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Chapter 33: Q33.5-2CC. (page 713)

The insect Drosophila melanogaster and the nematode Caenorhabditis elegans are prominent model organisms. Are these species the most appropriate invertebrates for making inferences about humans and other vertebrates? Explain.

Short Answer

Expert verified

Human beings are part of the phylum Chordata (a part of Deuterostomia clade), while insects and nematodes belong to the Ecdysozoa clade. Thus, due to the difference in clade, these invertebrates are not the most appropriate choice for inferring about human beings or any other chordate member.

Step by step solution

01

The Bilaterian clade

The phylogenetic tree of the Kingdom Animalia comprises several clades which display the diversification among animals. Bilateria is the clade that descended from the clade eumetazoa and is characterized by bilateral symmetry.

This clade comprises acoelomates and three other descendant clades (Ecdysozoa, Deuterostomia, and Lophotrochozoa).

02

The Ecdysozoa clade

In the Ecdysozoa clade, the members are divided into separate phyla, among which the major phyla are arthropod and nematode. The phylum arthropod is characterized by the presence of jointed appendages in their segmented body, which remains covered inside an exoskeleton.

The phylum nematode is characterized by an unsegmented and cylindrical body that has tapering ends. They lack an exoskeleton.

03

Model organism

A model organism is described as any biological species (apart from human beings) that are used in scientific studies to evaluate and understand different biological activities.

The insect Drosophila melanogaster and the nematode Caenorhabditis elegans are part of the Ecdysozoa clade, whereas humans or other vertebrate organisms are part of the Deuterostomia clade.

The difference in clade suggests that the characteristics exhibited by Caenorhabditis and Drosophila will provide information about other organisms belonging to the Ecdysozoa clade, but not for human beings or any vertebrate organism (member of Deuterostomia clade).

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Most popular questions from this chapter

In Figure 33.2, which two main clades branch from the most recent common ancestor of the eumetazoans?

(A) Porifera and Cnidaria

(B) Lophotrochozoa and Ecdysozoa

(C) Cnidaria and Bilateria

(D) Deuterostomia and Bilateria

In Figure 33.8, assume that the two medusae shown at step 4 were produced by one polyp colony. Review Concept 12.1 and Concept 13.3, and then use your understanding of mitosis and meiosis to evaluate whether the following sentence is true or false; if false, select the answer that provides the correct reason. Although the two medusae are genetically identical, a sperm produced by one will differ genetically from an egg produced by the other.

(A) False (both the medusae and the gametes are genetically identical)

(B) False (neither the medusae nor the gametes are genetically identical)

(C) False (the medusae are not identical but the gametes are)

(D) True

Why did the research team set up four different treatments?

EVOLUTION CONNECTION • INTERPRET THE DATA Draw a phylogenetic tree of Bilateria that includes the ten phyla of bilaterians discussed in detail in this chapter. Label each branch that leads to a phylum with a C, P, or A, depending on whether members of the phylum are coelomates (C), pseudocoelomates (P), or acoelomates (A). Use your labeled tree to answer the following questions:

(a) For each of the three major clades of bilaterians, what (if anything) can be inferred about whether the common ancestor of the clade had a true coelom?

(b) To what extent has the presence of a true coelom in animals changed over the course of evolution?

SCIENTIFIC INQUIRY Bats emit ultrasonic sounds and then use the returning echoes of those sounds to locate and capture flying insects, such as moths, in the dark. In response to bat attacks, some tiger moths make ultrasonic clicks of their own. Researchers hypothesize that tiger moth clicks likely either

  1. jam the bat’s sonar or (2) warn the bat about the moth’s toxic chemical defenses. The graph below shows two patterns observed in studies of moth capture rates over time.

Bats in these experiments were “naive,” meaning that prior to the study the bats had not previously hunted tiger moths. Indicate whether the results support hypothesis (1), hypothesis (2), or both. Explain why the researchers used naive bats in this study.
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