plant speciation – part 1 spring 2014. major topics variation in plant populations and species (1)...
TRANSCRIPT
Plant Speciation – Part 1
Spring 2014
Major topics
• Variation in plant populations and species (1)
• Gene flow and reproductive isolating barriers (1)
• Speciation mechanisms (2)• Species concepts (2)
Fig. 19.2
Fig. 19.3B-E
B C
clade
A B C ED F
Cladogenesis
Cladogenesis
Cladogenesis
Anagenesis
Cladogenesis
Anagenesis versus
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
One P. jeffreyiecotype isadapted toserpentine soils.
This ecotype hasless overallgenetic diversitythan ecotypesof this species adapted to morefertile soils.
Clinal variation within a species
Genetic variation withinand among species ofnative American canes
Mutation is the ultimate source of all genetic diversity.
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)
Genetic Recombination
http://www.pbs.org/wgbh/nova/miracle/divide.html
Review of Mitosis and Meiosis
Genetic Drift: chance fixation of genes (alleles) in small populations
Generation 1 Generation 2 Generation 3
(5/10 plants leave offspring)
(2/10plantsleaveoffspring)
Gene flow and reproductive isolating barriers
Figure 13.3A, B
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 longer distances.
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
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
Prairie Woodland
White lady’s slipper Yellow lady’s slipper
Habitat isolation
Temporal Isolation
Red = staminate plantsBlue = carpellate plants
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.
Variation in the orchid labellum
Two species of Aquilegia(Ranunculaceae)
Aquilegia formosamesic sites < 3,050 m
Aquilegia pubescensexposed, xeric sites > 2,750 m
Columbines(Aquilegia)in California
Habitat isolation & floral isolation
Post-mating: Mechanical or physiological isolation
See Ch. 13: 574-576.
Beetle pollination is relatively unspecialized andprobably ancestral for angiosperms.
http://vimeo.com/41976231
http://www.youtube.com/watch?v=B2S5c1s5mPA
Beetle pollination in water lilies:
Double flowering to avoid selfing:
Bee Pollination
-showy, colorful (blue, purple, yellow) flowers-fragrant-day-flowering-bilateral landing platform-nectar and/or pollen rewards
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
Fly pollination
-brown or maroon flowers-fetid odor (rotting meat)-day- or night-flowering-usually no reward-some operate as trap flowers
Bird pollination
-brightly colored, often red flowers-no scent-day-flowering-usually copious nectar reward-often tubular corolla, often with an inferior ovary
Bat pollination
-usually large, whitish or colorful flowers-musky, strong scent-night-flowering-usually copious nectar and/or pollen reward
Moraceae – The Fig and The Fig Wasp
Wind pollination
-small, numerous often unisexual flowers with reduced or absent perianth-large quantities of pollen, individual grains smooth-feathery styles-no scent
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, cross-pollinated flowers in Viola
Later season, closed, self-pollinated flowers in Viola
