Monitoring the feeding activity of individual fish with a demand feeding system

Feeding activity of individual Arctic charr ( Salvelinus alpinus ) was recorded automatically for 29 days using a demand feeding system. Each of three groups of 15 fish was kept in 1 m³ tanks, containing brackish water at 10° C. Individual biting activity was continuously monitored using a PIT-tag (Passive Integrated Transponders) system with unique individual codes. The accuracies of the bite detection system were 91, 93.1 and 99.5% respectively, in the three tanks. In all tanks, most of the individuals (12–14) bit on the releasing trigger a few times during the first 3 days. Thereafter, one or two individuals per tank accounted for almost all of the biting activity. This pronounced shift in bite-number distribution among individuals was probably due to the development of a dominance hierarchy, in which the dominant individuals monopolized the trigger. Growth rates appeared to be highest among high ranking fish. The implications of using demand feeding and PIT-tag devices in feeding studies are discussed.     

The effects of surgically-implanted dummy radio transmitters on the behaviour of wild Atlantic salmon smolts

The social behaviour of Atlantic salmon smolts was evaluated during their migration period under controlled conditions in an experimental stream tank. Agonistic behaviour, dominance, distance to nearest neighbour, and distance from substrate were examined pre- and post-surgical implantation of dummy radio transmitters (2.4–4.3% body weight). Smolts were able to quickly equilibrate after transmitter insertion. Social ranking changed in nine of the eleven trials with four fish, and in only one of the five trials with pairs. No significant differences were found (p>0.05) in any of the behavioural parameters measured. Overall, the only effect on smolts surgically implanted with radio transmitters was a large shift in dominance. The presence of an antenna also elicited aggressive attacks from other individuals.     

Behavioural influences on life-history variation in juvenile Atlantic salmon,Salmo salar

Synopsis Juvenile Atlantic salmon emigrate from the river in a given year as a consequence of a physiological decision influencing appetite and growth during the previous summer. The direction of the decision depends on developmental performance exceeding a genetically determined threshold at that time, and that performance is governed by environmental opportunity. The animal's foraging efficiency (ability to avoid predators, and to compete) determines how well that opportunity is used. Those fish which maintained relatively high growth after July preferred higher stream flows, and were more likely to hide than to flee from a predator. Predator vigilance reduced intake, and ability to discriminate edible particles. Early competitive ability depended on fierceness rather than size, and ultimate large size was a consequence of dominant status. Initial status among high ranking individuals (but not among low ones) predicted the likelihood of maintaining growth in late summer. Size by July was the better predictor for low ranked fish. The influence of high status on life-history variation depends on how much it suppresses the growth of those lower in the hierarchy. Invited review     

A twenty-year study of long-term and temporary dominance relations among stumptailed macaques (Macaca arctoides)

Consistent individual differences in long-term dominance are a basic underlying assumption of hypotheses linking dominance and reproductive success. Long-term and temporary dominance of a colony group of stumptailed macaques was studied for 20 years. There were two variously constituted groups for the first 4 years and a single group for the last 16. Stumptails displayed the matrilineal dominance organization found for several other cercopithecine species. A method was devised to standardize ranks so they could be compared over the years across groups of varying size and composition. No animal maintained the same dominance rank over the entire period of the research or over the last 16 years, but there was considerable consistency over long periods. Although occupants of the male and female alpha positions changed several times, one female was dominant for 18 of the 20 years. She was dominant in 1968, at the start of the study, and at its end in 1988 at which time her 18-year-old son was the dominant male. Variation in dominance ranks was greatest among members of mid-ranking matrilines and least for the lowest ranking. The same female or her son were the lowest ranking animals of their groups in all samples taken over the entire 20 years.     

