The influence of status and the social environment on energy stores in a social fish

Abstract

This study explores how muscle and liver energy stores are linked with social status and the social environment in Neolamprologus pulcher, a cooperatively breeding fish that lives in colonies comprised of up to 200 distinct social groups. Subordinate muscle energy stores were positively correlated with the number of neighbouring social groups in the colony, but this pattern was not observed in dominant N. pulcher. Furthermore, liver energy stores were smaller in dominants living at the edge of the colony compared with those living in the colony centre, with no differences among subordinates in liver energy stores. Subordinate N. pulcher may build up large energy stores in the muscles to fuel rapid growth after dispersal, which could occur more frequently in high-density environments. Dominant N. pulcher may use the more easily mobilized energy stores in the liver to fuel daily activities, which could be more energetically demanding on the edge of the colony as a result of the increased predation defence needed on the edge. Overall, this study demonstrates that both subordinate and dominant physiology in N. pulcher varies with characteristics of the social environment. Furthermore, dominant and subordinate energy storage strategies appear to differ due to status-dependent variation in daily activities and variation in the need to prepare for future reproductive or dispersal opportunities.

Within‐group relatedness is correlated with colony‐level social structure and reproductive sharing in a social fish

“…Fish were euthanized by immersion in a lethal concentration of benzocaine (ethyl p‐aminobenzoate, 1.0 μg/mL) for use in other studies (Hellmann et al . ). Sections of the dorsal fin were also taken from all individuals to be used as a genetic sample for relatedness analysis for this study.…”

“…While we collected more than 31 groups (Hellmann et al . , ), we limited the analyses to these 31 groups because (i) we were confident that group members were correctly collected from these groups, (ii) they contained two or more reproductively mature subordinates and (iii) samples from these groups produced sufficiently high‐quality DNA for generating RADseq data. Individually barcoded RAD libraries were generated using the protocol of Sovic et al .…”

“…A total of 31 groups (20 centre groups, 11 edge groups) with 171 individuals (31 dominant females, 30 dominant males, 51 subordinate females, 44 subordinate males and 15 reproductively immature subordinates) were analysed (see Table S1, Supporting information for distribution of dominants and subordinates across colonies). While we collected more than 31 groups (Hellmann et al 2015a(Hellmann et al , 2016, we limited the analyses to these 31 groups because (i) we were confident that group members were correctly collected from these groups, (ii) they contained two or more reproductively mature subordinates and (iii) samples from these groups produced sufficiently high-quality DNA for generating RADseq data. Individually barcoded RAD libraries were generated using the protocol of Sovic et al (2016) with the following modifications.…”

“…Dominants and subordinates that had been captured were then taken to the surface in mesh bags where they were weighed to the nearest 0.001 g and measured to the nearest 0.01 mm SL. Fish were euthanized by immersion in a lethal concentration of benzocaine (ethyl p-aminobenzoate, 1.0 lg/mL) for use in other studies (Hellmann et al 2016). Sections of the dorsal fin were also taken from all individuals to be used as a genetic sample for relatedness analysis for this study.…”

Physiological Regulation of Growth during Social Ascension in a Group-Living Fish

“…However, when a subordinate perceives the opportunity to ascend to a dominant position, it can rapidly grow and thus increase its likelihood of becoming dominant (Buston 2003;Russell et al 2004;Dengler-Crish and Catania 2007;Huchard et al 2016;Thorley et al 2018). Such periods of enhanced growth are energetically demanding, and although previous studies have hypothesized that subordinates accumulate energy reserves to meet these demands (Taborsky 1984;Hellmann et al 2016), energy regulation during periods of social transition has not yet been investigated. In fact, despite the fitness benefits that are typically associated with a large body size, few studies have investigated the physiological mechanisms by which individuals adjust their growth based on social circumstances.…”