Chapter 24 Edited Lecture Speciation Chapter 24 Edited Lecture

What do you need to know? Biological definition of species Prezygotic and postzygotic barriers Allopatric vs. sympatric speciation Autopolypolid or allopolyploid chromosomal changes  sympatric speciation Punctuated equilibrium and gradualism describe two different tempos of speciation

(a) Similarity between different species Figure 24.2 (a) Similarity between different species Speciation is how new species arise Biological species concept is based on ability to reproduce viable offspring rather than physical simliarities (b) Diversity within a species

Microevolution consists of changes in allele frequency in a population over time Macroevolution refers to broad patterns of evolutionary change above the species level

Prezygotic barriers (a) (c) (e) (f) (g) (d) (b) Figure 24.3_b Habitat Isolation Temporal Isolation Behavioral Isolation Mechanical Isolation Gametic Isolation Individuals of different species MATING ATTEMPT FERTILIZATION (a) (c) (e) (f) (g) (d) (b) Figure 24.3 Exploring: Reproductive Barriers Prevent mating or hinder fertilization!!!

Postzygotic barriers Reduced Hybrid Viability Reduced Hybrid Fertility Figure 24.3_c Postzygotic barriers Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown VIABLE, FERTILE OFFSPRING FERTILIZATION (h) (i) (l) (j) Figure 24.3 Exploring: Reproductive Barriers Prevent fertilized egg from developing into a fertile adult (k)

Limitation to Biological Species Concept Grizzly bear (U. arctos) Polar bear (U. maritimus) Not applied to fossils OR asexual organism Gene flow can occur between distinct species Hybrid “grolar bear”

Allopatric vs. Sympatric Speciation Allopatric speciation. A population forms a new species while geographically isolated from its parent population. (b) Sympatric speciation. A subset of a population forms a new species without geographic separation.

Allopatric Speciation Figure 24.6 Allopatric Speciation A. harrisii A. leucurus The definition of barrier depends on the ability of a population to disperse For example, a canyon may create a barrier for small rodents, but not birds, coyotes, or pollen Gene flow is interrupted by geologic events or processes

Sympatric Speciation Formation of autopolyploid plants through non-disjunction in meiosis. (Plants do this a lot!!) Oats, cotton, potatoes, wheat, tobaccos are polyploid Habitat Differentiation (new ecological niche)

Sympatric Speciation Species A 2n = 6 Species B 2n = 4 Meiotic error; Figure 24.11-4 Sympatric Speciation Species A 2n = 6 Species B 2n = 4 Meiotic error; chromosome number not reduced from 2n to n Normal gamete n = 3 Unreduced gamete with 4 chromosomes Hybrid with 7 chromosomes Normal gamete n = 3 Unreduced gamete with 7 chromosomes New species: viable fertile hybrid (allopolyploid) 2n = 10

Hybrid Zones Possible outcomes: Isolated population Hybrid diverges Figure 24.14-4 Hybrid Zones Possible outcomes: Isolated population diverges Hybrid zone Reinforcement OR Fusion OR Gene flow Population Hybrid individual Barrier to gene flow Stability

Tempo of Speciation