Social deprivation affects cooperative predator inspection in a cichlid fish

Abstract

The social environment individuals are exposed to during ontogeny shapes social skills and social competence in group-living animals. Consequently, social deprivation has serious effects on behaviour and development in animals but little is known about its impact on cooperation. In this study, we examined the effect of social environment on cooperative predator inspection. Predator inspection behaviour is a complex behaviour, which is present in a variety of shoaling fish species. Often, two fish leave the safety of the group and inspect a potentially dangerous predator in order to gather information about the current predation risk. As predator inspection is highly risky, it is prone to conflicts and cheating. However, cooperation among individuals may reduce the individual predation risk. We investigated this complex social behaviour in juveniles of the cichlid fish Pelvicachromis taeniatus that were reared in two different social environments throughout development. Fish reared in a group inspected more often than isolation-reared fish and were more likely to cooperate, i.e. they conducted conjoint inspection of a predator. By contrast, isolation-reared fish were more likely to perform a single inspection without a companion. These results suggest an impairment of cooperative behaviour in isolation-reared fish most probably due to lack of social experience and resulting in lowered social skills needed in coordinated behaviour.

Keywords: cichlids; cooperation; predator inspection; social environment; social isolation.

Figure 1.

Experimental set-up viewed from the side. The experimental tank (70× 35×35 cm) was divided into four compartments: predator compartment (15 cm), and experimental compartment (38.5 cm) containing the inspection zone (22 cm) and an acclimatization compartment (16.5 cm). The predator compartment was separated from the rest of the tank by a transparent perforated plastic sheet. The acclimatization compartment containing a plastic plant as refuge was separated by a removable opaque plastic sheet. Figure is not true to scale.

Figure 2.

Average number of inspections per trial (solitary and cooperative inspections combined) of the two treatment groups. Median, first and third quartile and whiskers are shown. **p<0.01.

Figure 3.

Percentage of test fish performing a conjoint and solitary inspection, respectively, relative to the total number of inspections depending on rearing environment (reared in isolation (light bars)/reared in a group (dark bars)). ***p<0.001; *p<0.05.

Figure 4.

Mean time (%)±s.e. that test fish of the different treatment groups spent in conjoint inspections during the trial. ***p<0.001.

Figure 5.

Distance (cm) between test fish of the different treatment groups. Median, first and third quartile and whiskers are shown. ***p<0.001.