1. Macroevolution & Speciation
Accel Bio 2014

2. What is a species? Species means “kind” or “type”
Older way of looking at this question:
Morphological Species Concept
Classified organisms into separate species based on ________________ differences.
Used by ____________ (Swedish doctor & naturalist, c.1735) but not adequate today.
structural / physical
Carl Linnaeus

3. What is a species? Biological Species Concept interbreeding fertile
With the help of population genetics, in 1940 Ernst Mayr came up with the:
Biological Species Concept
A species consists of groups of populations whose members are capable of ____________ in nature to produce ______ offspring AND who do not interbreed with members of different species.
(this last part is called ____________________)
interbreeding
fertile
reproductive isolation

4. Defining a species Biological Species Concept issues:
Still this definition is not perfect: what about asexually reproducing organisms like ________________ ?!
These are classified by structural and biochemical differences
bacteria or fungi
Budding Yeast
Asexual reproduction in E.coli bacteria

5. Defining a species Biological Species Concept issues:
Additionally, some different species that do not interbreed in nature can be made to do so in an artificial environment (ranch, circus, zoo, aquarium, or laboratory).
Ex) Zebroids, interspecies hybrids:
a cross between
a horse and a zebra
Zebroid, Mt. Kenya Game Ranch and Animal Orphanage, Kenya

6. How do you create a new species?
Usually through geographic isolation (separation) of some members of a population.
The mechanisms of genetic drift, mutation, & natural selection all (separately) act upon the newly founded population and the original population. Over time, these now separate populations evolve independently.
If the two populations are brought back together and are capable of successfully reproducing in nature, we say they are still the same species. If they are NOT capable of this, then we declare them different species.

7. Species boundaries are maintained through geographic and/or reproductive isolation
What separates two species whose space / range overlaps? Reproductive barriers usually keep species boundaries intact.
Reproductive barriers can be put into two categories:
Prezygotic barriers: prevent fertilization
Postzygotic barriers: prevent hybrid from developing into viable, fertile adult

8. Prezygotic Barriers to Species Interbreeding
Ecological / Habitat isolation
Two species occupy different microenvironments (in same area) and thus do not interbreed
Ex) Garter snakes: water v. land
Temporal isolation
Reproduce at different times (of day, year, season, etc.)
Ex1) flowers: open/pollinated at different time of day
Ex2) frogs: mate at different time of season (temp dependent)
Behavioral isolation
Different courtship rituals / mating behavior
Ex1) blue-footed boobies “dance”
Ex2) frog “calls” --> different “songs” among different species

9. More Prezygotic Barriers to Species Interbreeding
Mechanical isolation
Differences in anatomy / physical structure do not permit interbreeding
Ex) flowers: adapted for specific (insect) pollinators
Larger flowers only pollinated by larger bees, smaller bees cannot reach
Gametic isolation
Egg & sperm of two species biochemically incompatible
(different recognition proteins on surface usually)
This especially important to externally fertilizing aquatic organisms or organisms with wind-borne gametes
Ex1) flowers: will not accept/recognize “foreign” pollen
Ex2) fish that fertilize externally, in open water

10. Postzygotic Barriers to Species Interbreeding
Hybrid inviability (reduced hybrid viability)
Aborted development, usually at early embryonic stage
Ex1) bullfrog eggs & leopard frog sperm
Ex2) different species of irises
Hybrid breakdown
F1 hybrid can successfully reproduce with other F1 hybrids or a Parental individual but F2 hybrid unable to reproduce.
Ex1) sunflower species
Ex2) cotton species
Hybrid sterility (reduced hybrid fertility
Hybrid offspring survive (& may be strong) but are sterile (often due to abnormal gametes of hybrid)
Ex) female horse (2N = 64) and male donkey (2N = 62) results in sterile mule offspring (2N = 63).
Different diploid number prevents proper matching up of homologous chromosomes in meiosis

11. Speciation patterns and mechanisms

12. Speciation and Adaptive Radiation
Adaptive radiation refers to an evolutionary pattern in which one species gives rise to many (also referred to as divergent evolution)
This has happened several times in the history of the evolution of species… Evidence? Homologous structures (similar structure, different function)
Adaptive radiation most often follows mass extinctions or when a species moves into a new, unoccupied area. In both these cases, there is usually an abundance of available ecological niches, that can be filled by the new “daughter” species.

13. A Model of Adaptive Radiation in an Island Chain

14. Speciation in honeycreepers
The islands of Hawaii were colonized by a single species of finch-like birds. Eventually populations were isolated from each other on separate islands. The diagrams show how they evolved into the various modern honeycreeper species with beak shapes which adapt them for different feeding methods.

15. Allopatric Speciation
The term Allopatric Speciation is used to describe a speciation event in which the new species results due to geographic isolation and subsequent adaptation of the emigrants to a new environment. When the two species are brought together again, they do not interbreed.

16. Allopatric speciation of Grand Canyon sqirrels

17. Sympatric Speciation
The term Sympatric Speciation is used to describe a speciation event in which reproductive isolation arises within the boundaries/range of the parent species (without geographic isolation). This is most common among plants, and usually results due to an increase in a plant’s chromosome number. The resulting plant is thus considered to be polyploid.
Below: Sympatric speciation by autopolyploidy (within a single species).

18. Allopolyploid Sympatric Speciation
One mechanism for allopolyploid (from two different species) speciation in plants:

19. Patterns of Evolution: Gradualism & Punctuated Equilibrium
How long does speciation take? In one survey of 84 groups of plants and animals (for which we have evidence), the answer was from 4,000 to 40 million years. The average time between speciation events was 6.5 million years. That is a LONG time!

20. Gradualism
Punctuated Equilibrium

21. Image Sources Zebroid: www.ceotraveler.com/adventure/kenya.shtml
Budding yeast cells:
Bacteria:
Snail speciation & Honeycreeper Beaks:
Frog Mating Behavior:
Horse/Mule/Donkey:
Adaptive Radiation:
Boobie Mating Dance:
Linnaeus portrait & Cinchona watercolor:
Ernst Mayr:
Honeycreepers #2:
Picture: