Agonistic Interactions of Juvenile Savanna Baboons

19 juvenile members of known genealogies in two wild baboon groups were studied over a 16-month period to compare the ontogeny of agonistic experience and dominance relations for males and females. Juveniles of all age-sex classes were disproportionately likely to receive aggression from and submit to adult males per unit of time spent in proximity. This pattern intensified with increasing juvenile age. With age, juvenile females more often submitted to unrelated adult females from higher-ranking families, whereas this was not true for juvenile males. All juveniles received aggression from older group members more often during feeding than was expected by chance. High rates of agonistic interaction with unrelated adult females accounted for old juvenile females (3–5.5 years-old) interacting agonistically more frequently than male age peers and young juveniles of either sex (1–2.5 years-old). Adult females were also more aggressive toward females among young juveniles, suggesting that adult females target females among juveniles for aggression and resistance to rank reversal. Within juvenile age groups, males dominated all females and all younger males, irrespective of maternal dominance status. Dominance relations among female age-peers were generally isomorphic with relations among their mothers. No juvenile targeted any older male for rank reversal. Males targeted all older females, whereas females typically targeted only older females from families lower-ranking than their own. The strong sexual dimorphism in adult body size in baboons may explain why juvenile males' dominance relations with peers and adult females are not structured along lines of family membership as is true for the less dimorphic macaques. Acquisition of higher agonistic status probably allows juveniles of both sexes to increase their success in within-group feeding competition during late stages of juvenility, which, in turn, could affect important life-history traits such as age at menarche and adult body size.     

Ontogenetic changes and the stability of rhesus monkey dominance relationships

Dominance relationships were studied in a rhesus monkey group during five consecutive years. The group consisted of eight stable matriarchies and an adult male class which was replaced at the start, and again at the midpoint, of the study. Immature males were selectively harvested to maintain a sex ratio typical of natural troops. Maximum group size during the study was 77 animals.Dominance relationships were remarkably stable, with only 4.4% of dyads failing to show unidirectional relationships. Despite this stability, a linear ranking of all group members was not possible. Male dominance relationships with other males were among the most stable, following the fighting which ensued on male introductions. Male introductions did not disrupt female dominance relationships.Adult female dominance relationships were also quite stable, but immature females slowly achieved dominance over older sisters and females subordinate to their mothers. Such reversals were the result of processes lasting over many months. Many dominance assertions occurred prior to puberty but a significant number occurred following sexual maturity. Maturing females did not reverse dominance relationships according to any particular hierarchial order and, as a consequence, many were subordinate to animals that were dominated by others that they dominated.Although there was an alpha male that was dominant to all animals in the group, adult females dominated most adult males. Adult males, however, often reciprocated aggression directed at them. They almost invariably threatened or countercharged aggressive immature animals regardless of matriarchial membership. Adult males dominated some adult and most young females, even in families containing matriarchs and adult females to which the adult males always submitted.The dominance relationships of young males were similar to those of their sisters, until puberty. Young males did not necessarily bypass adult males that their mothers outranked, and often failed to win against adult females that their mothers dominated. Adolescent female aggression against females is seldom interfered with by adult males, and females may actively aid one another against males. In contrast, the aggression of young males often elicits interference by adult males, and young males often become the targets of redirected aggression in the group. As a consequence, whereas young females rise in rank to positions adjacent to their mothers, adolescent males often suffer losses to animals that they had dominated as juveniles.     

Agonistic interactions with asymmetric body size in two adult-age groups of the annual killifish Millerichthys robustus (Miller & Hubbs, 1974)

In this study, the author evaluated two adult age groups of the Mexican rivulus Millerichthys robustus with body size asymmetries to determine the strategies used by an annual killifish during agonistic interactions of different ontogenetic stages. To achieve this goal, the author first characterized the ethogram of agonistic interactions of M. robustus composed of seven behavioural units in males and five behavioural units in females. The author then analysed agonistic interaction strategies used by males and females with body size asymmetries in two groups of different adult ages that represent different ontogenetic stages: (a) just after sexual maturity was reached, at 5 weeks of age, and (b) near natural death, at 24 weeks of age. The agonistic behaviour patterns of M. robustus were compatible with the logic of mutual assessment. Large males had an advantage during their interactions in both age groups, winning all of the encounters. Nonetheless, there was more aggression in 5-week-old fish encounters. In addition, small 24-week-old fish were more aggressive than small 5-week-old fish. These changing strategies may be because of the cost–benefits required during a fight at each ontogenetic stage. In the female encounters, size did not predict winners, as both small and large fish won a similar number of encounters, and some contests remained unresolved regardless of age group. There was a tendency for small females of any age to risk more than males in fights to maintain reproductive fitness.     

