害怕黑暗可能有用

A first line of defence against infection can take the form of avoidance behaviour. In the case of a species of fly that lives on desert cacti this means moving into the light if mites are around.

Strategies that help combat infection with parasites and pathogens are ubiquitous amongst free-living organisms. These range from the development of barriers that prevent infection in the first place, to the deployment of complex immune systems composed of biochemical, physiological, and cellular mechanisms, when these barriers fail. These strategies are often costly, resulting in trade-offs between infection-protection and longevity or fecundity, and the degree of their deployment may be related to the prevailing risk of infection.

回避行为

除了上面列出的策略外,一些生物体还产生了回避行为,从而降低了暴露于感染的风险。然后,这些是第一道防线,并可能涉及避免在感染更可能发生或避免其他受感染者的地方。

引起特定研究注意力的回避行为包括响应于温度,光或化学物质梯度的变化,这可能是对特定寄生虫或病原体有害的条件。这些被审查了Transactions of the Royal Society B in 2018.

One less-researched change of response associated with parasite avoidance behaviour is that to light gradients. Phototaxis, or movement in response to light, can play a prominent role in the life history traits of a variety of organisms, whether it be positive (towards light) or negative (away from light).

Collin Horn and colleagues from the University of Alberta have used the fruit fly果蝇黑螺旋藻作为研究它们对光的响应的模型,是否在存在于to骨的存在下变化。

A cactus loving fruit fly

果蝇黑螺旋藻live on liquid extruded from rotting cacti in the Sonoron desert. They exhibit negative phototaxis, a behaviour that helps them feed and regulate their temperature in the fluctuating conditions of the desert. They are often infested withMacrocheles subbadius,吸血螨reduces survival and female fecundity. This research group haspreviously shown这种外载岩的侵扰会增加卧床和美容行为,既能量成本高昂,而且当苍蝇处于光线状态时,螨虫的侵扰比在黑暗中的可能性要小。研究人员报告了他们的发现最近发表的研究.

Phototropic responses

由于雌性苍蝇是螨虫的首选宿主,因此在实验中使用了这些。雌性苍蝇的处女在微侵蚀中单独使用,并暴露在螨虫中,在光或黑暗中持续一小时。在黑暗舞台上感染了苍蝇的比例明显更高,而在光中为8%。

In a second experiment, individual females, with or without a mite, were placed in a tiny choice chamber composed of a transparent tube with one end covered to darken it. A fly was placed in the centre and its position monitored once every minute for 10-15 minutes. The results demonstrated that unmated females are more photophobic than mated ones as they spent more time at the dark end. However, exposure to a single mite significantly increased the time spent in the light, whether the females were mated or virgins.

When males were tested in the chambers, they were substantially less photophobic than females, perhaps because they patrol territories outside of rotting crevices to attract mates.

单独或与女性的选择室中对螨虫的观察表明,它们没有表现出阳性或阴性光。作者指出,这些螨虫没有光感器官,因此这并不奇怪。

The initial observation that female fruit flies were more likely to be infected in the dark led to the hypothesis that females would increase their photophilic behaviour in the presence of a mite. The results supported this, suggesting the flies were exhibiting a form of behavioural immunity by moving to a condition where infestation was less likely.

Why is mite infestation less likely in the light than the dark?

The authors make two suggestions. Firstly, that it may be easier to detect mites in the light and thus use grooming and kicking behaviour to deter them. Alternatively, light may stimulate greater activity in the flies, whereas dark may stimulate rest/sleep and thus less resistance to the mites.

将避免避免与侵扰的繁殖力和寿命的丧失,可以避免越来越轻松的环境。但是,由于热应力和营养胁迫,通过从其仙人掌食品源中取出,它可能会施加健身成本,这是一种液体渗出液,在光线下迅速蒸发。

由于螨虫的侵染给这些果蝇种群造成了沉重的负担,因此尽管涉及权衡取舍,但有利于避免策略的强大选择性力量,例如本研究中所证明的策略。显然,它付出了代价,以避免黑暗。

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