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With respect to evolutionary pressure, which of the followi - FGV 2016

CHEMICAL WARFARE

1 Venoms, the debilitating chemical cocktails animals unleash to defend themselves or obtain a meal, are subject to an evolutionary arms race. Those creatures that are targets of toxins eventually develop beneficial mutations, granting them some degree of resistance. In response, animals that emit venoms undergo changes so their poisons remain effective.
2 This action-reaction narrative of venom evolution is incomplete, however, as evolutionary biologists Kartik Sunagar and Yehu Moran of Hebrew University in Jerusalem have shown in a new study. They realized that many venom studies have focused on snakes and cone snails — comparatively "young" animal groups, evolutionarily speaking, only going back roughly 50 million years. Over these groups’ histories, their venomous arsenals have expanded considerably, bolstering the arms race analogy, also known as positive, or Darwinian, selection.
3 Sunagar and Moran cast a wider net, looking at over 3,500 gene families for venom production in newer and older animal groups. The ancient animal types included spiders, scorpions, centipedes, octopus, squid, jellyfish, and sea anemones.
4 The scientists found that these ancient animals exhibited surprisingly low levels of genetic variation in their venoms. Sunagar and Moran reasoned that the venoms of primordial creatures had undergone substantial negative, or purifying, selection — evolutionary pressure to keep their potently optimized toxins roughly the same. “Negative selection filters out certain mutations that alter structure or function,” explained Moran. For species in long-established ecological niches, it makes sense to maintain what works.
5 Evolution does favor more radical experimentation, though, when creatures enter new habitats and begin adapting to the novel environment. As they find their place in local food chains, venomous animals’ toxic pharmacopeia should undergo rapid diversification — the better to catch strange new prey and withstand the attacks of previously unencountered predators. Yet over time, these adapting species settle into tried-and-true formulae.
6 The researchers call this model of venom evolution “two-speed,” with the venoms of old species evolving slowly and those of the new species evolving quickly. “Our analysis of numerous toxin families, covering the ample scope of the animal kingdom, has revealed a striking contrast between the evolution of venom in ancient and evolutionarily young animal groups,” said Sunagar.

Adapted from Natural History, February 2016.

With respect to evolutionary pressure, which of the following is most supported by the information in the article?

1. The extinction of any venom-producing animal group, young or old, is an example of negative selection.

2. If a venom-producing animal group is undergoing negative selection, then it probably has already undergone positive selection.

3. Because of positive selection, venoms produced by younger animal groups affect a greater number of target animals than do venoms produced by older animal groups.

4. When negative selection begins to influence an animal group’s venom production, rapid evolutionary changes become impossible.

5. After a venom-producing animal group undergoes negative selection, its evolutionary process can be considered complete.

Solução