Distinct morphological drivers of jumping and maneuvering performance in gerbils

Theoretically, animals with longer hindlimbs are better jumpers, while
those with shorter hindlimbs are better maneuverers. Yet experimental
evidence of this intuitive relationship is lacking. We experimentally
compared jump force and maneuverability in a lab colony of Mongolian
gerbils (Meriones unguiculatus). We hypothesized that gerbils with long
legs (ankle to knee) and thighs (knee to hip) would produce the greatest
jump forces, while gerbils with short legs and thighs would be able to run
most rapidly around turns. Consistent with these hypotheses, gerbils with
longer legs produced greater jump forces after accounting for sex and body
mass: a 1-mm greater leg length provided 1 body-weight-unit greater jump
force on average. Furthermore, gerbils with shorter thighs were more
maneuverable: each 1-mm greater thigh length reduced turn speed by 5%.
Rather than a trade-off, however, there was no significant correlation
between jump force and turn speed. The experiments revealed how distinct
hindlimb segments contributed in different ways to each performance
measure: legs to jumping and thighs to maneuvering. If variation in
jumping and maneuvering influences survival during predator encounters,
then hindlimb segment lengths may be subject to strong natural selection.