Download Essentials of Biology Sylvia S. Mader

Essentials of Biology
Sylvia S. Mader
Chapter 16
Lecture Outline
Prepared by: Dr. Stephen Ebbs
Southern Illinois University Carbondale
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
16.1 Macroevolution
• Microevolution involves changes on the
small scale at the level of gene pool
alleles.
• In contrast, macroevolution involves
evolution at the large scale as species
originate, adapt to their environment, and
possibly become extinct.
Defining Species
• Speciation is an evolutionary event that gives
rise to new species.
• The biological species concept provides one
definition of a species.
– A group of organisms that interbreed with each other
and share the same gene pool.
– A group of organisms that produce fertile offspring.
• Each species is reproductively isolated from
every other species.
Reproductive Barriers
• In order for species to be reproductively
isolated, they must be separated by
barriers which prevent gene flow.
• Reproductive barriers are also called
isolating mechanisms.
Reproductive Barriers (cont.)
Reproductive Barriers (cont.)
• Prezygotic isolating mechanisms prevent
reproduction and make fertilization unlikely.
• Habitat isolation occurs when organisms cannot
reproduce because they are in different habitats.
• Temporal isolation occurs if the reproductive
cycles of organisms occurs at different times.
Reproductive Barriers (cont.)
• The unique courtship patterns displayed
by organisms can create behavioral
isolation.
• Mechanical isolation occurs when the
genitalia are structurally incompatible.
• Genetic isolation occurs when the
fertilization does not occur, even when
sperm and egg are brought together.
Reproductive Barriers (cont.)
• Postzygotic isolating mechanisms prevent
hybrid organisms from developing (zygote
mortality) or reproducing (hybrid sterility).
• In the case of F2 fitness, even a hybrid
organism develops and reproduces, but
the offspring of the hybrid are sterile.
Reproductive Barriers (cont.)
Models of Speciation
• There are different ways in which the
process of speciation can occur.
• In allopatric speciation, an ancestral
population is geographically isolated,
resulting in the evolution of separate
species.
Models of Speciation (cont.)
Models of Speciation (cont.)
• Sympatric speciation involves speciation
without a geographic barrier.
• One example of sympatric speciation is
polyploidy, found more often in plants.
• Polyploidy occurs when the number of
chromosome sets increase to 3n or more.
Models of Speciation (cont.)
Adaptive Radiation
• Adaptive radiation involves the evolution
of several new species from an ancestral
species.
• Adaptive radiation occurs as natural
selection drives members of the ancestral
species to adapt to several different
environments.
Adaptive Radiation (cont.)
16.2 The History of Species
• The evolutionary history of a species, such
as is origin and extinction is reflected in
the fossil record.
• The study of fossils is called paleontology.
The Geological Timescale
• The geological timescale of the earth has
been constructed by studying the fossils in
the various strata of rock.
• Based upon the fossil record, the Earth’s
history can be divided into segments.
– Epochs are the shortest segments.
– A series of epochs form a period.
– Several periods comprise an era.
The Geological Timescale (cont.)
The Geological Timescale
(cont.)
The Geological Timescale
(cont.)
The Geological Timescale
(cont.)
The Pace of Speciation
• One school of thought maintains that
evolution is a gradual process, the
gradualistic model.
• More commonly, new species occur
suddenly in the fossil record followed by
long periods of little change, a pattern
called punctuated equilibrium.
The Pace of Speciation (cont.)
The Pace of Speciation (cont.)
Mass Extinction of Speciation
• Most species exist for a limited period of
geological time and then become extinct.
• Within the fossil record there are also
instances of mass extinctions.
• Evidence of six mass extinctions can be
seen in the fossil record.
Mass Extinction of Speciation
(cont.)
• There are two primary events that are
believed to have contributed to these
mass extinctions.
• The movement of the Earth’s surface via
continental drift is one such event.
• Plate tectonics provides the explanation
for why continental drift occurs.
Mass Extinction of Speciation
(cont.)
Mass Extinction of Speciation
(cont.)
• Habitat changes caused by continental drift
contributed to mass extinctions.
• The formation of the supercontinent Pangaea
created dramatic changes.
– All the oceans were joined.
– The amount of coastline was greatly reduced.
• This effect continued until Pangaea broke apart
and separated.
Mass Extinction of Speciation
(cont.)
Mass Extinction of Speciation
(cont.)
Mass Extinction of Speciation
(cont.)
• A meteorite impact was another event that
contributed to mass extinctions.
• The impact of a meteor in Central America
is thought to have caused the Cretaceous
extinction of the dinosaurs.
