Macroevolution

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Macroevolution

• How Species Evolve

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• Species
• A group of organisms that maintains a distinctive
  set of attributes in nature
• Macroevolution
• Evolutionary changes that create new species and
  groups of species
• Occurs by accumulation of microevolutionary
  changes (changes in a single gene)

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Insects 54

• Known number of species about 1.4 million
• Estimates of unidentified species range from 2 to
  100 million
• Difficulty in identifying a species
• A single species may exist in 2 distinct
  populations that are in the slow process of
  evolving into 2 or more different species

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• Amount of separation time for 2 populations
• Short time likely to be similar and considered
  the same species
• Long time more likely to show unequivocal
  differences
• May find situations where some differences are
  apparent but difficult to decide if the 2
  populations are truly different species
• Sometimes use subspecies classification

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Defining Species Species Concepts

• Classical species concept
• Morphological species concept
• Organisms that look the same are the same species
• Biological species concept
• Organisms that reproduce together represent the
  same species
• Phylogenetic Species Concept
• organisms that share the same evolutionary
  history are the same species
• Ecological Species Concept
• Organisms that occupy the same ecological niche
  are the same species

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Species Concepts

• Classical/Morphological is the same as Brooker
  Phylogenetic
• Biological (same)
• Phylogenetic is the same Brookers Evolutionary
• Ecological (same)

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Morphological species concept

• Species are identified by having a unique
  combination of traits
• Historically used physical traits
• Advantage
• Can be applied to all organisms
• Drawbacks
• how many traits to consider,
• traits that vary in a continuous way,
• choose degree of dissimilarity to use, and
• members of the same species can look very
  different while members of a different species
  can look very similar

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Morphological Species Concept

• Members of the same species can look very
  different. Two color morphs of the dyeing poison
  frog
• Two different species of frogs
• Top 2 color morphs of the dyeing poison frog
• Bottom Southern Leopard frog (right) The
  Northern Leopard frog (left)

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Biological species concept

• A species is a group of individuals whose members
  have the potential to interbreed with one another
  in nature to produce viable, fertile offspring
  but cannot successfully interbreed with members
  of other species
• Reproductive isolation prevents breeding with
  other species

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• Three problems
• May be difficult to determine if 2 populations
  reproductively isolated
• There are cases where 2 species can interbreed
  but do not
• Cannot be applied to asexual species

Subspecies of Ensatina salamanders
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Which species concept applies?
Liger
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Phylogenetic Species ConceptEvolutionary Species
concept

• A species is derived from a single lineage that
  is distinct from other lineages and has its own
  evolutionary tendencies and historical fate
• Lineage
• Genetic relationship between an individual or
  group of individuals and its ancestors
• Drawback no easy way to identify a unique
  species because lineages difficult to examine and
  quantitate

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Phylogenetic Species Cancept

• Each branch represents a lineage of species with
  a shared evolutionary history

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Ecological species concept

• Each species occupies an ecological niche
• Unique set of habitat resources that a species
  requires, as well as its influence on the
  environment and other species
• Within their own niche, members of a given
  species compete with each other for survival
• If two organisms are very similar, their needs
  will overlap, which results in competition
• Such competing individuals are likely to be of
  the same species
• Useful for bacterial species

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Which species concept applies?
Liger
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Reproductive isolating mechanisms help maintain
the distinctiveness of each species

• Prevent gene flow between species
• Intrinsic Isolating mechanisms
• Prezygotic barriers
• Prevent mating or fertilization
• Postzygotic barriers
• Reproductive failure after fertilization
• Extrinsic Isolating mechanisms

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The origin of species is simply the evolution of
some difference- any difference at all- that
prevents the production of fertile hybrids
between populations that live together in the
same geographical region
Intrinsic Isolating Mechanisms
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Speciation

• Intrinsic Isolatin Mechanisms
• Prezygotic barriers
• Habitat isolation
• Behavioral isolation
• Temporal isolation
• Mechanical isolation
• Gametic isolation
• Postzygotic barriers
• Hybridization

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Intrinsic Isolating Mechanisms Prezygotic
barriers

• Habitat isolation
• Behavioral isolation
• Temporal isolation
• Mechanical isolation
• Gametic isolation

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Habitat Isolation Species occupy different
habitats in the same geographic range. Ex
Flycatchers Empidonax
Least Flycatcher
open woods and farmlands
Alder Flycatcher
Alder swamps and wet thickets
Yellow-bellied Flycatcher
coniferous forests and cold bogs
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• Behavioral isolation
• Behaviors important in mate choice
• Changes in song

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Jumping SpidersWoods and Fields of New England
Differ in Appearance and Mating Dance
Behavioral Isolation
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Temporal isolation

• Mating at different times of year
• Mating at different times of day

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• Mechanical isolation
• Incompatible genital organs of two mint species

Salvia apiana Only large bees brush against the
stamens of the white sage Flowers in late spring
Salvia mellifera Only small bees can land on the
petal of the black sage Flowers in early spring
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Gametic isolation

• Sperm of one species may not survive the
  environment of a female in a closely related
  species
• Incompatible egg and sperm
• Molecular recognition on the surface of the cells
• Molecules (proteins) that coat the egg
• Pollen and stigma recognition in plants

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EX Sympatric speciation in animals

• Species that initially occupy the same habitat in
  the same range diverge into two or more species.
• Population occupies a new ecological niche
• No gene flow even though species live in the same
  area
• Example Two species of maggot flies are
  sympatric in the northern half of one flys range

