General Patterns in Evolution
Uses of Phylogenetic Analysis
• Allows mapping order of character state changes
• Documents evolutionary trends in development
• Reveals that Homoplasy is common
• Can attempt to equate timing with fossil record events
Stripes
Loss of spots
Bobbed tail
Rosettes
How the Leopard got its spots
Spots
Werdelin & Olsson (1997) Biol. J. Linn. Soc. 62: 383-400
Tracing the path of evolution to Homo sapiens from the universal ancestor of all life
Phylogenetic Analysis Documents Evolutionary Trends
in Development: In fruit flys
Phylogenies Reveal that Homoplasy is Common
• Convergent and parallel evolution - the independent gain of a trait
ATTAG ATTCG ATTAG ATTAG ATTAG ATTCG ATTAG
Convergent Evolution among
Placental Mammals and Marsupials
Structure of the p115RhoGEF rgRGS domain−Gα13/i1 chimera complex
suggests convergent evolution of a GTPase activator.
Zhe et al. (2005) Nature Structural & Molecular Biology. 12:191 – 197.
Parallel evolution: Special case of Convergent evolution
Feeding structures (maxillipeds) from thoracic legs in crustaceans.
Phylogenies Reveal that Homoplasy is Common
• Evolutionary reversal - the loss of a trait
ATTAG ATTAG ATTAG ATTCG ATTCG ATTAG ATTCG
C =>A
A => C
Reversal:
An example of the acquisition and loss of individualization
Homodonts vs. Heterodonts
(Early Eocene Whale)
Reconciling the Fossil Record
with phylogenetic analysis?
Can really only work with
morphology-based cladistics.
These images taken from Heck's
Iconographic Encyclopedia (1851).
The Evolution of Traits aka phenotypes
Linear interactions
Non-linear interactions
Polymorphic mimicry in Papilio dardanus (The mocker swallowtail):
accurate mimics of different species of distasteful butterflies.
Single Locus; ~11 mimicking alleles that are more variable.
Biological traits come about through developmental processes and
physiological regulatory mechanisms. Most of these processes are
nonlinear. Examples of nonlinear processes are:
• The sensitivity of reaction rate to substrate concentration
• inhibition
• negative feedback
• positive feedback
• cooperativity
• most non-steady state processes
• any process that depends on diffusion
Any mechanism that contains one or more of these processes
(and most regulatory mechanisms in biology do) will have a
nonlinear relationship between variation in its determinants and
variation in the trait affected by the process.
Rates of Evolution Vary Among Lineages
Rates of Evolution Vary Among Characters
Evolution of different characters
at different rates within a lineage:
Mosaic Evolution
Combines concepts of
Gradualism vs. Saltation
Molecular Clock?
Inferred pairwise nucleotide substitutions among 17 mammal species from seven gene products,
as estimated from protein studies, plotted against date of divergence, as estimated from the fossil
record. The line is drawn from the origin through the oldest point (marsupial/placental divergence
at 125 MYA). The strong linear relationship suggests that molecular differences between pairs
of species are proportional to the time of their separation, rather than the degree of organismal
difference. Therefore, measures of genetic divergence can be used to date the time of divergence
for species pairs for which no fossil data are available: genes function as Molecular Clocks.
(from A. C. Wilson 1976)
Change in Form is Often Correlated
with Change in Function
Heterochrony:
Changes in the Rate or Timing of Developmental Events
Paedomorphosis: the retention of Peramorphosis: ‘hyper-adult’
juvenile features in the reproductive features in the reproductive adult.
adult.
Heterotopy:
Changes in the Position in which a Trait is Expressed
Philodendron switching
stem and root positions.
Allometry:
Impact of body size
on biology
Are we just baby chimps?
A tale of heterochrony and
allometric growth.
Homo sapiens, whose prolonged brain
development period and relatively flat face
may be reflections of a prolonged juvenile
period, relative to that of our closest
relatives, the bonobos and chimpanzees
(Pan paniscus and P. troglodytes).
Allometric differences in the jaws among three closely related families of fishes.
Adaptive Radiation is Widespread
aka Divergent Evolution
Hawaiian Honeycreepers
Adaptive Radiation
is Widespread
Darwin’s Finches are
the classic example.
Adaptive Radiation
is Widespread
Lake Malawi Cichlids (>500 spp.)
Coevolution
• Predators and their prey.
• Parasites and their hosts.
• Plant-eating animals and the plants upon which they
feed.
• Coevolution is the joint change of two or more
species in close interaction.
• Plants and the animals that pollinate them.
Modification of Preexisting Features
Increases and decreases in complexity:
An example of reduction and loss of skull & lower jaw bones during evolution.
Devonian fish Permian tetrapod
Domestic dog
A model of the species Tiktaalik,
and a recreated skeleton of the animal.
Paleontologists working in northern Canada recently found an animal skeleton that may bridge the gap
between fish and the first four-legged land animals. The 375-million-year-old (Devonian) creature, with
a head like a crocodile's, has a body built for swimming. But its front legs are a compromise between
fins and feet. This new species also has a shortened skull roof, a modified ear region, a mobile neck,
a functional wrist joint, and other features that presage tetrapod conditions.
Daeschler E. B., Shubin N. H., Jenkins F. A. Jr, Nature, 440. 757 - 763 (2006).
Shubin N. H. Daeschler E. B., , Jenkins F. A. Jr, Nature, 440. 764 - 771 (2006).
