How do crickets, and many other animals, avoid collisions with objects in their path and guide themselves to walk in a particular direction? This becomes a more complex question when considering that the visual system may be compromised due to light conditions, spatial restrictions, or just by being less developed. So, how else would organisms, in this case insects, be able to collect the information they need to navigate their environment successfully? A huge variety of species, including humans, use mechanosensory systems to gain information about their environment and perceive obstacles around them. Mechanosensation is the way that mechanical stimuli are perceived, though it is often better understood as underpinning the sense of touch.
The field cricket species Gryllus bimaculatus has an escape response that enables it to respond to a signal that a predator may be near, and try to avoid an unfortunate fate. They use mechanosensing organs on their abdomens called cerci that respond to small puffs of air (a signal of a potential threat) to prompt a sudden escape motion. Clearly during an escape it would not be beneficial to run into an obstacle and lose precious time. This cricket species can use its antennae to sense objects that may be in its path. It is unclear though what significance this antennae function has for the escape behavior, and if one impacts the other.
A research paper by Nwuneke et al. published in the Journal of Experimental Biology sought to provide insight into the possibility of two separate cricket mechanosensation systems being used together to better inform an escape. Their overall question asked if the information gained by the antennae is used to inform the cricket’s escape behavior, integrating the functions of separate mechanosensing organs. They used Gryllus bimaculatus that were bred in a lab for their experimentation. They described how this question has the potential to shed light on the way that many species navigate complex environments, like those with many obstacles, using mechanosensation, and the way that this system could play a role in the functioning of important survival behaviors.
The researchers’ hypothesis was that the sensory input of the antennal mechanosensation provides information about the cricket’s surroundings that is integrated with the escape response induced by the cerci, causing modulation, or simply an adjustment of that escape behavior to avoid collisions. They made a general prediction that the crickets would both move away from the air puff that was used to signal a threat, but also away from obstacles around them.
To seek support for this hypothesis the researchers used a rather extensive collection of experiments conducted on crickets studying both the ability of the crickets to perceive the obstacles, as well as how the positioning of obstacles in relation to the air puff impacts the direction in which the cricket escapes. Some of these experiments required the ablation of one or both antennae, which is better described as the removal of the antennae at the base.
Immediately upon beginning their study, Nwuneke et al. wanted to identify that the antennae were sensing physical obstacles, as opposed to sensing the air puff like the cerci. To get this result, they tested the responses of the crickets to air puffs from eight different angles around them, then repeated this same test after ablating both antennae, finding no significant difference in their responses. They conducted another experiment in which no ablation occurred and two physical obstacles were tested, a cylinder and a wall. They found that the wall placed half an antenna length to the side of the cricket had the most significant effect as opposed to the cylinder near or further from the cricket or the plate at a far distance, defined as 5 mm from the tip of the antenna. Essentially, when the air puff came from behind, and the near wall was on the left, the cricket showed a significant change in the walking trajectory away from the wall compared to the control when no obstacle was present at all. When the air puff came from the side with the wall close to the opposite side, the cricket was significantly adjusting to move backward compared to the control without the obstacle.
Building off of those preliminary findings, the researchers determined that when they moved the wall parallel to the cricket towards the front of the animal, the direction that the cricket walked in was altered more than if the wall was moved toward the back of the cricket. This result was suggested to be caused by increased ability to sense the wall when it was further forward, due to proximity to one antenna. The last result that the paper
highlighted was that crickets showed evidence of not requiring input from both antennae to determine the appropriate direction of locomotion. When one antenna was ablated and the wall was positioned in front of the cricket but offset to the same side as the intact antenna, the cricket was able to use only that antenna to focus on the surface and edge of the wall, getting a sufficient idea of the space it occupies to navigate around it.
All of the results supported the hypothesis that input from the mechanosensation of the antennae would modulate (or alter) the escape behavior of the crickets. Their result that the wall obstacle had a significant effect on the cricket’s direction of locomotion supports the hypothesis by showing that the escape included navigation around obstacles that would be perceived by the antennae. They also were able to support their specific prediction that the behavior would show the cricket moving away from the air puff and away from the obstacle as during their experimentation even with alterations to the position of the obstacles, and the ablation of one antenna, the crickets were still able to recognize the space that obstacles were taking up, and respond accordingly to avoid a collision. When considered overall, the results communicated that the crickets were able to actively use their antennal mechanosensing to inform a successful and collision-free escape which was prompted by a separate mechanosensing organ. This implies integration of both systems, and modulation of a common behavior based on information about the environment.
This study provides really exciting insight into the way that sensory systems and strategies work together to create a comprehensive picture of the environment, which likely plays a significant role for survival. If we consider the cricket that was the subject of this study, failure to avoid obstacles during an escape could slow the individual down and result in predation. The ability of organisms to use the information they gain through one sensory process is undoubtedly important, but the significance of that information greatly increases when it can be used to build upon the knowledge gained from other systems and signals. There are so many places that future research can take the findings of this study, most notably to expand the idea of connected mechanosensation systems to other species, and increasingly complex environments. This research provides a roadmap and inspiration for further experimentation to learn more about other organisms, and possibly even humans. There are so many options for next steps, and the versatility of this topic makes it an exciting starting point for future exploration.
Nwuneke Okereke Ifere, Hisashi Shidara, Nodoka Sato, Hiroto Ogawa; Spatial perception mediated by insect antennal mechanosensory system. J Exp Biol 15 February 2022; 225 (4): jeb243276. doi: https://doi.org/10.1242/jeb.243276