Effects of kinship on aggression and RNA content in juvenile Arctic charr

The behaviour of juvenile Arctic charr Salvelinus alpinus was studied in groups of four siblings composed of familiar and unfamiliar individuals or in mixed groups of four where both siblings and unrelated individuals were present. The frequency of aggressive acts was significantly higher in the mixed groups compared to the pure sibling groups and the difference was present at all levels of the hierarchy rank order, based on a dominance index, except the lowest ranked individuals. The difference was significant after but not before feeding, implying that competition with non-kin for a food resource increased the aggression. No significant difference in weight gain was observed between sibling and mixed groups during the 6 days of the experiment, but the RNA contents of lateral musculature in dominant individuals from sibling groups were significantly higher than the corresponding fish in the mixed group, suggesting a difference in growth rate when the experiments ended. No significant difference in RNA content was observed between subordinate fish of the two treatments, i.e. siblings v . mixed.     

Social interactions and reproductive tactics in red–necked wallabies (Macropus rufogriseus banksianus)

Male red–necked wallabies established dominance relationships by fighting, and dominance rankings among males were positively correlated with body size. Females became outstandingly attractive to males during the week preceding mating, and males, who normally ranged widely and solitarily in search of mates, gathered in groups around such females. It is suggested that females, by prolonging their advertisement of oestrus, and thereby inciting sustained competitive interactions among the males who were attracted to them, contributed to a bias in the distribution of male mating success in favour of very large dominant individuals. High–ranking males mated within discrete but undefended areas of absolute dominance ('dominions'). Direct interactions between dominion–holding males were rare, but males just below dominion–holding status often fought with one another, and were frequently harassed by dominional males.     

Dominance hierarchies in group-living cleaning gobies: causes and foraging consequences

In species living in social groups, aggression among individuals to gain access to limiting resources can lead to the formation of stable social hierarchies. We tested whether dominance rank in social groups of sponge-dwelling cleaning gobies Elacatinus prochilos in Barbados was determined by physical attributes of individuals or by prior experience of dominance, and examined the foraging consequences of dominance rank. Intraspecific aggression within groups resulted in stable dominance hierarchies that were strongly correlated with fish length. Dominant individuals maintained exclusive territories while subordinate fish occupied broader home ranges. Larger, competitively dominant fish were able to monopolize areas inside the sponge lumen with the highest abundance of the polychaete Haplosyllis spp., a favoured prey item, and achieved the highest foraging rates. The removal of a territorial individual from large groups resulted in a domino-like effect in territory relocation of the remaining fish as individuals moved to the territory previously occupied by the individual just above them in the group hierarchy. Individuals added to existing groups generally failed to gain access to territories, despite being formerly dominant in their original groups. When given the opportunity to choose a location in the absence of larger competitors, gobies frequently preferred positions that were previously defended and that had abundant food. These results suggest that intraspecific competition for resources creates the observed dominance structures and provides support for the role of individual physical attributes in the formation and maintenance of dominance hierarchies.     

Merging social hierarchies: Effects on dominance rank in male green swordtail fish (Xiphophorus helleri)

When the same set of individuals are placed in different social contexts, some groups members often experience a change in dominance status. We examined the context-dependence of social status using a group fusion protocol in male green swordtail fish (Xiphophorus helleri). Six individuals were matched for size and separated into two groups of three fish. Each triad established a stable hierarchy after which time the two subgroups were merged into one larger assemblage. The maintenance of within- and between-group rank relationships was examined. Relative rank was preserved within each subgroup across social contexts but we found no evidence that familiarity with dominant animals assists individuals of one subgroup in achieving higher rank (coat-tail effects). Dominant individuals from the pre-fusion groups were significantly likely to obtain high status in the merged group and vice versa for subordinate pre-fusion animals. These results demonstrate that social rank in swordtails is relatively impervious to changes in social context, but we address some deviations from this trend. Small differences in standard length were a significant predictor of the most dominant rank in the post-fusion hierarchy, with the largest animals tending to occupy the alpha position. We discuss our results in terms of the potential factors involved in within- and between-group rank maintenance, including individual recognition, winner and loser effects, or asymmetries in dominance-related characteristics.     

