题目：
Day Length and Reproductive Timing in Animals
For many animals, producing offspring at a time of year when a maximum amount of food is available is essential. Producing young at the wrong time of year will invariably lead to death. As a result there has been intense evolutionary selection pressure to get seasonal reproduction right. There are potentially many environmental cues that could be used to anticipate the arrival of food and trigger the development of the reproductive organs. But the ultimate factor of evolution by natural selection-genetic change that improves a population’s environmental adaptation-will favor only the most reliable long-term indicator of the seasons. The change in day length is the indicator used by most seasonally breeding animals to adjust not only their annual reproductive cycle but also other seasonal events such as migration and hibernation.
The idea that day length might regulate seasonal breeding was first clearly formulated by E. A. Shafer in the early 1900s. But this theory was not tested until the 1920s. William Rowan was a British scientist whose interest in the annual migration of and breeding in birds had taken him to Edmonton, Alberta, in Canada. For fourteen years he observed the migration of the greater yellowlegs, a bird that breeds in Canada and then migrates south to Patagonia in the autumn, a round-trip of some 16,000 miles. Rowan was struck by the fact that the eggs all hatch between May 26 and May 29 each year, and wondered what could regulate this precisely timed series of events.
As with many great insights in biology, deciphering the role of day length in regulating seasonality started with the detailed observation of a large number of variables. Rowan considered environmental cues such as temperature and food availability, but he concluded that only the change in day length could provide such precision. He tested this hypothesis by capturing birds called Oregon juncos, which overwinter in Canada. Birds were kept in sheds and exposed to artificial springlike day lengths. Despite the subzero temperatures of the Canadian winter, the birds were triggered to breed by the artificially long days.
Rowan’s findings have been confirmed in many other temperate bird and mammalian species that have been examined in a similar fashion. All show a reproductive response to photoperiod, the duration of daily exposure to light. The use of artificial photoperiods demonstrated that although secondary factors such as a sudden cold or a warm spell might affect the rate of reproductive development, temperature or food availability by itself could not trigger it. Birds called great tits are heavily dependent on caterpillars to feed their young, and the number of eggs laid is determined by the availability of caterpillars just before egg-laying time. Caterpillar emergence is determined by environmental temperature, and so temperature indirectly modulates the reproductive potential of these birds, but only by regulating the number of eggs laid-not the timing.
Animals living at the equator, where there is little change in day length, are far less dependent on photoperiod. The weaverbird uses rainfall and the growth of new grass to trigger growth of the reproductive system. Fresh, flexible grass stems are of paramount importance to this bird, which builds its remarkably elaborate woven nest from the new growth grass stems. However, if weaverbirds are exposed to artificially long photoperiods, they are stimulated to breed, suggesting that they have retained some capacity to respond to photoperiod.
The changing day length is used to time reproduction, but the precise day length selected by a species varies greatly. Birds and small mammals with a relatively short period of development, either in an egg or in the uterus, use the increasing day lengths after December 21 (in the northern hemisphere). Large mammals such as sheep and deer have a pregnancy that varies between five and nine months. Breeding is triggered by the decreasing day lengths of autumn. Mating occurs between September and December and the young are born in the following spring or early summer. But in some mammals, gestation is even longer: in horses it is 11 months. These long-gestation mammals are stimulated to breed by the increasing day lengths after December 21. Mating occurs in the spring and summer, with birth nearly a year later.
1
For many animals, producing offspring at a time of year when a maximum amount of food is available is essential. Producing young at the wrong time of year will invariably lead to death. As a result there has been intense evolutionary selection pressure to get seasonal reproduction right. There are potentially many environmental cues that could be used to anticipate the arrival of food and trigger the development of the reproductive organs. But the ultimate factor of evolution by natural selection-genetic change that improves a population’s environmental adaptation-will favor only the most reliable long-term indicator of the seasons. The change in day length is the indicator used by most seasonally breeding animals to adjust not only their annual reproductive cycle but also other seasonal events such as migration and hibernation.
