The Genetical Theory of Natural Selection

The Genetical Theory of Natural Selection

Where natural selection occurs

Fundamental patterns of intraspecific natural selection

Disruptive

Rare

Carnivores

• Consume nutritionally-rich prey.• Problems involve capture

• Some prey defensive signals:• Aposomatic coloring - Warning colors.• Mullerian mimicry: Signal shared among

several species of noxious organisms.• Batesian mimicry: Edible species uses same

signal as a noxious species.• Crypticity: camouflage

Camouflage and directional selection

Directional selectionBiston betularia

Pre-pollution control

Original habitatPost pollution control

Directional selection

Disruptive selectionBlack-bellied seedcracker (an African finch)Multiple-niche polymorphism

Bimodal distribution

Black-bellied seedcracker

Balancing selectionPolymorphismMaintained because intermediate expression of a continuous character is favored by NSor by hetorozygote advantage

Genetic variation at beta-hemoglobin locus

Polymorphic in response to malarial organism

Two selectors: malaria and sickle-cell anemia

Uta stansburianaSide-blotched lizardPolymorphism: males

Color and behaviordetermined by levels ofprolactin and testosteronein early development.

Fixed for life.

1. Large territories,many females2. Small territories,one female.3. Non-territorial,sneak copulations from1.

Morph frequencies shiftbetween generations depending on success ofa particular tactic.

Polymorphic mating strategies

1.

2.

3.

Batesian mimicry

Müllerian mimicryMicrurus eryxanthus: Western coral snakeAposematic colorationProblem: how established?

A mimetic system

Batesian and MüllerianMimicry

Aposematic coloration

Parallel geographic variation

Micrurus 6 species. Highly venomousFixed front fangsNeotropicalElapidae

Pliocercus 1 or 2 species.Mildly venomousFixed rear fangsColubridae

Does aposematic coloration work?Plasticine models

Forest floor: on white paper and on forest floor

Experiment carried outin natural habitat

Resemblance does nothave to be perfect to confer protection

Significantdifferences

• Is avoidance of aposematic coloration innate?• Naïve motmots (Neotropical birds)• Caged birds presented with:

– 1. coral snake models– 2. models of natural prey species.

A famous Müllerian mimicrycomplex.

Each species withsubspecies defined bycolor pattern and geography.

What happens at subspecificboundaries?

Phenotypic plasticity: environmentally induced variationoperating on common genetic background.

Geometrid mothNemoria arizonaria

Water CrowfootRanunculus aquatilis

Phenology: relationshipbetween climate andthe timing of ecologicalevents.