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Postzygotic barriers

• Less common in nature because they are more
  costly in terms of energy and resources used
• Hybrid inviability
• hybrid embryos die when genetic regulation fails
  during development
• Two species mate, but the embryo never survives
• Hybrid sterility
• problems during meiosis cause abnormal gametes
• Hybrid organism is survives, but is sterile
• Hybrid breakdown
• Hybrid cannot reproduce because of some defect

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Hybrid Sterility
Horse (2N64) X Donkey (2N62) Mule
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Sterile hybrids in Sunflower and Corn

• Hybrid breakdown is the inability of a hybrid to
  reproduce because of some defect.
• Mating between two F1 hybrids produces F2
  generation
• The F2 generation can mate with one another but
  do not produce viable offspring
• Ex sunflowers
• 80 of F2 generation are defective in some way
  and could not reproduce successfully

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AND YET! Hybridization is responsible for the
origin of wheat and many other plant species

• Bread wheat is the evolutionary product of
• two meiotic error episodes producing
• allopolyploids.
• The first speciation event produced
• emmer wheat, derived from hybridization
• between a wild and a domesticated
• species (T. monococcum)
• A second hybridization, between emmer
• wheat and a wild species (T. tauschii),
• gave rise to bread wheat about 8000 years ago.
• The letters A, B, and D represent
• Chromosomes that can be traced to a
• particular species.
• Thus, bread wheat has chromosomes
• derived from three different ancestral
• species.

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• Summary of Intrinsic isolating mechanisms

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Mechanisms in speciation

• Underlying cause of speciation is the
  accumulation of genetic changes that ultimately
  promote enough differences so that we judge a
  population to constitute a unique species

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Defining Speciation

• Vertical change
• Anagenesis
• One species is replaced by another
• No net change in of species
• Speciation
• Cladogenesis
• One species gives rise to another species
• A net increase in of species

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Vertical Change
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Cladogenesis
Speciation
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Rate of evolutionary change

• Fossil record often lacks transitional forms
  between two species
• Is the fossil record simply incomplete?
• Or does it accurately reflect evolution as it
  really occurs?

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Gradualism

• Darwin believed in gradualism
• Continuous evolution over long periods
• The traditional view
• Populations gradually accumulate adaptations
• Different selective pressures in different
  environments

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Punctuated equilibrium

• Long periods of stasis (2 My)
• Punctuated by periods of rapid speciation
  (100,000 y)
• Triggered by changes in the environment
• Abrupt appearance of new species in the fossil
  record
• Often results in cladogenesis, which is rapid
  speciation

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Allopatric speciation

• Most prevalent method for cladogenesis
• Occurs when some members of a species become
  geographically separated

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Geographic Isolation Leading to Reproductive
Isolation and Speciation
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Allopatric speciation

• Can also occur when small population moves to a
  new location that is geographically separated
  founder effect
• Genetic drift and natural selection may quickly
  lead to differences
• Adaptive radiation single species evolves into
  array of descendents that differ greatly in
  habitat, form or behavior

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• Hawaiian honeycreepers ancestor is believed to
  be the Eurasian rosefinch that arrived on the
  island 3-7 mya.
• Since that time at least 54 species of
  honeycreepers have evolved on the islands to fill
  available niches on the islands

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Fig. 25.8
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Sympatric speciation

• Occurs when members of a species that initially
  occupy the same habitat within the same range
  diverge into two or more different species
• Tends to involve abrupt genetic changes that
  quickly lead to the reproductive isolation of a
  group of individuals
• Changes in chromosome number

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Hybridization is responsible for the origin of
wheat and many other plant species

• Bread wheat is the evolutionary product of
• two meiotic error episodes producing
• allopolyploids.
• The first speciation event produced
• emmer wheat, derived from hybridization
• between a wild and a domesticated
• species (T. monococcum)
• A second hybridization, between emmer
• wheat and a wild species (T. tauschii),
• gave rise to bread wheat about 8000 years
• ago.
• The letters A, B, and D represent
• Chromosomes that can be traced to a
• particular species.
• Thus, bread wheat has chromosomes
• derived from three different ancestral
• species.

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Fox Squirrels A local example of speciation

• Eastern Fox Squirrel

• Delmarva Fox Squirrel

Sciurus niger cinereus
Sciurus niger
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Distribution

• Eastern Fox Squirrel

• Delmarva Fox Squirrel

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• Eastern Fox Squirrel

• Delmarva Fox Squirrel

• Fur color Grey- brown
• Size 1.1-2.2 lbs.
• Distribution Eastern US to the prairies
• Habitat
• Hardwood forests and sometimes mixed
  pine-hardwood
• Open understory allows an open view of
  surroundings for quick retreat when threatened
• Shy, slow, and deliberate in its movements
• Favorite foods
• Forages on the forest floor for
• pine cones/seeds
• corn, soybeans, red maple seeds

• Fur Color Silver grey
• Size up to 3 lbs
• Distribution Delmarva peninsula
• Habitat
• Pine-hardwood forests

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• Maryland Endangered Species
• Reason habitat loss and fragmentation
• Original range included the entire Delmarva
  peninsula into southeastern PA.
• Remnant populations exist at Blackwater, Eastern
  Neck NWR (Kent Co.), and Assateague Island

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Evolution and Extinction are Related

• Adaptive radiation
• Mass extinction
• Appearance of evolutionary novelties

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Adaptive radiationthe connection between
ecology and evolution

• Speciation fills new ecological niches
• New adaptive zones may appear when the
  environment changes
• One species colonizes an island and diversifies
  into new species

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Adaptive radiation on a grand scale
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Extinction

• Facilitates evolution by opening adaptive zones
• Mass extinctions
• Five or six mass extinctions of many species and
  higher taxonomic groups
• Major climate changes
• Catastrophes such as asteroid impacts