Activity Patterns of Evolving Mole Rats

Activity patterns were tested in four actively speciating chromosomal forms of blind subterranean mole rats of the Spalax ehrenbergi complex (2n = 52, 54, 58, and 60) which inhabit humid (2n = 52 and 58) and xeric (2n = 54 and 60), as well as cool (2n = 52 and 54) and warm (2n = 58 and 60) environments, respectively. Experimental animals included 98 adult male mole rats representing 9 populations covering the entire species range in Israel. The test apparatus simulated a natural underground territorial runway of a solitary occupant and each test lasted 24 h. The results indicated that (a) the pattern of activity was multiphasic, but activity in all nine populations is remarkably higher during the day than during the night and (b) differences occur among chromosome forms in both levels and patterns of activity. First, the “humid chromosome forms” are more active than the “xeric chromosome forms” and, second, it appears that the activity of the “cool chromosome forms” display a pattern of smaller number of periods as compared with the “warm chromosome forms.” Both results appear to be climatically adaptive and support an optimal activity pattern theory assuming that natural selection maximizes fitness by optimizing net energy gain per unit activity.