16.3 Classification of Species
• Organisms are classified (organized)
based upon their evolutionary relationship.
• The branch of science that deals with the
classification of organisms is taxonomy.
• Taxonomists give each species a scientific
name, also called the binomial name.
16.3 Classification of Species
(cont.)
• The scientific name consists of a genus
and species.
– Peas: Genus = Pisum; species = sativa
– Humans: Genus = Homo; species = sapiens
• The species name is also called the
specific epithet.
16.3 Classification of Species
(cont.)
• Taxonomists use several hierarchical
categories to classify organisms.
– Species
– Genus
– Family
– Order
– Class
– Phylum
– Kingdom
– Domain
Least inclusive
Most inclusive
16.3 Classification of Species
(cont.)
16.3 Classification of Species
(cont.)
• Organisms are classified into the different
categories based upon shared structural,
chromosomal, or molecular features.
• These categories may also be divided into
three additional subcategories, creating
more than 30 categories in total.
Classification and Phylogeny
• Taxonomy and the classification of species are
part of systematics, the study of organismal
diversity.
• A goal of systematics is to establish the
evolutionary history (phylogeny) of a group of
organisms.
• One aspect of systematics is to identify groups
(taxa) of organisms with common ancestors.
Classification and Phylogeny
(cont.)
• The classification of organisms and their
common ancestry can be illustrated with a
phylogenetic tree.
• This tree is assembled based upon the
shared characters of different groups or
organisms.
Classification and Phylogeny
(cont.)
Classification and Phylogeny
(cont.)
• If the character is present in the common
ancestor and all taxa within that group, it is
called a primitive character.
• If the character is limited to a specific line
of descent it is a derived character.
Tracing Phylogeny
• Several types of data are used to
determine the evolutionary relationship
between organisms.
– Details from the fossil record
– Homology
– Molecular data
• This information can be used to determine
the sequence of common ancestors for a
particular organism.
Tracing Phylogeny (cont.)
• The homology of certain characters in
organisms is indicative of common
ancestry and can be used to classify
organisms.
• However this can be complicated by
convergent evolution for that character.
Tracing Phylogeny (cont.)
• Analogous structures may have arisen
from convergent evolution, but are not
derived from a common ancestor.
• Similarly, parallel evolution may lead to the
same character in different species not
derived from the same common ancestor.
Tracing Phylogeny (cont.)
• Since speciation occurs when mutations change
genes, DNA information can be used to classify
organisms.
• Closely related organisms have genes with
closely related sequences.
• The greater the divergence in gene sequence,
the greater the evolutionary distance between
the organisms.
Tracing Phylogeny (cont.)
Cladistic Systematics
• Cladistics strives to produce testable hypotheses
about the evolutionary relationships between
organisms.
• Systematic information is used to classify and
arrange organisms in a phylogenetic tree called
a cladogram.
• A cladogram can be used to trace the
evolutionary history of a group.
Cladistic Systematics (cont.)
Cladistic Systematics (cont.)
• The guiding principle of cladistics is
parsimony, which states that the least
number of assumptions is the most
probable.
• This means that the cladogram is
constructed to minimize the number of
evolutionary changes.
Cladistic Systematics (cont.)
• Within a cladogram, a clade is an evolutionary
branch that includes a common ancestor and all
its descendents.
• Clades are nested together to show how
characters emerge as evolution progresses.
• Since cladograms objectively arrange the data,
their structure can address specific hypotheses
about the evolutionary relationship of groups.
Cladistic Systematics (cont.)
Traditionalists Versus Cladists
• Traditional systematists use a greater
range of information to draw conclusions
about the evolutionary relationship
between organismal groups.
• Traditional systematists also believe that
organisms need not be classified based
upon their common ancestor.
Traditionalists Versus Cladists
(cont.)
• The phylogenetic trees constructed by
traditional systematists provide a different
view of the relationship between
organisms.
Traditionalists Versus Cladists
(cont.)
Traditionalists Versus Cladists
(cont.)
Classification Systems
• Classification systems evolve just as species do.
• Until recently, most biologists used a fivekingdom system of classification.
–
–
–
–
–
Animalia
Plantae
Fungi
Protista
Monera
Classification Systems (cont.)
• However, molecular and cellular data has
revealed problems with the five kingdom
system.
• Based upon that data, a three-domain
system has been proposed instead.
– Bacteria
– Archaea
– Eukarya
Classification Systems (cont.)
Classification Systems (cont.)
Classification Systems (cont.)