ecological genetics: adaptation and natural selection

Ecological Genetics:Adaptation

and Natural Selection

Prepared by: Jaycris C. Agnes

“Survival of the Fittest.”

Ecology is the science of

adaptation.

Genetic variation is the ingredient for

Natural Selection.

Prepared By: Jaycris C. Agnes 5

Mutation: inheritable changes in a gene or a chromosomeGene mutation: (point mutation)

Chromosome mutation deletion, duplication, inversion, translocation

Genetic RecombinationSexual reproduction

two individuals produce haploid gametes (egg or sperm) – that combine to form a diploid cell or zygote.

Reassortment of genes provided by two parents in the offspringIncreases dramatically the variation within a population by

creating new combinations of existing genes.

Asexual reproduction: less variation (only mutation)

Sources of Genetic Variation

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Nature Selection as a Force of Evolution

What is Darwin’s Natural Selection?

The differential success (survival and reproduction) of individuals within the

population that results from their interaction with their environment.

“Survival of fitness, elimination of ‘inferior’ individual”7-20-2014


There is variation in populations. Variation is heritable. In every generation some organisms are more successful

at surviving and reproducing than others. Survival and reproduction are not random, but are related to variation among individuals. Organisms with best characteristics

are ‘naturally selected.’

If 2 conditions are met then the population will change from one generation to the next. Evolution will occur.

Two Conditions in Natural Selection

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Prepared By: Jaycris C. Agnes 87-20-2014


Evolution by Natural Selection

The major factors affecting the organisms’ survival in the system is Fitness.

Darwinian fitness: ability of an organism to survive and reproduce in its environment.

Adaptation is a characteristic or trait of an organism that increases its fitness relative to

individuals that do not possess it. It is an inherited characteristic that increases the ability of an organism

to survive and reproduce.7-20-2014


Peter and Rosemary Grant

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Geospiza fortis

Medium Ground Finch

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Variation in Beak Size

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Before and After Natural Selection

In 1978, there was a severe drought, small

seeds declined more than large seeds.

Small beak birds have difficult to find seeds, and suffered heavy mortality,

especially females.

Conclusion:Beak size

evolve through Natural

Selection.7-20-2014

Types of Natural Selection


Directional Selection

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Directional Selection

Examples:

A long time ago…Small horses died: very disadvantageousMedium horses died: disadvantageousLarge horses prospered: advantageous

A long time ago…Short neck giraffes died: could not reach

leaves on treeMedium neck giraffes died: could not

reach leaves on treeLong neck giraffes prospered: leaves

were reachable

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Very light-colored or very dark-colored oysters might be more frequently preyed upon by

shore birds, simply because they are

more obvious on the oyster bar; as a

result, the intermediate hues

become more common.

Stabilizing Selection

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Stabilizing Selection

Examples:

Short flowers die: No sunlightMedium flowers live: Perfect conditionsTall Flowers die: Wind damage

Lightweight babies have higher mortality rate: weakerAverage weight babies survive more often: healthyHeavyweight babies have higher mortality rate: when being born 7-20-2014


This might happen in shallow water among rocks.

Light-colored oysters are more cryptic (less easy for a

predator to see) because they match the rock color.

Dark-colored oysters blend into the shadows cast by the

rocks. In this case, intermediate-colored oysters

would be most heavily preyed upon by the crabs,

and very light and very dark oysters would survive to

reproduce.

Disruptive Selection

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Disruptive Selection

Examples:In an environment with black and white rocks…White rabbit lives: CamouflagedGrey rabbit dies: Seen by predatorBlack rabbit lives: Camouflaged

In an environment with deep and shallow flowers…Short beak hummingbird lives: can get pollen from flowerMedium beak hummingbird dies: cannot get pollen from flowerLong beak hummingbird lives: can get pollen from flower

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Five Causes of Evolution

• Mutations• Gene flow - Emigration and immigration of

individuals (Flow of alleles)• Genetic Drift – Changes in the gene pool of a

small population due to chance• Nonrandom mating: (AA mates AA, Aa) • Natural Selection

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Evolution is a change in Gene Frequency

Evolution is a change of gene frequencies within a population (or species) over time

Individuals do not evolve, populations evolve.Focus on gene pool, collective.

But why do we see populations are still the ‘same’ over many generations?

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The Hardy-Weinberg Principle

The Hardy-Weinberg Principle:

Gene frequencies will remain the same in successive generations of a sexually reproducing population if the following five conditions hold:

– Random mating

– There is no mutation

– The population is very large

– There is no selection

– There is no migrations (isolated from other populations)7-20-2014


The Hardy-Weinberg Principle

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The variation in environmental conditions often give rise to a corresponding variation

in morphological, physiological and behavioral characteristics.

The process in which one species gives rise to multiple species that exploit different

features of the environment, such as food or habitats, is called Adaptive Radiation.

Genetic Differentiation & Adaptive Radiation

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Fox

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Bear

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Moth

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Finch

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Yarrow Plant

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END.

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ecological genetics: adaptation and natural selection

Education

reproduction of individuals

time individuals

small population

survival of fitness

chromosome gene mutation

gene frequency evolution

flower medium beak hummingbird

small beak birds