Exam 2 lecture 12

UIC BioS101 Nyberg

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Evolutionary History, Radiations and Rapid Change

There are times and situations in which species arise at very high rates.

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The world is always changing.

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Reading

• Read Box 27.1 on Molecular Clocks

• Read p. 551 – 564.

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Neutral Substitutions

• Redundancy in the genetic code means that base pairs in DNA can change without changing the amino acid in the protein.

• Most of the base substitutions that don’t change the amino acid sequence are in the third codon position.

• Neutral substitutions accumulate thru time.

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Redundancy refers to the fact that there are 64 combinations of 3 ordered bases, for 20 amino acids plus the STOP. Thus multiple 3 base combinations must code for the same amino acid.

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Exam 2 lecture 12

UIC BioS101 Nyberg

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The molecular clock

• Base pair differences accumulate between separate lineages which had an origin in a common ancestor.

• When accumulations of molecular differences are calibrated using fossils, the result suggests the number of differences can be used to estimate the time of divergence.

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If few substitutions are functionally equivalent then the clock runs slowly = long time between substitutions.

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Linear relationship of differences in sequence and time

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Exam 2 lecture 12

UIC BioS101 Nyberg

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History of life on earth

• Fifty years ago the earliest fossils were known from 500 million years ago, a long time, but ….

• Now there is a variety of evidence, much based on stable isotope ratios, that living things were on earth 3 billion years ago.

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Exam 2 lecture 12

UIC BioS101 Nyberg

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The Dynamic World

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Multicellularity

• Cells have constraints that limit how big they can become.

  • 100 μm = 0.1 mm is a big cell

• The organism you know are made up of many cells organized into a form that functions to serve the entire population of cells.

• HOX loci seem involved in development of multicellualr organisms.

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Hox genes

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Radiations

• If many species originate at about the same time the phylogeny will be difficult to force into a bifurcating pattern.

• Data analysis may say more than two species arise from a node at same time.

• If more than two branches arise from a node, the terms ‘star phylogeny’ or ‘polytomy’ are used.

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Populations may become isolated from one another by an event. When that happens a dozen or more populations could be isolated from one another all at the same time.

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Adaptive Radiations

• Are best known from islands

• Presumably, a few individuals of species arrive on the island and the population expands rapidly.

• Differentiation of species takes advantage of the diverse opportunities available in a habitat without many species.

• The Galapagos and Hawaiian islands are well studied examples. Both are very far from other islands or continents.

Speaker Notes:

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People have colonized islands and continents but have not differentiated into multiple species. Radiations don’t always occur after colonizations.

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Adaptive Radiations
on Islands

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Exam 2 lecture 12

UIC BioS101 Nyberg

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More on Islands

• Studies of lizards on Caribbean islands suggest that no matter which type of lizard arrives first, the island will end up with the same array of ecological types; according to height of foraging.

• The Hawaiian islands have produced an diversity of species types that is not replicated elsewhere to my knowledge.

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The Hawaiian islands have a special geological history which may play a critical role in the diversity of species.

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Mass Extinction

• Events have occurred in the history of the earth that resulted in the extinction of a large number of species in a short period of time.

• Five big events of extinction have occurred in the last 500 million years.

• The most recent mass extinction (65x106 ya) resulted in the disappearance of the dinosaurs and the rise of mammals.

Speaker Notes:

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Krakatau was a recent volcano that had a big impact on the world. Events occur that result in extinctions, but a lot of species have to disappear to be called a mass extinction.

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Extinction of Major Types versus time

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Events and mass extinction

• A variety of evidence (Iridium and ‘shocked quartz’) suggests that the Cretaceous (age of the dinosaurs) was ended when an asteroid hit the earth.

• Only 18,000 ya our current location was covered by a glacier a mile thick. Obviously things were quite different not very long ago.

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Soil was built since the glacier retreated. How did it get so thick so fast?

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Exam 2 lecture 12

UIC BioS101 Nyberg

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End of Cretaceous

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Mammalian radiation

• After the mass extinction that marked the end of the Cretaceous the diversity of mammals greatly expanded.

• Though Cretaceous mammals were all small and not very diverse within 15 million years of mass extinction all current orders of mammal existed.

  • No new mammal orders in last 50 million years.

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In a 2006 SCIENCE there is the description of some fossil mammals from the Cretaceous that are new and suggest greater diversity than heretofore appreciated.

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Rapid genetic change

• Instances of rapid genetic change have been discovered after it was possible to use museum skins to look at populations from the past.

• Pergams, Barnes & Nyberg (2003) Nature 423:397 reported that the mitochondrial haplotype of the white-footed mouse that was common in Chicago in 1900 is now very rare.

Speaker Notes:

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There is also evidence of morphological (=shape) changes during island colonizations.

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Human caused Extinction

• The passenger pigeon was the most abundant bird in North America at the time of the signing of the constitution.

• One hundred years later the Passenger pigeon existed only in zoos.

• It is now extinct.

• The behavior of the Passenger pigeon made it vulnerable to human hunting.

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Besides the passenger pigeon, the Carolina parquet is also extinct. What animals are threatened with extinction today?

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Biological Pollution

• Exotic or non-native species can be described as biological pollution.

• Biological pollution is a greater threat than garbage, because organisms reproduce (and can spread on their own).

• Biological pollution is a major cause of extinction of native species.

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Exam 2 lecture 12

UIC BioS101 Nyberg

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Vocabulary

• Redundancy

• Neutral substitution

• Polytomy

• Molecular clock

• HOX genes

• Adaptive radiation

• Mass extinction

• Biological pollution

• Cretaceous

• Rapid evolution

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