ADAPTATION AND CONSTRAINT IN THE EVOLUTION OF THE PHYSIOLOGY AND BEHAVIOR OF THE NAMIB DESERT TENEBRIONID BEETLE GENUS ONYMACRIS

A comparative phylogenetic approach was used to test the following ada ptive hypotheses pertaining to the physiological abilities of the Nami b desert tenebrionid beetle genus Onymacris to withstand the hot, dry desert environment: (1) Desert-interior species evolved longer legs (r elative to body size) than beetles in the cooler coastal region to fac ilitate stilting, i.e., elevating their bodies our of the hot boundary layer of air close to the substrate. (2) Wax blooms on the exoskeleto n, which reduce evaporative water loss, are more likely to evolve in d esert-interior species than in coastal species. (3) The high costs of activity in the extreme climates select for perfect coadaptation of pr eferred body temperatures (i.e., optimal temperatures for activity) an d those they achieve in the field. All three of these adaptive hypothe ses were supported by the results of squared-change parsimony and inde pendent-contrasts analyses. Additionally, a parsimony approach suggest ed that a novel means of obtaining water from periodic fogs, known as fog basking, has evolved independently on two occasions.