Plant Evolution

Question 1

What is hybridization, and how does it occur?

Answer 1

Hybridization is the crossing of two species, producing offspring with allele combinations that never existed before. It occurs when species overcome isolating barriers.

Question 2

What is a hybrid swarm, and what are its outcomes?

Answer 2

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).

Question 3

What are the prezygotic barriers to hybridization (2 categories, 6 overall)?

Answer 3

ISOLATION 1. Geographical isolation. 2. Habitat separation. 3. Temporal isolation.

POLLEN
4. Pollinator isolation. 5. Pollen compatibility. 6. Pollen competition.

Question 4

How does geographical isolation act as a barrier?

Answer 4

Physical distance prevents pollen transfer. It can be overcome through human movement of plants.

Question 5

How does temporal isolation contribute to speciation?

Answer 5

Different flowering times prevent hybridization. Climate change can disrupt this, enabling species to overlap in time.

Question 6

What is pollinator isolation, and how can it be overcome?

Answer 6

Plants specialize to attract specific pollinators. Stress or invasive generalist pollinators can break this isolation.

Question 7

Why is pollen compatibility critical in hybridization?

Answer 7

The stigma determines which pollen can germinate. Complete incompatibility acts as an absolute barrier.

Question 8

Name postzygotic barriers and their effects.

Answer 8

1. Hybrid viability: Hybrid fails to survive. 2. Hybrid fitness: Hybrid is weak or outcompeted. 3. Hybrid breakdown: Fitness decreases in later generations.

Question 9

What is Dobzhansky-Muller incompatibility?

Answer 9

Novel allele combinations in hybrids can be lethal due to genetic incompatibility between parent species.

Question 10

How can hybrids thrive in intermediate habitats?

Answer 10

Hybrids may perform best in transitional environments, where traits from both parents provide an advantage.

Question 11

Why are hybrids often sterile, and how can this barrier be overcome?

Answer 11

Hybrids have mismatched chromosomes. However, plants produce thousands of seeds, so a small proportion may be fertile.

Question 12

What are Barton-Hewitt tension zones?

Answer 12

These are regions where hybrid zones persist due to a balance between dispersal and selection against hybrids.

Question 13

Why do F2 hybrids often suffer hybrid breakdown?

Answer 13

F2 generations lose heterozygosity and gene complexes necessary for function, leading to reduced fitness.

Question 14

What is transgressive segregation, and how does it affect hybrids?

Answer 14

Mixing alleles in F2 hybrids can produce traits outside the parental range, leading to diversification and new morphologies.

Question 15

How does habitat disturbance promote hybridization?

Answer 15

New environments created by disturbance can favor hybrids with traits suited for these novel conditions.

Question 16

What is polyploidy, and how does it promote speciation?

Answer 16

Polyploidy is the duplication of chromosome sets. It creates reproductive isolation and allows hybrids to persist as new species.

Question 17

What are the differences between autopolyploidy and allopolyploidy?

Answer 17

Autopolyploidy: Chromosome doubling within a single species. Allopolyploidy: Chromosome doubling following hybridization between species.

Question 18

How did Senecio squalidus adapt to the UK environment?

Answer 18

Hybrid plants were introduced from Mt. Etna and adapted to the UK’s disturbed habitats. They spread via wind and rail infrastructure.

Question 19

How did Rhododendron ponticum thrive in Scotland?

Answer 19

Hybridization with other species improved cold tolerance, allowing it to survive harsh winters.

Question 20

How did hybridization between UK and US grasses create a new species?

Answer 20

Spartina anglica formed when Spartina maritima (UK) and Spartina alterniflora (US) hybridized and underwent chromosome doubling (polyploidy).

Question 21

What experimental observation supports hybrid success in transitional zones?

Answer 21

F1 hybrids thrive in habitats between parental environments, demonstrating intermediate fitness advantages.

Question 22

What evidence links habitat disturbance to hybrid success?

Answer 22

Disturbed environments create new niches favoring complex hybrids (F3+ generations) with diverse traits.

Question 23

How did herbivory on land plants evolved among arthropods?

Answer 23

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.

Question 24

Herbivory on land plants evolved among vertebrates

Answer 24

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.

Question 25

Describe how plants contributed to the evolution of flight

Answer 25

Plants contributed to the evolution of flight by providing abundant food sources for insects, which in turn contributed to the evolution of flight in certain insect species for better access to these resources. Easy for insects to climb up plants, more difficult for them to get down. FLight evolved to allow them to evade preadators.

Question 26

Describe a physiological adaptation in plants increased the number of large herbivores that
could be supported by populations in tropical savannah ecosystems

Answer 26

The evolution of C4 photosynthesis allowed plants in tropical savannah ecosystems to efficiently capture CO2 in hot, dry conditions, leading to higher primary productivity and enabling the support of a larger number of large herbivores in these ecosystems.

Question 27

Name three evolutionary innovations in land plants that contributed to major evolutionary changes in one or more groups of animals, saying how in each case. Indicate in which order these three occurred.

Answer 27

1. Development of Vascular Tissue (Xylem and Phloem)
   
   • How it contributed: The evolution of vascular tissue allowed plants to transport water, nutrients, and sugars over greater distances, enabling them to grow taller and colonize more diverse terrestrial environments. This innovation created new ecological niches for herbivores, like the evolution of large land-dwelling arthropods (e.g., millipedes) that could feed on taller plants.
   • Order: Occurred in early land plants, around 400 million years ago, during the Devonian period.
2. Development of Seeds
   
   • How it contributed: Seeds provided a means for plants to reproduce in dry, terrestrial environments by protecting the embryo in a protective coat with stored nutrients. This allowed plants to spread into a variety of new habitats, leading to the evolution of seed-eating herbivores and animals that dispersed seeds, like small mammals and birds.
   • Order: Evolved in seed plants (gymnosperms) around 350 million years ago.
3. Evolution of Flowers
   
   • How it contributed: The development of flowers and the co-evolution of plant-pollinator relationships led to the diversification of flowering plants (angiosperms). This innovation not only provided new food sources (nectar and pollen) for a wide range of animals, such as insects, but also promoted the evolution of complex pollination strategies and animal behaviors.
   • Order: Flowers evolved in angiosperms around 140 million years ago during the Cretaceous period.