Genetics of behavior: endocrine responses in lines selected for mating ability

Abstract

The role of androgens on mating behavior, packed cell volume (PCV), and comb size was studied in lines selected bidirectionally for mating ability. Combs of adult low-mating-line (LML) males were larger than those of the high-mating-line (HML) males while those of controls were intermediate. Chick comb response to androgen however, showed no line difference. Random samples of adults showed no differences among lines for POV. However, for an unexplainable reason, there was a difference among lines for birds used in the mating trials. Males were hatched from P7 matings of the selected and the control line. Half were caponized at five weeks or age and half served as intact controls. Fourteen daily injections of testosterone propionate (T.P.) were given to half of the castrates and half the intact birds commencing at 23 weeks of age. After the final injection, all males were released singly into pens of females for 10 minutes daily. The number of courts, mounts, treads, and completed matings were recorded. Sexual activity was greatest for the HML and least for the LML with the controls being intermediate. Castrates displayed no mating behavior. Administration of T.P. to castrates elicited sexual behavior but to a lesser degree than observed in intact males. No change in behavior was noted for intact males injected with T.P., suggesting that sufficient endogenous androgens were present for normal mating behavior. It was concluded, therefore, that the differences among lines for mating behavior were not due to unequal androgen titers.