12. Selection, adaptation, and the rise of biological complexity
Selection needs variation
0
20
40
60
80
100
0 20 40 60 80 100
Cumulative percentage of individuals
Cu
mu
latv
e p
erc
en
tag
e
x
of f
ruits
Oeceoclades maculataLepanthes wendlandiiEncyclia cordigera
Differences in reproductive success of three Orchid species
Isocline
Most species have great variation in reproductive success.
This variation is the basis for natural selectionthat means changes in gene frequencies.
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
00.10.20.30.40.50.60.70.80.9
1
1955 1965 1975 1985 1995 2005Year
Pro
po
rtio
n o
f th
e
z
me
lan
ic fo
rm
z
Industrial melanism
Biston betularia was in England represented by its light variation.
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.
Biston betularia
Pesticide resistance in insects
0
100
200
300
400
500
1940 1950 1960 1970 1980 1990Year
# s
pe
cie
s z
Pyrethroids
Carbamates
Organophosphates
Cyclodienes
DDT
Total
Recently more than 500 insect pest species evolved resistance against major classes of insecticides.
Mimicry
Batesian mimicry Müllerian mimicry
A harmless species mimics an unpalatable or poisonous species
A tropical fly mimics a bee
Several unpalatable or poisonous species have similar warning colours
Two tropical butterflies look similar
Wasmannian mimicry
A harmless species mimics another to live in the same
nest or structure
Some tropical jumping spiders mimic ants
A predator species mimics its prey species
A tropical spider mimics a prey beetle species
Peckhamian mimicry
I II III IV V1953 100 0 0 0 0
1962-1967 3 15.1 71.1 10.3 0.71968-1970 0 0 100 0 01971-1973 0 3.3 93.4 3.3 01974-1976 1.3 23.3 66.8 8.6 01977-1980 0 30.4 65.3 4.3 0
Virulence grade
Myxomatosis and rabbits
Period MortalityUnselected rabbits 1001961-1966 941967-1971 901972-1975 85
Virulence of myxoma virus
Mortality of rabbits
Virulence and mortality after the introduction of the myxoma virus in Australia to control the population of
European rabbits (Oryctolagus cuniculus).
The virus lost virulence and the rabbit evolved resistance.
The myxoma virus causes skin tumours in European rabbits.
In 1938 it was introduced in Australia and since 1950 it spreads throughout
Europe.
Their is a campaign for vaccination
Coevolution: flowering plants and pollinators
Lamarouxia hyssophifoliais hummingbird pollinated
Emorya suaveloensis butterfly pollinated
Magnolia grandiflorais beetle pollinated
Lamarouxia xalapensisis bee pollinated
Coadaptations
Figs produce flowers within inflorescences
Pollination and egg laying
Fig wasps emerge from their galls and
mate.
Most species are tree specific and find their
tree due to allochemicals produced
by this fig species.
The female fig wasp has to enter the gall
through a tiny opening.
The female body is particularly adapted
to this task.
Wasps develop within the galls
Galls are dispersed by fruit eaters
After pollination galls change colours and smells and become
attractive to fruit eating birds, bats,
monkeys, and lizards.
The 900 fig tree species produce flowers concealed within an enclosed inflorescence, the fig.
600 species of fig wasps (Agaonidae) form a mostly tropical
family of chalcid wasps that are morphologically and ecologically specialized fig tree pollinators.
A fig wasp pollinates and lays eggs.
The high degree of specializaton leads to fast diversification
Adaptive radiations
Darwin finches
13 species evolved within a few mya
Adaptive radiations mainly occur • when new adaptive peaks have been
reached• on newly colonized islands
Adaptive radiation refers to a fast rate of speciation within a lineage (fast
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
Drosophila from Hawaii
Hawaiian Drosophila
D. pseudoobsura/subobscura
pseudoobsura/persimilissimaulans/mauritianapseudoobscura/mirandapicticornis/16 other speciesmelanogaster/simulansyakuba/teissierorena/erecta
Paleogene
Neogene
23
5
1
Drosophila with spotted wings
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.
One explanation is sexual selection.
Freshwater fish of the great East African lakes
Cichlidae of Lake Malawi
Female preferences
Selection for a male trait
Reinforcement
Sexual dimorphism Maladaptations
Fisherian positive feedback loop
Neolamprologus callipterus has the largest sexual dimorphism in vertebrates.
