The lesser Egyptian jerboa, Jaculus jaculus: a unique rodent model for evolution and development.

Tetrapods that have evolved the ability to run or bound at great speeds over long distances have repeatedly converged on specific morphological limb adaptations, including the loss of lateral digits, elongation of limb segments, and fusion of individual elements. Many of the more familiar cursorial animals, such as horses and deer, are large and do not lend themselves well to experimental embryonic analyses. However, a group of lesser-known bipedal rodents, the three-toed jerboas, has become an exceptional model for studying the developmental and molecular mechanisms shaping these limb morphologies. The lesser Egyptian jerboa, Jaculus jaculus, represents the most derived subfamily of jerboas and shows loss of the anterior and posterior hindlimb digits, fusion of the three central metatarsals, and dramatic elongation of the hindlimb relative to the forelimb with disproportionate elongation of the metatarsals. In addition, several unique physiological and morphological characteristics make these excellent animals for evolutionary studies. As small docile rodents, they are amenable to rearing in a laboratory setting and, along with several related species with a variety of skeletal morphologies, are plentiful enough in the wild to support field collections. The close evolutionary relationship to Mus musculus and the development of genomic resources for J. jaculus support comparative developmental and molecular analyses.