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Selection , adaptation , and the rise of biological complexity. Selection needs variation. Most species have great variation in reproductive success . This variation is the basis for natural selection that means changes in gene frequencies.

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Selection, adaptation, and the rise of biological complexity

Selection needs variation

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 isabout 80%.

In Poland it’sabout 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 reproductiveoutput and variance


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

Biston betularia

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.


Pesticide resistance in insects

Recently more than 500 insect pest species evolved resistance against major classes of insecticides.



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

Some tropical jumping spiders mimic ants

A tropical spider mimics a prey beetle species

A harmless species mimics another to live in thesame nest or structure

A predator species mimics its prey species


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.

Their is a campaign for vaccination

Virulence of myxoma virus

Mortality of rabbits

The virus lost virulence and the rabbit evolved resistance.


Coevolution: flowering plants and pollinators

Lamarouxia hyssophifoliais hummingbird pollinated

Emorya suaveloensis butterfly pollinated

Lamarouxia xalapensisis bee pollinated

Magnolia grandiflorais beetle pollinated



The 900 fig tree species produce flowers concealed within an enclosed inflorescence, the fig.

A fig wasppollinates and lays eggs.

Fig wasps emerge from their galls and mate.

Wasps develop within the galls

Pollination and egg laying

After pollination galls change colours and smells and become attractive to fruit eating birds, bats, monkeys, and lizards.

Figs produce flowers within inflorescences

Galls are dispersed by fruit eaters

The female fig wasp has to enter the gall through a tiny opening.The female body is particularly adapted to this task.

Most species are tree specific and find their tree due to allochemicals produced by this fig species.

600 species of fig wasps (Agaonidae) form a mostly tropical family of chalcid wasps that are morphologically and ecologically specialized fig tree pollinators.

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

Change in feeding style


< 10000 species


> 200000 species


< 10000 species


> 300000 species





Change in mating system


5 species


319 species

Birds of paradise

33 species

Swifts103 species

Pair bonds


Pair bonds



Drosophila from Hawaii

pseudoobsura/persimilissimaulans/mauritianapseudoobscura/mirandapicticornis/16 other speciesmelanogaster/simulansyakuba/teissierorena/erecta




D. pseudoobsura/subobscura



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 alsosexual selection.

Cichlidae of Lake Malawi


Sexual selection

Intersexual selection

Intrasexual selection (male - male competition)

Sexual selection might cause maladaptive traits

Northern sea elephants



Female preferences


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
  • 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

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


The rise of biological complexity

Number of cell types

After Anbar (2008)

  • 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
  • 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)

Epigenetic DNA editing controls cell differentiation

Genes (and histones) are switched off by methylation of nucleotids (most often Cytosine)

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.

Triggers are long non-coding RNAs


Horizontal gene transfer

Elysiaincorporates 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.

The sea slug Elysiachloroticausing chloroplasts from ingested 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






Importance of horizontal gene transfer

Operational genes

Informational genes


Proterobacteria are closest relatives to mitochondria.

Eocyta (Crenarchaea) are thermophilous Archaea.

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.

In this model Eukaryotes emerged through a fusion of two complete genomes.

Today’s Eukaryote genomes contain many original mitochondrial genes.

The model implies that mitochondria are a basic constituent of Eukaryotes.


Evolutionary trends and major questions

Major evolutionary trends

  • Divergenttrends in thenumber of genes across clades (roughlyconstant in deuterostomes, decreasing in proterostomes).
  • Risingnumber of regulatory geneticelements.
  • Rising morphological complexity across clades.
  • Rising hierarchical organization.
  • Rising physiological and ecological flexibilityincreasing the independence of environmentalconditions.
  • Didevolvability (the ability to cope with changing environmental conditions)increase in evolutionarytime?
  • Didevolvabilityi design decrease?
  • Didecologicalcomplexity 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:


Coevolution and pollination:


Symbiosis: an online textbook:

Horizontal gene transfer:

The ring of life:

Sexual selection: