Horns in Beetle Competition
Intraspecific competition-that is, competition between members of the same species for limited resources-can be a complex phenomenon, as illustrated by studies on horned beetles. Beetle horns, which are the rigid extensions of the hard, shell-like exoskeleton of insects have evolved repeatedly within this order of insects and are generally only expressed in males, who use them in combat with other males for access to resources or females. These resources are in discrete, readily defensible patches, and the horns allow males to defend these sites and to mate with the females found there. The contests between males can be dramatic, and the winner is rewarded with mating privileges.
Horns constitute a large investment in energy, and as much as 10 percent of body mass may be devoted to them. Horn growth prolongs development time and risk of larval mortality, and there is a trade-off between horn development and the ability to fly. Finally, the development of horns leads to lowered visual acuity and to smaller eyes. Nevertheless, it appears that since larger horns are useful in gaining access to females, the reproductive benefits gained from large horns offset the costs of production and maintenance.
The ability of males to grow horns is based on larval nutrition. Both final adult body size and the size of horns in males depend on the amount of food they consume as larvae. Males exposed to poor conditions as larvae are small and do not produce horns, whereas well-fed males become large adults able to produce horns. Horn production shows an insignificant level of heritable genetic variation.
These complexities and trade-offs are illustrated through studies of dung beetles of the genus Onthophagus. The basic life history of these beetles is as follows. After finding a patch of dung (animal waste products), a female digs a tunnel in the soil beneath the dung. She then buries dung below ground to provide nutrition for the larvae. Females spend days inside a single tunnel, pulling down pieces of dung to various blind ends of tunnel branches, each with its “brood ball”of dung. A single egg is laid at the top of a brood ball, and a single larva develops in isolation within the brood ball.
Females mate repeatedly with males during the time of egg laying. Male reproductive behavior consists of securing their unique access to a female in a tunnel. The large, horned males guard the tunnels and fight other males trying to approach the females. Larger males with larger horns win these fights. For two males of the same size, the one with the larger horns usually wins. Thus, long horns provide males with significant advantages.
However, all is not lost for a small male. Although they are not adept at guarding entrances to tunnels or winning contests, small males have other tactics. They attempt to slip undetected past the large males, or they dig side tunnels that intercept a guarded tunnel well below ground. Thus hornless males may manage to sneak undetected into guarded tunnels and mate with the female. If such a sneaker male is caught, he is chased out by the resident male, who then returns to the female and mates with her. This dilutes or displaces sperm (reproductive cells contained within a fluid) from the sneaker male. Sneaker males actually do best when they have no horns at all, since horns get in the way of sneaking. Success for a small male depends on rapid and undetected entry into tunnels, and horns cause vibrations as they scrape against tunnel walls, which would alert the resident male. Finally, as mentioned earlier, beetles with very large horns tend to have undeveloped eyes and/or a diminished flying ability due to smaller wing size and greater body weight. Since dung is a temporary resource, another component of fitness is the ability to disperse and locate new dung heaps. As the dung resource diminishes, some of the males, as larvae, will receive a less-than-optimum amount of food. They will be small and lack horns. Thus, although they would be poorly equipped to defend a female in a burrow, they are well adapted to disperse and find a new dung pile.
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Intraspecific competition-that is, competition between members of the same species for limited resources-can be a complex phenomenon, as illustrated by studies on horned beetles. Beetle horns, which are the rigid extensions of the hard, shell-like exoskeleton of insects have evolved repeatedly within this order of insects and are generally only expressed in males, who use them in combat with other males for access to resources or females. These resources are in discrete, readily defensible patches, and the horns allow males to defend these sites and to mate with the females found there. The contests between males can be dramatic, and the winner is rewarded with mating privileges.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
Factual Information Questions事实信息题
AMale beetles have evolved horns so that they can compete for limited resources with females and insects of other orders.
BMale beetles have a hard, shell-like exoskeleton that is not found in females or insects of other orders.
CGenerally, only male beetles have horns that they evolved for use in fighting other males for resources or mating
DInsects with hard exoskeletons and horns, like beetles, have evolved repeatedly to develop their combat abilities.
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Horns constitute a large investment in energy, and as much as 10 percent of body mass may be devoted to them. Horn growth prolongs development time and risk of larval mortality, and there is a trade-off between horn development and the ability to fly. Finally, the development of horns leads to lowered visual acuity and to smaller eyes. Nevertheless, it appears that since larger horns are useful in gaining access to females, the reproductive benefits gained from large horns offset the costs of production and maintenance.
