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bluebear718Lv1

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There are several mechanisms for sexual selection. Fisherrunaway, direct benefit, good gene indicator, sensory bias. Can yougive examples with short explanations for each of these fourmechanisms?

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Related questions

1. Both miRNA and siRNA in eukaryotes and riboswitches inbacteria are capable of regulating gene expression. Explain twospecific differences in the mechanisms of miRNA/siRNA generegulation in eukaryotes and riboswitches in bacteria?

2. We are examining nucleotide substitutions in a histoneprotein gene and in a growth hormone gene in several species ofrodents. We observe that the ratio of nonsynonymous to synonymousnucleotide substitutions (Ka/Ks) is 0.1 for the histone proteingene, but is 1.5 for the growth hormone gene. For each gene, whatdoes this ratio tell us about evolution of these genes with regardto selection and neutrality? Give a brief explanation for eachanswer.

crimsonsnail59

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:

A)The organism must have multiple paired appendages along thelength of its body.
B)These genes are fundamental, and are expressed in all cells ofthe organism.
C)Most of its Hox genes owe their existence to gene fusionevents.
D)Its Hox genes cooperate to bring about sexual maturity at theproper stage of development.
E) The organism has the genetic potential to have a relativelycomplex anatomy.

q2)
Q1) The existence of the phenomenon of exaptation is most closelyassociated with which of the following observations that naturalselection cannot fashion perfect organisms?

A)Adaptations are often compromises.
B)Chance events affect the evolutionary history of populations inenvironments that can change unpredictably.
C)Evolution is limited by historical constraints.
D)Natural selection and sexual selection can work at cross-purposesto each other.