BIO152H5 Lecture Notes - Lecture 16: Pangaea, Reproductive Isolation, Fire-Bellied Toad

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26 Nov 2015
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Lecture 16: Speciation
Speciation: process by which one species splits into 2 or more, many shared characteristics
example: flightless and flying cormorant birds
MICROevolution – change in allele frequency over time
mutation, gene flow, genetic drift, natural selection
MACROevolution – evolution on a large scale
new groups of organisms, origin of new species
Define 'species'...
evolutionarily independent group or population
four approaches to identify
biological (actually/potentially interbreeding population which is reproductively isolated)
can't be applied to fossils or asexually reproducing organisms, downplays n. selection
reproductive isolation: barriers that prevent 2 species from interbreeding
- prezygotic: prevent zygote formation, block fertilization from occurring
habitat, temporal, behavioural, mechanical, gametic isolation, etc
- postzygotic: prevent proper development/function of zygote once formed
reduced survival, reduced fertility, decreased chance of survival
morphological (look at structural features, size, shape, and emphasize unifying chars)
great for fossils, applicable to sexual and asexual species, but morphology does not
always show relatedness, and is also very subjective- 2 people may not agree
ecological (ecological niches, how organisms adapt to different environments)
emphasizes role of natural selection, favors traits that benefit organisms in environment
phylogenetic (smallest group of individuals sharing a common ancestor)
look at all of the above- morphology, embryology, molecular data
what degree of difference do you stop at? what defines separation of species?
Subspecies: have their own identifying features but are not distinctly a separate species
Speciation
a) isolation of populations (no gene flow)
b) genetic divergence as a result
Two modes...
allopatric (geographic isolation)
adapting to new environment
example: flightless birds from pangaea -> ostrich, kiwi, etc
sympatric (no geographic isolation)
more rare than allopatric
may happen due to polyploidy resulting in fertile hybridization
most often found in flowers that self-pollinate
Speciation does NOT always occur when either of these happens- is only a POSSIBILITY.
Sexual selection can cause reproductive isolation (females choose certain mates).
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