Effect of male-to-male aggressiveness and feed-restriction during rearing on sexual behaviour and aggressiveness towards females by male domestic fowl

This experiment was one part of a larger study investigating problems of aggression towards females by male broiler breeder fowl. To investigate causal mechanisms, we were interested in determining (1) if feed-restriction during rearing affects behaviour towards females at sexual maturity and (2) if aggressiveness towards females is correlated with general levels of aggressiveness. We compared broiler breeder males with commercial laying strain males, which were either fed ad libitum or were feed-restricted during the rearing phase, and with game strain males, bred for fighting. Differences in behaviour were determined by observing males during interactions with small groups of females.Laying strain males did not behave aggressively towards females, whether feed-restricted or fed ad libitum during rearing. Despite genetic selection for fighting ability, game strain males also were not aggressive towards females. Conversely, broiler breeder males displayed significantly higher levels of aggression towards females than did feed-restricted laying strain males (P<0.02). Broiler breeder males were rough with females during mating, whereas laying strain and game strain males were not. Females struggled more frequently during mating attempts by broiler breeder males (P<0.002) and interfered frequently when these males attempted to mate with other females.From our results, we conclude that (1) feed-restriction during rearing has little effect on the sexual and aggressive behaviour of laying strain males at maturity and (2) selection for aggressiveness has not resulted in males which are more aggressive to females. Aggression towards females appears to be a unique problem occurring in broiler breeder male strains and not a function of feed-restriction.     

Reproductive success in male sunbleak, a recent invasive fish species in the U.K.

The spawning behaviour of male nest guarding sunbleak Leucaspius delineatus , a recent invasive species in southern England, was studied and quantified for the first time. In the absence of physical differences between territorial and non‐territorial males ( i.e . colour, size, etc .), the reproductive behaviour of territorial males was analysed and related to reproductive success. The results showed that females preferred high‐courting and highly aggressive males. The initial cue in female mate choice, however, was based on courtship, while aggression was the decisive behavioural trait in influencing mate choice, providing a direct signal of physical condition and 'paternal competence'. Some males picked nest sites which were subsequently preferred by other males taking over the nest of a previous male ('communal nest'), with the new territorial male adopting the eggs already present at the nest. It appears that either due to female preference for nests already containing eggs or lower rates of sired egg predation by dilution among unrelated eggs, sunbleak males have adopted the mating strategy of allopaternal care.     

Melanic body colour and aggressive mating behaviour are correlated traits in male mosquitofish (Gambusia holbrooki)

Correlated traits are important from an evolutionary perspective as natural selection acting on one trait may indirectly affect other traits. Further, the response to selection can be constrained or hastened as a result of correlations. Because mating behaviour and body colour can dramatically affect fitness, a correlation between them can have important fitness ramifications. In this work, melanic (black) male mosquitofishes (Gambusia holbrooki) with temperature-sensitive body-colour expression are bred in captivity. Half of the sons of each melanic sire are reared at 19 degrees C (and express a black body colour) and half are reared at 31 degrees C (and express a silver body colour). The two colour morphs are placed in the same social setting and monitored for behavioural differences. Mating behaviour and colour are correlated traits. Mating behaviour differs markedly between the two phenotypes, despite high genetic relatedness. Melanic (black) phenotypes are more aggressive towards females, chasing them and attempting more matings than their silver siblings. Females avoid melanic-male mating attempts more than silver-male mating attempts. When males with temperature-sensitive colour expression are melanic and aggressive, they probably experience a very different selective regime in nature from when they are silver and less aggressive. Under some conditions (e.g. predation), melanic coloration and/or aggression is advantageous compared with silver coloration and/or less aggressive behaviour. However, under different conditions (e.g. high-frequency melanism), melanism and/or aggression appears to be disadvantageous and melanic males have reduced survival and reproduction. Selective advantages to each morph under different conditions may enable the long-term persistence of this temperature-sensitive genotype.     

Inter-male Spacing and Aggression in African Painted Reed Frogs,Hyperolius marmoratus

Inter-male spacing and the role of aggression in the maintenance of spatial organization was examined in choruses of Hyperolius marmoratus males housed in a semi-natural enclosure. The effects of chorus size on spacing patterns, nearest neighbour distances and male aggressive behaviour were examined. Males were found to reduce nearest neighbour distances as chorus size increased. This was accompanied by a shift in spacing pattern from even in small choruses (5–9 males) to random in choruses of 10 to 13 males. In choruses of 14, spacing patterns were once again even. The reason for these shifts is unclear but may reflect a sudden, rather than gradual increased tolerance by individuals to high neighbour call intensity as space to call from becomes more limited. The level of male aggression was influenced by chorus size and the time of night. In general, more aggressive interactions occurred in high density choruses. However, this did not translate into higher levels of individual male aggression as density increased. Individual male aggression was high in early evening choruses and declined to a minimum at peak chorusing time. High levels of aggression during early evening may reflect the establishment of calling sites by males, while the drop in aggression at peak chorusing time may occur in response to the presence of females in the chorus at this time or as a consequence of masking of neighbours calls.     

