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 d efensive 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 selection Biston betularia Pre-pollution control

Original habitat Post pollution control

Directional selection

Disruptive selection Black-bellied seedcracker (an African finch) Multiple-niche polymorphism Bimodal distribution

Black-bellied seedcracker

Balancing selection Polymorphism Maintained because intermediate expression of a continuous character is favored by NS or by hetorozygote advantage Genetic variation at beta-hemoglobin locus Polymorphic in response to malarial organism Two selectors: malaria and sickle-cell anemia

Uta stansburiana Side-blotched lizard Polymorphism: males Color and behavior determined by levels of prolactin and testosterone in early development. Fixed for life. 1. Large territories, many females 2. Small territories, one female. 3. Non-territorial, sneak copulations from 1. Morph frequencies shift between generations depending on success of a particular tactic. Polymorphic mating strategies

Batesian mimicry

M ü llerian mimicry Micrurus eryxanthus: Western coral snake Aposematic coloration Problem: how established?

A mimetic system Batesian and Müllerian Mimicry Aposematic coloration Parallel geographic variation Micrurus 6 species. Highly venomous Fixed front fangs Neotropical Elapidae Pliocercus 1 or 2 species. Mildly venomous Fixed rear fangs Colubridae

Does aposematic coloration work? Plasticine models Forest floor: on white paper and on forest floor

Experiment carried out in natural habitat

Resemblance does not have to be perfect to confer protection Significant differences

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 mimicry complex. Each species with subspecies defined by color pattern and geography. What happens at subspecific boundaries?

Phenotypic plasticity: environmentally induced variation operating on common genetic background. Geometrid moth Nemoria arizonaria Water Crowfoot Ranunculus aquatilis Phenology: relationship between climate and the timing of ecological events.