Plant Evolution Flashcards
What is hybridization, and how does it occur?
Hybridization is the crossing of two species, producing offspring with allele combinations that never existed before. It occurs when species overcome isolating barriers.
What is a hybrid swarm, and what are its outcomes?
A hybrid swarm is a large population of hybrid descendants. Outcomes: 1. Gene transfer between species. 2. Evolution of new species. 3. No effect on parent species (most common).
What are the prezygotic barriers to hybridization (2 categories, 6 overall)?
ISOLATION 1. Geographical isolation. 2. Habitat separation. 3. Temporal isolation.
POLLEN
4. Pollinator isolation. 5. Pollen compatibility. 6. Pollen competition.
How does geographical isolation act as a barrier?
Physical distance prevents pollen transfer. It can be overcome through human movement of plants.
How does temporal isolation contribute to speciation?
Different flowering times prevent hybridization. Climate change can disrupt this, enabling species to overlap in time.
What is pollinator isolation, and how can it be overcome?
Plants specialize to attract specific pollinators. Stress or invasive generalist pollinators can break this isolation.
Why is pollen compatibility critical in hybridization?
The stigma determines which pollen can germinate. Complete incompatibility acts as an absolute barrier.
Name postzygotic barriers and their effects.
- Hybrid viability: Hybrid fails to survive. 2. Hybrid fitness: Hybrid is weak or outcompeted. 3. Hybrid breakdown: Fitness decreases in later generations.
What is Dobzhansky-Muller incompatibility?
Novel allele combinations in hybrids can be lethal due to genetic incompatibility between parent species.
How can hybrids thrive in intermediate habitats?
Hybrids may perform best in transitional environments, where traits from both parents provide an advantage.
Why are hybrids often sterile, and how can this barrier be overcome?
Hybrids have mismatched chromosomes. However, plants produce thousands of seeds, so a small proportion may be fertile.
What are Barton-Hewitt tension zones?
These are regions where hybrid zones persist due to a balance between dispersal and selection against hybrids.
Why do F2 hybrids often suffer hybrid breakdown?
F2 generations lose heterozygosity and gene complexes necessary for function, leading to reduced fitness.
What is transgressive segregation, and how does it affect hybrids?
Mixing alleles in F2 hybrids can produce traits outside the parental range, leading to diversification and new morphologies.
How does habitat disturbance promote hybridization?
New environments created by disturbance can favor hybrids with traits suited for these novel conditions.
What is polyploidy, and how does it promote speciation?
Polyploidy is the duplication of chromosome sets. It creates reproductive isolation and allows hybrids to persist as new species.
What are the differences between autopolyploidy and allopolyploidy?
Autopolyploidy: Chromosome doubling within a single species. Allopolyploidy: Chromosome doubling following hybridization between species.
How did Senecio squalidus adapt to the UK environment?
Hybrid plants were introduced from Mt. Etna and adapted to the UK’s disturbed habitats. They spread via wind and rail infrastructure.
How did Rhododendron ponticum thrive in Scotland?
Hybridization with other species improved cold tolerance, allowing it to survive harsh winters.
How did hybridization between UK and US grasses create a new species?
Spartina anglica formed when Spartina maritima (UK) and Spartina alterniflora (US) hybridized and underwent chromosome doubling (polyploidy).
What experimental observation supports hybrid success in transitional zones?
F1 hybrids thrive in habitats between parental environments, demonstrating intermediate fitness advantages.
What evidence links habitat disturbance to hybrid success?
Disturbed environments create new niches favoring complex hybrids (F3+ generations) with diverse traits.
How did herbivory on land plants evolved among arthropods?
Herbivory on land plants evolved among arthropods as some early arthropods adapted to consume plant material, driven by the availability of plant biomass and the emergence of defensive plant compounds.
Herbivory on land plants evolved among vertebrates
Herbivory on land plants evolved among vertebrates when early vertebrates, such as reptiles, began exploiting plants as a food source, aided by the rise of herbaceous plants in terrestrial ecosystems.