Behavioural mutagenesis in the convict cichlid fish, Cichlosoma nigrofasciatum guenther : I. The reduction of male aggressiveness in the first post-irradiation generation

Abstract

A comparison was made between the aggressive behaviour of groups of 10 convict cichlid males ( Cichlasoma nigrofasciatum) derived either from irradiated (500+500 R of X-rays, 24 h apart, both to oogonia and spermatogonia) or from sham-treated parents. The male level of aggression was measuerd as bites delivered to subadult conspecifics per 15 min observation time. For the same individual males the activity was determined by counting the number of 90° turns within 15 min. The aggression was also examined during the first 9 days of the breeding cycle from the day of spawning. A total of almost 10 000 data were computed for the present study. The aggressiveness of the nonmated control F 1 males was 3.5 times as high as that of the nonmated males of the irradiated series, and 2.1 times as high for the mated control F 1 males as that of the males of the irradiated series. Since the number of 90° turns of completely isolated males did not differ in any way for the two series, the reduction of male aggressiveness of the first postirradiation generation does not seem to be associated with a general lowering of activity. The evolutionary signficance of the present findings is discussed in terms of some views on behavioural genetics.