2020年8月31日托福阅读真题+题目+答案： Why Water Bugs Practice Paternal Care of Eggs

2020年8月31日托福阅读真题+题目+答案： Why Water Bugs Practice Paternal Care of Eggs

Although paternal care of young (fathers caring for their young) is common among fishes, the trait is rare among other animals, vertebrates and invertebrates alike. Among the few paternal insects are the giant water bugs. In Lethocerus water bugs, males guard and moisten clutches of eggs(eggs deposited during a single episode of laying) that females glue onto the stems of aquatic vegetation located above the waterline. Other kinds of male water bugs(e.g., Abedus and Belostoma)permit their mates to lay eggs directly on their backs, after which the male assumes responsibility for their welfare. A male Abedus caring for its eggs spends hours perched near the water's surface, pumping his body up and down to keep well-aerated water moving over the eggs. Clutches of Abedus eggs that are experimentally separated from a male attendant do not develop, demonstrating that male parental care is essential for offspring survival in this case.

21. The word "guard" in the passage is closest in meaning to

A. gather

B. watch over

C. transport

D. Spread

22. It can be inferred from paragraph 1 that Lethocerus water bugs differ from Abedus water bugs in which of the following ways?

A. The total number of hours spent caring for young

B. The number of eggs contained in a clutch

C. The survival rate of eggs separated from a surface

D. The way in which eggs are kept moist

Bob Smith has explored both the history and the adaptive value of these unusual paternal behaviors. Since the closest relatives of the family that contains the paternal water bugs are the Nepidae, a family of insects without male parental care, we can be confident that the brooding species(species caring for eggs) evolved from nonpaternal ancestors. Whether out-of-water brooding and back brooding evolved independently, or whether one preceded the other, is not known, although some evidence suggests that back brooding came later. In particular, female Lethocerus sometimes lay their eggs on the backs of other individuals, male or female, when they cannot find suitable vegetation for that purpose. This unusual behavior indicates how the transition from out-of-water brooding to back brooding might have occurred. Females with the tendency to lay their eggs on the backs of their mates could have reproduced in temporary ponds and pools where aquatic vegetation sticking out of the water was scarce or absent.

23. What is the author's purpose in mentioning that "female Lethocerus sometimes lay their eggs on the backs of other individuals" when they cannot find vegetation to lay their eggs on?

A. To argue that back brooding and out-of-water brooding evolved independently

B. To suggest that maternal care is just as important as paternal care in some species of giant water bugs

C. To provide evidence supporting the idea that back brooding evolved after out-of-water brooding

D. To point out a problem that water bugs would have faced in transitioning from out-of-water brooding to back brooding.

24. The word "suitable" in the passage is closest in meaning to

A. attractive

B. nearby

C. appropriate

D. Enough

But why do the eggs of water bugs require brooding? Huge numbers of aquatic insects lay eggs that do perfectly well without a caretaker of either sex. However, Smith notes that the eggs of giant water bugs are much larger than the standard aquatic insect egg, with correspondingly large requirement for oxygen, which is needed to sustain the high metabolic rates underlying embryonic development. But the relatively low surface-to-volume ratio of large aquatic egg leads to an oxygen deficit inside the egg. Since oxygen diffuses through air much more easily than through water, laying eggs out of water can solve that problem. But this solution creates another problem, which is the risk of drying out that the eggs face when they are high and dry. The solution, brooding by males that moisten the eggs repeatedly, sets the stage for the evolutionary transition to back brooding at the air-water interface.

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