Sex‐Specific Associations Between Nest Defence,Exploration and Breathing Rate in Breeding Pied Flycatchers

Correlations between behavioural traits constrain animals to a limited range of behavioural choices and set a limit to the available variation in behavioural phenotype of a population. These constraints are especially important during stressful situations, potentially limiting the ability to cope with stress appropriately. As yet, very little consideration has been given to a possible role for sexual selection in maintaining differences in behavioural stability within individuals: sex‐specific differences in behavioural correlations have been seldom studied, especially in the wild. In this field study, we investigated associations between neophobia (latency to enter nest in the presence of a novel object), nest defence (response to a model predator) and breathing rate in response to handling in breeding pied flycatchers (Ficedula hypoleuca). We did not find any significant difference in antipredator responses between males and females, which indicates low sexual conflict over parental care in the pied flycatcher. However, females were more neophobic than males, while males and females did not differ in their breathing rates. Further, our study demonstrated a strong positive correlation between nest defence behaviour and neophobia in male, but not in female pied flycatchers. Males that defended their nest more had lower breathing rate and higher latency to resume nestling feeding after encountering a predator decoy than males that mobbed less intensely. We found only weak evidence that nest partners might affect each other's behaviour in these contexts.     

Alternative mating strategies in Atlantic salmon and brown trout

By screening variable number of tandem repeat (VNTR) loci, multiple paternity within clutches has been found in wild populations of southern European Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). For Atlantic salmon, we determined the relative contribution of alternative male phenotypes to the next generation. Individual males that are morphologically juvenile yet sexually mature fertilized a large proportion of eggs, and they thereby contributed to an increase of genetic variability in wild populations via (1) balancing the sex ratio, (2) increasing outbreeding, and (3) enlarging the effective population size, in part a consequence of (1) and (2). In addition, these precocious males ensured that interspecific spawns involving Atlantic salmon females and brown trout males (a fairly common occurrence in southern Europe where the two species are sympatric) resulted mostly in Atlantic salmon progeny. For brown trout, preliminary genetic results indicated that multiple paternity, when present, was not due to alternative mating strategies by males, but rather to successive fertilizations by adult suitors.     

Winter sheltering by juvenile brown trout (Salmo trutta) – effects of stream wood and an instream ectothermic predator

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Sequential hermaphroditism and personality in a clonal vertebrate: the mangrove killifish

Individuals are regularly documented to consistently differ in their behavioural types (BTs). For example, some individuals are bold whereas others are shy. Within the human personality literature, the big five personality dimensions are commonly documented to be sex-specific with testosterone suggested to underpin traits such as aggressiveness. In non-human animals recent research suggests sex-specific BT expression may be influenced by ecology, mating system and sexual selection. While most research on sex-specific personality has focused on dioecious species, we explore sex differences in BT expression in a sequential hermaphrodite the mangrove killifish. We replicate within 7 isogenic genotypes and investigate sex differences (hermaphrodite and secondary male) in three BTs (exploration, boldness and aggression). This approach allows us to investigate sex differences in BT expression whilst controlling for genetic variation. In this study we find that both secondary males and hermaphrodites are repeatable at the individual level yet there was no difference between the sexes in average BT scores. Furthermore, aggression scores differed between genotypes, and were repeatable at the genotype level, suggesting strong genetic control. Finally, male boldness was significantly more repeatable than hermaphrodites potentially supporting recent proposals relating to sexual selection. We document a behavioural syndrome in male fish with bolder individuals being more aggressive, this behavioural syndrome was not observed however in hermaphrodites. In contrast to a previous developmental study in this species exploration did not correlate with either aggression or boldness in either males or hermaphrodites.     

The Influence of Age,Sex, and Rank on Yawning Behavior in Two Species of Macaques (Macaca fascicularis and M. fuscata)

Yawning behavior was studied in two species of macaques: the long-tailed macaque (Macaca fascicularis) and the Japanese macaque (M. fuscata). Japanese macaques yawned much more than long-tailed macaques. Age, sex, and dominance rank exerted different effects on yawning in the two species. In the long-tailed macaques, sex differences in frequency of yawning emerged only after sexual maturity; yawning rates increased significantly in both males and females as they reached sexual maturity; and, among males, dominance rank was positively correlated with frequency of yawning. Differently, in the Japanese macaques, males, both mature and immature, yawned more than same-aged females; sexual maturity was associated with an increase in yawning in males only; and male rank did not correlate with the frequency of yawning. Regardless of interspecific differences, the overall results supported only in part the finding that, in Old World monkeys, yawning is largely influenced by plasma concentrations of androgens. There was evidence that social factors were also important in influencing the age-sex class distribution of yawning.     

