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Lecture 13 The source of novelty Lecture 13 The source of novelty Natural Selection Adaptive Radiation Mutations Hybridization Polyploidy Introduction Every species is adapted to a combination of factors (Phy. Environment, Range of variation, food supply, competition,

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slide1

Lecture 13

The source of novelty

slide2

Lecture 13

The source of novelty

Natural Selection

Adaptive Radiation

Mutations

Hybridization

Polyploidy

slide3

Introduction

Every species is adapted to a combination of factors

(Phy. Environment,

Range of variation,

food supply,

competition,

occasional losses due to disease,

predation)

Puts demands on the Structure or Physiology of the organism

Some are obvious and some are more complex

slide4

Introduction

Early 19th Century

“accepted that each species had always

existed precisely as we now see it”

God was thought to have created each one

(including adaptations, and that these remained

unchanged through time)

slide5

“It (biological design) indeed doesdestroy the most

powerful arguments of God”.

Famous Reply of French

Mathematician

Pierre Simon de Laplace

(1749-1827)

to Napoleon is now

truer than ever.

Laplace argued for Biological design by natural

selection rather than divine creation.

slide6

Introduction

Explanation for Fossils

God had destroyed the species

during Catastrophes!

e.g. The Biblical Flood

slide7

Darwin’s Journey Around the World-HMS Beagle

Two Observations: Galapagos Islands/Mainland South America

Reconsidered the assumptions of the day (Finches and Fossils)

slide9

Natural Selection:

Basic Philosophy of Biological Science

Published by Darwin in 1858.

Natural selection is the evolutionary process by which

favorable traits that are heritable become more common in

successive generations of a population of reproducing

organisms and unfavorable traits that are heritable become

less common.

slide10

Natural Selection:

Natural selection acts on the phenotype, or the observable

characteristics of an organism, such that individuals with

favorable phenotypes are more likely to survive and

reproduce than those with less favorable phenotypes.

slide11

Natural Selection:

“The favorable phenotypes will have a

natural advantage in the competition for life”

“They will survive at the expense of their less fortunate

Relatives,”

“by their survival and eventual mating the process of NS will

to the persistence of these favorable characteristics”

slide12

Natural Selection:

So why should each species not be able to evolve

to one single answer to the demands that the

environment makes upon it?

All flowers of a particular plants species would then have

the same color? every sparrow have the same beak size?

Such a simple solution is not possible, because the Env.

is neither stable nor uniform

slide13

Natural Selection in Action

Darwin\'s Finches (Flock from SA 2-3 mya)

Darwin\'s finches are an excellent example

of the way in which species\' gene pools

have adapted in order for long term survival

via their offspring.

Once thought that evolution took place too

slowly for it to be detectable over the

timescale of scientific studies of living organisms-but no!

Adaptive Radiation: evolve and radiate into ways not

formerly available to it

slide14

Adaptive Radiation

In an adaptive radiation, a "founder" species enters a new environment

with many unoccupied niches.

This species expands (radiates) and evolves adaptations to fit

these niches better.

The process of becoming adapted to these different niches may

lead to, and in these cases has led to, the formation of new species.

slide15

Natural Selection in Action

Darwin\'s Finches

The finches hold a unique place in the history of science.

The birds, which live only on the Galapagos, were studied closely

by Charles Darwin on his Beagle voyage in the 1830s.

Observations on the shapes of the birds\' beaks were central in

helping Darwin formulate his theory of evolution.

slide16

Natural Selection in Action

Darwin\'s Finches

Among the Darwin\'s finches, there is general

agreement as to the existence of 13 Galapagos species, although there may be one or two more or one or two less,

depending on how one assesses several unusual populations.

slide17

Darwin\'s 13 Finches

Narrow Bills

-live on the ground and

feed on insects, snails etc

Strong, heavy bills

-live in cactus thickets, feed

on cactus seeds, flowers, pollen

Most live in bushes/trees

-feed on seeds, nuts, fruits

slide18

Darwin\'s Finches

Difficult to separate out!

Even for

Ornithologist’s

slide20

Natural Selection in Action

Darwin\'s Finches

All the species of finches on the Galápagos Islands appear

morphologically very similar, varying mostly in terms of

beak size and behavior; they all look very much like a

species of finch from the mainland of South America.

This suggests that all the finches on the Galápagos are descended

from one original colonist species that went through an adaptive

radiation.

slide21

Natural Selection in Action

Darwin\'s Finches

The Darwin\'s Finches diagram illustrates the way the

finch has adapted to take advantage of feeding in different

ecological niche\'s.

slide22

Natural Selection in Action

Darwin\'s Finches

Their beaks have evolved over time to be best suited to their function.

For example, the finches who eat grubs have a thin extended beak to

poke into holes in the ground and extract the grubs.

slide24

Natural Selection in Action

Darwin\'s Finches

Finches who eat buds and fruit would be less successful at

doing this, while their claw like beaks can grind down their

food and thus give them a selective advantage in circumstances

where buds are the only real food source for finches.

slide26

Galápagos Islands

Because of the small, isolated environment of the Galápagos,

the finches have become the topic of extensive

study into natural selection.

The studies that have been conducted on the finches show strong

selection for larger beaks during droughts (e.g. 1977).

slide27

Galápagos Islands

The studies that have been conducted on the finches show

strong selection for larger beaks during droughts

(11 mm ideal for drought years).

slide28

Galápagos Ground Finches with beaks of different size.

(11 mm ideal for drought years).

Tribulus Fruits-some

Having been opened by

Finches, who have

removed the seeds leaving

holes

slide29

Beak depth, which is correlated with body size and the ability to

crack larger seeds, varies according to drought conditions,

which produce fewer, harder seeds in dry years and more and

softer seeds in wet years. The change is ±5% in extreme years.

