Colour pattern and inhibition of aggression in the cichlid fish Astronotus ocellatus

Oscars Astronotus ocellatus defeated in combat often undergo a colour pattern change in which the normal olive-green to brown body coloration darkens to near black, interrupted with irregular white barring. Dummy oscars were used in two complementary tests which showed that the dark-and-banded colour pattern inhibits aggression in conspecifics under two different experimental designs and with two different subject groups.     

Colour biases in territorial aggression in a Neotropical cichlid fish

Discrete colour morphs have provided important insights into the evolution of phenotypic diversity. One of the mechanisms that can help to explain coexistence of ecologically similar colour morphs and incipient species is (colour) biased aggression, which has the potential to promote continued existence of the morphs in a frequency-dependent manner. I addressed colour biases in territorial aggression in a field-based study on a Neotropical cichlid fish species, Amphilophus sagittae, which has two ecologically indistinguishable colour morphs that mate assortatively. I found that A. sagittae, in particular females, were more aggressive towards models of their own colour than those mimicking colours of the other morph. Such a behavioural pattern should result in a selection regime that benefits the rarer morph, and hence could help explain how novel, rare phenotypes may avoid competitive exclusion.     

Predicting and assessing dominance from size and coloration in the polychromatic midas cichlid

To test whether gold morphs dominate normal ones, twelve groups were observed, each consisting of three golds and three normals paired by weight. Golds dominated comparable normals. Smaller golds also profited from sharing the colour of the dominant fish. Contest and approach declined across days, but attack and yield remained high. Standard deviation of rank was progressively greater with higher rank, but uncertainty of rank plotted as an inverted U. Behaviours important in dominance showed high dependence on type of fish but low dependence on day; these behaviours also had more variation attributable to the coloration factor. From a set of stated criteria, dominance is deemed best assessed here by an index: (attacks) ?o (yields + attacks); contesting (threat) is actually misleading.     

Sibling Age and Intragroup Aggression in Captive Saguinus midas midas

Different species of Callitrichidae show a consistent pattern in intragroup aggression. Aggression is more frequent between same-sex individuals, with males and older siblings being more aggressive. These findings have been associated with reproductive competition and dispersal events. However, the few studies dealing with intragroup aggression have not fully explored the effects of food availability on aggression or the relationship between age and aggression. I observed 3 family groups of Saguinus midas for 50 weeks and recorded all occurrences of aggression. A total of 138 agonistic events occurred at an average of 1.16 aggressive acts/hour per group, and 52.2% of aggressive acts occurred during a food shortage condition, which accounted for about 12% of all meals in the groups. During the food shortage, aggression was significantly higher, which suggests that food competition promoted an increase in aggression levels. Aggression amongst siblings accounted for 65.2% of all aggressive acts. Aggression from brothers to sisters was significantly more frequent than aggression between brothers. Aggression rates were significantly different between age classes. Young siblings were significantly more aggressive toward old ones than the reverse. Age and aggression received followed a linear relationship, while age and aggression initiated tended to follow a curvilinear relationship. Higher rates of aggression in young siblings probably were prompted by puberty and associated hormonal changes.     

Dynamics of sibling aggression of a cichlid fish in Lake Tanganyika

Hydrobiologia - Siblings often compete for limited resources, particularly food provided by their parents. Such competition is usually nonviolent, but direct aggression has evolved in some species....     

Colour forms of Amazonian cichlid fish represent reproductively isolated species

Laboratory mate choice experiments have confirmed species status for cichlid fish in the African Great Lakes that differ in colour and little else. Colour differences between allopatric populations of the South American cichlid genus Apistogramma are known for many species, yet the status of such populations has not been previously tested. Analysis of the genetic relationships and mate choice characteristics of populations previously described as Apistogramma caetei from eastern Amazonia indicates genetic differentiation into at least three allopatric lineages, which also show strong prezygotic isolation through female mate choice, confirming them as Biological species. If future studies confirm that this result is indicative of a general trend, the species richness of the South American cichlid fishes may presently be seriously underestimated.     

The insectivorous-frugivorous diet of the golden-handed tamarin (Saguinus midas midas) in French Guiana

The diet of Saguinus midas is characterised by analysis of stomach contents samples on an annual and seasonal basis. The diet comprises significant proportions of both fruit and insects all year round, although fruit use shows important seasonal variations. The tamarins reduce their use of fruit resources during the peak fruiting season and instead exploit increased opportunities for insectivory. This is suggested to be a response to differences in gross fruit availability as a function of both fruiting patterns and the presence of competitors for the available fruit resources.     

