Some species are spectacularly well adapted to their lifestyles, with long limbs for bounding or shorter limbs and compact frames to move more nimbly – just watch a sprinting cheetah or greyhound. Yet, most species are jacks-of-all-trades. They do just fine in most circumstances, getting about adequately, but they're never going to win Olympic gold for any particular manoeuvre. However, each creature is an individual, with a subtly different build, which could provide that animal with a slight advantage over others of the same species when it comes to manoeuvring. Animals with marginally longer hindlegs or longer thighs might make better jumpers, while stockier counterparts with shorter limbs might have traded in their ability to jump in order to take corners at higher speeds. Courtney Reed, Tyler Kartzinel and colleague s from Brown University, USA, were curious to find out how the build of Mongolian gerbils – which don't excel at either sprinting or jumping – impacts their individual athletic prowess.
To find out, the team recorded the force exerted by the rodents when they were startled into jumping and how quickly they took turns of increasing tightness (from a sharp 45 deg bend to a wider 135 deg turn). Sure enough, the gerbils with longer hindlimbs produced the most force when they jumped, and those with stockier limbs negotiated the bends at higher speeds than the gerbils with longer limbs. But when the team compared the gerbils’ agility with their leap force, none of the rodents excelled particularly at one activity over the other. They had not traded in their agility for an awesome leap to take tight turns faster, and vice versa, unless their hindlimbs were disproportionately long or short.
However, when the team compared the animals’ performance relative to the length of their thighs and shins, a pattern began to emerge. The gerbils with the longest shins were the best jumpers while the animals with the shortest thighs were the nimblest at taking turns. ‘These experiments revealed how each part of the leg contributes to each type of movement’, Reed says.
Reed and colleagues suspect that gerbils don't specialise in one manoeuvre at the expense of another because they also have to be reasonably competent over a range of other activities – from burrowing and climbing, to evading predators – which also shape their frames. Reed adds that the unexpected revelation that individuals do not prioritise one physical skill at the expense of another, ‘highlights how most animals probably have to be reasonably good at moving in a variety of complex ways to succeed’.
