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2. Phenotypic dimorphism in which some large male beetles havelarge horns and other males are small and lack horns is thought tobe an example of which of the following? Select ALL correctanswers. A. positive assortative mating B. intersexual selection C.intrasexual selection D. negative assortative mating E. runawayselection

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Reid WolffLv2

30 Sep 2019

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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:

According to the multiplication rule of probability, the chance of crossing two pea plants that are heterozygous for height and have none of four offspring showing the recessive short phenotype is:A. Â¼ Ã Â¼ Ã Â¼ Ã Â¼.

B. Â¾ Ã Â¾ Ã Â¾ Ã Â¾.

C. (Â¼ Ã Â¼ Ã Â¼ Ã Â¼) + (Â¾ Ã Â¾ Ã Â¾ Ã Â¾).

D. Â¼ + Â¼ + Â¼ + Â¼.

E. None of the above.

What characteristic is exhibited by an X-linked trait?

a) Only females have the trait.

Females inherit X-linked traits from their maternal parent only.

c) Females can inherit a gene for an X-linked trait from either parent.

d) Males inherit X-linked traits from their paternal parent only.

e) Males can inherit a gene for an X-linked trait from either parent but normally inherit it from their fathers.

What characteristic is exhibited by a Y-linked trait?

		a) Y-linked traits appear only in male offspring of men with the trait.
		b)Y-linked traits are only passed from father to son.
		c) Y-linked traits can be passed from mother to son.
		d) Both A and B are characteristics of Y-linked traits.
		e) Both A and C are characteristics of Y-linked traits.

Which of the following codes for a phenotypic human male?

		a) XO with a copy of SRY gene on an autosomal chromosome?
		b) XXYY with one copy of the SRY gene deleted?
		c) XX with a copy of SRY gene on an autosomal chromosome?
		d) All of the above sex compliments results in a person with a sex phenotype of male.
		e) XY with the SRY gene located on an autosomal chromosome?

In Drosophila, yellow body is due to an X-linked gene (X^y) that is recessive to the gene for gray body (X⁺). A homozygous gray female is crossed with a yellow male. What are the genotypes of the F₁ progeny?

In some goats, the presence of horns is produced by an autosomal gene that is dominant in males and recessive in females. A horned female is crossed with a hornless male. The F₁ offspring are intercrossed to produce the F₂. What proportion of the F₂ females will have horns?

		a)1/2
		b)3/4
		c)1/4
		d) All
		None

a)		Females are X⁺X⁺; males are X⁺Y.
		b)Females are X⁺X⁺; males are X^yX^y.
		c)Females are X⁺X⁺; males are X^yY.
		d) Females are X⁺X^y; males are X^yY.
		e) Females are X⁺X^y; males are X⁺Y.

	Females inherit X-linked traits from their maternal parent only.
		Females can inherit a gene for an X-linked trait from either parent.
		Males inherit X-linked traits from their paternal parent only.
		Males can inherit a gene for an X-linked trait from either parent but normally inherit it from their fathers.

Males can inherit a gene for an X-linked trait from either parent but normally inherit it from their fathers.

lilacmallard101

Random, chance events that change allele frequencies are knownas:

A. Gene flow

B. Genetic drift

C. Natural selection

D. Balancing selection

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Question 21 pts

What type of selection acts to maintain the two extremephenotypic variants in a population?

A. Disruptive selection

B. Directional selection

C. Positive selection

D. Artificial selection

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Question 31 pts

Approximately, how much of our DNA is shared with our closestrelatives, chimpanzees?

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Question 41 pts

The large canines of male baboons are likely the result of________, while the fact that some male baboons are very colorfulis probably the result of _______.

A. Mutation; balancing selection

B. Gene flow; sexual dimorphism

C. Male competition; female choice

D. Mate choice; genetic drift

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Question 51 pts

Negative assortative mating results in an increased frequency ofhomozygous genotypes within a population.

True

False

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Question 61 pts

Genetic evidence suggests that humans and Neandertals neverinterbred.

True

False

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Question 71 pts

The specific variant of the FOXP2 gene associated with languageacquisition in humans is found in both humans and Neandertals.

True

False

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Question 81 pts

Industrial melanism describes the change in moth color from paleto dark after pollution from factories resulted in coating treetrunks with a layer of dark soot. Which statement is trueconcerning industrial melanism?

A. After pollution levels increased, all moths became darkercolored because soot got on their wings

B. The dark moths survived better after pollution levelsincreased because they were not poisoned by the pollutants

C. Individual moths changed their color in response to thepollution

D. Dark moths were present in the population before pollutionlevels increased

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Question 91 pts

Patterns of evolution can be seen above the species level

True

False

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Question 101 pts

Inbreeding is problematic because it increases the probabilitythat offspring inherit two copies of a recessive mutation thatcauses disease.