Selection, adaptation, and the rise of biological complexity
100
Differences in reproductive success of three
Orchid species
80
of fruits
Cumulatve percentage
x
Selection needs variation
Oeceoclades maculata
Lepanthes wendlandii
Encyclia cordigera
60
40
20
Isocline
0
0
20
40
60
80
100
Cumulative percentage of individuals
Most species have great variation in reproductive success.
This variation is the basis for natural selection
that means changes in gene frequencies.
In the United states male reproduction rate is about 40%. Female
reproduction rate is about 80%.
In Poland it’s about 80% (males) and 90% (females).
Because the total number of children is fixed, in males the variance in
reproductive success is higher than in females.
Number of spiderlings
Sex differences in reproductive output and variance
Latrodectus hasselti
8000
7000
6000
5000
4000
3000
2000
1000
0
5000
4000
3000
2000
1000
0
0
1
2
3
Number of mates
0
1
2
Number of mates
Bateman's principle : the reproductive variance is generally greater in males
than in females.
This is a direct consequence of anisogamy, the fact that sperm is smaller than eggs.
The effect is greatest in polygamous species
Selection should result in higher frequencies (higher reproduction rates) of genotypes
that are better adapted to selection pressures
Adaptations are fits to environmental conditions (selection pressures)
Echolotes of bats are adaptations to
catch nocturnal insects
Mimese is an adaptation to escape
predators
Adaptations are
•
Heritable: adaptations are genetically determined
•
Functional: adaptations have been shaped by natural
selection for a particular task
•
Adaptive: adaptations increase fitness
In the course of evolution adaptations might become maladaptive. These are termed vestigial.
Adaptations and Exaptations
Via natural selection species become adapted to environmental
conditions.
But natural selection must act on something.
These preadaptational features are called exaptations
Feathers appeared in the Therapoda
lineages for thermoregulation.
This was an exaptation for later flight.
The lungs in Dipnoer are primitive.
This was an exaptation for the gas bladder to
control buoyancy in the Actinopterygii
Industrial melanism
The first melanic morph was detected in
1848. By 1950 in many regions only
melanic forms occurred.
Since then the light form again retained
dominance.
Both changes are assumed to be
correlated with air pollution during the
industrial revolution.
Main selective agent was bird predation.
z
melanic form
Biston betularia was in England
represented by its light variation.
Proportion of the z
Biston betularia
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1955 1965 1975 1985 1995 2005
Year
Pesticide resistance in insects
500
Pyrethroids
Carbamates
Organophosphates
# species z
400
Cyclodienes
DDT
300
Total
200
100
0
1940
1950
1960
1970
1980
1990
Year
Recently more than 500 insect pest species evolved resistance against major
classes of insecticides.
Mimicry
Batesian mimicry
Müllerian mimicry
A tropical fly mimics a bee
Two tropical butterflies look similar
A harmless species
mimics an unpalatable
or poisonous species
Several unpalatable or
poisonous species have
similar warning colours
Peckhamian mimicry
Wasmannian mimicry
A tropical spider mimics a
prey beetle species
Some tropical jumping spiders mimic ants
A predator species
mimics its prey species
A harmless species mimics
another to live in the same
nest or structure
Myxomatosis and rabbits
Virulence and mortality after the
introduction of the myxoma virus in
Australia to control the population of
European rabbits (Oryctolagus cuniculus).
The myxoma virus causes skin
tumours in European rabbits.
In 1938 it was introduced in Australia
and since 1950 it spreads throughout
Europe.
Virulence of myxoma virus
1953
1962-1967
1968-1970
1971-1973
1974-1976
1977-1980
I
100
3
0
0
1.3
0
II
0
15.1
0
3.3
23.3
30.4
Virulence grade
III
0
71.1
100
93.4
66.8
65.3
Their is a campaign for vaccination
IV
0
10.3
0
3.3
8.6
4.3
V
0
0.7
0
0
0
0
Mortality of rabbits
Period
Unselected rabbits
1961-1966
1967-1971
1972-1975
Mortality
100
94
90
85
The virus lost virulence and the rabbit evolved resistance.
Coevolution: flowering plants and pollinators
Lamarouxia hyssophifolia
is hummingbird pollinated
Magnolia grandiflora
is beetle pollinated
Emorya suaveloens
is butterfly pollinated
Lamarouxia xalapensis
is bee pollinated
Coadaptations
The 900 fig tree species produce flowers concealed within an enclosed inflorescence, the fig.
A fig wasp pollinates
and lays eggs.
Fig wasps emerge
from their galls and
mate.
Wasps develop
within the galls
Pollination and
egg laying
Figs produce
flowers within
inflorescences
The female fig wasp
has to enter the gall
through a tiny
Most species are tree
opening.
specific and find their
The female body is
tree due to
particularly adapted allochemicals produced
to this task.
by this fig species.
