I\'m not sure how to approach these questions: [1] What are polyphenic regulator

Question

I'm not sure how to approach these questions:

[1] What are polyphenic regulatory developmental mechanisms?

Polyphenic developmental mechanisms are threshold mechanisms which determine the future phenotypic form for an individual; for the scarab beetles mentioned before, this mechanism is used to assign horn presence/size with adolescent size (upon pupation); organisms with the same genotype can produce different phenotypes with mechanisms like this.

[2] The authors use the “rock-paper-scissors” 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.

No idea. Not totally sure what the question is asking.

[3] Why might a trimorphic system such as this evolve? Why wouldn’t natural selection just drive all males to have the biggest possible horn, spine, or whatever the ornament involved is?The "biggest" isn't always best - large ornamental accessories often get in the way and can be a detriment to the survival of its bearer. Traits also tend to follow a normal distribution in a population, so extremes exist, but most of the population won't fall in this region (?)

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

Explanation / Answer

1) The frequency of melanic moths at Candy common shows a feeling trend from the year 1959 to 1995.

2) The year at which the frequency of melanic moths is 50% is 1985.

3) The percentage of melanic moths in Michigan also shows a declining trend but with some occasional increase.

4) The expected and observed changes almost coincide with each other albeit with some discrepancy.

5) The discrepancies could be due to changes in environmental conditions.

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