Transcript UNIT II – PLANT DIVERSITY

UNIT II – PLANT DIVERSITY
Lecture 9:
Evidence for Evolution
and Plant Adaptations
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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
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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
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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
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• Mutualism or symbiosis: both organisms
benefit
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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
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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.