0919 GMT September 23, 2019
Key to the remora's adhesion are the disk's well-known capabilities for generating suction, as well as friction created by spiky bones within the disk called lamellae to maintain hold on its host, phys.org wrote.
However, the factors driving the evolution of remora's unique disc morphology have long eluded researchers seeking to understand, and even engineer new devices and adhesives that mimic, the fish's uncanny ability to lock on to various surface types without harming their host or expending much energy, often for hours at a time under extreme oceanic forces.
In a study led at New Jersey Institute of Technology (NJIT), researchers have showcased a new biologically inspired remora disc capable of replicating the passive forces of suction and friction that power the fish's ability, demonstrating up to 60 percent greater hold than has been measured for live remoras attached to shark skin.
Using the disc model to explore evolutionary drivers of the remora's disc, researchers said the study's findings provide evidence that today's living species of remora have evolved a greater number of lamellae over time to enhance their holding power and ability to attach to a broader range of hosts with smoother surfaces, thereby increasing their chance for survival.
According to Brooke Flammang, professor of biological sciences at NJIT, while scientists have shed some light on the origins of the remora's modified fin structure, fundamental aspects of the disk's evolution have largely remained unclear. The study, featured in Bioinspiration and Biomimetics, indicates the disc model may be used to inform the design of more effective, lower-cost adhesive technologies in the future.
"The beauty behind the remora's adhesive mechanism is that biological tissues inherently do most of the work," said Brooke Flammang, professor of biological sciences at NJIT who led the study. "The most significant aspect of this research is that our robotic disc relies completely on the fundamental physics driving the adhesive mechanism in remoras, allowing us to determine biologically relevant performance and gain insight into the evolution of the remora's disc. This was previously not possible with past designs that required a human operator to control the system."
Diverging from many of their closest scavenger-like ancestors, such as cobia (Rachycentron canadum), the remora fish (of the family Echeneidae) is believed to have first begun attaching to hosts with rough surfaces, akin to sharks, after having evolved its suction disc from dorsal fin spines nearly 32 million years ago. The disc of living remoras today now features a fleshy-soft outer lip for suction while the disc's interior houses many more linear rows of tissue (lamellae) with tooth-like tissue projections (spinules), which the fish raises to generate friction against various host bodies to prevent slipping during hitchhiking.
According to Flammang, while scientists have shed some light on the origins of the remora's modified fin structure, fundamental aspects of the disk's evolution have largely remained unclear.
"The evolution of the remora's disc is largely unknown," said Flammang. "There is one fossil remora, Opisthomyzon, in the fossil record that has a disc with fewer lamellae [than today's remoras] without spinules towards the back of the head."