The word “prolongs” in the passage is closest in meaning to
Vocabulary Questions词汇题
Ainvolves
Bextends
Cspeeds
Ddepends on
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The ability of males to grow horns is based on larval nutrition. Both final adult body size and the size of horns in males depend on the amount of food they consume as larvae. Males exposed to poor conditions as larvae are small and do not produce horns, whereas well-fed males become large adults able to produce horns. Horn production shows an insignificant level of heritable genetic variation.
Why does the author make the statement that “Horn production shows an insignificant level of heritable genetic variation”?
Rhetorical Purpose Questions修辞目的题
ATo identify the various mechanisms that contribute to growth in beetles
BTo help explain why it is uncommon for beetles to have small horns or no horns
CTo emphasize that the development of beetle horns depends only on the nutrition that the beetles obtain as larvae
DTo make note of an important difference between beetles and other insects
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These complexities and trade-offs are illustrated through studies of dung beetles of the genus Onthophagus. The basic life history of these beetles is as follows. After finding a patch of dung (animal waste products), a female digs a tunnel in the soil beneath the dung. She then buries dung below ground to provide nutrition for the larvae. Females spend days inside a single tunnel, pulling down pieces of dung to various blind ends of tunnel branches, each with its “brood ball”of dung. A single egg is laid at the top of a brood ball, and a single larva develops in isolation within the brood ball.
All of the following are mentioned in paragraph 4 as breeding-related activities of female dung beetles EXCEPT
Negative Factual Information Questions否定事实信息题
Alaying eggs in multiple locations within a tunnel
Bpreventing other females from using their tunnels and brood balls
Ccreating balls of dung to nourish larvae as they develop
Dmoving quantities of dung underground
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Females mate repeatedly with males during the time of egg laying. Male reproductive behavior consists of securing their unique access to a female in a tunnel. The large, horned males guard the tunnels and fight other males trying to approach the females. Larger males with larger horns win these fights. For two males of the same size, the one with the larger horns usually wins. Thus, long horns provide males with significant advantages.
According to paragraph 5, a large male beetle does which of the following to make sure he has unique access for reproduction to a chosen female?
Factual Information Questions事实信息题
ADig a tunnel for mating with the female
BMake the female feel secure while trying to approach her
CGuard the tunnel to prevent the female from leaving it
DPrevent other males from getting into the female’s tunnel
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However, all is not lost for a small male. Although they are not adept at guarding entrances to tunnels or winning contests, small males have other tactics. They attempt to slip undetected past the large males, or they dig side tunnels that intercept a guarded tunnel well below ground. Thus hornless males may manage to sneak undetected into guarded tunnels and mate with the female. If such a sneaker male is caught, he is chased out by the resident male, who then returns to the female and mates with her. This dilutes or displaces sperm (reproductive cells contained within a fluid) from the sneaker male. Sneaker males actually do best when they have no horns at all, since horns get in the way of sneaking. Success for a small male depends on rapid and undetected entry into tunnels, and horns cause vibrations as they scrape against tunnel walls, which would alert the resident male. Finally, as mentioned earlier, beetles with very large horns tend to have undeveloped eyes and/or a diminished flying ability due to smaller wing size and greater body weight. Since dung is a temporary resource, another component of fitness is the ability to disperse and locate new dung heaps. As the dung resource diminishes, some of the males, as larvae, will receive a less-than-optimum amount of food. They will be small and lack horns. Thus, although they would be poorly equipped to defend a female in a burrow, they are well adapted to disperse and find a new dung pile.
The phrase “adept at” in the passage is closest in meaning to
Vocabulary Questions词汇题
Askilled in
Bfocused on
Cused to
Dafraid of
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However, all is not lost for a small male. Although they are not adept at guarding entrances to tunnels or winning contests, small males have other tactics. They attempt to slip undetected past the large males, or they dig side tunnels that intercept a guarded tunnel well below ground. Thus hornless males may manage to sneak undetected into guarded tunnels and mate with the female. If such a sneaker male is caught, he is chased out by the resident male, who then returns to the female and mates with her. This dilutes or displaces sperm (reproductive cells contained within a fluid) from the sneaker male. Sneaker males actually do best when they have no horns at all, since horns get in the way of sneaking. Success for a small male depends on rapid and undetected entry into tunnels, and horns cause vibrations as they scrape against tunnel walls, which would alert the resident male. Finally, as mentioned earlier, beetles with very large horns tend to have undeveloped eyes and/or a diminished flying ability due to smaller wing size and greater body weight. Since dung is a temporary resource, another component of fitness is the ability to disperse and locate new dung heaps. As the dung resource diminishes, some of the males, as larvae, will receive a less-than-optimum amount of food. They will be small and lack horns. Thus, although they would be poorly equipped to defend a female in a burrow, they are well adapted to disperse and find a new dung pile.