The word “invariably” in the passage is closest in meaning to
Vocabulary Questions词汇题
Aalways
Bunfortunately
Clikely
Dquickly
2
For many animals, producing offspring at a time of year when a maximum amount of food is available is essential. Producing young at the wrong time of year will invariably lead to death. As a result there has been intense evolutionary selection pressure to get seasonal reproduction right. There are potentially many environmental cues that could be used to anticipate the arrival of food and trigger the development of the reproductive organs. But the ultimate factor of evolution by natural selection-genetic change that improves a population’s environmental adaptation-will favor only the most reliable long-term indicator of the seasons. The change in day length is the indicator used by most seasonally breeding animals to adjust not only their annual reproductive cycle but also other seasonal events such as migration and hibernation.
According to paragraph 1, which of the following statements is true of animals that reproduce seasonally?
Factual Information Questions事实信息题
AThe development of their reproductive organs is triggered by the arrival of food.
BTheir reproductive success depends on the accurate prediction of food accessibility.
CTheir reproductive cycles tend to be similar in length.
DThe development of their reproductive organs occurs during periods of hibernation.
3
The idea that day length might regulate seasonal breeding was first clearly formulated by E. A. Shafer in the early 1900s. But this theory was not tested until the 1920s. William Rowan was a British scientist whose interest in the annual migration of and breeding in birds had taken him to Edmonton, Alberta, in Canada. For fourteen years he observed the migration of the greater yellowlegs, a bird that breeds in Canada and then migrates south to Patagonia in the autumn, a round-trip of some 16,000 miles. Rowan was struck by the fact that the eggs all hatch between May 26 and May 29 each year, and wondered what could regulate this precisely timed series of events.
The word “formulated” in the passage is closest in meaning to
Vocabulary Questions词汇题
Aquestioned
Binvestigated
Cmodified
Dstated
4
The idea that day length might regulate seasonal breeding was first clearly formulated by E. A. Shafer in the early 1900s. But this theory was not tested until the 1920s. William Rowan was a British scientist whose interest in the annual migration of and breeding in birds had taken him to Edmonton, Alberta, in Canada. For fourteen years he observed the migration of the greater yellowlegs, a bird that breeds in Canada and then migrates south to Patagonia in the autumn, a round-trip of some 16,000 miles. Rowan was struck by the fact that the eggs all hatch between May 26 and May 29 each year, and wondered what could regulate this precisely timed series of events.
According to paragraph 2, all of the following are true of the greater yellowlegs EXCEPT:
Negative Factual Information Questions否定事实信息题
AThey travel 16,000 miles every year.
BThey spend part of the year in Canada.
CThey migrate south to Patagonia for breeding.
DTheir eggs hatch at the same time every year.
5
As with many great insights in biology, deciphering the role of day length in regulating seasonality started with the detailed observation of a large number of variables. Rowan considered environmental cues such as temperature and food availability, but he concluded that only the change in day length could provide such precision. He tested this hypothesis by capturing birds called Oregon juncos, which overwinter in Canada. Birds were kept in sheds and exposed to artificial springlike day lengths. Despite the subzero temperatures of the Canadian winter, the birds were triggered to breed by the artificially long days.
According to paragraph 3, Rowan succeeded in causing Oregon juncos to breed at a different time of year than usual by
Factual Information Questions事实信息题
Aexposing them to constantly changing day lengths
Bkeeping them in a warm environment that protected them from winter temperatures
Cproviding them with a more steady, reliable supply of food
Dproviding them with light for a longer period of time than occurred naturally in winter
6
Rowan’s findings have been confirmed in many other temperate bird and mammalian species that have been examined in a similar fashion. All show a reproductive response to photoperiod, the duration of daily exposure to light. The use of artificial photoperiods demonstrated that although secondary factors such as a sudden cold or a warm spell might affect the rate of reproductive development, temperature or food availability by itself could not trigger it. Birds called great tits are heavily dependent on caterpillars to feed their young, and the number of eggs laid is determined by the availability of caterpillars just before egg-laying time. Caterpillar emergence is determined by environmental temperature, and so temperature indirectly modulates the reproductive potential of these birds, but only by regulating the number of eggs laid-not the timing.
In paragraph 4, why does the author mention that the number of eggs laid by great tits is determined by the availability of caterpillars?
