UNIT II – PLANT DIVERSITY

Lecture 9:Lecture 9:

Evidence for EvolutionEvidence for Evolution

and Plant Adaptationsand Plant Adaptations

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

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

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)

• 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!

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

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

Protective coloration

• Coloration that allows an organism to blend with environment

• Moths in bark in polluted England

3. Developmental Biology• Early embryos of different mammal species look

very much alike – they share common features (gills, tail, etc.).

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)

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…

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

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.

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.

Examples of plant adaptations

• Protection: Plants try to avoid predation from herbivores.

• For example: desert plants with thorns;

• fruits distasteful when not ripe.

Coloration

• Coloration : Different flower colors attract different pollinators.

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

Plant adaptations

• Leaves: Adapted to many functions in different plants

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

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 + 0

• Mutualism or symbiosis: both organisms benefit + +

Parasitism• Interaction that benefits one organisms, but

negatively affects another

• Example: Mistletoes, dodder, broomrape

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”

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

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.

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

Examples of co-evolution: symbiosis• There’s ANTS in PLANTS!

• Acacia trees and ants – coevolution.

Pollination: coevolution of plants and insects

• Flowers & insects/birds coevolution for pollination.