Reversed plumage ontogeny in a female hummingbird: implications for the evolution of iridescent colours and sexual dichromatism

In polygynous birds, bright plumage is typically more extensive in the sexually competitive males and develops at or after sexual maturity. These patterns, coupled with the importance of male plumage in sexual displays, fostered the traditional hypothesis that bright plumages and sexual dichromatism develop through the actions of sexual selection on males. This view remains problematic for hummingbirds, all of which are polygynous, because their bright iridescent plumages are also important non-sexual signals associated with dominance at floral nectar sources. Here I show that female amethyst-throated sunangels [ Heliangelus amethysticollis (d'Orbigny & Lafresnaye)], moult from an immature plumage with an iridescent gorget to an adult plumage with a non-iridescent gorget. This 'reversed' ontogeny contradicts the notion that iridescent plumage has a sexual function because sexual selection in polygynous birds should be lowest among non-reproductive immature females. Moreover, loss of iridescent plumage in adult females indicates that adult sexual dichromatism in H. amethysticollis is due in large part to changes in female ontogeny. I suggest that both the ontogeny and sexual dichromatism evolved in response to competition for nectar.     

Individual Recognition Affects Aggression and Dominance Relations in Rainbow Trout,Oncorhynchus mykiss

In this study, the hypothesis that individual recognition is used as a cue to reduce the cost of contesting resources in rainbow trout Oncorhynchus mykiss, was addressed. The predictions were that the second contest between familiar individuals should be settled with less aggression, and lower probability of status reversal, than a contest between strangers. To test these predictions, similar-sized juvenile rainbow trout were subjected to two dyadic dominance contests in one of four treatment groups: in half of the pairs, the initially subordinate and dominant individuals were staged against an unfamiliar opponent (of opposite rank to their own) in a second contest, while in the other the initial pair was reunited for the second contest. Further, in half of the pairs, contestants were separated for 3 d between contests, while in the other the second contest was staged immediately after the first. Levels of aggression in contests between familiar individuals were lower than in contests between strangers, which supports the hypothesis that individual recognition reduces aggression. Dominance status was reversed in 31% of the 62 tested pairs. Although the probability of status reversal was not significantly affected by individual recognition, the degree of change in competitive success appeared to be lower in familiar pairs. Separation interacted with familiarity so that the effect of individual recognition generally was less pronounced when pairs were separated between contests, suggesting that the ability to remember opponents is time/limited. In natural streams, salmonids may use individual recognition to reduce the cost of contesting resources within groups, to reduce aggression between territory neighbours and to distinguish ‘cheaters’ from honest signallers.     

Sexual behaviour of immature male eastern mosquitofish: a way to measure intensity of intra-sexual selection?

Immature males of eastern mosquitofish Gambusia holbrooki start to be sexually active well before their copulatory organ (gonopodium) has completely developed and before they become able to transfer sperm. Sexual activity of males, consisting of copulatory attempts tending to bypass female acceptance, is intense (one attempt per minute) and is likely to be energetically very costly. The sexual behaviour of immature males relative to their maturation stage is described and tested against two possible adaptive explanations. Sexual activity was present in males from the beginning of the development of their gonopodium and increased during the following stages of maturation. Two to three weeks before gonopodium development was completed, sexual activity of immatures was as high as that of adults. Adult males showed aggressive behaviour against a male attempting a copulation, irrespective of the maturity of the latter. Since previous studies have shown that the reproductive success in this species is negatively correlated with male size when male–male competition is low (i.e. when the sex ratio is female biased), but decreases with male size when competition is high, the hypothesis was tested that sexual activity of immature males functions as a way to predict their future reproductive success if they mature at a given size. A second hypothesis tested was that precocious sexual experience improves the efficiency of copulatory attempts. Results were more in agreement with the first hypothesis, since size at maturity of males was influenced by the sex ratio experienced during maturation and precocious experience gave very little advantage.     

Boldness predicts social status in zebrafish (Danio rerio)

This study explored if boldness could be used to predict social status. First, boldness was assessed by monitoring individual zebrafish behaviour in (1) an unfamiliar barren environment with no shelter (open field), (2) the same environment when a roof was introduced as a shelter, and (3) when the roof was removed and an unfamiliar object (Lego® brick) was introduced. Next, after a resting period of minimum one week, social status of the fish was determined in a dyadic contest and dominant/subordinate individuals were determined as the winner/loser of two consecutive contests. Multivariate data analyses showed that males were bolder than females and that the behaviours expressed by the fish during the boldness tests could be used to predict which fish would later become dominant and subordinate in the ensuing dyadic contest. We conclude that bold behaviour is positively correlated to dominance in zebrafish and that boldness is not solely a consequence of social dominance.     

