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

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.

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

Which type is this?

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

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.

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.

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)

Modes of Speciation Sympatric Speciation: evolution of populations within the same geographic area into separate species. (ex. grey tree frogs)

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:

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.

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.

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.

Answers to homework p 576 #3 Gametic isolation Ecological isolation Behavioural isolation Gametic and/or mechanical isolation Mechanical isolation Zygotic isolation Hybrid infertility/Hybrid inviability Temporal isolation Hybrid infertility