1. Chapter 24
Species & Speciation

2. Chapter 24 in a nutshell Microevolution v. Macroevolution Speciation
Prezygotic
Postzygotic
Gradualism v. Punctuated equilibrium

3. Species Morphological species concept Biological species concept
Divisions of organisms into discrete units called species
If two organisms look different enough, then they are considered different species
Biological species concept
Population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring
This population is unable to produce viable, fertile offspring with members of another population

4. Micro- vs. Macro- Evolutions
Microevolution
Change in the genetic makeup of a population over generations
Changes (adaptations) confined to a particular gene pool or population
Macroevolution
Changes (evolution) above the species level
Changes used to define higher taxa

5. Speciation The process that produces a new species
May be the result of microevolution OR macroevolution
How could microevolution lead to speciation?
How could a new species arise from macroevolution?

7. Reproductive Isolation
Biological barriers that impede members of 2 species from producing viable, fertile offspring
There are 2 types of barriers that lead to reproductive isolation
Prezygotic
Pre-mating
Post-mating
Postzygotic

8. Prezygotic Barriers Pre-Mating Post-Mating Habitat isolation
Temporal isolation
Behavioral isolation
Post-Mating
Mechanical isolation
Gametic isolation

9. Prezygotic Barriers (Page 1)
Pre-Mating
Habitat isolation
2 species occupy different habitats in the geographic area
Tree-dwelling species, Bush-dwelling species
Temporal isolation
Temporal = time
Species breed at different times
Different time of day, different seasons, or different years
Behavioral isolation
Certain signals or types of behavior are integral to courtship, and these signals/behaviors are unique to the species
Other species do not respond to these signals or behaviors

10. Boobies!!
(blue-footed)
Different mating season – late winter or late summer
Different habitats – water or terrestrial

11. Prezygotic Barriers (Post-Mating)
Mechanical isolation
Anatomical incompatibility
Insect copulatory organs are elaborated for a particular species
Gametic isolation
Even if gametes meet, they are unable to fuse
Sperm may not be able to survive in the reproductive tract of females from another species
Purple + Red sea urchins cannot mate b/c gametes cannot fuse

12. Postzygotic Barriers Reduced hybrid vitality Reduced hybrid fertility
Hybrid Breakdown

13. Postzygotic Barriers Reduced Hybrid vitality Reduced Hybrid fertility
Although zygote forms, genetic incompatibility causes developmental cessation
In some salamanders, hybrids form but do not complete development
Reduced Hybrid fertility
Sterile hybrids
Donkey + Horse = mule (Sterile)
Hybrid breakdown
Although first-generation hybrids survive & reproduce, their offspring are feeble or sterile

15.  No Geographic Barrier

16. Allopatric Speciation
Causes
Geologic events or processes that fragment the population
Emergence of a mountain range
Formation of a land bridge
Evaporation of a large lake into multiple smaller lakes
Leads to a significant alteration of a gene pool

18. Sympatric Speciation Sympatric = sym (same) + patr (fatherland)
Same country
Geographically overlapping populations
Major mechanism of sympatric speciation is Polyploidy
Autopolyploidy
Allopolyploidy
Preferential Habitation

19. Polyploidy Extra set(s) of chromosomes Autopolyploidy Example > 2n
Typically, nondisjunction (Meiosis) in Plants
All chromosomes from the same species
Example
Tetraploid (4n) + diploid (2n)
Produce triploid (3n) offspring which are sterile
But plant tetraploids can self fertilize or mate with other tetraploids = viable, fertile polyploid offspring
Tetraploids are reproductively isolated from the diploid population

20. Polyploidy (Page 2) Allopolyploidy Plants
2 different species interbreed = hybrid
Hybrids cannot breed with either original species
But hybrids can successfully mate with each other
Self-pollination successfully occurs as well

21. Polyploidy (Page 3) Can happen in animals but not common
In animals, sympatric speciation is usually due to part of the population switching to a new habitat, food source, or other resource

22. Adaptive Radiation
Many new species arise from a common ancestor given new environmental opportunities or challenges
Think Darwin’s finches & Galapagos islands
As the finches moved from South America to the Galapagos, different environments and food sources were encountered
Hawaiian Plants
As the plants spread to Hawaiian islands, different environments on different islands = evolution into several distinct forms

24. Hawaiian Plants that had a common ancestor
 Arose from Adaptive Radiation

25. Gradualism vs. Punctuated Equilibrium
Gradualism – species descended from a common ancestor and gradually diverge in morphology (acquiring unique adaptations) until they are reproductively isolated
Punctuated Equilibrium – long periods of apparent stasis punctuated by brief periods of sudden and rapid change
Fossil record confirms the punctuated equilibrium model
Also eliminates the necessity of finding “missing links”