Noninvolvement of testosterone in aggressive defense behavior in the male blind mole rat Spalax ehrenbergi

Blind mole rats (Spalax ehrenbergi) are solitary and aggressive subterranea n rodents, Aggressive defense behavior in the mole rat functions to deter n eighboring competitors from territory, food, and mates and includes seismic and odor signals. The aim of the present study was to determine whether th e aggressive defense behavior displayed by male mole rats is testosterone d ependent. Five behavioral variables were taken as being representative of s uch aggressive interaction: exposing teeth, biting, bulldozing movements of the head, soil blocking, and self-grooming. We monitored male testosterone Levels and aggressiveness throughout the annual cycle, which can be divide d into three main climatic periods: cold and rainy (September-February); wa rm, during which the soil is still moist and easily excavated (March-May); and hot (June-August), when the soil is hard and dry. In a second experimen t the effect of endogenous and exogenous testosterone on male aggressive de fense behavior was determined before and after castration and following tes tosterone propionate replacement. We found fluctuations in male testosteron e concentrations, with three peaks: in November, May, and August, one in ea ch of the three climatic periods. However, these fluctuations did not corre late with male aggressive behavior, which remained constant throughout the year. Furthermore, because neither castration nor testosterone propionate r eplacement in castrated individuals affected their defense behavior, we sug gest that such behavior in male mole rats is testosterone independent. The continuous excavation and maintenance of the mole rat's underground tunnel system demands high energy expenditure year-round and constant defense of t erritory sites and food caches from intraspecific rivals. Thus, although te stosterone may fluctuate as a result of seasonal breeding cycles, constant high levels of aggressive defense throughout the year are crucial for the s urvival of the male mole rat in its solitary subterranean environment. (C) 2001 Wiley-Liss. Inc.