12. Selection, adaptation, and the rise of biological complexity

Selection needs variation

0

20

40

60

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100

0 20 40 60 80 100Cumulative percentage of individuals

Cum

ulat

ve p

erce

ntag

e

x o

f fru

its

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

porti

on o

f the

z

mel

anic

form

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

# sp

ecie

s z

PyrethroidsCarbamatesOrganophosphatesCyclodienes

DDTTotal

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

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100 1000 10000 100000 1000000 10000000

Genome size [mB]

Num

ber o

f gen

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

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1

1.2

100 1000 10000 100000 1000000 10000000

Genome size [mB]

Non

-cod

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/ to

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NA

z

Procaryotes

Eucaryotes

Data from Taft, Mattick 2004

y = 2E-05x1.96

0100200300400500600700800900

0 2000 4000 6000 8000 10000

Number of genes

Num

ber o

f reg

ulat

ory

z

gene

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

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5000

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20000

25000

30000

35000

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-5E+09 -4E+09 -3E+09 -2E+09 -1E+09 0

Time before present

Num

ber o

f gen

es

z

Caenorhabditis

Anopheles

Homo

DictyosteliumNeurospora

PseudomonasDeinococcus

Nanoarchaeum

Y=35300ex/1000000000

The rise of biological complexityN

umber of cell

types

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 protocellsCell membranes provide selective barriers, increased metabolic efficacy

Independent replicators ChromosomesReduced competition among genes

RNA as gene and enzyme DNA genes, protein enzymesEfficient catalysators and replicators

Procaryotes Cells with nucleus and organelles (eukaryotes)Effective metabolisms, increased interior surfaces

Asexual clones Sexual populationsGene repair, higher adaptive potential

Single-celled organisms Multicellular organismsEfficient division of labour, competitive advantage in early food webs

Solitary individuals Colonies of non-reproductive castsEfficient division of labour, maximized inclusive fitness

Primate societies Human societiesEffective 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 pisumPhoto: 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 noxiaAcyrtosiphon pisumMyzus persicae

Rhopalosiphum padiRhopalosiphum maidisSchizaphs graminumUroleucon sonchi

30-80 mya

80-120 mya

Chaitophorus viminalisMindarus 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 transferHorizontal 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