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Unformatted text preview: BIS2B Fall 2009 (Keen) Lecture 30. Biological diversification and a Brief history of Life I
20 November Ring species, lineage splitting and the origin of life Students should be able to: Discuss ways in which hybrid zones and ring species pose problems for biological pigeon-holes (species descriptions) Relate speciation events to the diversification of life Understand how speciation results in successive change Outline the age of the earth and the time line for the evolution of the first life forms, including the types of evidence used to infer these dates Outline the major changes in earth’s geological history
http://blogs.discovermagazine.com/intersection/2009/11/19/on-comforts-origin-of-species/ When things are not neat and tidy: Hybrid zone
A1 A2 alleles common A3 A4 alleles common Forest Marsh Hybrid fitness = ? short-lived zone or stable zone • Q. Some species of Drosophila hum during courtship. D. simulans hums at 35 second intervals whereas D. melanogaster hums at 55 second intervals. Pure-bred females prefer males with the normal humming frequency for their species. Laboratory -produced hybrid females prefer males that hum at 45 second intervals. Are the species likely to stay reproductively isolated in nature?
• • • • • a) b) c) d) e) yes, hybrid females are unlikely to mate with either parent type yes, temporal isolation should keep the species apart no, hybrids will have high relative fitness no, hybrids will mate with either parental species no, hybrids will mate with D. simulans males • Does it matter how hybrid males hum? Study sites (black filled circles) and native "control" sites (open circles) in California, USA. Hybridization in the wild between California Tiger Salamanders (Ambystoma californiense) and Barred Tiger Salamanders (A. tigrinum mavortium or A. mavortium) began in the 1940's when Barred Tiger Salamanders were imported from Texas and released near Salinas (Monterey County, CA) in a deliberate attempt to improve the local bait fishery . strong selection appears to be eliminating native alleles at a smaller set of loci. Such rapid fixation of alleles is detectable only in recently formed hybrid zones • 2009 Fitzpatrick BM, Johnson JR, Kump DK, Shaffer HB, Smith JJ, Voss SR. Rapid fixation of non-native alleles revealed by genome-wide SNP analysis of hybrid tiger salamanders. BMC Evol Biol, 9: 176. Ensatina in California Is there complete gene flow? How many species are present? Ring species Summing up for speciation
• Lineage splitting results in new species. • Species are not always genetically isolated from other species over their entire ranges. • Hybridization can result in new species or in stable hybrid zones. Darwin’s Finches Blue-black Grassquit Blue(Presumed ancestral species: S. American mainland) What is an evolutionary radiation? We can study speciation in lineages on small scales, but the same processes have produced the diversity of life on earth. "There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved." Charles Darwin, 'On The Origin Of Species', Chapter 14 ORIGINS OF DIVERSITY ORIGINS
1. There are 30-50 million species of living organisms alive today. • Probably ≈ 500,000,000 have existed; most are extinct 2. All of these species descended from a single ancestor. 3. All of these species must have arisen over the last 4.5 billion years by the repeated division of an ancestral species into two daughter species. 4. The same processes that underlie small scale diversification have been operating since life originated. 5. Diversification is the result of successive evolutionary change. 6. The taxa we see now remain after speciation and extinction. First cell Ancestordescendant relationships constantly refine the starting points for evolution. Very ancient prokaryotes BACTERIA Origin of life ARCHAEA EUKARYA Ancient Present Time The Earth is old: ≈4.5 billion years (by) old The planet has changed since it was formed Life has been around for a long time: ≈3.5 billion years All life on Earth has descended from a single ancestor The degree of resemblance among organisms corresponds to their relatedness The existence of life has changed the earth How do we learn about Ancient Events? How
Radioisotopes provide a way to date rocks From: Evolutionary Analysis, 4th Ed, Freeman and Herron Different isotopes can be used to date ancient and more recent events. The fossil record is patchy and there are few fossils from very early periods. A modern surprise for paleobiologists. Gromia is a single-celled organism that reaches 1.2 inches in diameter. It rolls along the sea bottom leaving trails in soft mud; trail may be 20 inches long. Limits of the fossil record and Limits geological strata
There are only ~250 million fossil species, of 50 billion that have lived on earth! So we must understand both what So we know, and the limits of our knowledge... Suppose we know the age of a particular rock bearing fossils. Do we know when that fossil taxon originated? The history of life is divided into 4 eons (Hadean, Archaean, Proterozoic, and Phanerozoic). Perhaps the first life was in the Hadean seas. The Phanerozoic is divided into 3 eras: Paleozoic, Mesozoic, and the Cenozoic. Eras are divided into periods. • The boundaries are based on changes in types of fossils • The eras were established before actual ages of rocks were known PREgnant CAMels ORDinarily SIt Down CARefully. PERhaps Their Joints CREak, Though QUietly. Some approximate divergence times for life’s lineages. What physical changes have taken place since the earth formed? Continental Drift
The idea that land masses have moved over time was first suggested by Alfred Wegener in 1912; By the 1960s, evidence of plate tectonics Alfred in convinced geologists that he was right Earth’s crust is divided into solid plates about 40 km thick The plates float on a fluid layer of liquid rock (magma) Heat from radioactive decay in Earth’s core causes convection currents Animation of continental drift Continental drift influenced the distributions of Continental organisms present at particular times.
possums http://life8eiml.sinauer.com/ Changes in the Earth’s Climate
Sometimes Earth was considerably hotter than today; sometimes colder, Sometimes with extensive glaciation Some climate changes have been associated with volcanic eruptions or meteor impacts—we see extinctions that appear to be “instantaneous” in the fossil record Summary of Geological History Summary Changes in the Earth’s Atmosphere Earth’s atmosphere has also changed Earth Early atmosphere probably contained little or no free oxygen (O2). O2 began to increase when some bacteria evolved the ability to use H2O as a source of H+ ions in photosynthesis. O2 was a photosynthesis waste product (electrons were available to reduce CO2 to form organic compounds). to • Cyanobacteria formed rock-like structures called stromatolites which are abundant in the fossil record • Enough O2 was liberated to allow evolution of oxidation reactions to synthesize ATP Changes in the Earth’s Atmosphere
The evolution of life changed the physical nature of Earth, which The in turn changed the evolution of life... When O2 first appeared in the atmosphere it was poisonous to the anaerobic prokaryotes, but then some evolved the ability to metabolize the O2 Advantages: aerobic metabolism is faster and more energy is harvested; so aerobes replaced anaerobes in most environments Atmospheric O2 also made possible larger cells and more complex organisms. About 1 billion years ago, eukaryote cells appeared Permian Permian extinction ...
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This note was uploaded on 04/21/2010 for the course BIS 2C BIS 2C taught by Professor Rizzo during the Winter '09 term at UC Davis.
- Winter '09