plant speciation – part 1 spring 2014. major topics variation in plant populations and species (1)...
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Plant Speciation – Part 1
Spring 2014
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Major topics
• Variation in plant populations and species (1)
• Gene flow and reproductive isolating barriers (1)
• Speciation mechanisms (2)• Species concepts (2)
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Fig. 19.2
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Fig. 19.3B-E
B C
clade
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A B C ED F
Cladogenesis
Cladogenesis
Cladogenesis
Anagenesis
Cladogenesis
Anagenesis versus
Cladogenesis
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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
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Variation in Plant Populations and Species
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One P. jeffreyiecotype isadapted toserpentine soils.
This ecotype hasless overallgenetic diversitythan ecotypesof this species adapted to morefertile soils.
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Clinal variation within a species
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Genetic variation withinand among species ofnative American canes
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Mutation is the ultimate source of all genetic diversity.
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Types of mutations
• Point mutations (change in one base)• Insertions, deletions, inversions,
duplications of parts of a chromosome• Gains or losses of whole chromosomes
(aneuploidy)• Multiples of whole genomes (the full set of
chromosomes in the nucleus) (polyploidy)
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Genetic Recombination
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http://www.pbs.org/wgbh/nova/miracle/divide.html
Review of Mitosis and Meiosis
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Genetic Drift: chance fixation of genes (alleles) in small populations
Generation 1 Generation 2 Generation 3
(5/10 plants leave offspring)
(2/10plantsleaveoffspring)
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Gene flow and reproductive isolating barriers
Figure 13.3A, B
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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)
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Usually measured in meters, but can occur over longer distances.
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Gene flow
• Gene flow within and between populations of a species tends to maintain the cohesiveness of a species
• Lack of gene flow (due to reproductive isolating barriers) between populations is normally required for speciation to occur
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Reproductive Isolating Barriers
Pre-mating
Ecological or habitatisolation
Temporal isolation
Behavioral isolation
Post-mating
Mechanical orphysiologicalisolation
Gametic isolation
Post-zygotic
Hybrid inviability
Hybrid sterility
Hybrid breakdown
See Table 19.1
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Prairie Woodland
White lady’s slipper Yellow lady’s slipper
Habitat isolation
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Temporal Isolation
Red = staminate plantsBlue = carpellate plants
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Behavioral Isolation: Adaptation to different pollinators
Two species of orchids each with a different bee pollinator.
The labellum may be a “key” innovation driving diversification.
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Variation in the orchid labellum
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Two species of Aquilegia(Ranunculaceae)
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Aquilegia formosamesic sites < 3,050 m
Aquilegia pubescensexposed, xeric sites > 2,750 m
Columbines(Aquilegia)in California
Habitat isolation & floral isolation
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Post-mating: Mechanical or physiological isolation
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See Ch. 13: 574-576.
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Beetle pollination is relatively unspecialized andprobably ancestral for angiosperms.
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http://vimeo.com/41976231
http://www.youtube.com/watch?v=B2S5c1s5mPA
Beetle pollination in water lilies:
Double flowering to avoid selfing:
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Bee Pollination
-showy, colorful (blue, purple, yellow) flowers-fragrant-day-flowering-bilateral landing platform-nectar and/or pollen rewards
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Moth pollination
-white or pale, usually large flowers-sweet, strong scent-nectar reward-no nectar guides but may have nectar spurs-night- or dusk-flowering
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Fly pollination
-brown or maroon flowers-fetid odor (rotting meat)-day- or night-flowering-usually no reward-some operate as trap flowers
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Bird pollination
-brightly colored, often red flowers-no scent-day-flowering-usually copious nectar reward-often tubular corolla, often with an inferior ovary
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Bat pollination
-usually large, whitish or colorful flowers-musky, strong scent-night-flowering-usually copious nectar and/or pollen reward
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Moraceae – The Fig and The Fig Wasp
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Wind pollination
-small, numerous often unisexual flowers with reduced or absent perianth-large quantities of pollen, individual grains smooth-feathery styles-no scent
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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)
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Breeding systems are not necessarily mutually exclusive!
Early season, open, cross-pollinated flowers in Viola
Later season, closed, self-pollinated flowers in Viola