1. Speciation: How Species Form
Lesson 6

2. SBI 4U: Metablic Processes
SPECIATION
Microevolution: changes in allele frequencies and phenotypic traits within populations and species; can result in new species.
Speciation: The evolutionary formation of new species.
Species: members of groups or populations that interbreed or have the ability to interbreed with each other under natural conditions.
reproductively isolated from other groups
evolve independently
Section 1.3 2

3. Reproductive Isolation
Whether or not different species interbreed successfully in the wild can be difficult to examine.
Differentiating species is mainly done by physical appearance/morphology, however, subspecies (or races) are morphologically distinct subpopulations that can interbreed.
Where morphology is not possible, behaviour or reproductive isolating mechanisms are used.
A reproductive isolating mechanism is any behavioural, structural or biochemical trait that prevents individuals of different species from reproducing successfully together.

4. Means of Reproductive Isolation:
SBI 4U: Metablic Processes
Means of Reproductive Isolation:
PREZYGOTIC (prevention of interspecies mating or fertilization)
Prevention of mating:
Ecological isolation: different habitat, niches,
Temporal isolation: different reproductive cycles (timing of day, seasons)
Behavioural isolation: different signals
Section 1.3 4

5. Which type is this?

6. Means of Reproductive Isolation:
Prevention of fertilization:
Mechanical isolation: structural differences in reproductive organs (arthropod, flowers)
Gametic isolation: molecular recognition of sperm and egg (water animals)
Different penis structures of damselflies

7. Means of Reproductive Isolation:
POSTZYGOTIC (prevent maturation and reproduction in offspring from interspecies reproduction)
Zygotic Mortality: different species can mate but no embryos develop to maturity,
Hybrid Inviability: baby hybrids aren't viable, don't live long
Hybrid Infertility: baby hybrid viable but not fertile.

8. Reproductive isolation and Speciation
Reproductive isolation may lead to speciation.
The gene pool is isolated, any mutation and selection that occurs is no longer shared;
any significant evolutionary changes that occur in either population (new or old) will result in the formation of separate species.

9. In class work
Pg 363, Q 13-18

10. Modes of Speciation
Sympatric Speciation: evolution of populations within the same geographic area into separate species. (ex. grey tree frogs)
Chromosomal changes (plants) and non- random mating (animals) alter gene flow
More common in plants
Polyploidy (3 or more sets of chromosomes) can lead to speciation

12. Modes of Speciation
Allopatric Speciation: evolution of populations into separate species as a result of geographic isolation. Ex. water, canyon, mountain range, human construction (dams, highways, canals)
Darwin’s finches pg 336

16. In class work
Pg 365, Q 19-24

17. Adaptive Radiation
Adaptive radiation is an increase in the morphological (what they look like) and ecological (where they live) diversity of a species eventually resulting in the formation of new species.

18. Adaptive Radiation
It usually occurs very rapidly when a species colonizes a new environment (Darwin’s Finches) OR by survivors after a massive extinction event (Mammals after the extinction of the Dinosaurs).

19. Adaptive Radiation
Darwin’s Finches: An ancestral finch population got blown off the mainland of South America onto the Galapagos Islands. Over time that finch species evolved to fulfill all the niches on the islands and thereby give rise to the variety of finches seen on the islands.
Mammals after the extinction of the Dinosaurs: With Dinosaurs out of the way, mammals were able to grow bigger and fill all the niches vacated by the larger reptiles, which explains the wide diversity of forms we see in mammals today.

20. Adaptive Radiation
It supports evolution by showing that groups of organisms (i.e. mammals) are all related to each other and came from a common ancestor that inhabited new environments and evolved to adapt to these environments.
All mammalian forelimbs contain the same bones which shows that they all evolved from a common ancestor.

21. Divergent and Convergent Evolution
Species that were once similar diverge or become increasingly distinct
Eg/ Darwin’s finches
Convergent
A pattern of evolution in which similar traits arise because different species have independently adapted to similar environmental conditions
Eg/ bats and birds

22. CONVERGENT EVOLUTION
Species from different evolutionary branches may come to resemble one another if they live in very similar environments.
Example:
1. Sidewinder (Mojave Desert) and
Horned Viper (Middle East Desert) 22

23. CONVERGENT EVOLUTION - EXAMPLE
1. Ostrich (Africa) and Emu (Australia).

24. Macroevolution
Large scale evolutionary change significant enough to warrant the classification of groups into genera or even higher-taxa level.
For example
the separation of eubacteria and archaebacteria.
Cambrian explosion – rapid speciation and diversification in the animal kingdom for about 40 million years starting 565 mya. Early arthropods, echinoderms, molluscs, primitive chordates
Burgess Shale in B.C.
2 major theories for macroevolution / the rate of evolution:

25. Theory of Gradualism
The accumulation of many small and ongoing changes and processes.
When new species first evolve, they appear very similar to the originator species and only become more distinctive, as natural selection and genetic drift act on both species.
One would expect then to find many transitional species in the fossil record.
This is explained by an incomplete fossil record, and the possibility that intermediate forms were not preserved.

26. Theory of Punctuated Equilibrium
Eldredge and Gould (1972) rejected the explanation of the incomplete fossil record and proposed the Theory of Punctuated Equilibrium
Relatively rapid spurts of change followed by long periods of little or no change.
Species evolve very rapidly in evolutionary time
Speciation usually occurs in small isolated populations and thus intermediate fossils (transitional species) are very rare.
After the initial burst of evolution, species do not change significantly over long periods of time.

28. Which one do we use today?
Today both theories are needed to understand the fossil record.
It is widely accepted that both gradual and rapid evolutionary processes are at work.
Example:
Before a major extinction event, an environment may be host to many well adapted species and evolutionary change would be slow.
An environmental crisis resulting in extinction of many species would leave many niches empty.
Surviving species have many new opportunities and experience disruptive selection, evolving into many species which fill the niches.
Once they become well adapted, stabilizing selection kicks in again and more gradual change occurs.

29. Consequences of Human Activities
Human-made barriers may prevent gene flow between the split populations
Isolated populations may undergo adaptive radiation
Severely fragmented populations may eventually die out if there is insufficient genetic diversity
E.g. giant panda in China

30. Speciation and Mass Extinctions
Five major mass extinctions have been identified

31. In class work Pg 370, Q 25-30 Final Evolution Quiz Wed May 16
Evolution unit test Wed May 23
Assignment, pg 375, due Wednesday May 23