1. UNIT II – PLANT DIVERSITY
Lecture 9:
Evidence for Evolution
and Plant Adaptations

2. Today: Evidence for evolution in living organisms:
1. Comparative anatomy
2. Protective coloration
3. Developmental biology
4. Biogeography
5. DNA
Evidence from extinct organisms: Fossils
Adaptations
Coevolution

3. Evidence in support of evolution
Evidence of evolution can be found in extant organisms (living organisms):
1. Comparative anatomy
2. Mimicry and protective coloration
3. Developmental biology
4. Biogeography
5. Biochemistry and Molecular Biology

4. 1. Comparative Anatomy
Homologous organs: organs similar in form in different organisms due to a common evolutionary origin.
Share same common origin, but may have different functions.
For example: same bone structure found in a human arm, bat wing, dolphin flipper, bird wing…
Lettuce leaves, vine tendrils, cactus spines – have different functions, but same origin (leaf)

5. Analogous organs: organs that have similar look and/or functions in different organisms, but do not share a common evolutionary origin.
For example:
Wings of insects vs. wings of birds
In some plants, stems may look and function like leaves… but they have different origins!

6. Vestigial organs
Vestigial organs: organs or parts of organs that are non-functional and degenerate
An organ loses its function, no selective advantage to have it, but no selective pressure to get rid of it… For example:
Wisdom teeth, Appendix
Vestigial leg bones in snakes, whales

7. 2. Mimicry and protective coloration
Mimicry: a harmless species may resemble a dangerous species.
Ex. Some moths resemble wasps
Coral snake: venomous vs. impostor
“Red on black, venom lack. Red on yellow, kill a fellow”
Monarch butterfly is toxic, Viceroy is not,
But Viceroy mimics the Monarch

8. Protective coloration
Coloration that allows an organism to blend with environment
Moths in bark in polluted England

9. 3. Developmental Biology
Early embryos of different mammal species look very much alike – they share common features (gills, tail, etc.).

10. 4. Biogeography Unequal distribution of organisms on earth
Kangaroos in Australia;
Saguaro Cacti in southwestern U.S. deserts
Each species originated only once, in one place – point of origin…
Species spread out until they encounter a barrier (physical, environmental, ecological)

11. 5. Biochemistry & Molecular Biology
Our genes provide an ‘evolutionary record’
If we evolved from a common ancestor:
We should have same genetic molecule (DNA)
We should use the DNA in the same way (dogma)
Portions of our DNA should be the same (they’re)
Closely related organisms share large portions of DNA sequence…

12. FOSSIL EVIDENCE FOR EVOLUTION
Fossils – any trace left by a previous organism
Rocks, ice, amber, bogs, tar, etc.
Most are preserved in sedimentary rocks
Oldest rocks (fossils) have simplest life forms
Most recent rocks – have more complex life forms

13. ADAPTATIONS Adaptation: A process by which genetic changes occur…
ADAPTATIONS are traits that promote the survival and reproductive success of an organism in a particular environment.
Specific anatomical, physiological or biochemical structures/mechanisms that arise during evolution, as a response to specific environmental pressures.

14. Adaptations
Adaptations may originate as mutations in one individual organism.
Adaptations are universal: life occurs everywhere on earth…
Organisms adapt to a specific niche (place in the environment)
Without adaptations, species can become extinct.

15. Examples of plant adaptations
Protection: Plants try to avoid predation from herbivores.
For example: desert plants with thorns;
fruits distasteful when not ripe.

16. Coloration
Coloration : Different flower colors attract different pollinators.

17. Morphological adaptations
For example: Strawberries grow underground stems (stolons) that break so that a new plant grows asexually.
Also, some leaves of desert plants are hairy, to reduce water loss, leaves in tropics are smooth

18. Plant adaptations
Leaves: Adapted to many functions in different plants

19. Coevolution
Coevolution: the long term evolutionary adjustment of one group of organisms to another.
Coevolution is a reciprocal process in which characteristics of one organism evolve in response to specific characteristics of another

20. Ways in which two organisms can interact
Three ways of interaction:
Parasitism: interaction benefits one organism, but is detrimental to the other (pathogens, parasites, etc.)
Commensualism: benefits one, but neutral to the other
Mutualism or symbiosis: both organisms benefit

21. Parasitism
Interaction that benefits one organisms, but negatively affects another
Example: Mistletoes, dodder, broomrape

22. Commensualism
Interaction benefits one organism, and neutral to the other. Examples:
Epiphytes – plants that grow on top of another plant for support and position.
Orchids, bromeliads, “Spanish moss”

23. Mutualism or symbiosis
Both organisms benefit (“win-win” situation)
Examples:
Lichens: Fungus and algae
Coral and algae
Bacteria and fungi living in roots
Flowers and their pollinators
Plants and insects

24. Coevolution
Mutual evolutionary influence between two species (the evolution of two species totally dependent on each other). Each of the species involved exerts selective pressure on the other, so they evolve together.
For example: Moth and Yucca plant
Yucca flowers are a certain shape so only that tiny moth can pollinate them. The moths lay their eggs in the yucca flowers and the larvae (caterpillars) live in the developing ovary and eat yucca seeds.

25. Plant-Microorganism symbiosis
Nitrogen-fixing bacteria and legume plants
Bacteria receives sugars (food)
Plant receives Nitrogen for nutrient
Mycorrhizae: fungal growth in plant roots
Fungus receives sugars (food)
Plant receives phosphate and water

26. Examples of co-evolution: symbiosis
There’s ANTS in PLANTS!
Acacia trees and ants – coevolution.

27. Pollination: coevolution of plants and insects
Flowers & insects/birds coevolution for pollination.