© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e1 Adaptation & Speciation Normally over 2...

Adaptation & Speciation

Normally over 2 days, going to ≥ slide 18 on day one, but we do not have this luxury this term.

Adaptation

An improvement to an organism over time Changes a population to better fit its

environment The result of natural selection acting on genetic

variation Environments change and new genetic variation

arises, so adaptation never reaches perfection

Adaptation

Matches organisms to their environment

Adaptation:

1. Matches organisms to environment

2. Can be complex

3. Accomplishes specific functions

Populations Can Adjust

Sometimes adaptations can be rapid

Soapberry bugs, Fl adapted to an introduced species by obtaining shorter beaks in 30-50 years.

Adaptations Are Not Perfect

Natural selection has limitations: Genetic constraints

No variation, no adapting

Multiple effects of

genes in development Ecological trade-offs

What is good for one thing may hurt in another

What are Species?

Members of a species generally look alike Bald eagles in Alaska (top) &

Colorado (bottom) But not always

Species –are reproductively isolated from other species

Barriers to reproduction between species

Barriers to reproduction

Prevent a zygote from being formed Ecological isolation –species physically separated Behavioral isolation –mating calls, rituals Mechanical isolation –physically unable to mate

Chihuahua and wolf cannot mate

Gametic isolation –gametes do not fuse

Barriers to reproduction

Barriers after zygote has formed Zygote dies –offspring is never born Hybrid performance –not as fit as parents

Mules cannot reproduce w/ each other or w/ donkey or horse

Some Species Interbreed But the species stay

distinct Live at different

elevations: Gray – lower Gambel – higher hybrids - intermediate

Complications: Some Species Can Interbreed But the species stay

distinct for complex reasons

Chihuahua -> small dog-> collie -> shepherd ->

wolf Cat and bobcat We will keep it simple &

ignore these

Walking Sticks Adapting to match their environment (two mating pairs)

Striped form (L) is well-hidden among the needle-like leaves w/ stripes, solid form among solid leaves

The striped form of the species prefers needle-like leaves of the chemise (sheh-mēz) bush.

The solid-green form prefers the solid green leaves of the wild lilac.

The two forms are more likely to survive on their preferred plant. Predators (birds) more likely to catch them if they are

not on their preferred plant.

Walking Sticks

Is a complex adaptation, more than coloration. Lilac and chemise bush leaves have different

pulp, fiber, chemical contents, and plant toxins. The solid-green walking sticks have enzymes to

better digest the leaves of the wild lilac. The striped form has enzymes adapted to better

digest the leaves of the leaves of the chemise bush.

Walking Sticks

“Hybrid offspring” of a cross between solid and striped parents are less fit than offspring of a single form mating. Do not blend as well on either Lilac or chemise

bush leaves. Predators are more likely to eat them. Do not digest either plant as well as single forms.

Walking Sticks

Because “Hybrid offspring” (a solid & striped cross) are less fit than “single form” offspring, the population is adapting in one other way: Individuals prefer to mate with others of the

same color pattern. In nature, the two forms do not see each other

much (they stay on their preferred plants). Mating experiments done in the lab.

Walking Sticks

Population is diverging with respect to alleles for: coloration, digestion, dealing with plant toxins, mating behavior.

Disruptive selection is better adapting each form to their preferred plant.

W/ time, disruptive selection will further diverge the two forms & further decrease their interbreeding.

When the two forms loose the ability to interbreed, they will become two different species.

Lecture To Here!

Speciation

When one species splits to form two species Results from reproductive isolation Often, it is a secondary consequence of

changing populations Occasionally, is a direct consequence of a

diverging population The hybrid is less fit, walking sticks

Speciation Without geographic isolation is called:

Sympatric speciation Such as chromosomal changes

Due to geographical isolation is called:Allopatric speciation (N & S rim of Grand Canyon)

Allopatric Speciation

Geographical separation prevents species from mating

When reintroduced, they no longer mate

Sympatric Speciation: Lake Victoria Cichlids

Species reproductively isolated from:

Sexual selection & mating behaviors

Species differ in their diets

Rates of Speciation

Rates differ in different organisms Can occur in thousands or millions of years

Walking sticks, have a reason to evolve reproductive isolation quickly, hybrids are less fit

speciation may occur in a couple thousand years. European and N. American sycamore trees do not

have a reason to evolve reproductive isolation they were separated geographically 20 mya & do not

normally interbreed speciation has not yet occurred

Speciation

The splitting of one species into two has never been seen in animals check back in a couple thousand years

Walking sticks Apple maggots (worms)

Russian Mad Scientist

He wanted a plant where you

could eat both the roots and the leaves (beets).

Promised the Soviet Union he could do it if given enough funding.

Russian scientist who crossed radishes with cabbage.

He crossed cabbage & radishes The hybrid offspring were sterileThe chromosomes did not match

in meiosis Not a problem

Plants can be grafted (clones)He obtained many hybrid clonesHe grew the grafts for years

He was either very lucky or very insane In one plant, a freak chromosomal

abnormality occurred The chromosomes doubled and were able to

match in meiosisThis rarely happens

He then bred the one fertile hybrid and studied it (it could self-pollinate)

Russian Mad Scientist His breeding was a failure Instead of the leaves of a cabbage and the

roots of a radish, he got the leaves of a radish and the roots of a cabbage!

Yet, his creation could not breed with either a cabbage or a radish, due to chromosomal incompatibilities

Cabbage

Radishes

Look what his failure obtained:

Cabbage

Radishes

Cab-Rad

Cabbage

Radishes

He had witnessed the birth of a new species He obtained three species from two

Cabbage

Radishes

Cab-Rad

Not sure if it kept him from being sent to Siberia

Implications of Adaptation and Speciation Understanding used to combat diseases

HIV Bacteria

Concept Quiz

Which of the following is not a true

example of an adaptation?

A. Bats wanting to fly and developing wings

B. Spots on a leopard for camouflage

C. Long tongues in frogs for catching flies

Fruit flies were

raised on two food sources

Flies preferred to mate with others raised on same

food source

Selection Causing Reproductive Isolation

Concept Quiz

One species of frog in a pond splits into two

species because males develop two different

mating calls. This is an example of:

A. Ecological isolation

B. Polyploidy

C. Behavioral isolation

Concept Quiz

Which of the following is not a reproductive

isolation mechanism?

A. Hybrid fertility

B. Zygote death

C. Gametic isolation

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e1 Adaptation & Speciation Normally over 2...

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