Sex-Specific Aggression and Antipredator Behaviour in Young Brown Trout

Sex differences in adult behaviour are often interpreted as consequences of sexual selection and/or different reproductive roles in males and females. Sex-specific juvenile behaviour, however, has received less attention. Adult brown trout males are more aggressive than females during spawning and juvenile aggression may be genetically correlated with adult aggression in fish. We therefore tested the prediction that immature brown trout males are more aggressive and bolder than immature females. Because previous work has suggested that precocious maturation increases dominance in salmonids, we included precocious males in the study to test the prediction that early sexual maturation increase male aggression and boldness. Aggression and dominance relations were estimated in dyadic contests, whereas boldness was measured as a response to simulated predation risk using a model heron. Independent of maturity state, males initiated more than twice as many agonistic interactions as females in intersexual contests. However, males were not significantly more likely to win these contests than females. The response to a first predator attack did not differ between sex categories, but males reacted less to a second predator attack than females. Sexual maturity did not affect the antipredator response in males. Since there is no evidence from field studies that stream-living immature male and female salmonids differ in growth rate, it appears unlikely that the sex differences demonstrated are behavioural consequences of sex-specific investment in growth. It seems more likely that sex-specific behaviour arises as a correlated response to sexually selected gene actions promoting differential behaviour in adult males and females during reproduction. Alternatively, sex differences may develop gradually during juvenile life, because a gradual developmental program should be less costly than a sudden behavioural change at the onset of sexual maturity.     

The breeding behaviour of a northern temperate orconectid crayfish, Orconectes rusticus

Observations of breeding activities of male and female crayfish (Orconectes rusticus) in a natural stream population during the explosive spring breeding period, and supplemental laboratory observations, indicate a promiscuous mating system characterized by intense intermale aggression. Males wandered extensively over the substrate, fought frequently with each other, and attempted to disrupt copulating pairs. Larger males (as distinguished by large chela size) more frequently initiated and won aggressive encounters and interrupted copulating pairs more successfully than smaller males, but were subjected to greater predation. Intense intermale aggression ceased when females sequestered themselves under rocks in the stream or were removed from the laboratory population. Brief resistance by females to approaching males, along with sequestering behaviour, suggests that female choice may also occur.     

Virgin females compete for mates in the male lekking species Ceratitis capitata

Abstract. Aggressive behaviour occurring in intrasexual competition is an important trait for animal fitness. Although female intrasexual aggression is reported in several insect species, little is known about female competition and aggressive interactions in polygynous male lekking species. The interactions of female Mediterranean fruit flies, Ceratitis capitata (a male lekking species), with other females and mating pairs under laboratory conditions are investigated. Mature, unmated (virgin) females are aggressive against each other and against mating pairs, whereas immature females are not. Female aggression against other females decreases dramatically after mating; however, mated females maintain aggression against mating pairs. In addition, higher intrasexual aggression rates are observed for mature, virgin females than for virgin males of the same age. The results show that female aggressiveness is virginity related, suggesting female competition for mates. These findings have important implications for understanding the physiological aspects of a complex social behaviour such as aggression and should stimulate further research on female agonistic behaviour in male lekking mating systems.     

Male harassment drives females to alter habitat use and leads to segregation of the sexes

Sexual conflict is ubiquitous across taxa. It often results in male harassment of females for mating opportunities that are costly for females, in some cases reducing reproductive success and increasing mortality. One strategy that females may employ to avoid sexual harassment is to segregate spatially from males. In fact, we do find sexual segregation in habitat use in species that have high levels of sexual conflict; however, the role of sexual harassment in driving such segregation remains poorly understood. Here, we demonstrate experimentally in a population of wild Trinidadian guppies Poecilia reticulata that male sexual harassment drives females into habitats that they otherwise do not prefer to occupy. In support of the social factors hypothesis for sexual segregation, which states that social factors such as harassment drive sexual segregation, this female behaviour leads to segregation of the sexes. In the presence of males, females actively select areas of high predation risk, but low male presence, and thus trade off increased predation risk against reduced sexual harassment.     

Paternal defence,cannibalism and polygamy: factors influencing the reproductive success of painted greenling (Pisces,Hexagrammidae)

The relative costs and benefits of paternal egg-guarding behaviour were identified for painted greenling, Oxylebius pictus, a small fish inhabiting temperate rock reefs. Because males must guard embryos against conspecifics of both sexes and against other fishes, their movements were curtailed, and an energy cost resulted. The males' somatic condition declined in proportion to the time spent guarding. Paternal males partially compensated by cannibalizing a small fraction of their progeny. Male O. pictus thus parasitize females by consuming their spawn. Polygamous matings were nonetheless advantageous for individual females as well as for males. The reproductive success of males and females increased for male broods with greater numbers of clutches, because there was a general dilution of predation loss in larger broods. The success of females, moreover, varied depending on the rank (chronological) order of spawning; success was greater for those that contributed earliest to the male's brood. The results support the hypothesis that the breeding cycles typical of paternal teleosts have evolved partly because of energy costs imposed by site-dependent care. For multiple-clutch species with protracted breeding seasons like O. pictus, the long-term benefits of polygamous spawnings perhaps outweight short-term losses sufficiently for filial cannibalism to evolve and be maintained. Alternatively (or in addition), the foraging milieu may exert a stronger average environmental influence than kin selection does.     