The graph shows a pattern of stabilizing selection, in which beak

depth fluctuates around a mean of about 9.6mm.

slide30

Galápagos Islands

These data show that climatic changes can have profound effects on

the morphology of a species and potentially lead to the formation

of new species.

slide31

Galápagos Islands

Short term climatic change

Rainfall

Finch population

Biomass of small seeds

slide32

The difficulty in identifying the finches is rooted in precisely what

makes them so interesting and important -the evolutionary process.

If we believe that two species share a common ancestor,

then as one traces the species back in time, they should become

closer and closer in form.

At the branch point, the species should become ambiguous.

That is precisely the point at which we find the Darwin\'s finches.

slide33

They are in the process of separating, but they haven\'t completely

done so at this point in time.

The definition of the term "species" includes the presence

of a fertility barrier between individuals of different species.

  • In the case of Darwin\'s finches, those barriers are not completely
  • formed yet, and there is a certain amount of documented
  • hybridization between species.
  • This also contributes to the ambiguity of the birds.
slide34

Our current understanding of evolution is that new species are born

when the population of the ancestor species is split.

Once the gene pool is separated, the two populations may be

subject to different natural selection pressures, and hence,

evolve in separate ways.

slide36

The splitting of a population followed by subsequent evolution is known as allopatric speciation.

slide37

Our current understanding of evolution is that new species are born

when the population of the ancestor species is split.

Once the gene pool is separated, the two populations may be

subject to different natural selection pressures, and hence,

evolve in separate ways.

The splitting of a population followed by subsequent evolution is known as allopatric speciation.

At some point, the populations may come back together again,

that is, they may become sympatric.

slide41

Darwin\'s finches have many other evolutionary tales to tell.

  • Darwin himself used the finches in the The Voyage of the Beagle to
  • quietly announce the theory of evolution:
    • "Seeing this gradation and diversity of structure in one small,
    • intimately related group of birds, one might really fancy
    • that from an original paucity of birds in this archipelago,
    • one species had been taken and modified for different ends."
slide42

Interesting side note

When Darwin visited the Galápagos, he observed and collected

some of the finch species, believing that they represented a very

diverse set of birds that were not closely related.

slide43

Interesting side note

When Darwin visited the Galápagos, he observed and collected

some of the finch species, believing that they represented a very

diverse set of birds that were not closely related.

Their significance was not recognized until later,

when ornithologist John Gould pointed out that the birds were

all closely related finches

slide44

Interesting side note

When Darwin visited the Galápagos, he observed and collected

some of the finch species, believing that they represented a very

diverse set of birds that were not closely related.

Their significance was not recognized until later,

when ornithologist John Gould pointed out that the birds were

all closely related finches

But because Darwin originally collected some of the specimens

and because the finches showed so much evidence for evolution

and natural selection, they have been dubbed "Darwin\'s finches."

This has led many people to conclude (mistakenly) that Darwin\'s

theory of evolution was specifically inspired by the finches

slide45

Controlling Forces Within the organism

Mutations

Sudden alterations in the genetic make up of individuals.

Sometimes there is a slight error from time to time the in

gene duplication during cell division

(biological a very complex process and mistakes occur!).

Cell-Nucleus-Chromosomes-Genes-Alleles (different versions of the

Gene -hair color (brown, red, black, blonde)

slide46

Controlling Forces Within the organism

Mutations

Changes in the genetic system can lead to changes in the

characteristics of an isolated population in two ways.

Mutations may appear and prove advantageous

Second, each ind. carries several thousand genes, and each maybe

present in one of its several thousand alleles, no two

individuals carries the same genetic code or genotype-unless

they are identical twins.

slide47

Controlling Forces Within the organism

Mutations

Inevitably, isolated populations will come to differ from others

in its genetic content, some alleles being rarer or absent.

As mating continues new combinations appear leading to

further differences later

slide48

Controlling Forces Within the organism

Genetic Drift

In small populations, where chance plays a greater role

in controlling whether a particular allele becomes common or

Rare or disappears.

Smaller populations contain less genetic variability and

are closely adapted to the environment.

slide49

Controlling Forces Within the organism

Phenotype

The way in which a genotype of an organism is expressed in

its morphology, physiology, behavior etc is known

as the phenotype.

Plasticity of an organism-adapted to the demands of

the environment

slide50

Hybridization

(Hybrids of Two Independent Pops-usually along a

narrow zone of contact where the two meet).

The offspring of two different species, or of two different genera.

Once separated (barriers), they speciate in isolation, but once they

are re-united they can still interbreed-resulting in reduced fertility or

sterility.

slide51

Hybridization

(Hybrids of Two Independent pops-usually along a

narrow zone of contact where the two meet)

Mule, a cross of female horse and a male donkey.

Hinny, a cross between a female donkey and a male horse.

slide52

Hybridization

Natural interspecific hybridization in oaks (Quercus):

California Black Oak (Q. kelloggii), a tall, deciduous tree;

Interior Live Oak (Q. wislizenii var. frutescens),

a large, evergreen shrub;

C. Oracle Oak (Q. x morehus), a small, partly deciduous tree

that retains numerous leaves during the winter months.

slide53

Polyploidy:

the condition of having three, four, or more sets of

chromosomes instead of the two present in diploids.

Is the doubling of the whole set

of chromosomes in the nucleus

of a developing egg or seed,

so that each has a identical

partner. This is an important

mechanism in speciation.

slide54

Polyploidy

Common in groups in which self fertilize:

e.g. weeds, wheat breads of the world,

potatoe, sugar cane, coffee, maize,

cabbage!

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