According to paragraph 6, one reason small males without horns are not easily detected by resident males is that
Factual Information Questions事实信息题
Asmall males without horns are less visible than small horned males
Bsmall males without horns are often mistaken for females because of the absence of horns
Csmall males without horns do not cause tunnel walls to vibrate
Dsmall males without horns are quickly chased away by females who prefer to mate with larger beetles
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However, all is not lost for a small male. Although they are not adept at guarding entrances to tunnels or winning contests, small males have other tactics. They attempt to slip undetected past the large males, or they dig side tunnels that intercept a guarded tunnel well below ground. Thus hornless males may manage to sneak undetected into guarded tunnels and mate with the female. If such a sneaker male is caught, he is chased out by the resident male, who then returns to the female and mates with her. This dilutes or displaces sperm (reproductive cells contained within a fluid) from the sneaker male. Sneaker males actually do best when they have no horns at all, since horns get in the way of sneaking. Success for a small male depends on rapid and undetected entry into tunnels, and horns cause vibrations as they scrape against tunnel walls, which would alert the resident male. Finally, as mentioned earlier, beetles with very large horns tend to have undeveloped eyes and/or a diminished flying ability due to smaller wing size and greater body weight. Since dung is a temporary resource, another component of fitness is the ability to disperse and locate new dung heaps. As the dung resource diminishes, some of the males, as larvae, will receive a less-than-optimum amount of food. They will be small and lack horns. Thus, although they would be poorly equipped to defend a female in a burrow, they are well adapted to disperse and find a new dung pile.
What can be inferred from paragraph 6 about a sneaker male who has mated with a female?
Inference Questions推理题
AIf he was chased away by a resident male after mating, he is unlikely to have been successful at reproduction.
BHis success at mating with a female will make him return to the same tunnel frequently.
CHe will be rejected by other females in the tunnel
DHe will defend the female with whom he mated.
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Intraspecific competition-that is, competition between members of the same species for limited resources-can be a complex phenomenon, as illustrated by studies on horned beetles. Beetle horns, which are the rigid extensions of the hard, shell-like exoskeleton of insects have evolved repeatedly within this order of insects and are generally only expressed in males, who use them in combat with other males for access to resources or females. These resources are in discrete, readily defensible patches, and the horns allow males to defend these sites and to mate with the females found there. [■] The contests between males can be dramatic, and the winner is rewarded with mating privileges.
[■] Horns constitute a large investment in energy, and as much as 10 percent of body mass may be devoted to them. Horn growth prolongs development time and risk of larval mortality, and there is a trade-off between horn development and the ability to fly. [■] Finally, the development of horns leads to lowered visual acuity and to smaller eyes. [■] Nevertheless, it appears that since larger horns are useful in gaining access to females, the reproductive benefits gained from large horns offset the costs of production and maintenance.
Look at the four squares [■] that indicate where the following sentence could be added to the passage
Although clearly helpful in combat, horns are not entirely advantageousInsert Text Questions句子插入题
Where would the sentence best fit？Click on a square sentence to the passage.
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Horned beetles demonstrate the complexity of competition among members of a species.
Prose Summary Questions概要小结题
Select 3 answers
AHorned male beetles use their horns in combat as a way of gaining access to various important resources as well as to female beetles.
BMales gain significant reproductive benefits from having horns because female beetles more often seek to mate with horned beetles than with hornless ones
CMale beetles with small horns often lose them completely in order to become sneaker males and gain entry to tunnels and the dung resources stored there.
DThe development and use of horns comes at the cost of trading off certain physical characteristics and their advantages
EHorns provide such a great advantage in battles that small beetles that have horns usually win battles against larger beetles that do not have horns.
FAlthough less able to engage in defensive behaviors, male beetles without horns have some advantages over horned males and use these advantages in several ways.
