Transcript Evolution II - contents - Chittka Lab

Evolution II - contents
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Macroevolution and Microevolution
Phylogenetic trees and cladistics
Examples of convergent evolution
How to identify cases of convergent
evolution
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.
Macroand Microevolution
Patterns of macroevolution
Phyletic evolution (anagenesis) envisions gradual divergence of a lineage as the bellshaped 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.
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.”
Mode and tempo of
evolution
• Gradual and rapid
appearance of new
species occurs in the
fossil record.
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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.
Cladogenesis
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
Taxonomic units above the
species level
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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.
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
Are warm blooded animals (birds and
mammals) a monophyletic taxon?
• In other words,
did warmbloodedness
evolve once in
the common
ancestor of
birds and
No – they
mammals?
are
polyphyleti
c: a totally
unnatural
assemblage
of animals!
What came first, the chicken or
the egg?
Convergent evolution
• Evolution of similar features independently
in different evolutionary lineages, usually
from different antedecent features or by
different developmental pathways
Convergent evolution – Cacti and
other prickly plants
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Different families of desert plants have evolved similar adaptations to the
desert’s 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).
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.
Six legs in insects – have they
evolved multiple times by
convergence?
Convergent evolution - wings
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Are insects red-blind? Convergent evolution of red
sensitivity in several lineages
From: Chittka 1996
Naturwissenschaften
Lens eyes exist in vertebrates,
many molluscs, some medusas,
some annelids, and some
cephalopods
Development of vertebrate and Cephalopod
eyes
Cephalopod Vertebrate
(everse)
(inverse)
Public lecture series on insect vision
Wednesdays 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
Practical this Thursday!!
• Walter Besant Building, 2nd floor
15/02/2007, at 2pm
Evolution II - contents
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Define Macroevolution and Microevolution
What do phylogenetic trees represent
Examples of convergent evolution
How to identify cases of convergent
evolution