Northern sea elephants
Intersexual selectionSexual selection
Peacock
Intrasexual selection (male - male competition)
Sexual selection
might cause maladaptive
traits
100
1000
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100000
100 1000 10000 100000 1000000 10000000
Genome size [mB]
Nu
mb
er
of g
en
es
Arabidopsis thalianaOryza sativa Homo sapiens
Mus musculus
The rise of biological complexity
Preliminary genome data suggest
• Differential increase of gene number with genome size
• A non-linear increase in higher animals
• A linear increase in genome number towards vascular plants
• Differential trends in genome organization in plants and animals
• A constant increase in the number of non-coding DNA within Eucaryotes
• High degrees of non-coding DNA in higher Eucaryotes
• A doubling of non-coding DNA at the procaryote / eucaryote boundary 0
0.2
0.4
0.6
0.8
1
1.2
100 1000 10000 100000 1000000 10000000
Genome size [mB]
No
n-c
od
ing
/ to
tal D
NA
z
Procaryotes
Eucaryotes
Data from Taft, Mattick 2004
y = 2E-05x1.96
0
100200
300
400500
600
700800
900
0 2000 4000 6000 8000 10000
Number of genes
Nu
mb
er
of r
eg
ula
tory
z
ge
ne
s
Procaryotes
The rise of regulatory genes
Data from Croft et al. 2003
In prokaryotes the number of regulatory genes rises to the quadrate of the total number of genes
1
10
100
1000
01234
Num
ber o
f cel
l typ
es
Billion years
First major oxidation
event
MitochondriaFirst eucaryotes
Plastids
After Anbar (2008)
What factors allowed complexity to increase?
• Rising oxygen level• The appearance of food chains • Sex• Effective genomic repair mechanisms
0
5000
10000
15000
20000
25000
30000
35000
40000
-5E+09 -4E+09 -3E+09 -2E+09 -1E+09 0
Time before present
Nu
mb
er
of g
en
es
z
Caenorhabditis
Anopheles
Homo
DictyosteliumNeurospora
PseudomonasDeinococcus
Nanoarchaeum
Y=35300ex/1000000000
The rise of biological complexityN
umb
er of cell typ
es
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
The constant increase in gene number generated a step wise increase in morphological complexity.
Numbers of genes and cell types are not correlated
From Vogel, Chothia (2006)
Cell type estimates in higher animals highly diverge.
Eight major transitions in evolutionary history
adapted from John Maynard Smith, Eros Szathmary (1995)
Replicating molecules Populations of molecules in protocells
Cell membranes provide selective barriers, increased metabolic efficacy
Independent replicators Chromosomes
Reduced competition among genes
RNA as gene and enzyme DNA genes, protein enzymes
Efficient catalysators and replicators
Procaryotes Cells with nucleus and organelles (eukaryotes)
Effective metabolisms, increased interior surfaces
Asexual clones Sexual populations
Gene repair, higher adaptive potential
Single-celled organisms Multicellular organisms
Efficient division of labour, competitive advantage in early food webs
Solitary individuals Colonies of non-reproductive casts
Efficient division of labour, maximized inclusive fitness
Primate societies Human societies
Effective managing of environmental changes, high dispersal ability
„Life did not take over the globe by combat, but by networking” Lynn Margulis
Symbiosis are species interactions where species live in close association over a longer time period
In symbiosis, at least one member of association benefits from the relationship. The other members may be
injured = parasitism relatively unaffected ( = commensalism)
may also benefit ( = mutualism)
Aerobic Proterobacterium Archaea Spiro-
chaetesCyano-
bacterium
Unikont
Bikont plant
Fungi
Animal
Mitochondria
Flagellum
Plastids
Lichen: Ascomycetes+CyanobacteriaAcyrthosiphon pisum
Photo: J. White, N. Moran
Buchnera aphidicolaSymbionticBacteria
Aphid nucleus
Mitochondria
Four genomes in one cell
Nucleus
Coevolution of endosymbiosisProteus vulgaris
Escherichia coli
Pemphigus betae
Schlectendalia chinensis
Melaphis rois
Diuraphis noxia
Acyrtosiphon pisum
Myzus persicae
Rhopalosiphum padi
Rhopalosiphum maidisSchizaphs graminumUroleucon sonchi
30-80 mya
80-120 mya
Chaitophorus viminalis
Mindarus victoriae
80-160 mya
50-70 mya
Bacterial lineages Aphid host lineages
Origin of endosymbiontic association
Coevolutionary studies can gives estimates about the age of
lineages.
It might cause evolutionary arms races.
Horizontal gene transfer
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)
From Ochman et al. (2000)
Horizontal gene transfer
Eukaryotes
EuryarchaeaCyanobacteria
Root
Proterobacteria
Operational genes
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.
Eocyta
Informational genes
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.
Importance of horizontal gene transfer
The model implies that mitochondria are a basic constituent of Eukaryotes.
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
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