Factual Information Questions事实信息题
ATo emphasize the differences between certain temperate birds like Oregon juncos and great tits
BTo provide an example of how secondary factors, like temperature, affect elements of reproduction other than timing
CTo support the claim that not all temperate bird species have a photoperiodic reproductive response
DTo argue that there are a variety of factors that trigger reproduction in temperate bird and mammalian species
7
Animals living at the equator, where there is little change in day length, are far less dependent on photoperiod. The weaverbird uses rainfall and the growth of new grass to trigger growth of the reproductive system. Fresh, flexible grass stems are of paramount importance to this bird, which builds its remarkably elaborate woven nest from the new growth grass stems. However, if weaverbirds are exposed to artificially long photoperiods, they are stimulated to breed, suggesting that they have retained some capacity to respond to photoperiod.
It can be inferred from paragraph 5 that the weaver bird does not depend on day length to cause reproductive growth because
Inference Questions推理题
Athe uniformity of day length makes it an unreliable indicator for reproduction
Benvironmental conditions in the bird’s habitat are always suitable for nest building
Cover the course of its evolution, the weaver bird has lost the ability to respond to photoperiod
Dthe elaborate nests that the weaver bird builds can protect its young whenever they are born
8
The changing day length is used to time reproduction, but the precise day length selected by a species varies greatly. Birds and small mammals with a relatively short period of development, either in an egg or in the uterus, use the increasing day lengths after December 21 (in the northern hemisphere). Large mammals such as sheep and deer have a pregnancy that varies between five and nine months. Breeding is triggered by the decreasing day lengths of autumn. Mating occurs between September and December and the young are born in the following spring or early summer. But in some mammals, gestation is even longer: in horses it is 11 months. These long-gestation mammals are stimulated to breed by the increasing day lengths after December 21. Mating occurs in the spring and summer, with birth nearly a year later.
Paragraph 6 answers all of the following questions EXCEPT:
Negative Factual Information Questions否定事实信息题
AWhat determines breeding in large mammals like sheep and deer?
BHow does reproduction in long-gestation mammals differ from reproduction in other mammals?
CWhat is the length of the gestation period for sheep and deer?
DHow long after mating do small mammals and birds give birth?
9
As with many great insights in biology, deciphering the role of day length in regulating seasonality started with the detailed observation of a large number of variables. Rowan considered environmental cues such as temperature and food availability, but he concluded that only the change in day length could provide such precision. [■]He tested this hypothesis by capturing birds called Oregon juncos, which overwinter in Canada. [■]Birds were kept in sheds and exposed to artificial springlike day lengths. [■]Despite the subzero temperatures of the Canadian winter, the birds were triggered to breed by the artificially long days.[■]
Rowan’s findings have been confirmed in many other temperate bird and mammalian species that have been examined in a similar fashion. All show a reproductive response to photoperiod, the duration of daily exposure to light. The use of artificial photoperiods demonstrated that although secondary factors such as a sudden cold or a warm spell might affect the rate of reproductive development, temperature or food availability by itself could not trigger it. Birds called great tits are heavily dependent on caterpillars to feed their young, and the number of eggs laid is determined by the availability of caterpillars just before egg-laying time. Caterpillar emergence is determined by environmental temperature, and so temperature indirectly modulates the reproductive potential of these birds, but only by regulating the number of eggs laid-not the timing.
Look at the four squares that indicate where the following sentence could be added to the passage
However, birds that were not exposed to extended periods of daylight did not reproduce.Insert Text Questions句子插入题
Where would the sentence best fit？Click on a square sentence to the passage.
10
To ensure the survival of their young, many animals must reproduce at a specific time of year.
Prose Summary Questions概要小结题
Select 3 answers
AMost seasonally breeding animals adjust reproduction so that it occurs at the same time as migration and hibernation.
BStudies of birds and mammals after Rowan’s studies indicate that factors like food availability and temperature can change reproductive rate but not reproductive timing.
CThe timing of the reproductive cycle of equatorial birds is dependent more on local climate and growing conditions than on photoperiod.
DWilliam Rowan’s experiments with birds confirmed that photoperiod determines the timing of seasonal reproduction in temperate climates.
EStudies suggest that animals that live in areas where day length does not change respond to photoperiod when there is a sudden cold or warm spell.
FThe day length that determines seasonal breeding is more likely to vary for mammals of different sizes and species than for birds.
