Natural SelectionNatural Selection

1. Do we see the same variation within different wild species that we do in domesticated ones like dogs, pigeons and horses?

Lemurs of Madagascar

Amazonian Frogs

Natural SelectionNatural Selection

2. If humans select traits for dogs, pigeons and the five major mammals, who selects the traits of all those Lemurs, Frogs, and other wild animals?

WHICHEVER TRAITS WORK BEST FOR THE ENVIRONMENT THEY LIVE IN ARE THE

ONES THAT ARE PASSED ON THROUGH THE GENES

NOBODY

Animals not possessing the beneficial traits don’t do as well, or just die

Example #1:Example #1:

The neck of the The neck of the GiraffeGiraffe

And LamarckAnd Lamarck The slow The slow

hypothetical hypothetical evolution: Response evolution: Response to Acacia Treesto Acacia Trees

The Red Queen The Red Queen Hypothesis...Hypothesis...

Example #2: Example #2: Versicolor MothVersicolor Moth

Early trees had light-colored barkEarly trees had light-colored bark Only the light-colored moths survived. Only the light-colored moths survived.

Selection was for Selection was for lessless melanin. melanin. After industrialization, the tree bark was After industrialization, the tree bark was

darker.darker. Only the darker colored moths now Only the darker colored moths now

survived. Selection was for survived. Selection was for moremore melanin.melanin.

Example #3Example #3

The leaf bugThe leaf bug

What serve as pressures?What serve as pressures?

Weather: changes in local weather (e.g. when an Ice Age comes on),migration to a new area (e.g. Alaska down into California)

Change in surroundings/cover:change in density of vegetation (e.g. scrub to forest)change in color of vegetation (e.g. versicolor moth)

Change in food or predators:food grows defenses (e.g. Acacia Trees and Giraffes)only fastest predators survive (e.g. speed of Cheetahs)

The Main Types of Selection The Main Types of Selection PressuresPressures

Directional SelectionDirectional Selection– Easiest to identifyEasiest to identify– Camouflage and mimicry usually fall hereCamouflage and mimicry usually fall here

Disruptive SelectionDisruptive Selection– Causes species to divergeCauses species to diverge

Stabilizing SelectionStabilizing Selection– Drives a population to specializeDrives a population to specialize

Sexual SelectionSexual Selection

Directional SelectionDirectional Selection

Most quantifiable Most quantifiable changes in a changes in a population are population are directional, for directional, for example...example...

Neck of GiraffeNeck of Giraffe Moth color (melanin) Moth color (melanin) Camouflage/MimicsCamouflage/Mimics Many sexually selected Many sexually selected

traitstraits

Directional Selection: Mimicry Directional Selection: Mimicry (mimic environment)(mimic environment)

Directional Selection: Mimicry Directional Selection: Mimicry (mimic other animal)(mimic other animal)

Other Mimicry Examples Other Mimicry Examples (from video clips)(from video clips)

1. Viceroy and Monarch butterflies

2. Orchid and the Echnumatid wasp

3. Firefly mimic

4. Cobra mimic

5. Angler Fish with lure

Stabilizing SelectionStabilizing Selection

When the extremes When the extremes of the trait aren’t as of the trait aren’t as well suitedwell suited

Causes Causes specializationspecialization

E.g. bird clutch sizeE.g. bird clutch size

Disruptive SelectionDisruptive Selection

Causes divergence Causes divergence within the specieswithin the species

Results in Results in specialization for specialization for each branched each branched groupgroup

E.g. Darwin’s E.g. Darwin’s FinchesFinches

Sexual Selection: FemalesSexual Selection: Females

Females must behave in a way that ensures that their offspring survive and mate, and that they have as many offspring as possible

If they behave this way, the genes for this behavior are passed on. If they don’t behave this way, the genes are not passed on.(remember, over millions of years all of your ancestors havesuccessfully mated…)

Behavior #1: Pick a mate who will help you raise the young(if young have long infancy period)

Behavior #2: Pick a mate who has the “fittest genes” for your environment and mate with them

(if young have short infancy period)

Sexual Selection: MalesSexual Selection: Males

Males also behave in a way that maximizes the propogation of their genes. The ones who possess traits that allow them to mateand have many surviving offspring pass on those “prolific” genes.

Behavior #1: Choose one female to raise the young with(if young have long infancy period)

Behavior #2: Convince the females that they have the “fittest genes”for their environment

(if young have short infancy period)

Behavior #1: male and female Behavior #1: male and female identical and best adapted identical and best adapted

(Gibbons, Albatrosses, many seals)

Behavior #2: Males compete Behavior #2: Males compete so that females choose themso that females choose them

(Elephant Seals, Elk, Lions, Gorillas, Widowbird)

These “Tournament Species” These “Tournament Species” tend to be Sexually Dimorphictend to be Sexually Dimorphic

Males and females of the same species have different formsand are easily distinguishible

The male sexual characteristics identify which males are dominant

Often the superficial sexual characteristics imply more essential ones- the probiscus, size and deepness of voice ofelephant seals are probably all controlled by the same gene

Some of these characteristics allow males to fight each other moreeffectively. But what about the ones that don’t help them physically compete against each other?

Males and females of the same species have Males and females of the same species have different forms and are easily distinguishabledifferent forms and are easily distinguishable

The male sexual characteristics identify which The male sexual characteristics identify which males are dominantmales are dominant

Often the superficial sexual characteristics imply more Often the superficial sexual characteristics imply more essential ones- the probiscus, size and deepness of voice ofessential ones- the probiscus, size and deepness of voice ofelephant seals are probably all controlled by the same geneelephant seals are probably all controlled by the same gene

Some of these characteristics allow males to fight each other Some of these characteristics allow males to fight each other more effectively. But what about the ones that don’t help more effectively. But what about the ones that don’t help

them physically compete against each other?them physically compete against each other?

Do the females really go for it?Do the females really go for it?

1. Catch long-tailed birds and cut off tails.

2. Paste these tails onto short-tailed widowbirds.

3. Catch some long-tailed birds, cut tails and paste back on.

Findings:The long-tailed widowbirds were more successful at mating

and had more offspring(whether their tails were long naturally or pasted on)

How did these characteristics come How did these characteristics come about if they advertise to predators?about if they advertise to predators?

Theory #1: A bottleneck occurred in the population. An outward, superficial gene was linked on the chromosome near a more essential one. The females began choosing the best mate on superficial cues. The superficial cues have been undergoing selection eversince.

Theory #2: That dumb characteristic risks the life of the male.If he can survive with all those colors and obvious feathers, he must be some kind of stud.