Ecotype differences in aggression,neural activity and behaviorally relevant gene expression in cichlid fish

In Lake Malawi, two ecologically distinct lineages of cichlid fishes (rock‐ vs sand‐dwelling ecotypes, each comprised of over 200 species) evolved within the last million years. The rock‐dwelling species (Mbuna) are aggressively territorial year‐round and males court and spawn with females over rocky substrate. In contrast, males of sand‐dwelling species are not territorial and instead aggregate on seasonal breeding leks in which males construct courtship “bowers” in the sand. However, little is known about how phenotypic variation in aggression is produced by the genome. In this study, we first quantify and compare behavior in seven cichlid species, demonstrating substantial ecotype and species differences in unconditioned mirror‐elicited aggression. Second, we compare neural activity in mirror‐elicited aggression in two representative species, Mchenga conophoros (sand‐dwelling) and Petrotilapia chitimba (rock‐dwelling). Finally, we compare gene expression patterns between these two species, specifically within neurons activated during mirror aggression. We identified a large number of genes showing differential expression in mirror‐elicited aggression, as well as many genes that differ between ecotypes. These genes, which may underly species differences in behavior, include several neuropeptides, genes involved in the synthesis of steroid hormones and neurotransmitter activity. This work lays the foundation for future experiments using this emerging genetic model system to investigate the genomic basis of evolved species differences in both brain and behavior.     

Effects of salinity on the survival and aggression of the invasive Rio Grande cichlid (Herichthys cyanoguttatus)

The spread of non-native Rio Grande cichlids (Herichthys cyanoguttatus) in southeast Louisiana includes brackish habitats. We studied the effects of three different salinity levels on the biology of juvenile H. cyanoguttatus for 13 months to determine the potential of this species to spread through local estuaries. The highest salinity tolerated was 30.0 psu, and these fish did not survive acclimation to the 32 psu treatment. Fish in brackish conditions grew slower than fish in freshwater conditions, indicating a potential long-term detriment to juvenile fish living in brackish conditions. Aggression levels were notably higher for fish in brackish (15 psu) vs. freshwater conditions. This persisted through the entire experiment even after acclimation back to freshwater. This study indicates that higher salinity habitats in Louisiana can be tolerated by this species. It also raises a question about the effect of higher salinities on aggressive behavior.     

Genetic basis of continuous variation in the levels and modular inheritance of pigmentation in cichlid fishes

Variation in pigmentation type and levels is a hallmark of myriad evolutionary radiations, and biologists have long been fascinated by the factors that promote and maintain variation in coloration across populations. Here, we provide insights into the genetic basis of complex and continuous patterns of colour variation in cichlid fishes, which offer a vast diversity of pigmentation patterns that have evolved in response to both natural and sexual selection. Specifically, we crossed two divergent cichlid species to generate an F₂ mapping population that exhibited extensive variation in pigmentation levels and patterns. Our experimental design is robust in that it combines traditional quantitative trait locus (QTL) analysis with population genomics, which has allowed us to move efficiently from QTL interval to candidate gene. In total, we detected 41 QTL and 13 epistatic interactions that underlie melanocyte‐ and xanthophore‐based coloration across the fins and flanks of these fishes. We also identified 2 QTL and 1 interaction for variation in the magnitude of integration among these colour traits. This finding in particular is notable as there are marked differences both within and between species with respect to the complexity of pigmentation patterns. While certain individuals are characterized by more uniform ‘integrated’ colour patterns, others exhibit many more degrees of freedom with respect to the distribution of colour ‘modules’ across the fins and flank. Our data reveal, for the first time, a genetic basis for this difference. Finally, we implicate pax3a as a mediator of continuous variation in the levels of xanthophore‐based colour along the cichlid flank.     

Behavioral coping strategies in a cichlid fish: the role of social status and acute stress response in direct and displaced aggression

The African cichlid fish, Astatotilapia burtoni, has a complex social system with a sophisticated social hierarchy that offers unique opportunities to understand how social rank and its physiological substrates relate to behavioral strategies. In A. burtoni, a small fraction of the males are dominant (T, territorial), as distinguished by being large, brightly colored, reproductively active, and aggressively defending territories. In contrast, the majority of males are non-dominant (NT, non-territorial), being smaller, drably colored, sexually immature, and typically schooling with females. The social system is regulated by aggressive interactions between males and behavioral responses to aggression can be direct or displaced with respect to the animal that acts. To determine whether direct and displaced behaviors are differentially exhibited by T and NT males, individuals were shown a video presentation of a dominant male displaying aggressively. Analysis of aggressive acts toward the video display and displaced activity toward a tank mate revealed that T males exhibited more direct behavior (toward the video display), while NT males engaged in more displaced behavior (toward tank mates). Because similar experiments with primates suggest that shifts in behavioral strategies are linked to changes in the stress response (as measured by circulating cortisol levels), we measured cortisol levels of T and NT males following exposure to the aggressive stimulus. Although in some animals subordinate males are reported to have higher cortisol levels, here we show that in A. burtoni the endocrine response to specific situations can vary considerably even among animals of the same status. Interestingly, NT males with intermediate cortisol levels showed more directed behavior while NT males with both high and low cortisol levels showed more displaced. This suggests an optimal physiological stress response in NT males that predisposes them to challenge aggressors perhaps making it more likely for them to ascend in status.     

Suppurative peritonitis by Klebsiella pneumoniae in captive gold‐handed tamarin (Saguinus midas midas)

This report describes an outbreak of suppurative peritonitis caused by Klebsiella pneumoniae in an adult female of captive golden‐handed tamarin (Saguinus midas midas). Two virulent and multidrug‐resistant strains were isolated and classified through MLST as ST60 and ST1263. The microbiological diagnosis works as a support tool for preventive measures.     