Female rank instability in newly formed groups of familiar sooty mangabeys (Cercocebus torquatus atys)

The formation of two new groups of sooty mangabeys (N=6; N=11) comprised of individuals removed from their natal group of 98 animals led to dominance rank challenges with aggression and wounding, though this occurred after an interval of months. Dominance rank challenges were not expected because, unlike rhesus macaques, adult female sooty mangabeys do not affiliate with adult kin significantly more than nonkin and show minimal agonistic aiding even with adult kin, thus rank would seem to be independent of aiding. Moreover, during the last nine years, severe wounding of adults in a large stable group of sooty mangabeys has been virtually absent and agonistic behavior in a stable group of sooty mangabeys is exhibited at a low rate compared to some macaque species. New members in the group of six maintained their relative ranks for 12 weeks after which the beta supplanted the alpha female with no serious wounding. This ranking remained stable for 29 weeks after which the alpha and beta females were supplanted with fatal wounds inflicted to the alpha and less severe wounds to the beta female. The second subgroup also kept their relative ranks initially. However, after 27 weeks the lowest ranking female severely wounded the next to last ranking female and 1 week later attacked and displaced the alpha female with minimal wounding. Fourteen weeks later the beta female (formerly the alpha) attacked and severely wounded the new alpha female and regained the top dominance position. These events suggest that although sooty mangabeys do not exhibit strong kin preferential behavior among adults, they do have defined relationships within the long term, stable group. Removal from those defined relationships allows the possibility of social reorganization that may be mediated by serious aggression.     

Competition between brown trout and Atlantic salmon parr over pool refuges during rapid dewatering

Variations in distributions and behaviours of Atlantic salmon Salmo salar in allopatry (homogeneous) and in sympatry with brown trout Salmo trutta (mixed) were observed before, during and after 2 day periods of dewatering in a large glass-sided indoor stream at densities typical of Scottish upland streams. Brown trout utilized pools more than Atlantic salmon at normal flows and in both species the majority of fishes moved into pools during dewatering. There was no significant effect of brown trout, which was the more dominant species, on the overall ability of Atlantic salmon to use pool habitat as a refuge during dewatering. Within mixed and homogeneous groups, average feeding levels decreased during dewatering. The highest ranking fish, which was always a brown trout in mixed groups, predominantly monopolized the pool and other individuals in pools adopted a more cryptic, stationary behaviour. Dewatering effectively increased local population density with the result that dominance status became much more important in maintaining food intake, and polarization between the top ranking fish and others increased. During the first day of dewatering, there was extreme behavioural polarization such that the dominant fish exhibited most aggression and least feeding within the group. Among dominant fish on the second day of dewatering, aggression had largely abated and feeding had returned to pretreatment levels despite the reduced average feeding within the group. The main difference between mixed and homogeneous groups was in the behaviour of the most dominant Atlantic salmon, which was near-despotic in allopatry and subordinate to brown trout in sympatry.     

Female-mediated causes and consequences of status change in a social fish

In highly social species, dominant individuals often monopolize reproduction, resulting in reproductive investment that is status dependent. Yet, for subordinates, who typically invest less in reproduction, social status can change and opportunities to ascend to dominant social positions are presented suddenly, requiring abrupt changes in behaviour and physiology. In this study, we examined male reproductive anatomy, physiology and behaviour following experimental manipulations of social status in the cooperatively breeding cichlid fish, Neolamprologus pulcher. This unusual fish species lives in permanent social groups composed of a dominant breeding pair and 1-20 subordinates that form a linear social dominance hierarchy. By removing male breeders, we created 18 breeding vacancies and thus provided an opportunity for subordinate males to ascend in status. Dominant females play an important role in regulating status change, as males successfully ascended to breeder status only when they were slightly larger than the female breeder in their social group. Ascending males rapidly assumed behavioural dominance, demonstrated elevated gonadal investment and androgen concentrations compared with males remaining socially subordinate. Interestingly, to increase gonadal investment ascending males appeared to temporarily restrain somatic growth. These results highlight the complex interactions between social status, reproductive physiology and group dynamics, and underscore a convergent pattern of reproductive investment among highly social, cooperative species.     

