Evolution II contents

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Evolution II - contents

• Macroevolution and Microevolution
• Phylogenetic trees and cladistics
• Examples of convergent evolution
• How to identify cases of convergent evolution

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Definitions

• Macroevolution A term for the evolution of great
  phenotypic changes, usually great enough to
  allocate the changed lineage and its descendants
  to a distinct genus or higher taxon (Futuyma).
  Examples patterns of the divergence of lineages,
  families or classes patterns of emergence of new
  lineages (e.g. mammals, dinosaurs) or their
  disappearance.
• Microevolution A term for slight, short term
  evolutionary changes within species (Futuyma)
• Examples changes of allele frequencies within a
  species over time, emergence of population
  differences.

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Macro-and Micro-evolution
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Patterns of macroevolution
Phyletic evolution (anagenesis) envisions gradual
divergence of a lineage as the bell-shaped mean
of successive populations changes, until a new
species if formed. Punctuated equilibrium
(cladogenesis) envisions long periods of more or
less unchanging species persistence, suddenly
interrupted by speciation, producing a new
species.
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Pace of macroevolution

• For some biologists, each pattern implies a
  different rate of new species appearance.
  Punctuated equilibrium produces new species
  relatively rapidly. Phyletic evolution produces
  new species more gradually and sometimes termed
  Gradualism.

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Mode and tempo of evolution

• Gradual and rapid appearance of new species
  occurs in the fossil record.

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Cladogenesis

• Where sudden changes occur, they can be
  represented with an angular, branching
  phylogenetic tree (cf. phyletic evolution, figure
  12.7 or slide 4). Each independent lineage
  produced is a clade, shown here as Clade 1 and
  Clade 2. Vertical sections represent more or less
  unchanging persistence of a species branch
  points represent the time of speciation where
  populations diverge and become two distinct
  species. Time runs upward species divergence is
  indicated along the horizontal scale. The
  balloons show details of the phylogeny in a
  species before speciation (light shading), at a
  branching point of speciation wherein two species
  form (light and dark shading), and the subsequent
  fate of each species thereafter.

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Definition cladistics

• Dividing (categorising) organisms based on
  quantitative analysis of biological traits.
• Building trees based on similarity between
  species similar species on short branches in
  close proximity, distantly related ones on
  remote, long branches
• A clade is a lineage within a tree (or cladogram)
  and contains a group of species with a
  monophyletic origin
• A phylogenetic tree is a branched diagram that
  recaptures the history of a set of species

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Taxonomic units above the species level

• Species Apis mellifera
• Genus Apis
• Family Apidae
• Order Hymenoptera
• Class Insecta
• Phylum Arthropoda
• note that these categories (except the species)
  have no clear biological basis, except that they
  should be monophyletic.

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• A monophyletic group is one which contains a
  common ancestor and all its descendents
• A paraphyletic group is one which contains a
  common ancestor and some, but not all of its
  descendents
• A polyphyletic group is a group of taxa that are
  derived from two or more ancestral forms not
  common to all members

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• Under a system of phylogenetic classification, we
  could name any clade on this tree. For example,
  the Testudines, Squamata, Archosauria, and
  Crocodylomorpha all form clades.
• However, the reptiles do not form a monophyletic
  clade, as shown in the cladogram. That means that
  "reptile" is not a valid phylogenetic grouping,
  or we would have to start thinking of birds as
  reptiles.

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• Consider non-avian dinosaurs (which is what
  people mean by the informal term dinosaurs'').
  This is a paraphyletic group, because it can't be
  defined simply as this animal plus all its
  descendants'', but must be described as one clade
  minus another in this case, Dinosauria minus
  Aves.
• Reminder a paraphyletic group is one which
  contains a common ancestor and some, but not all
  of its descendents

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Are warm blooded animals (birds and mammals) a
monophyletic taxon?

• In other words, did warm-bloodedness evolve once
  in the common ancestor of birds and mammals?

No they are polyphyletic a totally unnatural
assemblage of animals!
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What came first, the chicken or the egg?
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Convergent evolution

• Evolution of similar features independently in
  different evolutionary lineages, usually from
  different antedecent features or by different
  developmental pathways

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Convergent evolution Cacti and other prickly
plants

• Different families of desert plants have evolved
  similar adaptations to the deserts dry, hot
  conditions - namely, succulent shoots with
  spines. Two such plant species are shown from
  Africa. The third, from the New World, is the
  endemic member of the true cactus family
  (Cactaceae).

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Convergent evolution - mammals

• Australian marsupials resemble placental mammals
  in the rest of the world. Within the relative
  isolation of Australia, the marsupials entered
  similar habitats as counterparts among the
  placentals elsewhere. Under similar selective
  pressures, similar features and ecological
  lifestyles evolved, but upon a marsupial theme.

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Six legs in insects have they evolved multiple
times by convergence?
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Convergent evolution - wings

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Are insects red-blind? Convergent evolution of
red sensitivity in several lineages
From Chittka 1996 Naturwissenschaften
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Lens eyes exist in vertebrates, many molluscs,
some medusas, some annelids, and some cephalopods
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Development of vertebrate and Cephalopod eyes

• Cephalopod
  Vertebrate
• (everse)
  (inverse)

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Public lecture series on insect visionWednesdays
6pm Skeel Lecture theatre

• Thomas Döring Queen Mary, University of London
  Tricks, traps, and treatments insect vision in
  agriculture.
• 14th February 2007
• Claire Rind University of Newcastle Locust
  motion detectors for collision avoidance in
  cars.21st February 2007
• Almut Kelber University of Lund, Sweden How
  nocturnal insects see in dim light.28th February
  2007

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Practical this Thursday!!

• Walter Besant Building, 2nd floor 15/02/2007, at
  2pm

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Evolution II - contents

• Define Macroevolution and Microevolution
• What do phylogenetic trees represent
• Examples of convergent evolution
• How to identify cases of convergent evolution