answer

watching

views

17 May 2018

1. Life history is clearly a different kind of trait than, say, tail length, body color, or tooth shape. Explain how natural selection can affect life history characteristics (and what count as/are examples of life history characteristics).

2. What are some of the tradeoffs involved in life history evolution? Provide and explain at least three different real examples. Which are microevolutionary, and which are macroevolutionary?

answer

watching

164

views

For unlimited access to Homework Help, a Homework+ subscription is required.

You have 0 free answers left.
Get unlimited access to 3.8 million step-by-step answers.

Get unlimited access

Already have an account? Log in

Patrina SchowalterLv2

19 May 2018

Unlock all answers

Get 1 free homework help answer.

Already have an account? Log in

Related questions

1. Discuss and decide upon characteristics that define each of the following broad groups

(domains, kingdoms) of organisms in order to attempt to define these major groups of life

on the planet. Although many characteristics may overlap from one group to the next,

attempt to define some traits that could be used to definitively (exclusively) place an

organism into a specific group. Finally, for each, what would the small subunit ribosomal

rRNA gene sequence tell us?

Viruses

Bacteria

Archaea

Protists (algae, protozoa)

Fungi

Animals

Plants

2. For the previous groups, which include representatives of ones that live as part of the

âhuman ecosystemâ? Provide some examples of each and where they can be found,

including both those that are part of our normal microbiota (i.e., not pathogens) and some

that are.

3. Considering the above and what weâve covered about these groups of organisms,

identify some structures/processes that hypothetically could be used to inhibit or kill

different types of pathogens without (hypothetically, at least) harming the human host.

4. Consider the microbial world. Which has a greater impact or importance â pathogens,

or benign microbes? Explain, giving examples.

5. A number of antibiotics target the bacterial 70S ribosome, exploiting structural

differences from the 80S ribosome found in humans and other eukaryotes. Although

effective at killing bacteria, these drugs can still have some toxicity to humans. In the

context of the endosymbiotic theory of evolution, provide a hypothesis as to why this

might be.

viridianeel412

Excerpts from âOn the Tendency of Varieties to Depart Indefinitely from the Original Type,â by Alfred Russel Wallace [Read July 1st, 1858].

The life of wild animals is a struggle for existence. The full exertion of all their
faculties and all their energies is required to preserve their own existence and
provide for that of their infant offspring. The possibility of procuring food during
the least favourable seasons, and of escaping the attacks of their most dangerous
enemies, are the primary conditions which determine the existence both of
individuals and of entire species. These conditions will also determine the population of a species; and by a careful consideration of all the circumstances we may be enabled to comprehend, and in some degree to explain, what at first sight appears so inexplicableâthe excessive abundance of some species, while others closely allied to them are very rare. ...

... It is also evident that most changes would affect, either favourably or adversely, the powers of prolonging existence. An antelope with shorter or weaker legs must necessarily suffer more from the attacks of the feline carnivora; the passenger pigeon with less powerful wings would sooner or later be affected in its powers of procuring a regular
supply of food; and in both cases the result must necessarily be a diminution of the population of the modified species. If, on the other hand, any species should produce a variety having slightly increased powers of preserving existence that variety must inevitably in time acquire a superiority in numbers. ...

Complete the chart below for the excerpt from Wallaceâs paper. Provide examples of evolution by natural selection that Wallace used in his writing. Describe the species, the variations among individuals, the selective pressure, and how species change over time.

2 examples must be provided for each question and species.

Wallace âNatural Selection

Species:

What trait varies within the species?

What is the selective pressure? (In other words, what causes some individuals to produce more offspring than others?)

How would the population change over time?

QUESTION SET 3

Sexual Selection, Developmental Thresholds, and Ornamentation

INTRODUCTION

In Chapter 10 you read about how sexual selection can drive the evolution of bizarre and sometimes costly ornamentation or weaponry in animals, often in males. This paper reveals a situation where sexual selection is the driver, but the result is more complex than might be expected at first glance. The authors describe some beetle species where different thresholds encountered as larvae result in different levels of ornamentation, and consequently different reproductive strategies.

The authors show that in one family of beetles (the Scarabeidae [dung beetles]), two different threshold mechanisms have independently evolved. Each of these thresholds has a different effect on horn development in the males of these beetles. Both mechanisms are triggered by body size in larvae. For one mechanism, if a larva attains the threshold size its adult morphology (the phenotype it will have after it pupates) switches from being hornless to being horned. The second threshold, also based on larval body size, similarly results in either having a short or a long horn (see Figure 2).

This discovery led the authors to look more closely at other beetle species where male polymorphism was known to occur, and they found two other examples where this double threshold mechanism was operating (see Figure 1). In the family Lucanidae (stag beetles), they found that male trimorphism was characterized by differences in the mandibles, with male mandibles exhibiting three increasing sizes moderated by the thresholds. In the family Curculionidae (weevils), the thresholds controlled the development of ventral body spines. Here, the beetles either lacked spines (and thus resembled females), had short spines, or had long spines.

The authors suggest that this multiple-threshold system may be more prevalent than previously thought, and anticipate more examples coming to light.

QUESTIONS

Question 1

What are polyphenic regulatory developmental mechanisms?

Answer:

Question 2

Can you think of an example of polyphenic regulatory developmental mechanisms besides the beetles mentioned in this paper.

Answer:

Question 3

The authors use the ârock-paper-scissorsâ analogy to describe the potential result of this two threshold system when it comes to reproductive success in dung beetles. As in the game of rock-paper-scissors, each possible pair-wise comparison has a clearly defined winner. Give a hypothetical example of what this might look like in the context of dung beetle mating success.

Answer:

Question 4

What is the difference between the systems described in this paper and the other examples of male trimorphism cited by the authors (in isopods, lizards, and birds)?

Answer:

Question 5

Why might a trimorphic system such as this evolve? Why wouldnât natural selection just drive all males to have the biggest possible horn, spine, or whatever the ornament involved is?

Answer: