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

Abstract

Blind mole rats (Spalax ehrenbergi) are solitary and aggressive subterranean rodents. Aggressive defense behavior in the mole rat functions to deter neighboring competitors from territory, food, and mates and includes seismic and odor signals. The aim of the present study was to determine whether the aggressive defense behavior displayed by male mole rats is testosterone dependent. Five behavioral variables were taken as being representative of such 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 divided into three main climatic periods: cold and rainy (September–February); warm, 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 experiment the effect of endogenous and exogenous testosterone on male aggressive defense behavior was determined before and after castration and following testosterone propionate replacement. We found fluctuations in male testosterone concentrations, with three peaks: in November, May, and August, one in each of the three climatic periods. However, these fluctuations did not correlate with male aggressive behavior, which remained constant throughout the year. Furthermore, because neither castration nor testosterone propionate replacement in castrated individuals affected their defense behavior, we suggest 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 territory sites and food caches from intraspecific rivals. Thus, although testosterone may fluctuate as a result of seasonal breeding cycles, constant high levels of aggressive defense throughout the year are crucial for the survival of the male mole rat in its solitary subterranean environment. Aggr. Behav. 27:64–72, 2001. © 2001 Wiley-Liss, Inc.