Predators are thought to prey on individuals that are in poor physical condition, although the evidence supporting this is ambiguous. We tested if sick individuals where more predated using Drosophila melanogaster flies as manipulable preys. We asked whether hunting spiders, trapped from the wild, would selectively prey upon flies with compromised health (i.e. chronically infected or cancerous) versus healthy flies under laboratory conditions. Flies chronically infected with the bacterium Providencia rettgeri, a natural Drosophila pathogen, were not selectively preyed upon by jumping spiders. We strengthened and confirmed our finding with another hunting spider species, small wolf spiders. We discuss that this result supports the hypothesis that chronic infection is associated with reduced symptoms notably to avoid the potentially deadly consequences of host predation on pathogens. We then induced colon cancer in some of the flies and asked whether the presence of cancer led to selective predation; there is little evidence for this, even in vertebrates. As the cancer developed, the incidence of predation by jumping spiders on the afflicted flies increased. We conclude that disease can have different lethal consequences through predation, even in invertebrate species, and that cancer is a factor in selective predation. Our results may explain why early tumours, but not metastasized cancers, are commonly detected in organisms in the wild, as cancer bearing individuals are rapidly eliminated due to the strong selective pressure against them.

中文翻译：

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肠道癌会增加果蝇被蜘蛛捕食的风险

捕食者被认为捕食身体状况不佳的个体，尽管支持这一点的证据不明确。我们测试了更早使用黑腹果蝇作为可操纵猎物的患病个体。我们询问了从野外捕获的狩猎蜘蛛是否会在实验室条件下选择性地捕食健康受损（即慢性感染或癌变）的苍蝇，而不是健康的苍蝇。苍蝇长期感染普罗维登西亚雷特盖里细菌，一种天然果蝇病原体，不会被跳蛛选择性地捕食。我们用另一种狩猎蜘蛛物种小狼蛛加强并证实了我们的发现。我们讨论该结果支持慢性感染与症状减轻相关的假设，这显着避免了宿主捕食病原体的潜在致命后果。然后我们在一些果蝇中诱发了结肠癌，并询问癌症的存在是否会导致选择性捕食；几乎没有证据表明这一点，即使在脊椎动物中也是如此。随着癌症的发展，跳蛛捕食患病苍蝇的发生率增加。我们得出的结论是，即使在无脊椎动物物种中，疾病也会通过捕食产生不同的致命后果，并且癌症是选择性捕食的一个因素。我们的结果可以解释为什么早期肿瘤，