New research published in the journal Nature Ecology & Evolution details the findings of a study on Anelosimus studiosus, a species of spider which lives along the Gulf and Atlantic coasts of the United States and Mexico. Scientists from McMaster University say that the spiders are evolving because of their continuous exposure to hurricanes.
The damage that hurricanes leave in their wake can change habitats and allow room for opportunistic species to thrive, say the researchers. But exactly which species will survive and thrive is still to be determined.
Lead author Jonathan Pruitt is an evolutionary biologist and Canada 150 Chair in McMaster's Department of Psychology, Neuroscience & Behavior. He and his team looked at the female colonies of Anelosimus studiosus in order to conclude their evolutionary adaptations to extreme weather events.
Anelosimus studiosus is unique in that there are two clear inherited personality traits that colonies can take on: docile and aggressive. According to Science Daily, “The aggressiveness of a colony is determined by the speed and number of attackers that respond to prey, the tendency to cannibalize males and eggs, the vulnerability to infiltration by predatory foreign spiders, among other characteristics. Aggressive colonies, for example, are better at acquiring resources when scarce but are also more prone to infighting when deprived of food for long periods of time or when colonies become overheated.”
The researchers wanted to figure out if a colony’s aggressiveness would benefit or detriment its ability to survive in extreme weather – and, more interestingly, if exposure to extreme weather was selecting for particular spider traits. To gather their data, the researchers had to really get in the thick of it – going to hurricane sites right before and within 48 hours after the landfall of the cyclone. During the hurricane season of 2018, they took samples of 240 colonies and compared them to control sites.
As Pruitt explains, "Tropical cyclones likely impact these stressors by altering the numbers of flying prey and increasing sun exposure from a more open canopy layer. 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 found that following a hurricane, colonies with more aggressive foraging responses produced more egg cases and had more spiderlings survive into early winter. Despite adjusting the data for variables such as storm size, duration, and intensity, the trend remained consistent.
"It is tremendously important to understand the environmental impacts of these 'black swan' weather events on evolution and natural selection," says Pruitt. "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.”
Sources: Nature Ecology & Evolution, Science Daily