Parenting. Useless in Fish

        For humans, experiences in our early lives can drastically influence who we are as adults. These can include anything from the quality of parenting we receive to our socioeconomic standing. Often these factors can mean the difference between a child becoming a successful CEO or a degenerate criminal in a penitentiary.

               

        The importance of early life experiences isn’t a phenomenon exclusive to mankind however. Many studies on monkeys, birds, mice, and even fish show that differences in social experience at a young age can change the individual in adulthood.

                 

         Parenting is an activity that not many species of fish subscribe to. In fact most species of fish have their offspring and then leave them to their own devices. This lack of parental care means that juvenile fish have to fend for themselves, which often ends badly. The success of this type of reproduction lies in the enormous number of offspring that are initially produced by the parents. Even if the majority of them die there are still a significant number of them that survive to adulthood.

                

         Although that is the case for the majority of fish, some species do provide some sort of rudimentary parental care. Neolamprologus pulcher is a species of highly social cichlid endemic to Lake Tanganyika in East Africa. They live in family groups that defend small territories that encompass breeding sites (usually caves or hollows). Groups consist of a breeding pair of adults, 1-14 adult or juvenile brood care helpers, and young. “Parenting” in N. pulcher is restricted to the older individuals (breeding pair and brood helpers) cleaning the eggs and defending the brood. Within these groups there exists a highly complex size and sex dependant hierarchy and presumably group members must have well developed social skills in order to behave appropriately in their respective roles.

                 

          Arnold and Taborsky (2010) wanted to see if the absence or presence of adults during the development of young N. pulcher influenced ability to socially interact with their peers later in life. This is a critical ability for an animal like N. pulcher that lives in complex social groups. To do this they designed four experimental groups; +B (with breeders), -B (without breeders), +BH (with breeders and helpers), and –BH (without breeders and helpers). Since behaviour was shown not to differ between +B and +BH and –B and –BH they were later termed +F and –F respectively.

                 

          The experiments all began by putting a breeding pair of adults with two sexually immature helpers into a large tank together. Eventually the breeding pair would produce a brood and if that brood had a sufficient number of eggs it would be allowed to hatch. 10 days after hatching the fry were removed (this was the earliest that they were large enough to be moved) and an opaque partition put in the tank. One side of the tank had all the breeders and/or helpers and the other was empty. Arnold and Taborsky then evenly distributed the fry from the brood between the two compartments.

                 

           The next 62 days was the social experience phase of the experiment where they fry grew up and interacted with one another. After the 62 days the fry from each treatment group were put into their own respective tanks. After a 35 day neutral phase where fry stayed in these tanks the performance tests took place (see Figure 1 for overview).

            

Figure 1: Experimental set-up indicating the different phases of the experiment with a timeline. The large numbers on the timeline represent the start of each experimental phase, the smaller numbers are days of behavioural observations and size measurements.

           The performance involved two juveniles (no longer called fry) being placed into an experimental tank. Inside the tank there was a shelter and whichever one of the juveniles was put into the tank first became the shelter owner. The second fish introduced was then termed the intruder. The idea was to see if shelter owners or intruders behaved differently if they were +F or –F fish.

                 

           The results of the experiment were that +F fish responded more appropriately that their –F counterparts in all social settings. Arnold and Taborsky present three excellent reasons as to why the types of behaviour exhibited by the +F fish is indicative of having acquired better social skills. The first is that +F fish adjusted their behaviour to the social context. For example, when +F was a shelter owner they used more threat displays and less overt aggression (Figure 2). This is advantageous as it is both energetically cheaper and the risk of escalation is much lower.

Figure 2: Rate of threat displays by shelter owners. Black bars represent the mean of the +F shelter owners, grey bars the mean of –F shelter owners. The top indicates whether the intruder was raised with or without older conspecifics.

            The second reason is that generally the rates of submission when +F fish were the intruder were much higher (Figure 3). Again this helps the individual as the risk of escalation decreases and the probability of the intruder becoming a member of the group as a helper (critical to survival) increases as well.

               

Figure 3: Rate of submissive behaviour by intruders. Black bars represent the mean of the +F intruders, grey bars the mean of –F intruders. The top indicates whether the intruder was raised with or without older conspecifics.

            The third and final reason is that the time that it took the +F fish to respond appropriately was lower (Figure 4). This helps +F fish because the cost that comes with performing submissive or aggressive/threat behaviours is energetically higher than regular activity.

          

Figure 4: Duration of contest between the shelter owner and intruder Black bars represent the mean of the +F shelter owners, grey bars the mean of –F shelter owners. The top indicates whether the intruder was raised with or without older conspecifics.

             Throughout the experiment Arnold and Taborsky tried to keep the conditions between the two treatment groups virtually identical with the exception of the presence of adults. They made sure to use fish from the same brood when making comparisons and when assigning them to treatment groups, they ensured that during the performance tests the fish were always matched for size, and they even randomized the side of the tank that each treatment group was assigned to.

All of this is excellent experimental practice but I think they missed one thing. They forgot to mention whether or not the large tanks that they initially kept the fish in during the larval and social experience phases were visually isolated from each other. Even if the tank had an opaque partition separating the two treatment groups nothing would be stopping the fish from looking outside their own tank into neighbouring tanks and learning some behaviours from those fish.

Aside from that one issue, I thought that this article was very well done and is particularly interesting as it is one of the first to show this type of effect in fish and demonstrate that social competence may be as important for animals living in complex societies as it is for humans.