Speciation Mechanisms of Macroevolution
Recall: Types of Evolution • Microevolution – changes within a population of a particular species • Macroevolution – changes that produce entirely new species = speciation • Speciation is evident in the fossil record and can lead to an increase in biodiversity on Earth
Darwin’s Hypothesis • Darwin was the first to propose this concept of diversification from a common ancestor A page from Darwin’s notebook, while travelling on the Beagle Modern ‘tree of life’ classification diagram
A Species is… • When discussing speciation, it is important to have a clear understanding of what defines a species. • What criteria make one group of organisms a different species from another group?
Definitions of Species • Biological concept • Morphological concept • Phylogeneticconcept
Modes of Speciation • A variety of circumstances can result in the formation of new species, but all involve reproductive isolation of populations. • Different populations can evolve into separate species if some factor prevents those populations from interbreeding (prevents gene flow).
Allopatric Speciation • Speciation caused by geographic isolation 1) Great distance between populations • Ancestors migrate to different islands (Galapagos finches)
Allopatric Speciation (cont) 2) Physical barrier between populations • Isthmus of Panama divides Pacific Ocean and Caribbean Sea (snapper shrimp) • Formation of Rocky Mountains created different environmental conditions on either side • Human influence
Sympatric Speciation • A new species evolves within a large population; the new species coexist in the same environment. 1) Gradual: Due to changes in behaviour • Hawthorn flies vs Apple Flies
Sympatric Speciation (cont) 2) Sudden: Due to mutation or polyploidy • Ontario’s eastern gray treefrog and Cope’s gray treefrog Orange day lily is triploid (3n) and produces 3x as many petals as diploid varieties Ontario variety is tetraploid (4n) while Cope variety is diploid (2n)
Factors that Prevent Interbreeding • Mechanical differences • Incompatible shape of genitalia • Chemical Markers • sperms and egg cells don’t recognize one another • Different haploid chromosome number • Horses and donkeys can mate to produce infertile mules • Behaviour • Breeding during differentseasons or times of day • Different mating rituals