BIO 101 Name:______
Microevloution, Survival, Adaptation Learning and Coevolution:
Objectives
The purpose of this exploration is to . . .
1. Explore the micro-evolutionary processes.
2. Explore the impact of effects such as selection and predation on allele frequencies.
3. Understand the relationship between variation in a population and natural selection.
4. Recognize the selective advantage of various adaptations.
5. Distinguish between physiological and developmental responses of the individual and adaptive responses of the population.
Background:
ANearly every part of the earth=s surface is inhabited by life. Living organisms are found in the surface of the sea and in the great ocean depths, on the land from the tropics to the polar latitudes, and thousands of feet high in the atmosphere. Bare rocks are colonized by lichens, glaciers by red algae, and hot springs by bluegreen algae. No one kind of organism, however, lives in all these varied environments.
Each kind of organism normally lives in a particular zone of the earth=s surface characterized by a certain range of environmental conditions. We expect to find sponges on the ocean bottom, earthworms in moist humuscontaining soil, cacti in warm deserts, ducks in fresh water ponds and air above, and colon bacteria in the human intestine. The natural abode of an organism in which it can sustain life is its habitat. Every kind of organism occurs in a particular habitat; removed from its normal habitat it is like a fish out of water.
The reason why each kind of organism is restricted in nature to its own habitat and is not normally found elsewhere is that it is specialized or adapted for making a living under one particular set of conditions. Adaptation, or the hereditary adjustment to the environment, is one of the universal features of life. Earthworms are well fitted to live on the organic materials in soil. No other kind of organism can compete with them in their own territory. But, conversely, earthworms are unable to live in the habitats of ducks or sponges and if they are accidentally dispersed to such places they soon die.
Each kind of animal, plant, or microorganism is a complex of adaptations for performing its life functions in its normal habitat.@
Verne Grant 1963
Organisms can and do respond to changes in their environment. One type of response acts at the level of the individual and the other acts on the population. The type of response described by Verne Grant, adaptation, is a change in the population over time. Adaptations are products of microevloutionary processes: natural selection, genetic drift, gene flow, and mutation. If a population is examined at any point in time, variation among the individuals is evident.
The variations are a result of the different genotypes in the population. Selection acts on the existing variation. Those individuals with traits that allow them to survive and reproduce are more likely to pass their genotypes on to descendents. In successive generations, the population will have a greater proportion of the successful (or more fit) genotypes than the unsuccessful genotypes. The nature of the population as a whole, or the gene pool, will have changed or evolved. It=s important to remember that although selection acts on the phenotype of an individual, the individual does not evolve; populations evolve. individuals do not! Thus adaptations are products of evolution.
The other type of response to the environment occurs at the level of an individual organism. All organisms can respond to stimuli. Often these are physiological responses such as when you stand in the hot sun, you will sweat. Other responses are modifications at key steps in development. For example, genetically identical clones of many herbs will be taller and have larger leaves when growing in moist, shady environments compared to dry, sunny environments. The leaves also have different shapes and thicknesses in the different environments. The range of responses, whether physiological or developmental, allows individuals to survive over a range of conditions. Because they are Achanges@ in the individual they are often confused with adaptations. The major difference is that both physiological and developmental responses do not directly change the genotypes of the individual. They can only indirectly affect the change in the population by contributing to the survival of the individual.
The focus of this lab is to explore the relationship between the changes in organisms and survival. The distinction between responses of the individual (both physiological and developmental) and the responses of the population (adaptation).
Part 1
1. Natural Selection Simulation
In this laboratory session we will set up a simulation of a community. The community will be composed of one PREDATOR and one PREY; but each of these species will consist of different MORPHOLOGICAL VARIANTS. We will examine how the process of natural selection results in the evloution of PREDATORS and PREY~ thus co-evolution
When one species interacts extensively with other species in the environment, the effect of natural selection on one group will affect the others. This is probably self-evident to most of you. This process is called CO-EVOLUTION. If, for example, a significant change in the phenotype of a PREY species occurs, it is likely that identifiable changes in the PREDATOR will eventually result. However, observing these changes in nature is difficult because evolutionary changes occur over many generations. Since most of you probably do not want to be in BIO 110 lab for several generations, we are going to simulate the process of CO-EVOLUTION.
