1. SGN 27 The Origin of Species

2. Macroevolution describes the origination of new taxonomic groups (vs microevolution, which deals with change in allele frequency, and frequencies of genotype and phenotype)

3. What is a species? Biological species concept – the largest set of populations in which genetic exchange is possible; species are reproductively isolated, separated by reproductive barriers Each species is isolated by biological factors that prevent interbreeding

4. Different species are typically sequestered genetically by more than one postzygotic or prezygotic barriers, which make it impossible to reproduce together, even if they occupy the same general area (so simple geographic separation is not a prezygotic or postzygotic barrier, although as we will; see it might lead to them forming)
Barriers – make successful fertilization or reproduction impossible
Prezygotic – before fertilization
Postzygotic – after fertilization

6. Prezygotic barriers – impede courtship, mating and related events (but not simply physical isolation)
Types of barriers – habitat, behavior, temporal, mechanical, gametic
Not simply physical isolation, as cause of physical isolation can be removed and two group as will once again interbreed
PreZ and PostZ barriers cannot be removed – two groups are different species

7. Anole lizards

8. Temporal, mechanical, gametic
Diurnal
Nocturnal

9. Postzygotic barriers – results of fertilization (hybrid) will not thrive or be fertile Reduced hybrid viability – typically embryo not viable, or offspring are frail Reduced hybrid fertility – cannot back breed, or meiosis malfunctions so gametes not viable or offspring of hybrids not viable Hybrid breakdown – offspring of hybrids have reduced fertility or viability

10. Limitations of BSC In many instances (extinct and many existing groups) information about interbreeding is lacking BSC inapplicable to asexually reproducing groups Is geographic isolation enough to consider nonbreeding groups different species?
Grolar bear

11. Alternative concepts of species But problems with each Morphological (a species has a unique set of adaptations) species concept Genealogical/Phylogenetic (species has unique genetic history) species concepts
These happy face spiders look different, but since they can interbreed, they are considered the same species: Theridion grallator.

12. 2 Primary Modes of speciation – how do barriers arise?
Allopatric – “different country”
Sympatric – “same country”

13. Allopatric speciation – occurs due to populations diverging into geographically different ranges and therefore exposure to different environmental pressures

14. Ring species (distributed around a geographic barrier) – shows population at various stages in their gradual divergence from common ancestors
Island species – adaptive radiation (see below) is common

15. Adaptive radiation occurs because of allopatric speciation
Many species (existing in different environments) might evolve from a common ancestor migrating into those different environments
In regard to AS, geographic isolation alone may create separate populations but is not in itself a reproductive barrier defining species; natural selection under different conditions, genetic drift and mutation have to create genetic barriers

17. Sympatric speciation – a new species originates in the geographic midst of the parent species
Genetic events can produce barriers to separate populations
Mistakes in meiosis can produce polyploidy (extra sets of chromosomes)

18. Autopolyploidy in plants and possibly other types of living things; more than 2 chromosome sets contributed by parents of the same species
Allopolyploidy – two different species reproduce to make a polyploid hybrid
Hybrid typically sterile but often vigorous and able to reproduce using asexual propagation; certain events can restore fertility in hybrids, which can then self fertilize or reproduce with other of the same type of polyploid with restored fertility
Many important agricultural plants are polyploids (wheat, cotton, potatoes, tobacco, oats, etc.); when successful seems to increase size and vigor of plant and/or grain

19. Sympatric speciation in animals occurs occasionally when groups take
Sympatric speciation in animals occurs occasionally when groups take on different behaviors
Groups pursue different food sources in an environment, which leads to divergence of populations
Nonrandom mating causes subgroups to emerge, and establishes reproductive barrier

20. Tempo of speciation
Gradualism model – slow accumulation of many small changes leads to new species
Punctuated Equilibrium model – species undergo most of their morphological modification as they first bud off from parent species, and then change little
Initial species forming changes may take 10’s of thousands of years, in a species that will then exist for millions of years unchanged due to stabilizing selection
Probable that both can lead to speciation, as could a combination of the two

21. From microevolution to speciation to macroevolution
Microevolution – change in population’s allele frequency (nat sel, gen drift, etc.)
Speciation – enough microevolution to make new species (allopatric or sympatric speciation erects reproductive barriers)
Macroevolution – level of change that is evident over the time scale of the fossil record; development of new taxonomic groups
Macroevolution occurs when genetic divergence leads to reproductive barriers/isolation, and over vast tracts of time divergent change leads to the complexity and diversity we see in life today
Vicariance – event or process that erects barrier to gene flow between two populations and establishes them as different species

22. What kind of events involving microevolution (change in alleles) lead to macroevolution (emergence of new species with significant differences)? What events lead to the emergence of evolutionary novelties? Gradual change in allopatric speciation Example: Older structures modified in increments Rapid change due to mutation Example: Evo-Devo

23. Older structures modified in increments to make more modern structures Structures might be refined to become better at the same thing; example - the eye Structures might be co- opted for another purpose (exaptations); example - honeycombed bones and feathers of reptiles/birds

25. Evo-Devo: genes that control development play a major role in evolution
Genes that program development control the rate, timing and spatial pattern of change in an organism’s form as it is transfigured from a zygote to an adult

26. Allometric growth – growth rates of different parts are unequal and disproportionate, which gives body its specific shape
Heterochrony – temporal evolutionary change in the rate or timing of developmental events; evolution of morphology that arises by a modification in allometric growth
Can affect timing of reproductive maturity and other important developmental events (paedomorphosis)
Axolotl- retains juvenile characteristics but becomes reproductively mature

27. Changes in genes that control placement and spatial arrangement of body parts (homeotic genes) can result in macroevolution Hox genes