How Biological Diversity Evolves
Chapter 14
Winter 2015
Biology and Society: The Sixth Mass Extinction
• Over the past 540 million years, the fossil record reveals five periods
of mass extinction when 50–90% of living species suddenly died out.
• Unfolded over hundreds of thousands of years
• current rate of extinction, over the past 400 years, indicates that we
may be living in, and contributing to, the sixth mass extinction period
• Nature 2011; 1000 species in 400 years.
• Mass extinctions pave the way for the evolution of new and diverse
forms, but it takes millions of years for Earth to recover
The Origin of Species - History
• Galápagos Islands - a place of origins.
• Although the volcanic islands were geologically young, they were home to
many plants and animals known nowhere else in the world.
• Darwin thought it unlikely that all of these species could have been among
the original colonists of the islands.
• In the 150 years since the publication of Darwin’s book On the Origin
of Species by Means of Natural Selection, new discoveries and
technological advances have given scientists a wealth of new
information about the evolution of life.
• The diversity of life evolved through speciation, the process in which
one species splits into two or more species.
What is a Species?
• Species
• A group of populations whose members have the potential to interbreed with
one another in nature to produce fertile offspring
• Difficult to apply to
• fossils and
• asexual organisms.
• Other definitions of species are based on
• measurable physical traits,
• the use of ecological resources, or
• unique adaptations to particular roles in a biological community.
http://www.bing.com/images/search?q=Living+Things+Taxonomy+Chart&FORM=RESTAB#view=detail&id=B01DF40F689819DA830357645C1269EF75017D1F&selectedIndex=0
Reproductive Barriers between Species - 1
Prezygotic barriers prevent mating or fertilization between species.
• Figure 14.4, page 272
• temporal isolation
• habitat isolation
• behavioral isolation
• mechanical isolation
• gametic isolation
Reproductive Barriers between Species - 2
• Postzygotic barriers operate if an unsuccessful zygote is formed
• interspecies mating occurs and
• hybrid zygotes form.
• Figure 14.5, page 273
• include
• reduced hybrid viability
• reduced hybrid fertility
• hybrid breakdown
The Speciation Process
• Begins with isolation of two subsets of a population
• sympatric speciation, without geographic isolation.
• allopatric speciation, due to geographic isolation
• Geologic processes
• Migration across or around physical barriers
• Figure 14.8, page 275
• Sympatric speciation occurs when some other barrier exists between populations
• Reproductive barriers arise between isolated populations
• Random mutation
• Often involves differences in chromosome number or structure
• Even if the two populations should come back into contact at some later
time, the reproductive barriers will keep them as separate species.
Mechanisms of Speciation
• Prezygotic barriers interfere with meiosis
• Gametes that are formed are no longer compatible with their opposites.
• An accident during cell division that results in an extra set of chromosomes is
a common route to sympatric speciation in plants.
• Chromosomal inversions can occur during hybridization and block later
duplication.
• Post-zygotic barriers
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polyploid species arise from the hybridization of two parent species
Chromosome numbers in their gametes will be unequal.
potatoes, bananas, peanuts, apples, coffee, and wheat
Figure 14.9, page 276
Timelines for Speciation
• Two contrasting patterns for the pace of evolution:
• the gradual pattern, in which big changes (speciations) occur by the steady
accumulation of many small changes and
• the punctuated equilibria pattern, in which there are
• long periods of little apparent change, (equilibria) interrupted (punctuated) by
• relatively brief periods of rapid change.
• Figure 14.10, page 277
Macroevolution
• Above the species level
• Exadaptation:
• a structure that evolves in one context but becomes adapted for another function
• a type of evolutionary remodeling.
• account for the evolution of novel structures.
• e.g. Birds
• are derived from a lineage of earthbound reptiles and
• evolved flight from flightless ancestors.
• wings are modified forelimbs that were previously adapted for non-flight functions, such as
• thermal regulation,
• courtship displays, and/or
• camouflage.
• The first flights may have been only glides or extended hops as the animal pursued prey or
fled from a predator.
Evolutionary Developmental Biology
• the study of the evolution of developmental processes in multicellular
organisms.
• Homeotic genes
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master control genes
active during embryonic development from a zygote into an adult
regulate the rate, timing, and spatial pattern of changes in an organism’s form
mutations in homeotic genes can profoundly affect body form.
• Paedomorphosis
• the retention into adulthood of features that were solely juvenile in ancestral species
and
• has occurred in the evolution of axolotl salamanders and humans
• Figure 13.12, p 279
Earth History and Macroevolution
• Fossil record is
• the sequence in which fossils appear in rock strata and
• an archive of macroevolution.
• Geologic time scale that divides Earth’s history into a consistent sequence of geologic
periods.
• Table 14.1, p 281
• Fossils are reliable chronological records only if we can determine their ages, using
• the relative age of fossils, revealing the order in which groups of species evolved, and/or
• the absolute age of fossils, requiring other methods such as radiometric dating.
• Radiometric dating
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is the most common method for dating fossils,
is based on the decay of radioactive isotopes, and
helped establish the geologic time scale
Figure 14.15, page 282
Plate Tectonics and Macroevolution 1
• Figure 14.7, page 283
• Continents drift about Earth’s surface on
• plates of crust floating on a
• flexible layer of hot, underlying material called the mantle.