The high degree of specializaton
leads to fast diversification
After pollination galls
change colours and
smells and become
attractive to fruit
eating birds, bats,
monkeys, and
lizards.
Galls are dispersed
by fruit eaters
600 species of fig wasps
(Agaonidae) form a mostly tropical
family of chalcid wasps that are
morphologically and ecologically
specialized fig tree pollinators.
Adaptive radiations
Darwin finches
13 species evolved within a few
mya
Adaptive radiations mainly occur
Adaptive radiation refers to a fast rate • when new adaptive peaks have been
reached
of speciation within a lineage (fast
• on newly colonized islands
cladogenesis)
Adaptive radiation
Number of genera of Ammonites
Adaptive radiation refers to a fast increase of species richness.
This increase is related to the accquition of features that allow for the invasion into previously
unoccupied ecological niches and/or habitats.
Fast occupation of empty niches means initially:
• low degree of competition
• low selection pressure
• proportionally higher fitness of aberrant individuals
• wider morphological, behavioural or dispersal potential
• Higher probability of speciation
Adaptation to herbivory and promiscuity might cause high rates of speciation
Change in feeding style
Cucujoidea
Curculionoidea
< 10000 species > 200000 species
Trichoptera
< 10000 species
Herbivores
Herbivores
Detritivores
Predators
Change in mating system
Manucodes Birds of paradise
Swifts
5 species
33 species
103 species
Pair bonds
Lepidoptera
> 300000 species
Promiscuity
Pair bonds
Hummingbirds
319 species
Promiscuity
Drosophila from Hawaii
1
3
pseudoobsura/persimilis
simaulans/mauritiana
pseudoobscura/miranda
picticornis/16 other species
melanogaster/simulans
yakuba/teissier
orena/erecta
Neogene
D. pseudoobsura/subobscura
23
Paleogene
Hawaiian Drosophila
Drosophila with
spotted wings
Freshwater fish of the great East African lakes
The Cichlidae is one of the most species-rich family
of vertebrates.
Most of these species occur in three East African
lakes, Lake Victoria, Lake Tanganyika and Lake
Malawi.
At least 500 endemic species have been described
in Lake Malawi. They are of monoplyletic origin.
Lake Malawi is 4.5-8.6 million years old.
Cichlids underwent a rapid adaptive radiation.
Genetic studies revealed very fast changes in genes
responsible for trophic niches.
Important is also sexual selection.
Cichlidae of Lake Malawi
Sexual selection
Intersexual selection
Intrasexual selection (male - male competition)
Sexual
selection
might cause
maladaptive
traits
Northern sea elephants
Peacock
Fisherian positive feedback loop
Female
preferences
Reinforcement
Selection for a
male trait
Sexual dimorphism
Maladaptations
Neolamprologus callipterus has the largest sexual
dimorphism in vertebrates.
The rise of biological complexity
Data from Taft, Mattick 2004
Preliminary genome data suggest
Arabidopsis thaliana
Oryza sativa
Homo sapiens
Mus musculus
10000
• Differential increase of gene number
with genome size
• A non-linear increase in higher
animals
1000
• A linear increase in genome number
towards vascular plants
1000
10000
100000
1000000 10000000
Genome size [mB]
• A constant increase in the number
of non-coding DNA within
Eukaryotes
• High degrees of non-coding DNA in
higher Eukaryotes
• A doubling of non-coding DNA at
the prokaryote / eukaryote
boundary
• Differential trends in genome
organization in plants and animals
z
100
100
Non-coding / total DNA
Number of genes
100000
1.2
1
Eucaryotes
0.8
0.6
0.4
0.2
Procaryotes
0
100
1000
10000
100000
Genome size [mB]
1000000
10000000
genes
Number of regulatory
z
The rise of regulatory genes
900
800
700
600
500
400
300
200
100
0
Data from Croft et al. 2003
y = 2E-05x1.96
Procaryotes
0
2000
4000
6000
8000
10000
Number of genes
In prokaryotes the number of regulatory genes
rises to the quadrate of the total number of genes
The rise of biological complexity
Y=35300e
35000
x/1000000000
30000
25000
Caenorhabditis
20000
15000
Anopheles
Dictyostelium
10000
5000
100
Homo
Neurospora
Deinococcus
Nanoarchaeum
0
-5E+09
-4E+09
Plastids
First
eucaryotes
Pseudomonas
-3E+09
-2E+09
-1E+09
10
Mitochondria
Number of cell types
Number of genes
First major
oxidation
event
40000
Number of cell types
z
1000
1
0
4
3
Time before present
Billion years
Preliminary genome size data suggest
• A 2.5 fold increase of gene number per
one billion years
• An approximate 100 fold increase in gene
number within the last 4 billion years
• An initial fast increase in gene number
2
1
0
After Anbar (2008)
What factors allowed complexity to increase?
