Selection, adaptation, and the rise of biological complexity

Selection needs variation

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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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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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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

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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

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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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First major oxidation

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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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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