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Lecture

BIO120H1 Lecture Notes - Reproductive Isolation, Polyploid, Glossary Of Leaf Morphology


Department
Biology
Course Code
BIO120H1
Professor
Benjamin Wright

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Lecture 8
Speciation
Required readings:
Evolution: A lizards tale (textbook)
Key Concepts/ Terms:
Polyploidy
Taxonomic and biological species
Hybridization
Allopatric and sympatric speciation
Autopolyploidy
Adaptive radiation
Allopolyploidy
1)The major issues: Species concepts, Modes of speciation
2)Adaptive radiation of plants and animals on islands
3)Hybridization and Polyploidy: Types of polyploidy, Evolutionary significance
Number One:
Since populations of a species frequently become adapted to different local environments, it is not
unexpected that some will diverge to the point of being unable to interbreed. If this is the case, the
process of speciation has occurred. What types of biological changes are necessary for the establishment of
a new species? Do the changes that result in a new species occur quickly and result from a few genes? Are
speciation mechanisms different between plants and animals? Although simple answers are tempting,
such questions are difficult to answer explicitly. In fact, it is doubtful that simple answers exist since new
species may become established via several avenues. The factors important in a particular situation are
likely to depend upon the characteristics of the organism, the environment, and the genetic variation
available for selection.
The term species refers to both a taxonomic category and a biological concept. Taxonomic species are
usually based on distinct morphological differences. In most animals, taxonomic species are in general
equivalent to biological species where biological species are defined as:
groups of actually or potentially interbreeding populations, which are reproductively isolated from
other such groups
However, in certain plants the two concepts are frequently not equivalent, because taxonomic species are
frequently interfertile, despite clear morphological differences between them. This pattern is particularly
well developed in island groups, where rapid adaptive radiation results in striking morphological and
ecological differentiation between species, without strong genetic divergence. This situation has led some
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evolutionists to suggest that speciation in plants may involve less genetic differentiation than occurs in
most animal groups.
The traditional classification of modes of speciation is based upon the location of the speciation event in
the species distribution. Speciation may occur when the incipient species are:
1)Geographically separate = Allopatric
2)Coexistent = Sympatric
Allopatric speciation is the most widely accepted model of speciation and can be viewed as a simple
extension of the differential evolution of populations in different areas discussed above. On the other
hand, no real consensus exists about the relative importance of sympatric speciation, and some biologists
have even doubted that sympatric speciation can even occur, except in special circumstances (eg.
polyploidy in plants, see below)
Have to have successful fertilization
Pre-zygotic isolation (anything preventing a zygote from forming)
Reproductive Isolation- if a species is only mating in May or only in June for example
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