N. pulcher

Home is Where the Dominant Is: Selective Conspecific Attraction in a Cooperatively Breeding Fish

Abstract
In hierarchical groups where individuals have different ranks and thus different resource access, rank is likely to influence who is watched and learned from. The cooperatively breeding cichlid Neolamprologus pulcher forms dominance hierarchies largely based on size, and so we tested whether dominance influenced use of social cues in this system. We hypothesized that dominant fish would have a stronger influence on use of social cues because more attention should be paid to higher ranked fish so that an individual can modulate their behavior to potentially reduce aggression or because the information may be more valuable. We predicted that individuals would change their behavior more after the opportunity to watch a higher ranked individual versus a lower ranked. To test this, we performed a series of shelter choice experiments. First, a focal individual was allowed to observe two shelters with one occupied by a familiar demonstrator. Demonstrators were either of higher or lower rank. The demonstrator was removed and the focal allowed access to both shelters. We found that only the dominant female influenced space use with observers using the area around shelters demonstrated by dominant females more frequently than expected, indicating they paid attention. Subordinates may be innately paying more attention to dominant individuals due to the possibility of receiving aggression or being evicted by a dominant. Subordinate males may also be attracted to the dominant female herself, rather than or in addition to the shelter. Interacting with dominant individuals can provide opportunities for performing submissive or affiliative behaviors. Dominant female presence is liable to influence subordinate behavior more than other group members and may have a larger influence on the behavior of the group as a whole.

Methods and Results
Fourteen groups of 6 fish were created and allowed to acclimate for a minimum of one month before trials were conducted. The dominant male and female were the largest two individuals in the group. The next largest and highest ranked subordinate was female, followed by a male (the focal individual during trials), and then another male. The smallest subordinate, used as a companion for the focal during trials, was either male or female. The designated demonstrators were the dominant female, first ranked subordinate female, and third ranked subordinate male.Experimental tank setup. The companion fish was contained to the left most side of the tank throughout the entire trial. Focal individuals were contained for 10 minutes during the observation period and then allowed to explore the rest of the tank for 15 minutes following observation. Both shelters were contained in the clear apparatus regardless of whether a demonstrator was present.
We found a significant two-way interaction of rank and demonstrated shelter (𝐷𝑓 = 2, 𝑝 = 0.0022) on the number of occurrences in the area around a shelter (panel a). There was a significant difference between the number of occurrences in the shelter area demonstrated by the dominant female and the shelter area not demonstrated by the dominant female, with focals occurring more often in the demonstrated area than nondemonstrated area ( 𝑝 = 0.0046).

Discussion
We found that both the presence and the rank of demonstrators influenced one aspect of space use. However, only dominant females had an effect on shelter use. Specifically, the area around the shelters used by dominant females were visited more frequently by the focal individuals, while neither higher- nor lower-ranked subordinates influenced use of demonstrated and undemonstrated shelters. This could mean that they are not giving much attention to subordinate demonstrators or that the information they gain from them is not being used. There are at least two, not mutually exclusive, reasons why subordinate males may alter space use depending on the presence of dominant females but not other demonstrators: Subordinates may gain more relevant information from dominant females about desirable shelters, and they may inherently be paying more attention to dominant females over other subordinates.

The most dominant individuals in a hierarchical group are often the most successful. In N. pulcher the most dominant individuals are both larger and older (Stiver et al. 2007, Josi et al. 2021). Being larger is typically correlated with success in conflicts (Nakano 1995) and being older (Vervaecke et al. 2005) indicates an ability to survive and eventually gain dominance. Thus, the presence of a dominant individual could be an indicator that the resources they are using are of high quality and reliable. In N. pulcher hierarchies where size is a major indicator of dominance (Heg et al. 2004, Hamilton et al. 2005), shelters in which dominants can fit are consequentially also able to accommodate smaller subordinate individuals. Therefore, it is possible that subordinates visited these locations more frequently because they were used by successful, large dominants, and doing so yields increased survival and success.

Subordinates may also use regions demonstrated by dominants simply because they are paying more attention to dominants. Dominant females have the power to evict subordinates (Taborsky 1985, Fischer et al. 2014) and are liable to punish subordinates (Fischer et al. 2014, Reddon et al. 2019). Subordinate N. pulcher, when prevented from helping, will increase helping behaviors potentially as appeasement to dominants (Bergmüller and Taborsky 2005). Submission to dominants is also correlated with increased time spent in shelters, suggesting that submission allows subordinates to spend more time in protected areas where social interactions are likely to occur, although this result was found for dominant males but not females (Hooley et al. 2025). Paying attention to where the dominant female is can help a subordinate identify where to go and how to behave to reduce potential aggression.

We found that the presence of dominant females influences space use by subordinate males. If dominant groupmates are facilitating behaviors such as shelter use for subordinate individuals, then differences in dominant behaviors will lead to differences in subordinate behaviors. For example, the individuals in a group, rather than the species, were a stronger predictor of co-feeding tolerance in chimpanzees and bonobos, even in similar environments (van Leeuwen et. al. 2023), suggesting strong influences of some key individuals on group-level behaviors (Hamilton and Ligocki 2012, Beisner et al. 2020). Differences between dominant females between groups due to aspects such as personality, ecological situation, or group dynamics could then result in differences in subordinate space use between groups. Understanding the underlying mechanisms influencing differences in dominant females could help elucidate the effect of each of our suggested reasons for their influence on space use by subordinates. We have shown that the mere presence of dominant females is liable to influence subordinate behavior, therefore accounting for variation among dominant females may help explain variation in between-group space use.

Credits and Bibliography
Research by Kinnoyu
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