Researchers have discovered a fascinating defense mechanism employed by a species of tiny, colorful jumping spiders. These spiders utilize a combination of camouflage and ant-like movement to avoid being preyed upon by other spiders. The study, published in the journal iScience, revealed that while this defense tactic is effective against spider-eating spiders, it does not deter praying mantises.
Mimicking ants is a clever strategy as ants possess formidable defenses, such as spines, mandibles for biting, and the ability to fight back. Additionally, ants often carry chemical repellants or venom. The focus of the study, Siler collingwoodi, was already known to move in a manner similar to ants, but the researchers sought to determine the accuracy of its mimicry, whether it mimics multiple ant species, and how successful this mimicry is in discouraging predators.
The research team also investigated the significance of the spider’s vibrant coloration. Unlike typical ant-mimicking spiders that imitate the brown or black body color of ants, S. collingwoodi boasts brilliant body coloration. The researchers aimed to ascertain whether this colorful appearance serves as camouflage to protect the spiders from predators.
To unravel the role of ant-mimicry in the spiders’ defense, the researchers captured wild ant-mimicking spiders from four different locations in southern Hainan, China, and brought them back to the laboratory. They also collected another type of jumping spider that does not mimic ants, as well as five co-occurring ant species that they believed could serve as models for the spiders’ mimicry.
In the laboratory, the researchers analyzed and compared the movement patterns of the ants and spiders, including the use of individual limbs, speed, acceleration, and whether they followed a straight path or took more convoluted routes.
The findings revealed that instead of jumping like typical jumping spiders, S. collingwoodi imitates the movement of ants. They raise their front legs to mimic ant antennae, bob their abdomens, and walk by lifting their legs in an ant-like manner. Among the five ant species studied, the spiders’ walking style most closely resembled that of the three smaller ant species, which are also similar in size to the spiders.
According to Zeng, S. collingwoodi is not a perfect mimic since its gait and trajectory closely resemble multiple ant species. However, this general mimicry strategy could benefit the spiders by allowing them to inhabit different habitats if the ant models occupy varied environments.
The researchers proceeded to test the spider’s defenses against two potential predators: a similarly sized jumping spider, Portia labiata, which specializes in preying on other spiders and has color vision, and a generalist predator with a monochromatic visual system, the praying mantis, Gonypeta brunneri.
To examine the role of color camouflage, the researchers created models to visualize how the two predators perceived S. collingwoodi compared to other prey species against the backgrounds of two plants that the spiders inhabit: the red-flowering West Indian jasmine (Ixora chinensis) and the Fukien tea tree (Carmona microphylla). The findings indicated that the ant-mimicking spiders were better camouflaged from both spider and praying mantis predators on the jasmine plant compared to the tea tree plant.
During experiments where the predators were given a choice between the ant-mimicking spider and the non-mimicking jumping spider, the predatory spider was more likely to attack the non-mimic. Out of 17 trials, the spider launched five attacks, all of which were directed towards the non-mimic. However, praying mantises displayed equal aggression towards both prey species.
“We initially expected both predators to behave similarly in the antipredation experiments, but the simulated ant locomotion of Siler collingwoodi only deterred the jumping spider predator, whereas the praying mantis attacked both ants and mimics without discrimination,” explains senior author Wei Zhang, an evolutionary ecologist at Peking University.
This difference in behavior could be attributed to the risk of injury that each predator faces when consuming ants. Praying mantises are much larger than their prey, so they can consume spiny ants without significant danger, whereas predatory spiders are more vulnerable to injury.
Zhang explains that for the spider predator, launching a random attack on an ant could potentially lead to injury. Therefore, these predators are cautious and will only attack if they can clearly distinguish S. collingwoodi from actual ants with a high level of certainty.
Interestingly, the researchers discovered that the ant-mimicking spiders’ ability to avoid the attention of the predatory spiders was compromised when they lost a limb. This suggests that the spiders’ accurate mimicry of ants is hindered when they are unable to fully imitate the movements and appearance of ants due to the loss of a limb.
Source: Cell Press