Biology 106: Lecture Topic # 10 Natural Selection and Adaptation

I. Importance

Natural Selection = Differential survival and reproduction

Adaptation = Traits that increase an individual's ability to survive and reproduce.

II. Are all Traits Adaptive?

Natural selection vs genetic drift

III. Unit of Selection?

1. Individual Selection*******

- Most Important

- occurs within populations

- acts on the phenotype

Will an adaptation spread if associated with a recessive allele?

2. Kin Selection = natural selection acts on the inclusive fitness of an individual

3. Inclusive Fitness =surv. and repro. of YOU and your RELATIVES offspring.

Ex's of Altruism (Unselfish Act), a. Burning building, b. prairie dog

Types of Selection (REVIEW on own)

Limits to Selection (REVIEW on own)

Agents of Selection (REVIEW on own)

IV. Examples of Adaptation

A. Defensive Adaptations

1. Cryptic Coloration

ex., flounders, leaflike mantis

2. Aposematic Coloration

ex., poison arrow frogs

3. Mimicry = visual appearance and behavior imitated.

i. Batesian- 1 species mimics the model with benefit only to the mimic

a. mimic palatable

b. model unpalatable

c. frequency dependent

ex., bee and beefly, starling exper.

ii. Mullerian- both species mimic or converge on common color (or other traits) to benefit both

a. both unpalatable

b. frequency dependent

ex., monarch and viceroy

B. Symbiotic Adaptations

SYMBIOSIS = Close association of 2 or more dissimilar organisms without any implied value judgments, ex's. parasitism, commensalism, mutualisms

1. Parasitism + / - = A special form of predation, close association, necessary for predator

* Predator much smaller than prey

* Internal association more specialized than external association

* Evolutionary loss of structures = Degenerative

ex. intestinal worms, lice, parasitic plants

2. Commensalism + / o = Interaction is necessary for benefiting organism

*One species physically attached to other species that exhibits no ill effects

ex. remora fish and shark, epiphytes

3. Mutualisms + / + = A necessary association for both species

ex., mycorrhizae fungi and plant roots, lichens, human being and bacteria in intestine, flowering plants and pollinators

4. Coevolved Mutualisms

ex. ants and acacia trees in tropics

ex. yucca moth and yucca plant in S. W. USA

V. Take Home Message

- Adaptations are what make organisms different

- natural selection needed for evolution of adaptations

- agents of selection are omnipresent

- traits may not be adaptive (neutral)

Genetic Drift = random changes in gene freq.

Evolution =

A. Genes

-virus like properties of self replication

- gene evolution

C. Groups or populations

1. Differences in survivorship and repro. among groups

ex. Industrial melanism

ex. human birth weight, clutch size in birds

ex. selection for both small and large plants in a popln

ex. predator / prey

1. Alternative alleles may interact with other genes.

The spread of neutral traits because of pleitrophy, epistasis, and/or linkage.

ex. tradeoff between #'s of eggs and strength of shell

2. Selection acts on phenotypes

3. Dependent on the presence of genetic variation

3. Intimidation

ex., bluff - swallowtail larvae

unrelated, but protected spp resemble one another. Group defense enhanced via larger #'s

ex. yellow and black coloration of flies, wasps, and bees