雅思阅读 77: Assisted Evolution on the Coral Reef（珊瑚礁上的辅助进化）

改编自 Australian Institute of Marine Science（2026年7月）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://www.aims.gov.au/information-centre/news-and-stories/one-size-does-not-fit-all-assisted-evolution-tests-corals-bring-complex-results

Reading Passage

A. Coral reefs are among the ecosystems most exposed to a warming climate. When marine heatwaves push sea temperatures a few degrees above normal, corals expel the colourful algae that live inside their tissues, turn white and, if the heat persists, die. Repeated bleaching has laid waste to large stretches of the Great Barrier Reef and reefs across the tropics. Faced with a warming that outpaces the rate at which wild populations can adapt naturally, researchers have turned to a provocative strategy: helping evolution along. Rather than waiting for resistant corals to emerge on their own, they deliberately breed and manipulate corals to make them tougher — an approach known as assisted evolution. Its pioneers insist they are not rewriting the rules of nature but merely accelerating processes that happen in the wild, compressing into a few years the adaptation that might otherwise take centuries. The hope is to stock damaged reefs with corals hardy enough to survive the heatwaves that now arrive almost every summer.

B. Assisted evolution is an umbrella term for several techniques aimed at the coral itself or the microscopic algae that sustain it. Corals are animals, but they depend on tiny photosynthetic algae called Symbiodiniaceae that live within their cells and supply them with the energy they need to grow and reproduce. Heat tolerance is therefore a property of both partners. One approach is selective breeding: identify adult corals that survive unusually warm water, cross them, and let the most heat-resistant offspring be replanted on damaged reefs. Another is to grow the symbiotic algae under elevated temperatures in the laboratory for many generations, so that they evolve their own heat tolerance, and then introduce these "heat-evolved" symbionts into young corals. A 2026 study led by the Australian Institute of Marine Science, with coral evolution pioneer Madeleine van Oppen as senior author, tested both approaches separately and in combination on corals from the Great Barrier Reef. Its headline finding was encouraging but complicated: helping corals survive heat is possible, yet no single recipe works equally well on every reef. The work sits at the awkward intersection of two imperatives. Reefs are already dying faster than natural adaptation can save them, so standing aside and waiting for evolution to run its course is not a serious option. But stepping in too clumsily — seeding reefs with a handful of hardy strains — risks reducing the very genetic diversity that lets ecosystems weather the next surprise. The art, as much as the science, lies in intervening just enough without erasing the variation that wild populations depend on.

C. The breeding experiment was carefully controlled. The team collected adults of a reef-building species, Acropora spathulata, from reefs in the northern and central Great Barrier Reef, and ranked each colony by how well it survived a rapid heat-stress test. They then mixed eggs and sperm to create four groups of offspring: young from the most heat-tolerant parents, young from the most heat-sensitive parents, young from parents of intermediate tolerance, and young from all parents pooled together. The larvae were inoculated with ordinary "wild type" algae and raised for two months under elevated temperatures in the laboratory's sea simulator. This design let the researchers ask a precise question: does heat tolerance in a parent reliably predict heat tolerance in its offspring, and does breeding the toughest stock actually produce tougher children? The answer turned out to depend on where the parent corals had come from, a nuance that the researchers had not expected to surface so clearly.

D. The results split sharply along geography. Offspring of the most heat-tolerant corals from Davies Reef, in the central Great Barrier Reef, showed improved survival and growth compared with control groups — a clear win for selective breeding. But young from the equally tolerant parents at Moore Reef, in the northern section of the reef, gained no such benefit. Parents that looked equally resistant under a heat-stress test did not pass that resistance on to their young in the same way. The finding explains why "one size does not fit all": the heritability of heat tolerance varies between populations, and a breeding programme that succeeds on one reef may disappoint on another. Before deploying heat-hardened stock at scale, managers will need to test each local population, rather than assuming that the toughest coral anywhere will automatically produce tough children everywhere.

E. The second experiment added the heat-evolved algae. Young corals raised with these lab-adapted symbionts survived better at high temperatures and resisted bleaching more effectively than those given ordinary algae, confirming earlier work. But the researchers also found a cost: when temperatures were normal, the same corals grew more slowly. Enhanced heat tolerance, in other words, came with a trade-off — a phenomenon familiar from breeding programmes, where stress resistance often trades against rapid growth. Taken together, the results suggest that assisted evolution is a promising but imperfect tool. It can raise the odds that corals survive the next heatwave, yet it cannot substitute for cutting the emissions that drive those heatwaves in the first place, and any out-planting must weigh benefits against the hidden cost of slower growth. The future of the reefs, the study implies, will be decided less by a single technological fix than by whether determined action on climate arrives before the reefs themselves do. Even the most successful out-planting programme covers only a tiny fraction of a reef; the vast majority of any reef's corals will have to cope on their own, by acclimatising, migrating or dying. This is why researchers are careful not to sell assisted evolution as a replacement for emissions cuts. It is, rather, a holding action — a way to buy decades for the most vulnerable habitats while the harder political work of limiting warming is still unfinished.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. The bleaching crisis and the idea of assisted evolution ii. Two ways to make a heat-tolerant coral iii. A carefully controlled breeding design iv. Geography splits the results v. Heat-evolved symbionts help — but at a hidden cost vi. Why tourists prefer colourful coral reefs vii. The complete disappearance of marine algae

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. What does "assisted evolution" mean in this context? A. Letting corals adapt to warming completely on their own B. Deliberately breeding and manipulating corals to boost heat tolerance C. Moving every coral into a controlled aquarium D. Adding more herbivorous fish to damaged reefs

6. Why are the symbiotic algae important to corals? A. They supply the coral with energy through photosynthesis. B. They physically clean parasites from the coral's surface. C. They give the coral a heavier calcium skeleton. D. They protect the coral from predators.

7. What was the key finding about geography? A. Davies Reef tolerant parents produced tougher offspring, while Moore Reef did not. B. The two reefs gave completely identical results. C. Northern reefs always outperform central reefs. D. The location of the parents had no effect at all.

8. What trade-off accompanied the use of heat-evolved symbionts? A. The corals grew more slowly at normal temperatures. B. The corals became noticeably less colourful. C. The corals required far more oxygen. D. The corals reproduced more quickly.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. Marine heatwaves can cause corals to expel their symbiotic algae and turn white.
10. Selective breeding worked equally well at every reef that was tested.
11. The study was funded entirely by a private oil company.
12. Acropora spathulata was the species used in the breeding experiment.
13. Assisted evolution has already restored the Great Barrier Reef to its original state.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

Young corals raised with heat-evolved (14) __________ survived better at high temperatures, but grew more slowly at (15) __________ temperatures.

答案与解析

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