Remember that in natural populations, phenotypic variability is standard. Some phenotypes or
MORPHS (morphological variants) of a species will be able to exploit the environment more effectively than others. If one now considers a large population and many generations, these individuals with this particular characteristic will produce more offspring and eventually the characteristic(s) (phenotype) will become predominant in the population. This change in the genetic make-up of a population is what we call evolution. Keep in mind that evolution is an ongoing process and only involves characteristics that can be genetically inherited.
PROCEDURE: Our simulated community will be composed of:
PREY:
The PREY MORPHS (members of the same species with different alleles) are represented by:
red beans, white beans, green peas, macaroni.
PREDATORS:
The PREDATORS are the students and the different MORPHS will be represented by different collecting devices: clothes pins, forceps, and test-tube holders (all are the same species but like individual birds have different beaks)
At the beginning of the selection game, both PREDATOR and PREY MORPHS will be equally common; but after the first round of “predation” the relative numbers of MORPHS for the next generation (reproductive success) will be determined by the degree of PREDATOR success at obtaining PREY and the success of PREY at avoiding capture.
Prediction:
Ideally we expect that a balance between PREDATORS and PREY MORPHS should be reached (best catchers and best escapees predominating).
SPECIFIC GAME RULES (no cheating)
1. One hundred (100) of each type of PREY will be scattered over a defined area (60”x 21”) at the start of the game.
2. PREDATORS simultaneously begin a 35 second search-and-capture round using their designated collecting devises. Only the tool may be used and each PREY must be placed in the cup one at a time. Stop immediately when time is called. Count all the items in the cup by morph.
3. PREDATORS report their catch to two recorders:
a. Total Prey Captured by Morph (Sheet1, Prey Recorder) and,
b. Predator Capture Total by Prey Morph (Sheet 2,Predator recorder).
4. Recorders will calculate the composition of the next generation of PREDATOR and PREY as described on the worksheets.
5. Reseed the plot with PREY and redistribute the collection devices according to the work sheet calculations. At the start of each round there should always be 400 prey on the capture field.
6. Continue the process for 4 rounds.
Data Sheet1. Total Prey Captured by Morph
Round 1
White Beans
Red Beans
Green Peas
Macaroni
Total
Round 2
White Beans
Red Beans
Green Peas
Macaroni
Total
Round 3
White Beans
Red Beans
Green Peas
Macaroni
Total
Round 4
White Beans
Red Beans
Green Peas
Macaroni
Total
Data Sheet 2. Predator Capture Total by Prey Morph
Beans / Beans / Peas / Captured by / Prey by
Preator Morph / Predator morph
Round 1
Clothes Pin
Forceps
Test-tube Holder
Total
Round 2
Clothes Pin
Forceps
Test-tube Holder
Total
Round 3
Clothes Pin
Forceps
Test-tube Holder
Total
Round 4
Clothes Pin
Forceps
Test-tube Holder
Total
2. Seed Dispersal Adaptations
All organisms have specialized characteristics that allow them to grow and reproduce in specific habitats. As explored above, certain morphological and physiological features are more advantageous than others in any given habitat. These adaptations are directly programmed by the genetic codes of the organisms. The adaptations have allowed survival and reproduction.
An interesting dilemma of sedentary organisms like plants is getting the offspring away from the parents. Many plants have evolved specialized structures that help transport the seed to new sites. The type of dispersal adaptation greatly affects the distance and speed of distribution of plants. The modifications make use of mediums such as air, water, and animals. Examine the seeds (and fruits) provided in lab and determine what is the most likely seed dispersal agent (i.e. wind, water, animal, etc.) then record what specific seed structures suggest this.
