Before starting something new, we tend to make sure that we are well-rested and conserving energy for what lies ahead. Fish are the same way, particularly Neolamprologus pulcher, a type of cichlid fish found in Lake Tanganyika, East Africa. There are two options for subordinate N. pulcher fish to take after they reach sexual maturity – they can choose to wait in line to inherit the dominant breeding position of the group or they can disperse and reproduce independently of the group. Other studies have been done researching dispersal and inheritance of the breeder position, including a study on paper wasps. However, this study, unlike the study on cichlids, did not account for whether dispersal was successful. Other studies also looked at defense in terms of future fitness – defending the entire group rather than just the individual for the future success of that group, such as is the case with meerkats.
It’s a question of stay or go
Scientists took a look at cichlid fish colonies for two types of subordinate fish: territory inheritors and dispersers. They were particularly interested in the long-term and short-term behavior of each type of subordinate fish before the dispersers left the group for other breeding opportunities. According to the researchers, the fish that would inherit the environment should show high investment in their territory (especially when it came to defense) and the fish that would disperse should reduce the amount of energy they invested in defense and other group aspects. They also predicted that cichlids that had decided to disperse would differ in behavior from those inheriting the breeding position before territory inheritance or dispersal.
How it was done
341 individual cichlids in 96 cooperative groups were captured, marked, and then released back into their original group. These marked fish were observed weekly. Also noted were group size and the composition of the groups, along with recording dispersal and territory inheritance. During the study, the behavior of the fish was observed 3-7 times for seven minutes each using The Observer XT and focal observation protocol. The study focused on how often the fish would defend and maintain the territory in both dispersers and territory inheritors.
Long-term behavioral differences
Researchers expected to see a difference between the behavior of dispersers and territory inheritors over a longer period of time before successful dispersal or inheritance. They examined the time period of 1 to 9 months before dispersal or inheritance to see if there was really any difference in behavior and found none. The amount of investment placed into territorial defense and maintenance was the same by fish that would remain and inherit the territory and fish that would later disperse.
Short-term behavioral differences
While there was no real difference in behavior over a long period of time before the fish either dispersed or stayed, changes in behavior did happen in the time period right before the fish made their decision. Fish that were planning to disperse lowered their commitment to the group, particularly with defense. However, fish that planned on taking their place in line to become the dominant breeder tended to increase their investment in the group. This only happened in the short period of time before the fish actually made their choice, and dispersed or stayed to inherit the territory.
After acquiring a breeding position
Scientists predicted (based on the benefits and costs of the behavior for each type of cichlid) some difference in the behavior of the disperser cichlids and the inheritor cichlids after they had found a breeding position. Their behavior was different when they had made their decision, however researchers found no difference in territory defense after acquiring a breeding position. The behavior shifted back to being the same – equal amounts of investment in defense and maintenance for the dispersers and the territory inheritors.
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- Zöttl, M.; Chapuis, L.; Freiburghaus, M.; Taborsky, M. (2013). Strategic reduction of help before dispersal in a cooperative breeder. Biology Letters, 9, 20120878.