Natural Selection and Speciation Another way to look

Natural Selection and Speciation

Another way to look at it… Fitness • Directional Selection Trait Positive Directional Selection Trait Negative Directional Selection

Fitness • Stabilizing selection average trait value

Egg laying wasp that eventually kills the cactus

Fitness • Disruptive Selection average trait value

Black-bellied seed cracker (Pyrenestes ostrinus)

• Smith, T. B. 1990. Evolution. 44(4): 832 • Black-bellied seed crackers (Pyrenestes) in Cameroon

Same birds different study Open portion of bar – Number hatched Black portion of bar – Number survived

Two more types of selection • Correlational – working on combinations of traits at once. (body size) (Wing length)

• Frequency Dependent Selection – Level of selection dependent upon most common phenotype (at the time) Genyochromis Scale eater

Scalebiters – frequency dependent selection Right “mouthedness” Left “mouthedness”

Frequency of left “mouthedness” Frequency of right “mouthedness” Time

• Selection can lead to speciation • Speciation: – Splitting of one species into two or more species – Transformation of one species into a new species over time

Anagenetic (gradual) versus Cladistic (punctuated) Speciation B A TIME B A A PHENOTYPIC VARIATION

Species • Many, many definitions • Biological species definition: A group of actually or potentially breeding individuals which are reproductively isolated from all other groups. • Doesn’t work in all situations – Fossils – Asexual organisms

Isolating mechanisms • Prezygotic – • Postzygotic -

• Pre-zygotic barriers include – Temporal isolation – Behavioral – Mechanical – Gametic

Prezygotic I. M. s • Habitat isolation – Dendroica warblers in Eastern US

Modes of speciation • Allopatric – allo = different, patri = fatherland • Sympatric – sym = together • Has to do with location or habitat

Speciation only occurs with reproductive isolation

Sympatric speciation • Polyploidy in plants • Hybrids

Adaptive Radiation • Evolution of ecological (& morphological) diversity within a rapidly speciating lineage.

• Hawaiian honeycreepers