•
•
•
•
•
Rising oxygen level
Effective energy production by mitochondria
The appearance of food chains
Sex
Effective genomic repair mechanisms
The constant increase in gene number generated
a step wise increase in morphological complexity.
Numbers of genes and cell types are not correlated
Cell type estimates in higher animals highly diverge.
From Vogel, Chothia (2006)
Was Lamarck right?
Epigenetics and the heritability of acquired characters
Epigenetics refers to the editing of the genome that defines which genes will be silenced in
order to streamline protein production or squelch unnecessary redundancy.
The editing is triggered by environmental factors.
This does not permanently change the original manuscript (i.e., DNA), but merely access to
the manuscript.
Epigenetic changes might be passed through generations.
(examples are aggressive behaviour and darkness fear in mice, growth factors expression in
Humans. Cancer cells have altered epigenetic markers)
Genes (and histones) are
switched off by methylation of
nucleotids (most often Cytosine)
Triggers are long non-coding
RNAs
Epigenetic DNA editing controls cell
differentiation
Epigenetic control of DNA expression is
common in bacteria to promote a fast
genetic answer to environmental changes
In bees learning triggers a fast change (some
hours) in neuron DNA methylation and therefore
gene expression.
These changes are not heritable.
Horizontal gene transfer
The sea slug Elysia
chlorotica using
chloroplasts from ingested
green algae
Elysia incorporates genes in
her nucleus transferred from
the algal nucleus to make
photosynthesis running.
The process is not heritable.
Each young slug has first to
digest green algae.
Horizontal gene transfer is the exchange of genes between unrelated organisms.
Mechanisms are:
• viral transduction (transfer of genetic material between organisms by viruses),
• endosymbiosis,
• transformation (the uptake of foreign genetic material),
• bacterial conjugation (cell to cell contact of two bacteria).
Horizontal gene transfer is most important in
• chemical (antibiotic) restistance,
• fast adaptation to new metabolic pathways,
• fast adaptation to new trophic niches.
Horizontal gene transfer
Percentages of the genome aquired by horizontal gene transfer
From Ochman et al. (2000)
Horizontal gene transfer is very common among prokaryotes,
common among protists and
occasional among multicellular organisms
Horizontal gene transfer
Eukaryotes
Eocyta
Proterobacteria
Euryarchaea
Cyanobacteria
Operational Informational
genes
genes
Importance of
horizontal gene
transfer
Root
The ring of life
Rivera and Lake (2004) provided evidence that
the first eukaryotes resulted from the genomes
of two prokaryotes, an archaean and a
bacterium.
The model implies that mitochondria are a
basic constituent of Eukaryotes.
Proterobacteria are closest relatives to
mitochondria.
Eocyta (Crenarchaea) are thermophilous
Archaea.
In this model Eukaryotes emerged through a
fusion of two complete genomes.
Today’s Eukaryote genomes contain many
original mitochondrial genes.
Evolutionary trends and major questions
Major evolutionary trends
•
•
•
•
•
•
•
•
Divergent trends in the number of genes across clades (roughly constant in
deuterostomes, decreasing in proterostomes).
Rising number of regulatory genetic elements.
Rising morphological complexity across clades.
Rising hierarchical organization.
Rising physiological and ecological flexibility increasing the independence of
environmental conditions.
Did evolvability (the ability to cope with changing environmental conditions)
increase in evolutionary time?
Did evolvability i design decrease?
Did ecological complexity increase?
Evolutionary constraints
•
•
•
•
•
•
•
What made vertebrates prone to evolve large brains?
Why did insects never get large?
Why did plants never evolve nerves and muscles?
Why did Dinosaurs not become smart?
Why did marine taxa stop evolving since the Cambrian?
Why did major taxa (phyla) only evolve in the late Proterozoic?
Did life appear only once?
Today’s reading
Raise and fall of industrial melanism: http://www.arn.org/docs/wells/jw_pepmoth.htm
and http://www.streaming.mmu.ac.uk/cook/
Coevolution and pollination: http://biology.clc.uc.edu/courses/bio303/coevolution.htm
and http://biology.clc.uc.edu/courses/bio106/pollinat.htm
Symbiosis: an online textbook:
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/Symbiosis.html
Horizontal gene transfer:
http://www.pnas.org/cgi/reprint/104/11/4489
The ring of life:
jnason.eeob.iastate.edu:8200/courses/EEB698/papers/rivera-lake-2004.pdf
Sexual selection:
http://en.wikipedia.org/wiki/Sexual_selection
http://www.worlddeer.org/sexualselection/home.html