12. Selection, adaptation - PowerPoint Presentation

Slide1

12. 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. Slide2

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 adaptat

i

ons 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 taskAdaptive: adaptations increase fitness

In the course of evolution adaptations might become maladaptive. These are termed vestigial.Slide3

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 Slide4

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 betulariaSlide5

Pesticide resistance in insects

Recently more than 500 insect pest species evolved resistance against major classes of insecticides.Slide6

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 similarSlide7

Wasmannian mimicry

A harm

less

species mimics another to live in the

same nest or structure

Some tropical jumping spi

d

ers mimic ants

A predator species mimics its prey species

A tropical spider mimics a prey beetle species

Peckhamian mimicrySlide8

Myxomatosis and rabbits

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 vaccinationSlide9

Coevolution: flowering plants and pollinators

Lamarouxia hyssophifolia

is hummingbird pollinated

Emorya suaveloens

is butterfly pollinated

Magnolia grandiflora

is beetle pollinated

Lamarouxia xalapensis

is bee pollinatedSlide10

Coadaptations

Figs produce

f

lowers 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 f

ig 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 diversificationSlide11

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)Slide12

Adaptive radiation

Number of genera of Ammonites

Adaptive radiation refers to a fast increase of species richness.

This increase is related to the ac

c

quition of features that allow for the invasion into previously unoccupied ecological niches and/or habitats.Slide13

Fast occupation of empty niches means initially:

low degree of competitionlow selection pressureproportionally higher fitness of aberrant individuals

wider morphological, behavioural or dispersal potentialHigher probability of speciationSlide14

Drosophila from Hawaii

Hawaiian Drosophila

D. pseudoobsura/subobscura

pseudoobsura/persimilis

simaulans/mauritiana

pseudoobscura/miranda

picticornis/16 other species

melanogaster/simulans

yakuba/teissier

orena/erecta

Paleogene

Neogene

35

23

5

1

Drosophila

with spotted wings Slide15

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 MalawiSlide16

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 selection

Sexual selection

Peacock

Intrasexual selection

(male - male competition)

Sexual selection might cause maladaptive traitsSlide17

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

Data from Taft, Mattick 2004Slide18

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 Slide19

After

Anbar (2008)

What factors allowed complexity to increase?

Rising oxygen level

The appearance of food chains

Sex

Effective genomic repair mechanisms

The rise of biological complexity

Number 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. Slide20

Numbers of genes and cell types are not correlated

From Vogel, Chothia (2006)

Cell type estimates in higher animals highly diverge.Slide21

Eight major transitions in evolutionary history adapted from John Maynard Smith, Eros Szathmary (1995)

Replicating molecules Populations of molecules in protocells

Cell membranes provide selective barriers, increased metabolic efficacy Independent replicators Chromosomes

Reduced competition among genes

RNA as gene and enzyme DNA genes, protein enzymes

Efficient catalysators and replicators

Procaryotes Cells with nucleus and organelles (eukaryotes)

Effective metabolisms, increased interior surfacesAsexual clones Sexual populations Gene repair, higher adaptive potential

Single-celled organisms Multicellular organisms Efficient division of labour, competitive advantage in early food websSolitary individuals Colonies of non-reproductive casts Efficient division of labour, maximized inclusive fitness

Primate societies Human societies Effective managing of environmental changes, high dispersal abilitySlide22

„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-chaetes

Cyano-bacterium

Unikont

Bikont plant

Fungi

Animal

Mitochondria

Flagellum

Plastids

Lichen: Ascomycetes+Cyanobacteria

Acyrthosiphon pisum

Photo: J. White, N. Moran

Buchnera aphidicola

Symbiontic

Bacteria

Aphid nucleus

Mitochondria

Four genomes in one cell

NucleusSlide23

Coevolution of endosymbiosis

Proteus vulgaris

Escherichia coli

Pemphigus betae

Schlectendalia chinensis

Melaphis rois

Diuraphis noxia

Acyrtosiphon pisum

Myzus persicae

Rhopalosiphum padi

Rhopalosiphum maidis

Schizaphs graminum

Uroleucon sonchi

30-80 mya

80-120 mya

Chaitophorus viminalis

Mindarus 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 evo

l

utionary arms races.Slide24

Horizontal gene transfer

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)

From Ochman et al. (2000)Slide25

Horizontal gene transfer

Eukaryotes

Euryarchaea

Cyanobacteria

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 A

r

chaea.

In this model Eukaryotes emerge

d

through a fusion of two complete genomes.

Today

’

s Eukaryote genomes co

n

tain many original mitochondrial genes.

Importance of horizontal gene transfer

The model implies that mitochondria are a basic constituent of Eukaryotes.Slide26

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.htmlHorizontal 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.pdfSexual selection:

http://en.wikipedia.org/wiki/Sexual_selectionhttp://www.worlddeer.org/sexualselection/home.html