Ab. Lucion et al., TERRITORIAL AGGRESSION, BODY-WEIGHT, CARBOHYDRATE-METABOLISM AND TESTOSTERONE LEVELS OF WILD RATS MAINTAINED IN LABORATORY COLONIES, Brazilian journal of medical and biological research, 29(12), 1996, pp. 1657-1662
Aggressive territorial behavior was studied in 15 colonies of wild rat
s (Rattus norvegicus), each consisting of 2 males and 1 female. One of
the males attacked an intruder rat more frequently and had a higher d
e body weight than the less aggressive one. In another experiment, mal
e and female rats were raised in colonies from weaning to adulthood. A
nimals were weighed every 7 days until 90 days of age when plasma test
osterone was measured in males, and plasma glucose, hepatic and muscle
glycogen were measured in both males and females. The heavier (and th
us possibly dominant) males in the colonies of 3 males and 1 female al
so had a higher body weight than males raised with females, but withou
t any male partner. In this long-term social relationship there were n
o significant differences in carbohydrate metabolism among the animals
. The differential growth rate among males was established around the
period of sexual maturity. Moreover, when adult, heavier males had hig
her plasma testosterone levels compared to the other members of the co
lony and also to males that had no other competitive male partner. Thi
s higher androgenic hormone level may be one of the causal factors inv
olved in the weight increase of the dominant male in the colony.