Download Systematic Implications of DNA variation in subfamily

Plant Speciation – Part 1
Spring 2011
Major topics
• Variation in plant populations and
species (1)
• Gene flow and reproductive isolating
barriers (1)
• Speciation mechanisms (2)
• Species concepts (2)
A
B
C
D
E
F
Cladogenesis
Cladogenesis
Cladogenesis
Anagenesis
Cladogenesis
Biological Variation
•
•
•
•
All populations of organisms have inherent variation
within them – a range of genetic variation of which part
is expressed as phenotypic variation
Influences of the environment can change how this
variation is expressed = phenotypic plasticity
Observations by biologists can be interpreted in a
number of ways to determine the similarities or
differences in groups of organisms, depending on
which characteristics are measured or emphasized
Need to understand speciation (the process) in order to
understand patterns of diversity (and vice versa) and to
provide a means to define species
Variation in Plant Populations and
Species
Figure 6.4 from the text
Variation in
the orchid labellum
Clinal variation within a species
One P. jeffreyi
ecotype is
adapted to
serpentine soils.
This ecotype has
less overall
genetic diversity
than ecotypes
of this species
adapted to more
fertile soils.
Figure 6.6 from the text
Genetic variation within
and among species of
native American canes
Mutation is the ultimate source of all genetic diversity.
Figure 6.7 from the text
Types of mutations
• Point mutations (Fig. 6.7)
• Insertions, deletions, inversions,
duplications of parts of a chromosome
• Gains or losses of whole chromosomes
(aneuploidy)
• Changes in whole genomes (the full set of
chromosomes in the nucleus) (polyploidy)
Genetic Recombination
Figure 6.8 from the text
Review of Mitosis and Meiosis
http://www.pbs.org/wgbh/nova/miracle/divide.html
Genetic Drift: chance fixation of
genes (alleles) in small populations
Generation 1
(5/10
plants
Generation
leave
offspring)
2
(2/10
plants
Generation
leave
offspring)
3
Gene flow and reproductive
isolating barriers
Gene flow
• Gene flow = exchange of genes (alleles)
between populations
• In plants, occurs through the dispersal of
pollen or fruits/seeds
• Expected to occur between populations of
the same species, but in plants also
occurs between populations of different
species (hybridization)
Usually measured in meters, but can occur over long distances.
Figure 6.9 from the text
Gene flow
• Gene flow between populations of a
species tends to maintain the
cohesiveness of a species
• Lack of gene flow (due to
reproductive isolating barriers) is
normally required for speciation to
occur
Reproductive Isolating Barriers
Table 6.1 from the text
Habitat isolation
Prairie
Woodland
White lady’s slipper
Yellow lady’s slipper
Adaptation to different pollinators
Figure 6.13 from the text
Figure 6.14 from the text
Habitat isolation & floral isolation
Columbines
(Aquilegia)
in California
Aquilegia formosa
mesic sites < 3,050 m
Aquilegia pubescens
exposed, xeric sites > 2,750 m
Table 4.1 from the text
Beetle pollination is relatively unspecialized
Figure 4.23 from the text
Moraceae – The Fig and The Fig Wasp
Breeding Systems
• Outcrossing = fertilization between
different individuals; depends on ability to
screen pollen by the stigma and style
(incompatibility)
• Uniparental reproduction
– Self-fertilization (pollen from a flower fertilizes
ovules of the same individual)
– Agamospermy (production of seed without
fertilization)
Breeding systems are not
necessarily mutually exclusive!
Early season, open, crosspollinated flowers in Viola
Later season, closed, selfpollinated flowers in Viola
http://www.youtube.com/watch?v=4YQ5q1cjEU4