Sibling rivalry: training effects, emergence of dominance and incomplete control

Within-brood or -litter dominance provides fitness-related benefits if dominant siblings selfishly skew access to food provided by parents in their favour. Models of facultative siblicide assume that dominants exert complete control over their subordinate sibling's access to food and that control is maintained, irrespective of the subordinate's hunger level. By contrast, a recent functional hypothesis suggests that subordinates should contest access to food when the cost of not doing so is high. Here, we show that within spotted hyena (Crocuta crocuta) twin litters, dominants most effectively skew access to maternal milk in their favour when their aggression prompts a highly submissive response. When hungry, subordinates were less submissive in response to aggression, thereby decreasing lost suckling time and increasing suckling time lost by dominants. In a species where adult females socially dominate adult males, juvenile females were more often dominant than males in mixed-sex litters, and subordinate sisters used more effective counter-tactics against dominant brothers than subordinate brothers against dominant sisters. Our results provide, to our knowledge, the first evidence in a mammal that dominant offspring in twin litters do not exert complete control over their sibling's access to resources (milk), and that sibling dominance relationships are influenced by sibling sex and training effects.     

Morphological ontogeny of the gonad of three plectropomid species through sex differentiation and transition

The gonadal ontogeny through sex differentiation and transition of three protogynous coral trout species, Plectropomus leopardus , P. maculatus and P. laevis was described, based on anatomical and germinal differences along the length of the reproductive tract. Gonads of immature and mature females, sex changing individuals (transitionals) and males were examined. Specific anatomical features that were compared between sexual phases included the presence and structure of sperm sinuses, gonadal musculature and germinal cell types. All three coral trout species first differentiated as an immature female. The sexual pattern of P. leopardus and P. maculatus was concluded to be diandric protogynous hermaphroditism (males were derived from the juvenile phase as well as through sex change of mature females). Plectropomus laevis was found to be monandric as males were only derived through sex change in mature females. Structural changes did not occur concomitantly with the germinal changes associated with sex change in these Plectropomus species, which is atypical for protogynous species described to date. Precursory sperm sinuses in the dorso-medial region of the gonad were present, although non-functional, in a proportion of immature and mature females of all three species. These proportions, however, varied between species depending on the sexual pattern. The structural and germinal changes observed were hypothesized as anatomical adaptations that aid in minimizing time spent in the (non-reproductive) sexual transition phase and maximizing flexibility in male development in the diandric species.     

Sex differences in the behaviour of immature captive lowland gorillas

Studies of the behaviour of 26 (12 males and 14 females) captive infant and juvenile lowland gorillas showed clear sex differences. Females showed greater interest in young infants and were more active in nest building as well as in solitary and social grooming. Males were more active in locomotive, dominance, and aggressive behaviour and in social play. Hand-rearing further increased aggression. Males were more aggressive when they lived with only one partner, and they rose in rank even above older females, a pattern that has not been observed in naturally reared gorillas.     

The influence of sex and spawning on levels of tryptophan, serotonin and 5-hydroxyindoleacetic acid in the brains of wild brook trout, Salvelinus fontinalis

Levels of tryptophan (TP), serotonin (5-hydroxytryptamine, 5HT) and 5-hydroxyindoleacetic acid (5HIAA) have been determined in the brains of wild brook trout, Salvelinus fontinalis (Mitchill), and brown trout, Salmo trutta L., using high performance liquid chromatography with electrochemical detection. Immediately prior to spawning, adult female brook trout exhibit higher levels of 5HT in the brain than adult males, immature brook trout and immature brown trout. After spawning, the highest levels of TP are found in spent males, which also have higher levels of 5HT in the brain than spent females and immature brook trout. Immature brook trout exhibit higher levels of 5HIAA than prespawning adults. This difference disappears after the spawning season. Serum protein levels and condition factors are lower in spent female brook trout; however, haematocrit values for both sexes remain unchanged after spawning.     

