about half of all marine species and many terrestrial plants and animals, including most dinosaurs

Consequences of Mass Extinctions 1. Mass extinction can alter ecological communities and the niches available to organisms 2. It can take from 5 to 100 million years for diversity to recover following a mass extinction 3. The percentage of marine organisms that were predators increased after the Permian and Cretaceous mass extinctions 4. Mass extinction can pave the way for adaptive radiations

Adaptive Radiations Adaptive radiation is the evolution of diversely adapted species from a common ancestor Organismal groups form many new species with adaptations specific for different niches Adaptive radiations may follow Mass extinctions The evolution of novel characteristics The colonization of new regions

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

Close North American relative, the tarweed Carlquistia muirii Figure 25.20 Close North American relative, the tarweed Carlquistia muirii Dubautia laxa KAUAI 5.1 million years MOLOKAI 1.3 million years Argyroxiphium sandwicense OAHU 3.7 million years LANAI MAUI N HAWAII 0.4 million years Figure 25.20 Adaptive radiation on the Hawaiian Islands. Dubautia waialealae Dubautia scabra Dubautia linearis

KAUAI 5.1 million years MOLOKAI 1.3 million OAHU years 3.7 million Figure 25.20a KAUAI 5.1 million years MOLOKAI 1.3 million years OAHU 3.7 million years MAUI LANAI N HAWAII Figure 25.20 Adaptive radiation on the Hawaiian Islands. 0.4 million years

25.5 Major changes in body form can result from changes in sequences and regulation of developmental genes Small genetic changes can cause major morphological differences between species EX: Japanese Euhadra snails, the direction of shell spiral affects mating and is controlled by a single gene

25.5 Major changes in body form can result from changes in sequences and regulation of developmental genes Heterochrony- evolutionary change in rate/timing of developmental events Organismal shape depends on relative growth rates of different body parts Example: skeletal structure for bat rings results from increased growth rates of finger bones

25.5 Major changes in body form can result from changes in sequences and regulation of developmental genes Altering homeotic genes could lead to major evolutionary changes These genes control the placement and arrangement of body parts Example: Hox genes, class of genes that instruct cells in a particular location to develop into the correct body structure

Hox gene 6 Hox gene 7 Hox gene 8 Ubx About 400 mya Drosophila Artemia Figure 25.24 Hox gene 6 Hox gene 7 Hox gene 8 Ubx About 400 mya Figure 25.24 Origin of the insect body plan. Drosophila Artemia

Changes in Gene Regulation Changes in morphology likely result from changes in the regulation of developmental genes rather than changes in the sequence of developmental genes Ex: threespine sticklebacks in lakes have fewer spines than their marine relatives

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 It is simply the change in allele frequencies, or genetic composition, in populations from generation to generation Evolution can be random or adaptive, in which case, individuals adapt to their specific environment

Evolutionary Novelties These structures that evolve to have a new function or have evolved from simple to complex structures Ex: simple to complex eyes

(a) Patch of pigmented cells (b) Eyecup Figure 25.26 (a) Patch of pigmented cells (b) Eyecup Pigmented cells (photoreceptors) Pigmented cells Epithelium Nerve fibers Nerve fibers (c) Pinhole camera-type eye (d) Eye with primitive lens (e) Complex camera lens-type eye Epithelium Cornea Cellular mass (lens) Fluid-filled cavity Cornea Lens Figure 25.26 A range of eye complexity among molluscs. Retina Optic nerve Optic nerve Optic nerve Pigmented layer (retina)