Many animals use jumping to escape predators, overcome obstacles, or capture prey. While many insects jump, only 6 out of 300 genera of ants can do it, and these jumping behaviors use different body parts to propel themselves. For example, trap-jaw ants use their mandibles to jump backwards, while other ants use their legs to jump forward. Ye and colleagues have described how Gigantiops ants with very large abdomens, that make it difficult to jump, manage the trick. Their center of mass also happens to be right between the abdomen and thorax- which is further back than most ants. During takeoff, these ants raise their abdomens to move their center of mass and produce enough thrust to jump.
What role does abdominal movement play in ant jumping performance? What happens if this movement is restricted? Abdominal movement could stabilize body rotation during a jump by repositioning the ant’s center of mass. This may be similar to how cats twist their abdomens and use their tails to stabilize themselves during jumps and falls. The abdominal movements seen in these ants could help to provide thrust at the beginning of the jump so that the ant can jump faster and further.
To better understand the role of abdominal movements on jumping in Gigantiops ants, the authors compared jumping performance in ants before and after their abdomens where restrained. The goal was to see how jumping kinematics might change when the abdomen is restricted, so the authors compared abdomen and body rotation, velocity, acceleration, takeoff angle, height reached, distance moved, and movement in the legs.
When the abdomen is restricted in movement, a host of kinematic changes occur. Jumping performance is overall reduced when the abdomen in restricted. For example, velocities are reduced, jump heights are decreased, and jump distances are decreased during abdominal restriction. These changes suggest that abdominal movements generate thrust during takeoff so that the ant jumps higher, faster, and further. This behavior is also seen in other insects and even vertebrates, like tadpoles!
Despite the many kinematic changes that occur when abdominal movements are restricted in ants, it did not appear to influence rotational stability during jumps. Balance may not be as affected by the short and round shape of the Gigantiops abdomen compared to insects with long abdomens in which slight angle changes can mean large changes in center of mass. It is also possible that ants may raise their legs while jumping to counteract instability when their abdomens are restricted. To fully understand this mechanism, future experiments will need to analyze other subtle kinematic changes during jumps.
This study describes a new mechanism that some species of ants may use to overcome the challenges of jumping with a hefty abdomen (and thus, an unusual center of mass!) By raising the abdomen during takeoff, these ants can jump further, faster, and higher. If movement in the abdomen is restrained, ants may compensate by changing the movements of their legs to increase stability in jumping and landing.
Amanda M. Palecek-McClung is a PhD student at Clemson University. She studies functional morphology, biomechanics, and adhesion mechanisms in fish and other vertebrates. You can find more about her at ampalecek.weebly.com or contact her at firstname.lastname@example.org.