Colour discrimination learning in black-handed tamarin (<Emphasis Type="Italic">Saguinus midas niger</Emphasis>)

Colour is one cue that monkeys use for perceptual segregation of targets and to identify food resources. For fruit-eating primates such as Saguinus, an accurate colour perception would be advantageous to help find ripe fruits at distance. The colour vision abilities of black-handed tamarins (Saguinus midas niger) were assessed through a discrimination learning paradigm using Munsell colour chips as stimuli. Pairs of chips were chosen from an early experiment with protan and deutan humans. The monkeys (three males and one female) were tested with stimuli of the same hue, but different brightness values, in order to make sure that discriminations were based on colour rather than brightness cues. The results showed that the female, but not the males, presented an above-chance performance for stimuli resembling hue conditions under which tamarins forage (oranges vs greens). Colour vision in S. m. niger is discussed according to the advantages and disadvantages of dichromatism in daily search for food as well as to aspects regarding polymorphism in New World monkeys.     

Brain levels of arginine-vasotocin and isotocin in dominant and subordinate males of a cichlid fish

The nonapeptides arginine-vasotocin (AVT) and isotocin (IT), which are the teleost homologues of arginine-vasopressin and oxytocin in mammals, have well established peripheral effects on osmoregulation and stress response, and central effects on social behavior. However, all studies that have looked so far into the relationship between these nonapeptides and social behavior have used indirect measures of AVT/IT activity (i.e. immunohistochemistry of AVT/IT immunoreactive neurons, or AVT/IT or their receptors mRNA expression with in situ hybridization or qPCR) and therefore direct measures of peptide levels in relation to social behavior are still lacking. Here we use a recently developed high-performance liquid chromatography analysis with fluorescence detection (HPLC-FL) method to quantify the levels of both AVT and IT in macro-dissected brain areas [i.e. olfactory bulbs, telencephalon, diencephalon, optic tectum, cerebellum, and hindbrain (= rhombencephalon minus cerebellum)] and pituitary of dominant and subordinate male cichlid fish (Oreochromis mossambicus). The pituitary shows higher levels of both peptides than any of the brain macroareas, and the olfactory bulbs have the highest AVT among all brain areas. Except for IT in the telencephalon there is a lack of correlations between central levels and pituitary peptide levels, suggesting an independent control of hypophysial and CNS nonapeptide secretion. There were also no correlations between AVT and IT levels either for each brain region or for the pituitary gland, suggesting a decoupled activity of the AVT and IT systems at the CNS level. Subordinate AVT pituitary levels are significantly higher than those of dominants, and dominant hindbrain IT levels are significantly higher than those of subordinates, suggesting a potential involvement of AVT in social stress in subordinate fish and of IT in the regulation of dominant behavior at the level of the hindbrain. Since in this species dominant males use urine to communicate social status and since AVT is known to have an antidiuretic effect, we have also investigated the effect of social status on urine storage. As predicted, dominant males stored significantly more urine than subordinates. Given these results we suggest that AVT/IT play a key role in orchestrating social phenotypes, acting both as central neuromodulators that promote behavioral plasticity and as peripheral hormones that promote integrated physiological changes.     

Androgen levels of reproductive competitors in a co‐operatively breeding cichlid

Androgen levels of family groups of Neolamprologus pulcher were assessed using non‐invasive methods. There were no significant differences in the excretion rates neither of testosterone nor of 11‐ketotestosterone between territorial and helper males.     

Dominance and prestige as differential predictors of aggression and testosterone levels in men

The relationship between self-esteem and aggression has yielded mixed results and generated much recent debate in the social psychology literature. Based on an evolutionary-psychological theory of self-esteem, Kirkpatrick et al. [Kirkpatrick, L. A., Waugh, C. E., Valencia, A., Webster, G., 2002. The functional domain-specificity of self-esteem and the differential prediction of aggression. Journal of Personality and Social Psychology 825, 756–767] showed that multiple, functionally distinct self-esteem mechanisms predict aggression differentially: e.g., “self-perceived superiority” is positively related, and “social inclusion” inversely related, to behavioral aggression. The present study extends this research by further differentiating two distinct forms of “superiority,” dominance and prestige [Henrich, J., Gil-White, F. J. 2001. The evolution of prestige: Freely conferred deference as a mechanism for enhancing the benefits of cultural transmission. Evolution and Human Behavior 22, 165–196], in the prediction of aggression in men and women and testosterone levels (measured in saliva samples) in men. Dominance was positively related, but prestige was either unrelated or inversely related, to self-report aggression measures. Dominance was unrelated but prestige inversely related to testosterone levels in men, perhaps suggesting a method of testosterone inhibition in individuals attaining prestige-based superiority. In addition to contributing to the growing literature on the aggression–self-esteem link, the results provide validation for the prestige–dominance distinction and support, but also suggest an important refinement to, a theory of self-esteem as a collection of functionally distinct adaptations.