Correlation among dominance status, metabolic rate and otolith size in masu salmon

In spatial competition between individuals, neither fish sex nor body mass affected dominance status in masu salmon Oncorhynchus masou . In contrast, resting metabolic rate ( M _R) was significantly correlated with dominance status, indicating that a high metabolic rate can increase the dominance rank of juvenile salmon. Whole animal growth rate was significantly correlated with M _R, but not with initial body weight. This suggests that the body size of masu salmon is not a cause, but rather a consequence, of dominance status which is closely related to M _R. The increment width between otolith daily rings was also significantly correlated with M _R. Thus, the size of the Otolith may indicate the degree of M _R.     

Food selection of Coregonus lavaretus in a brackish water ecosystem

This study examined how variability in the abundance and biomass structure of benthic invertebrates affected the feeding choice of the whitefish Coregonus lavaretus on a hard bottom habitat of the brackish Baltic Sea. In general, crustaceans such as Idotea balthica and Gammarus spp. were preferred over molluscs. Although being the most numerous taxon in the invertebrate samples, Mytilus trossulus was the lowest ranking in C. lavaretus food preference. The availability of benthic invertebrate prey set the dietary range of fish but the selectivity largely described fish feeding within this range. There was no clear link between fish predation and the dominance structure of benthic invertebrate communities, suggesting that species composition, abundance and biomass of invertebrate species had no impact on the feeding selectivity of the fish. Thus, while fish predation may not affect the dominant species within a benthic community, due to strong selectivity fish may impose strong pressure on some rarer but highly preferred invertebrate prey species.     

The performance advantage of a high resting metabolic rate in juvenile salmon is habitat dependent

1.?Basal levels of metabolism vary significantly among individuals in many taxa, but the effects of this on fitness are generally unknown. Resting metabolic rate (RMR) in juvenile salmon and trout is positively related to dominance status and ability to obtain a feeding territory, but it is not clear how this translates into performance in natural conditions. 2.?The relationships between RMR, dominance, territoriality and growth rates of yearling Atlantic salmon Salmo salar were examined in relation to predictability in food supply and habitat complexity, using replicate sections of a large-scale controlled semi-natural stream. 3.?Estimated RMR was a strong predictor of dominance, and under conditions of a predictable food supply in a structurally simple habitat, high estimated RMR fish obtained the best feeding territories and grew faster. 4.?When the spatial distribution of food was made less predictable, dominant (high estimated RMR) fish were still able to occupy the most profitable feeding locations by periodically moving location to track the changes in food availability, but RMR was no longer a predictor of growth rate. Moreover, when a less predictable food supply was combined with a visually more complex (and realistic) habitat, fish were unable to track changes in food availability, grew more slowly and exhibited greater site fidelity, and there were no relationships between estimated RMR and quality of occupied territory or growth rate. 5.?The relative benefit of RMR is thus context dependent, depending on both habitat complexity and the predictability of the food supply. Higher habitat complexity and lower food predictability decrease the performance advantages associated with a high RMR.     

Juvenile growth and aggression in diploid and triploid Chinook salmon Oncorhynchus tshawytscha (Walbaum)

Multilocus heterozygosity, aggressive and feeding behaviour, plasma cortisol levels and growth rate were evaluated among three groups of juvenile Chinook salmon Oncorhynchus tshawytscha : diploid, triploid and mixed groups of diploid and triploid fish. There was no difference between diploid and triploid fish in measurements of heterozygosity calculated using seven microsatellite loci, and these measurements did not correlate with performance measurements including feeding rate and growth rate. Aggression trials that examined small groups of fish revealed that after 4 days together in tanks, triploid fish were significantly less aggressive during feeding than diploid fish or fish in mixed groups. At the end of the trials, however, plasma cortisol levels did not differ among the three groups. Thirty-day growth trials in duplicate tanks of 60 fish revealed no difference in growth rate among diploid, triploid and mixed groups, but plasma cortisol levels were significantly lower in triploid fish than in either diploid fish or the mixed fish. Overall, independent of the above differences in aggressive behaviour and cortisol levels, these results suggest similar performance in diploid and triploid Chinook salmon, and thus provide support for the viability of triploid Chinook salmon culture in commercial aquaculture.     

