A University of Haifa press release says, without giving much detail, that
Israeli gerbils are more cautious than their Jordanian friends… According to the researchers, the … higher number of agricultural farms in Israel… [not only creates] a gulf between habitats and thereby cause an increase in the number of species in the region, but they also hail one of the most problematic of intruders in the world: the red fox. On the Jordanian side, the red fox is far less common, so that Jordanian gerbils can allow themselves to be more carefree.
This is in some ways reminiscent of a 2005 University of Florida study called “Effect of Prenatal or Postnatal High Fat Diet on Physiology and Behavior of Borderline Hypertensive Rats“, and in many ways not. (Thanks to improbable researcher Steve Nadis for bringing this to our attention.)