Until recently, scientists did not know of a close vertebrate analogue to the extreme form of altruism observed in eusocial insects like ants and bees, whereby individuals cooperate, sometimes even sacrificing their own opportunities to survive and reproduce, for the good of others. However, such a vertebrate society may exist among underground colonies of the highly social rodent Heterocephalus glaber, the naked mole rat.
A naked mole rat colony, like a beehive, wasp’s nest, or termite mound, is ruled by its queen, or reproducing female. Other adult female mole rats neither ovulate nor breed. The queen is the largest member of the colony, and she maintains her breeding status through a mixture of behavioral and, presumably, chemical control. Queens have been long-lived in captivity, and when they die or are removed from a colony one sees violent fighting for breeding status among the larger remaining females, leading to a takeover by a new queen.
Eusocial insect societies have rigid caste systems, each insect’s role being defined by its behavior, body shape, and physiology. In naked mole rat societies, on the other hand, differences in behavior are related primarily to reproductive status (reproduction being limited to the queen and a few males), body size, and perhaps age. Smaller non-breeding members, both male and female, seem to participate primarily in gathering food, transporting nest material, and tunneling. Larger nonbreeders are active in defending the colony and perhaps in removing dirt from the tunnels. Jarvis’ work has suggested that differences in growth rates may influence the length of time that an individual performs a task, regardless of its age.
Cooperative breeding has evolved many times in vertebrates, but unlike naked mole rats, most cooperatively breeding vertebrates (except the wild dog, Lycaon pictus) are dominated by a pair of breeders rather than by a single breeding female. The division of labor within social groups is less pronounced among other vertebrates than among naked mole rats, colony size is much smaller, and mating by subordinate females may not be totally suppressed, whereas in naked mole rat colonies subordinate females are not sexually active, and many never breed.
1. Which of the following most accurately states the main idea of the passage?
(A) Naked mole rat colonies are the only known examples of cooperatively breeding vertebrate societies.
(B) Naked mole rat colonies exhibit social organization based on a rigid caste system.
(C) Behavior in naked mole rat colonies may well be a close vertebrate analogue to behavior in eusocial insect societies.
(D) The mating habits of naked mole rats differ from those of any other vertebrate species.
(E) The basis for the division of labor among naked mole rats is the same as that among eusocial insects.
2. The passage suggests that Jarvis’ work has called into question which of the following explanatory variables for naked mole rat behavior?
(A) Size
(B) Age
(C) Reproductive status
(D) Rate of growth
(E) Previously exhibited behavior
3. It can be inferred from the passage that the performance of tasks in naked mole rat colonies differs from task performance in eusocial insect societies in which of the following ways?
(A) In naked mole rat colonies, all tasks ate performed cooperatively.
(B) In naked mole rat colonies, the performance of tasks is less rigidly determined by body shape.
(C) In naked mole rat colonies, breeding is limited to the largest animals.
(D) In eusocial insect societies, reproduction is limited to a single female.
(E) In eusocial insect societies, the distribution of tasks is based on body size.
4. According to the passage, which of the following is a supposition rather than a fact concerning the queen in a naked mole rat colony?
(A) She is the largest member of the colony.
(B) She exerts chemical control over the colony.
(C) She mates with more than one male.
(D) She attains her status through aggression.
(E) She is the only breeding female.
5. The passage supports which of the following inferences about breeding among Lycaon pictus?
(A) The largest female in the social group does not maintain reproductive status by means of behavioral control.
(B) An individual’s ability to breed is related primarily to its rate of growth.
(C) Breeding is the only task performed by the breeding female.
(D) Breeding in the social group is not cooperative.
(E) Breeding is not dominated by a single pair of dogs.
6. According to the passage, naked mole rat colonies may differ from all other known vertebrate groups in which of the following ways?
(A) Naked mole rats exhibit an extreme form of altruism.
(B) Naked mole rats are cooperative breeders.
(C) Among naked mole rats, many males are permitted to breed with a single dominant female.
(D) Among naked mole rats, different tasks are performed at different times in an individual’s life.
(E) Among naked mole rats, fighting results in the selection of a breeding female.
7. One function of the third paragraph of the passage is to
(A) state a conclusion about facts presented in an earlier paragraph
(B) introduce information that is contradicted by information in the fourth paragraph
(C) qualify the extent to which two previously mentioned groups might be similar
(D) show the chain of reasoning that led to the conclusions of a specific study
(E) demonstrate that of three explanatory factors offered, two may be of equal significance