Effects of the juvenile hormone analogue methoprene and dietary protein on male melon fly Bactrocera cucurbitae (Diptera: Tephritidae) mating success

The effect of access to dietary protein (P) and the topical application of a juvenile hormone analogue (methoprene (M)) on mating behaviour of male melon fly Bactrocera cucurbitae was assessed in the laboratory and in field cages. Age, dietary protein and methoprene application increased the mating success and influenced the mating behaviour. Treatment with methoprene (M+) to protein-deprived (P−) males had only a modest effect on the acceleration of sexual maturity, but application of methoprene (M+) to protein-fed (P+) males greatly accelerated sexual maturity. Protein diet (P+) increased mating success of males in comparison to protein-deprived (P−) males. Protein and methoprene have a synergistic effect on mating behaviour, since M + P+ treated males exhibit reduced mating latency and achieved higher mating in younger ages than methoprene and/or protein-deprived males. Copulation duration was correlated with nutritional status and M + P+ males copulated longer at the age of advanced sexual maturity than M − P+ males. Our results suggest that in this species with a lek mating system, females discriminate between the males based on their sexual signals, which were influenced by protein in the adult diet, methoprene application and age. The results are discussed in the light of mating competitiveness of precocious treated young males and their relevance to Sterile Insect Technique application against this pest species.     

Individual variation in behavioural plasticity: direct and indirect effects of boldness,exploration and sociability on habituation to predators in lizards

Little is known about the factors causing variation in behavioural plasticity and the interplay between personality and plasticity. Habituation to predators is a special case of behavioural plasticity. We investigated the direct and indirect effects of boldness, exploration and sociability traits on the habituation ability of Iberian wall lizards, considering exposure and sex effects. Individual boldness was consistent across several non-habituation contexts, but it did not significantly affect habituation. Exploration had a strong direct effect on habituation, with more exploratory individuals being able to habituate faster than less exploratory ones, probably because of their ability to assess risk better. Individual variation in habituation was also affected by sociability, but this was an indirect effect mediated by exposure to the predator. Less social individuals avoided refuges with conspecific cues, increasing exposure to the predator and eventually habituation. Finally, the direct effects of sex (females habituated faster than males) were opposite to its indirect effects through exposure. We conclude that risk assessment, instead of the proactivity–reactivity gradient usually considered in the literature, can affect behavioural plasticity through complex interactions between direct and indirect effects, including exploratory behaviour, degree of exposure to the predator and sex, which represent novel mechanisms generating inter-individual variation in plasticity.     

Aggregation of whelks, Buccinum undatum, near feeding predators: the role of reproductive requirements

In the Mingan Islands, northern Gulf of St Lawrence (eastern Canada), the whelk Buccinum undatum displays a strong escape response to its predator, the asteroid Leptasterias polaris, nevertheless large sexually mature individuals occasionally approach feeding L. polaris to obtain food. In this study, we investigated the hypothesis that reproductive requirements increase the tendency of sexually mature whelks to approach feeding asteroids. Prior to egg laying, females (which invest more energy than males into the production of reproductive structures) represented 72% of the adult whelks that approached feeding L. polaris, but only 36% of the adults randomly collected from the study area. Furthermore, females that were attracted to feeding asteroids had smaller reproductive organs (after accounting for body size) than females randomly collected from the study area. Similarly, prior to egg laying, females fed longer and ingested more food than males when tested in the presence of L. polaris in the laboratory. After egg laying, however, females and males displayed a similar tendency to feed in the presence of a predator, both in the field and in the laboratory. Predator-impact indices, computed by contrasting the feeding activity of whelks in the absence and presence of a predator, indicated that females (but not males) responded more boldly to predators prior to than after egg laying, despite a general decrease in feeding activity at that period. Taken together, our observations indicate that the tendency of adult whelks to approach feeding predators is influenced by potential reproductive gains. Because such gains are presumably more directly linked to a given feeding opportunity in sexually active individuals, whelks may be selected to display increased levels of boldness towards predators with the onset of sexual maturity. Thus, potential reproductive benefits may partly explain the size-dependent tendency of whelks to approach feeding asteroids. Copyright 2001 The Association for the Study of Animal Behaviour.     

Effects of age, dominance, and seasonal changes on proximity relationships in female Japanese macaques (Macaca fuscata) in a free-ranging group at Katsuyama

The present study compares the behavior of old female Japanese macaques (Macaca fuscata) with that of their full adult daughters in a free-ranging group, with respect to dominance and seasonal changes. Old mothers (21 to 25 years old) spent more time resting and alone than did their middle-aged adult daughters (10 to 17 yr old). However, the number of skin-related animals in proximity to the subject females, did not differ between mothers and their adult daughters. Mothers maintained proximity to more non-kin-related immature animals in the mating season than did their adult daughters, perhaps to avoid sexual aggression from males and to reduce the loss of body temperature in the cold. Dominance rank clearly influenced the social interactions of old mothers: high-ranking mothers interacted with more non-related adult females and immature animals than did low-ranking mothers, indicating that old age does not decrease the attractiveness of high-ranking animals.