飓风使蜘蛛更凶猛

艾希礼·斯特里克兰

In regions of the United States and Mexico that are prone to hurricanes， aggressive spiders are evolving to survive and ride out the storm.

When hurricanes rage along the Gulf of Mexico or charge up the East Coast， they can reshape an entire habitat in a short time. The winds destroy trees and spread debris for miles， putting new pressure on the creatures living in these environments. But how do creatures adapt when their habitats are so disturbed？ Researchers looked at Anelosimus studiosus spiders that live in storm-prone areas along the coast to see how they changed. Their study was published in the journal Nature Ecology and Evolution.

These weather systems are called “black swan events”： a surprising event with a major impact that is explained with the benefit of hindsight. They dont offer much lead time， so the researchers had to scramble to study the spider colonies before and after projected storms.

The team monitored Subtropical Storm Alberto and Hurricanes Florence and Michael during the 2018 hurricane season. They tried to anticipate the systems trajectories and study areas that included 240 female spider colonies， comparing them with areas where spider colonies were unaffected by such storms. The researchers returned to the sites hit by the storms 48 hours later. About 75% of the colonies survived the initial storm strikes.

“It is tremendously important to understand the environmental impacts of these ‘black swan weather events on evolution and natural selection，” said Jonathan Pruitt， lead study author， evolutionary biologist and Canada 150 Chair in McMaster Universitys Department of Psychology， Neuroscience & Behaviour. “As sea levels rise， the incidence of tropical storms will only increase. Now more than ever we need to contend with what the ecological and evolutionary impacts of these storms will be for non-human animals.”

The A. studiosis spider species has two main personality traits that are inherited： docile and aggressive. Aggressiveness can be determined based on their speed， attackers pursuing prey， cannibalizing male spiders as well as eggs and their vulnerability to the invasion of predatory spiders. On the one hand， aggressive colonies are better at gathering resources in times of scarcity. But when deprived of food or subjected to overheating， aggressive colonies can also suffer from infighting.

“Tropical cyclones likely impact both of these stressors by altering the numbers of flying prey and increasing sun exposure from a more open canopy layer，” Pruitt said. “Aggressiveness is passed down through generations in these colonies， from parent to daughter， and is a major factor in their survival and ability to reproduce.”

The researchers determined that after a storm passed， the colonies that aggressively pursued food and resources were able to produce more egg cases. The spiderlings also had a better chance of surviving into early winter. In areas that werent hit by storms， docile colonies thrived.

These findings were consistent even as the storms varied in duration， intensity and size. The researchers believe this shows that extreme events can shape animal behaviors. They would like to conduct more long-term studies to learn whether this is the case.

在美國和墨西哥经常遭受飓风袭扰的地区，凶猛好斗的蜘蛛变得对风暴更有抵御力，能安然度过灾难。

飓风沿墨西哥湾肆虐或席卷美国东海岸时，短时间内可能就会把所到之处的生物栖息地弄得面目全非。强风摧毁树木，残枝碎屑散落数英里，给生活在这些地方的动植物造成新的生存压力。那么，当生存环境遭到如此严重的破坏，各种生物是如何应变以继续生存的呢？研究人员观察了生活在沿海风暴频发地区的栉足蛛，探知它们的变化过程。该研究报告发表在了《自然·生态学与进化》杂志上。

这些天气系统被称为“黑天鹅事件”：突如其来，影响重大，人们往往后知后觉。它们来去匆匆，不会给研究提供很多时间，研究人员必须在预报的风暴发生前后抓紧研究蜘蛛群。

2018年飓风季，该研究团队对亚热带风暴“艾伯托”、飓风“佛罗伦萨”和“迈克尔”进行了监测。研究人员尽力预测这些天气系统的行进轨迹，在生活有240个雌蛛群的地区展开调研，把这些蛛群与没受到风暴影响地区的蛛群进行对比。风暴过去48小时后，研究人员返回受灾地区，发现约75%的蛛群抵抗住风暴最初的侵袭生存了下来。

该研究报告的主要作者、进化生物学家乔纳森·普鲁伊特是加拿大麦克马斯特大学心理学、神经科学与行为学系获得加拿大150“百人计划”项目资助的首席专家。普鲁伊特说：“这些‘黑天鹅天气现象在环境方面对生物进化和自然选择会产生诸多影响，搞清楚这些影响极为重要。随着海平面上升，热带风暴只会更频繁发生。我们现在比以往任何时候都需要去应对这些风暴对人类以外的动物造成的生态和进化影响。”

这种栉足蛛在性情上主要有两种遗传特征：平和温顺和凶猛好斗。凶猛好斗可以从四个方面来判断：行动迅速，进攻型捕食，吃雄蛛和卵，易受其他捕食性蜘蛛入侵。一方面，物资匮乏时，凶猛好斗型蛛群更善于积攒可用资源;但缺少食物或遭遇高温时，它们也会发生内斗。

“热带气旋可能改变飞行猎物的数量并利用更开阔的树冠层增加阳光照射，以此影响那两种压力因素。”普鲁伊特说，“凶猛好斗的特征在这些栉足蛛群中会代代相传，从父体或母体遗传给雌性后代，这是它们得以生存繁衍的一个关键因素。”

研究人员发现，风暴结束后，攻击型获取食物和资源的蛛群能产下更多卵袋，它们的后代也更有机会活到入冬。而在没有受到风暴袭击的地区，繁衍旺盛的是平和温顺的蛛群。

即使风暴在持续时间、强度和规模上各不相同，但研究得到的结果一致。研究人员认为，这表明极端事件会对动物行为产生重要影响。他们希望开展更多的长期研究，弄清情况是否果真如此。