Background Information
Dispersal by Wind
Fruits and seeds have a variety of adaptations for wind dispersal. The samara of a maple has a curved wing that causes the fruit to spin as it is released from the tree. In a brisk wind, samaras may be carried up to 1 0 kilometers (6 miles) away from their source, although usually most are relatively evenly distributed within a few meters of the tree. In hop hornbeams, the seed is enclosed in an inflated sac that gives it some buoyancy in the wind. In some members of the Buttercup and Sunflower Families (Ranunculaceae and Asteraceae), the fruits have plumes, and in the Willow Family (Salicaceae), the fruits are surrounded by cottony or woolly hairs that aid in wind dispersal. In button snakeroots and Jerusalem sage, the fruits are too large to be airborne, but they are spherical enough to be rolled along the ground by the wind.
Seeds themselves may be so tiny and light that they can be blown great distances by the wind. Orchids and heaths, for example, produce seeds with no endosperm that are as fine as dust and equally light in weight. In catalpa and jacaranda trees, the seeds themselves are winged rather than the fruits, which remain on the branches and split, releasing their contents. Dandelion fruitlets have plumes that radiate out at the ends like tiny parachutes; these catch even a slight breeze. In tumble mustard and other tumbleweeds, the whole aboveground portion of the plant may abscise (separate from the root) and be blown away by the wind, releasing seeds as it bumps along.
Dispersal by Animals
The adaptations of fruits and seeds for animal dispersal are legion. Birds, mammals, and ants all act as disseminating agents (Pig. 8.23). Shore birds may carry seeds great distances in mud that adheres to their feet. Other birds and mammals eat fruits whose seeds pass unharmed through their digestive tracts. Some bird-disseminated fruits contain laxatives that speed their passage through the birds’ digestive tracts. In blackbirds, the seeds may remain in the tract as little as 15 minutes, but in mammals, the period is more commonly about 24 hours. In the giant tortoises of the Galapagos Islands, seeds do not pass through the tract for 2 weeks or more, and the seeds usually will not germinate unless they have been subjected to such treatment. Some seeds and fruits are gathered and stored by rodents, such as squirrels and mice, and then are abandoned. Blue jays, woodpeckers, and other birds carry away nuts and other fruits, which they may drop in flight and abandon.
Many fruits and seeds catch in or adhere to the fur or feathers of animals and birds. Bedstraw and bur clover fruits are covered with small hooks that catch in fur (or a hiker’s socks). The large capsules of unicorn plants have two giant, curved extensions about 15 centimeters (6 inches) long. These catch on the fetlock of a deer or other animal that happens to step on the fruit, and the seeds are scattered as the animal moves along. Twinflowers and flax have fruits with sticky appendages that adhere to fur on contact, and those of the puncture vine penetrate the skin and stick by means of hard little prickles.
Dispersal by Water
Some fruits contain trapped air, adapting them to water dispersal. Many sedges, for example, have seeds surrounded by inflated sacs that enable the seeds to float (Fig. 8.26). Others have waxy material on the surface of the seeds, which temporarily prevents them from absorbing water while they are floating. Sometimes, a heavy downpour will create a torrent of water that dislodges masses of vegetation along a stream bank, carrying whole plants and their fruits to new locations. Large raindrops themselves may splash seeds out of their opened capsules. Seeds and fruits of a few plants have thick, spongy pericarps that absorb water very slowly. Such fruits are adapted to dispersal by ocean currents, even though salt water eventually may penetrate enough to kill the delicate embryos. Enough fruits are beached before this occurs to ensure the survival of the species. Contrary to popular belief, coconuts that fall into water usually become waterlogged and sink in a few days. Rarely, if ever, are they carried hundreds of kilometers out to sea.