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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.
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.
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
In the course of evolution adaptations might become maladaptive. These are termed vestigial.
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
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.
Recently more than 500 insect pest species evolved resistance against major classes of insecticides.
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
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
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.
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
13 species evolved within a few mya
Adaptive radiation refers to a fast rate of speciation within a lineage (fast cladogenesis)
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.
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
Birds of paradise
pseudoobsura/persimilissimaulans/mauritianapseudoobscura/mirandapicticornis/16 other speciesmelanogaster/simulansyakuba/teissierorena/erecta
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 alsosexual selection.
Cichlidae of Lake Malawi
Intrasexual selection (male - male competition)
Sexual selection might cause maladaptive traits
Northern sea elephants
Selection for a male trait
Sexual dimorphism Maladaptations
Neolamprologus callipterus has the largest sexual dimorphism in vertebrates.
Data from Taft, Mattick 2004
Data from Croft et al. 2003
In prokaryotes the number of regulatory genes rises to the quadrate of the total number of genes
Number of cell types
After Anbar (2008)
The constant increase in gene number generated a step wise increase in morphological complexity.
Cell type estimates in higher animals highly diverge.
From Vogel, Chothia (2006)
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
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
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
Importance of horizontal gene transfer
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.
Major evolutionary trends
Raise and fall of industrial melanism: http://www.arn.org/docs/wells/jw_pepmoth.htm
Coevolution and pollination: http://biology.clc.uc.edu/courses/bio303/coevolution.htm
Symbiosis: an online textbook: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/Symbiosis.html
Horizontal gene transfer:
The ring of life: