Invertebrates II

From last week

Invertebrates: No backbone

Acoelomates and coelomates today

Flatworms: Phylum Platyhelminthes

Bilateral symmetryThree germ layersOrgansAcoelomates Incomplete digestive system (one opening)Cephalization (concentration of sensory

organs and nerves in head)Some are hemaphrodites; Some are parasiticPlanaria: Organ systems ladder-like

Advantage?

Planaria (flatworm)

Tapeworm (parasitic flatworm) Taenia pisiformism (view slides)

Bilaterally symmetrical Three germ layers Cephalization Coelomate Mostly marine

◦ Some freshwater and terrestrial Visceral mass: includes internal organs Mantle: thin tissue

◦ Secretes shell in some molluscs Muscular foot for locomotion

Mollusca

Mollusk Diversity

Gastropods: snails, slugs, nudibranchs Chitons Cephalopods: octopuses, squid Bivalves: oysters, mussels Today:

◦ Dissect a clam◦ Dissect a squid◦ Compare

Segmented worms 3 germ layers Bilateral symmetry Coelomates Cephalization Include leeches, earthworms and

marine worms Have setae to assist in

movement (bristles) Earthworms have clitellum for

reproduction Today: view earthworm model

◦ No dissection

Annelida

Bean Beetles--Callosobruchus maculatus Phylum Arthropoda Herbivorous pests that live 1-2 weeks as

adults Lay single eggs that change into larvae

several days later Larvae burrow into bean and pupate Emerge 24-36 hours later

Eggs on a bean

Experiment

Do female bean beetles discriminate between types of beans when choosing a place to lay eggs?◦ Design your own experiment◦ Collect results next week

We will use a Chi Square to analyze our data◦ Used to test an alternative hypothesis (Ha) vs. a

null hypothesis (Ho) Ha: There is a difference Ho: There is no difference

Chi2 Test Statistical test to test our hypothesis Test based on differences between the

observed results and the expected values (based on null hypothesis)

The formula for X2 is as follows:

◦ o is the observed frequency ◦ e is the frequency expected under the null

hypothesis of no difference between groups.

Example: Snail sediment type preference

20 snails 2 sediments: mud and sandNull hypothesis: There is no difference in

sediment preference for this species of snail. Expected results: 10 in mud, 10 in sand Actual results: 13 in mud, 7 in sand

Chi2 Test on snail results

Mud Sand

Observed 13 7

Expected 10 10

• Now you compare your experimental value (1.8) to a critical chi2 value.

Chi2 Test comparison

Degrees of Freedom: the number of independent cases◦ (number of rows-1)(number of columns-1)◦ (2-1)(2-1)=1 degree of freedom

p level: level at which the given statistic is on the border between rejecting or not the null hypothesis◦ Probability that values outside this set level are

due to chance sampling errors rather than real differences

Use p=0.05◦ At p=0.05 you are 95% sure your results are

real

Chi2 Table

If test>critical value @ p level, reject null hypothesis

If test<critical value @ alpha level, fail to reject null hypothesis

Bean Beetle Experiment Outline Week 1:

◦ Design your experiment Work first in your groups. Then we will come together as a class to

determine a final procedure

◦ Things to consider: How many beetles? How many different types of beans?

Beetles were raised on mung beans How many beans of each type? How many replicates?

Week 2◦ Record results◦ Compile class data◦ Statistical analyses using class data◦ Discuss lab report