BIOE 109 Evolution
Greenhouse Exercise
PART I: Studying evolution in plants
Algae:
- small unicellular to multi-cellular complex forms (e.g. giant kelps that can grow 65
meters)
- photosynthetic organisms
Non-vascular plants:
- simplest of all land-dwelling plants
- closest ancestor is green algae (charophytes)
- waxy cuticle
- lack true stems, leaves, roots, no flowers
- lack an internal means of water transportation
- dominant generation is gametophyte (haploid).
Examples: mosses (bryophyta) and liverworts (hepatophyta)
Questions:
1. Why non-vascular plants do not grow beyond few centimeters?
2. Why these plants have never dominated much of the earth’s landscape?
Vascular plants:
- True roots, stem and leaves present
- Vascular system to circulate resources through plants. This allows vascular plants to
evolve larger size.
- stomata present
- Dominant generation phase is sporophyte (diploid).
Example: Fern (Pteridophytes)
Question: 1. Why does a vascular system provide an evolutionary advantage?
Gymnosperms:
- The gymnosperms translates as 'naked seeds'
- their seeds not enclosed in an ovary but borne in cones.
- No flowers, ovaries
- Gymnosperm sperm do not swim to the egg using water as the transfer vector.
- Pollen grain is carried by wind or animal to the female gametophyte. - Vascular
cambium, Wood
- many have economical or human use
Examples: Conifers/Cycads
Question: Gymnosperms dominated earth’s landscape before flowering plants evolved.
Which adaptations made them so successful?
Angiosperms (Flowering plants):
- Greek angion= container. In contrast to the gymnosperms, the angiosperms have their
ovules and seeds enclosed inside the ovary.
- Flowers!!!
- the male gametophyte is the pollen grain, and the female gametophyte is the ovule, after
pollination and fertilization the ovule develops into the seed.
- double fertilization: This leads to an additional novel tissue with maternal
protuberance, the triploid endosperm. In mature seeds of most angiosperm species, the
embryo is enclosed by endosperm tissue.
- A seed consists of an embryo, stored food and a seed coat. The seed replaces the spore
(like in seed-less fern plants) as a means of propagation, dispersal and genetic storage
unit.
- angiosperm seeds can be dispersed as fruits, i.e. the seeds can have additional pericarp
(fruit coat) around the testa (seed coat). Fruit aids in seed dispersal by attracting animals
and may also protect the seed from external elements.
Spore vs. Seed
A primary difference between spore-based and seed-based reproduction is that in seed
producing plants, the act of fertilization (union of the male and female cells) takes place
before the seed leaves the parent plant, while in spore-producing plants, fertilization takes
place after the spore leaves the parent.
Another difference is that self-fertilization is more likely in the process of spore-based
reproduction than in the pollination of a flowering plant. The seed-based process,
therefore, has more possibilities for genetic adaptation and evolution.
Questions:
1. Why is endosperm important for flowering plant success and why is it important
for our success as a species?
2. Why would the production of fragrance, color, or nectaries save energy for the
flowering plant group?
PART II: Studying adaptations to different habitats in plants
CARNIVOROUS PLANTS
- These usually grow in nutrient poor habitats such as bogs and fens.
- Sarracenia sp.:A common plant in the bogs of the northeastern part of North America.
Uses pitfall trap. Bacteria living in the pitcher provide digestive enzymes.
- Nepenthes sp.: a native of Southeast Asia and Australia, forms pitchers (cups) that hang
from trees. (note: the cupped leaves and very fine spines)
Pitcher is a highly modified leaf. They attract insects with the odor of nectar. Digest the
prey using very strong digestive acids.
1. Both of these plants evolved from nutrient poor environments. Why is being a
carnivore advantageous in this type of environment?
DEFENSE
- Plant defense mechanisms against herbivores include spines, toxins (alkaloids).
- Chorisia sp.- Brazil, has huge spines on trunk
- Acacia sp.- Abundant in Mexico, Costa Rica. Plants growing in arid regions have thorns
and alkaloids
2. Acacia and ants are associated with another type of evolution? What is it?
DRY CLIMATE
- Euphorbia sp.- Morocco
- Mytillacactus sp.- Mexico
- both have same body plan despite their far geographic distance from each other.
3. What information would you need to determine whether this is parallel or
convergent evolution?
WIND VS. INSECT POLLINATION
Gymnosperms- mostly wind pollinated
Grasses- mostly wind pollinated
Angiosperms- mostly insect/ bird pollinated
4. What type of environment would necessitate insect pollination rather than wind?
PART III: Monkey-flower plants and their pollinators-a case study
Aim:- To understand how plants can evolve traits that allow them to be pollinated by
different pollinators using two closely related species of monkey-flower plants (Mimulus
sp.)
Materials:- Mimulus cardinalis
Mimulus lewisii
Mimulus hybrid
A small plastic ruler
Razor blade
Writing material (pen/ pencil)
A calculator
Method:- Each group is going to measure various floral characteristics listed below using
any 3 flowers of the given species of Mimulus. Record your observations in the table
given below.
Use following diagram as a guide to identify various parts of the flower-
Observations:Floral
Character
Yellow
Red
Corolla Floral
pigment pigment aperture tube
(high/low) (high/ width
length
low)
Stamen
length
(scaled
to floral
tube
length)
Pistil
length
(scaled
to floral
tube
length)
Sample 1
Sample 2
Sample 3
Average
Sample 1
Sample 2
Sample 3
Average
Any other special observation(s) you want to note down:
Discuss the observations in your group with respect to following points:
1. Is there variation in floral traits between the flowers that you measured?
2. Are floral characters important in deciding pollination mechanisms?
3. Looking at the floral characters what kind of pollinating agent do you suggest for
this species? (wind/ water/ insect/ bird as a pollinator)
4. Justify why that pollinating agent is best suited for the species.