Paternity and dominance loss in male breeders: the cost of helpers in a cooperatively breeding mammal

Paternity insurance and dominance tenure length are two important components of male reproductive success, particularly in species where reproduction is highly skewed towards a few individuals. Identifying the factors affecting these two components is crucial to better understand the pattern of variation in reproductive success among males. In social species, the social context (i.e. group size and composition) is likely to influence the ability of males to secure dominance and to monopolize reproduction. Most studies have analyzed the factors affecting paternity insurance and dominance tenure separately. We use a long term data set on Alpine marmots to investigate the effect of the number of subordinate males on both paternity insurance and tenure of dominant males. We show that individuals which are unable to monopolize reproduction in their family groups in the presence of many subordinate males are likely to lose dominance the following year. We also report that dominant males lose body mass in the year they lose both paternity and dominance. Our results suggest that controlling many subordinate males is energetically costly for dominant males, and those unable to support this cost lose the control over both reproduction and dominance. A large number of subordinate males in social groups is therefore costly for dominant males in terms of fitness.     

Alpha male chimpanzee grooming patterns: implications for dominance “style”

In social primates, individuals use various tactics to compete for dominance rank. Grooming, displays and contact aggression are common components of a male chimpanzee's dominance repertoire. The optimal combination of these behaviors is likely to differ among males with individuals exhibiting a dominance “style” that reflects their tendency to use cooperative and/or agonistic dominance tactics. Here, we examine the grooming behavior of three alpha male chimpanzees at Gombe National Park, Tanzania. We found that (1) these males differed significantly in their tendency to groom with other males; (2) each male's grooming patterns remained consistent before, during and after his tenure as alpha, and (3) the three males tended to groom with high‐ middle‐ and low‐ranking partners equally. We suggest that body mass may be one possible determinant of differences in grooming behavior. The largest male exhibited the lowest overall grooming rates, whereas the smallest male spent the most time grooming others. This is probably because large males are more effective at physically intimidating subordinates. To achieve alpha status, a small male may need to compensate for reduced size by investing more time and energy in grooming, thereby ensuring coalitionary support from others. Rates of contact aggression and charging displays conformed to this prediction, suggesting that each male exhibited a different dominance “style.” Am. J. Primatol. 71:136–144, 2009. © 2008 Wiley‐Liss, Inc.     

Sociometrics of Macaca mulatta: II. Decoupling centrality and dominance in rhesus monkey social networks

The concept of the linear dominance hierarchy and a much less precise notion of a central/peripheral ordering of individuals have been prominent among the ideas about social organization of monkey groups. Although the latter has seldom been quantified, the ranks of individuals in the two orders are usually assumed to be correlated. This paper reports on a longitudinal study of a free-ranging group of rhesus monkeys. The individual histories of progression of dominance rank and an independently determined measure of centrality in the social grooming network are compared among a set of males. Centrality is not a static correlate of dominance rank as implied by the findings of short-term studies. Rather, centrality is a more sensitive indicator of status than is dominance rank, to which it is related in a dynamic fashion. Small changes in dominance rank may be followed by large changes in centrality. An increase in centrality may facilitate rise in dominance rank. These findings suggest a complex psychology of status, rather than a simple causative relation between the two variables.     

Dominance status reversal based on pair-bond formation in the convict cichlid (Amatitlania nigrofasciata)

Dominant individuals have access to higher-quality resource; thus, reversing their dominance status would be important for subordinate individuals. Using the convict cichlid fish (Amatitlania nigrofasciata), this study examines whether forming a pair bond can reverse dominance status. Furthermore, I hypothesize that female convict cichlids will incur more dominance reversals from pair-bond formation than males. Dyadic, same-sex contests were conducted to determine dominant and subordinate individuals. Forced pairing of these individuals based on status was followed by polyadic, between-pair contests. The results indicate that individual dominance status does carry over into between-pair competition. Furthermore, dominance reversals do occur in convict cichlids and occur more frequently in females than in males. In addition, dominant males assist their mates during aggressive encounters, and these assists may account for subordinate females winning against dominant females during polyadic contests.