• Matéria: Inglês
  • Autor: silvanafratuce8749
  • Perguntado 8 anos atrás

CHEMICAL WARFAREAdam Hadhazy1Venoms, 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.2This 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.3Sunagar 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.4The 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 aeatures 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.5Evolution does favor more radical experimentation, though, when aeatures 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.6The 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 5unagar.Adapted from Natural History, February 2016.38In paragraph 1, the phrase "Venoms... are subject to an evolutionary armsrace" most likely means which of the following?A Many of the animal groups that now rely on venoms for survival evolved from species that were not themselves venomous.B If animal that are the targets of venom did not develop a venom resistance, they v/ould run the risk of extinction.C Like all animals, those that rely on venoms for survival must constantly adapt to new environmental conditions.D Animals that produce venoms and animals that are the targets of venoms generally evolve more quickly than do other animal species.E When the targets of venoms develop a resistance, venom-producing animals must develop new venoms to counter that resistance.

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respondido por: numero20
0

No primeiro parágrafo, é comentado sobre os venenos, que são doses químicas que os animais emitem para atacar uma presa ou se defender de um ataque. Contudo, os animais que sofrem ataques desse venenos geram resistência com o passar do tempo, e vão criando espécies resistentes. Com isso, o veneno também dever ser desenvolvido, para conseguir combater os animais mais resistentes. Portanto, a alternativa correta é a letra E, que diz que os animais que produzem veneno também devem desenvolver novos venenos enquanto suas presas desenvolvem resistência.

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