Selection, adaptation, and the rise of biological complexity
Selection needs variation
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Cumulative percentage of individuals
Cu
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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.
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.
Sex differences in reproductive output and variance
Bateman's principle : the reproductive variance is generally greater in males than in females.
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Latrodectus hasselti
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
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1955 1965 1975 1985 1995 2005Year
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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
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1940 1950 1960 1970 1980 1990Year
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Pyrethroids
Carbamates
Organophosphates
Cyclodienes
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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
Adaptation to herbivory and promiscuity might cause high rates of speciation
Cucujoidea< 10000 species
Curculionoidea> 200000 species
Trichoptera< 10000 species
Lepidoptera> 300000 species
Herbivores Herbivores
Predators Detritivores
Manucodes5 species
Birds of paradise33 species
Hummingbirds319 species
Promiscuity PromiscuityPair bonds Pair bonds
Change in feeding style
Change in mating systemSwifts
103 species
Drosophila from Hawaii
Hawaiian Drosophila
D. pseudoobsura/subobscura
pseudoobsura/persimilissimaulans/mauritianapseudoobscura/mirandapicticornis/16 other speciesmelanogaster/simulansyakuba/teissierorena/erecta
Paleogene
Neogene
23
3
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.
Genetic studies revealed very fast changes in genes responsible for trophic niches.
Important is also 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
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Genome size [mB]
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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 Eukaryotes
• High degrees of non-coding DNA in higher Eukaryotes
• A doubling of non-coding DNA at the prokaryote / eukaryote boundary 0
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Procaryotes
Eucaryotes
Data from Taft, Mattick 2004
y = 2E-05x1.96
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Number of genes
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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
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Billion years
First major oxidation
event
MitochondriaFirst eucaryotes
Plastids
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
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Time before present
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Caenorhabditis
Anopheles
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DictyosteliumNeurospora
PseudomonasDeinococcus
Nanoarchaeum
Y=35300ex/1000000000
The rise of biological complexityN
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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.
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 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.
Epigenetic DNA editing controls cell differentiation
The sea slug Elysia chlorotica using
chloroplasts from ingested green algae
Horizontal gene transfer
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
From Ochman et al. (2000)
Horizontal gene transfer is very common among prokaryotes, common among protists and occasional among multicellular organisms
Percentages of the genome aquired by horizontal gene transfer
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.
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