Frequent earthquakes occur as the plates move and bump against each other.
Pangaea: supercontinent,
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About 250 million years ago
ocean basins increased in depth, sea levels dropped,
the dry continental interior increased in size, and
many extinctions occurred.
• About 180 million years ago, Pangaea began to break up,
• large continents drifted increasingly apart,
• climates changed, and
• the organisms of the different biogeographic realms diverged.
Plate tectonics helps to explain
• why Mesozoic reptiles in Ghana (West Africa) and Brazil look so similar and
• how marsupials were free to evolve in isolation in Australia.
Mass Extinctions
• Five mass extinctions have occurred
• The fossil record
• Over the last 540 million years
• Permian mass extinction
• occurred at about the time the merging continents formed Pangaea (250 million
years ago) and
• claimed about 96% of marine species.
• Cretaceous extinction
• occurred at the end of the cretaceous period, about 65 million years ago,
• included the extinction of all the dinosaurs except birds, and
• permitted the rise of mammals.
• Explosive diversifications of life followed each extinction event
Discussion 1 Did a Meteor Kill the Dinosaurs?
• Observation: About 65 million years ago, the fossil record shows that
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the climate cooled,
seas were receding,
many plant species died out,
dinosaurs (except birds) became extinct, and
a thin layer of clay rich in iridium was deposited.
• Question: Is the iridium layer the result of fallout from a huge cloud of dust that
billowed into the atmosphere when a large meteor or asteroid hit Earth?
• Hypothesis:
• Prediction:.
• Results:
• Interpretation: These data do or do not support the hypothesis
Discussion 1 Did a Meteor Kill the Dinosaurs?
• Observation: About 65 million years ago, the fossil record shows that
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•
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the climate cooled,
seas were receding,
many plant species died out,
dinosaurs (except birds) became extinct, and
a thin layer of clay rich in iridium was deposited.
• Question: Is the iridium layer the result of fallout from a huge cloud of dust that billowed into the
atmosphere when a large meteor or asteroid hit Earth?
• Hypothesis: The mass extinction 65 million years ago was caused by the impact of an extraterrestrial object.
• Prediction: A huge impact crater of the right age should be found somewhere on Earth’s surface.
• Results: Near the Yucatán Peninsula, a huge impact crater was found that
• dated from the predicted time,
• was about the right size, and
• was capable of creating a cloud that could have blocked enough sunlight to change the Earth’s climate for months.
• Interpretation: These data support the hypothesis
Discussion 2: Rise of the Mammals
• Fossil evidence indicates that
• mammals first appeared about 180 million years ago
• the number of mammalian species remained steady and low in number until
about 65 million years ago
• Increase coincided with the extinction of the dinosaurs
• What might have been the basis for this increase in mammals?
Classifying the Diversity of Life
• Systematics focuses on
• classifying organisms and
• determining their evolutionary relationships.
• Taxonomy is the
• identification,
• naming, and
• classification of species.
• Systematics includes taxonomy.
Systematic Names
• The taxonomic hierarchy extends to
progressively broader categories of
classification, from
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Species
genus
family
order
class
phylum
kingdom
domain.
• Use these terms to describe the taxonomic
relationships among
• Leopards, Lions, Tigers and Jaguars, Fig 14.19
p. 285
• Humans and leopards Fig 14.20, p 286
• Carnivores Fig 14.21, p 286
Classification and Phylogeny
• Schemes
• describe evolutionary relationships
• depict hypotheses about the evolutionary history of species
• Homologous structures
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Evolved from the same structure in an evolutionary ancestor
reflect variations of a common ancestral plan and
used to develop phylogenetic trees
classify organisms according to their evolutionary history.
Whale fins and bird wings
Pitfalls in the search for homology
• Convergent evolution involves superficially similar structures from
different evolutionary branches that result from natural selection
shaping analogous adaptations.
• Similarity due to convergence is called analogy, not homology.
• To develop phylogenetic trees and classify organisms according to
their evolutionary history, we use only homologous similarities
• Embryonic development can help
Use the tree of life diagram to
determine the relationships
between following
organisms?
• Lizards and birds
• Wheat and corn
• Pine trees and flowering
plants
• Bacteria and fungi
Molecular systematics
• compares nucleotide and amino acid sequences between organisms
• can reveal evolutionary relationships
• The more recently two species have branched from a common
ancestor, the more similar their nucleotide and amino acid sequences
should be.
• Some fossils are preserved in such a way that DNA fragments can be
extracted for comparison with living organisms.
The Cladistic Revolution
• A clade consists of an ancestral species and all its evolutionary descendants and
forms a distinct branch in the tree of life.
• In cladistics, organisms are grouped by common ancestry.
• based on the Darwinian concept of “descent with modification from a common ancestor.”
• To identify clades, scientists compare an ingroup with an outgroup.
• Figure 14.23, p 287
• In group: the set of species being analyzed
• Outgroup: a species known to have diverged before the lineage that contains the ingroups
appeared
• Result is a Phylogenetic tree
• Cladistics has changed the traditional classification of some organisms, including
the relationships between
• Figure 14.24, p 288 dinosaurs, birds, crocodiles, lizards, and snakes.