Mating Behavior of Daphnia: Impacts of Predation Risk,Food Quantity,and Reproductive Phase of Females

High predation risk and food depletion lead to sexual reproduction in cyclically parthenogenetic Daphnia. Mating, the core of sexual reproduction, also occurs under these conditions. Assessment of the environmental conditions and alteration of mating efforts may aid in determining the success of sexual reproduction. Here, we evaluated the impacts of predation risk, food quantity, and reproductive phase of females on the mating behavior of Daphnia obtusa males including contact frequency and duration using video analysis. Mating–related behavior involved male–female contact (mating) as well as male–male contact (fighting). Mating frequency increased while unnecessary fighting decreased in the presence of predation risk. In addition, low food concentration reduced fighting between males. Males attempted to attach to sexual females more than asexual females, and fighting occurred more frequently in the presence of sexual females. Duration of mating was relatively long; however, males separated shortly after contact in terms of fighting behavior. Thus, assessment of environmental factors and primary sexing of mates were performed before actual contact, possibly mechanically, and precise sex discrimination was conducted after contact. These results suggest that mating in Daphnia is not a random process but rather a balance between predation risk and energetic cost that results in changes in mating and fighting strategies.     

SEXUAL SELECTION AND MALE CHARACTERISTICS IN THE BLUEHEAD WRASSE,THALASSOMA BIFASCIATUM: MATING SITE ACQUISITION,MATING SITE DEFENSE,AND FEMALE CHOICE

Through a series of replacement experiments with the bluehead wrasse, Thalassoma bifasciatum, we have identified male morphological characteristics that appear to be under phenotypic sexual selection. We were particularly interested in whether the various sources of sexual selection (male-male competition for unoccupied mating sites, defense of mating sites against small males, and female choice of males) were (1) independently associated with different phenotypic characteristics; (2) jointly affected the same characteristic in the same way; or (3) jointly affected the same characteristic in an antagonistic fashion. We replaced the resident large, brightly colored Terminal Phase (TP) males on a reef with the same number of TP males from other reefs. When transplanted, these males contest with each other to take over mating sites. The transplanted group of males were then scored for three components of fitness: (1) the quality of the site obtained through competition with other large males; (2) the male's ability to defend arriving females from small intruding males; and (3) changes in female visits to the site once the new male takes over. The first and second components are part of intrasexual selection; the third represents intersexual selection. We measured the opportunity for selection by partitioning variance in mating success, and measured the direct effects of sexual selection by estimating the covariance between morphology and fitness components. Opportunities for selection: Because females generally remain faithful to particular mating sites, most (54%) of the explainable variation in male mating success is due to the acquisition of a particular mating territory, which is the outcome of competition among TP males. There was less variation in mating success due to shifts in site use by females and defense of females against the intrusions of smaller males, but all components were significant. Effects of selection: Success in male–male competition among TP males, estimated by the quality of the territory acquired, was positively associated with body length and the relative length of the pectoral fin. Success in territorial defense against small males was primarily related to body length, with lesser contributions from body depth and the area of a white band on the flank. Contribution to fitness through female choice of males was positively associated with white band area. In the two instances where a character was associated with two fitness components, the direction of selection was the same. While body length was positively associated with winning intrasexual contests, it was not correlated to any behavioral measures of aggression. Similarly, the white band associated with attractiveness was not correlated with any aspect of courtship or aggression. Parasite load was uncorrelated with other morphological characters, and did not appear to affect any aspect of sexual selection. There was no evidence for stabilizing selection or significant additional contributions from second-order effects to the fitness surfaces. Fitness functions calculated using cubic splines were generally linear except for body length, which appeared sigmoid in its effect on site acquisition ability; this same feature tended to plateau in its effect on site defense. Analyses of the interactions of selection gradients with reef or experiment indicated that the effect of particular male characters on estimates of fitness was generally homogeneous in both time and space.     

Maternal Aggression and Litter Size in the Female House Mouse

It has been commonly argued that, in house mice, female post-partum fighting against a male intruder functions to protect the offspring from infanticide. The aim of this study was to test the hypothesis that maternal aggression is actually related to pup defence and, specifically, according to parental investment theory, that its intensity should increase with litter size. 60 nulliparous albino female mice were mated and randomly assigned to four experimental groups in which litters were culled at birth to 0, 4, 8, or 12 pups, respectively. On day 8 after delivery all females were tested for maternal aggression against a stranger adult male conspecific (5-min exposure). No aggression occurred in the group in which all pups had been removed. In the other groups, the proportion of females displaying overt aggression increased with litter size. Several scores of female agonistic behaviour (proportion of females displaying overt aggression, total attacking time, frequency of tail rattling) were significantly higher for the females rearing 8 and 12 pups than for the females rearing 4 pups. Aggressive behaviour of females rearing 12 pups was not significantly higher than that of females rearing 8 pups. No male committed infanticide. These results support the hypothesis that rodent maternal aggression is strictly related to offspring defence and are consistent with the theoretical prediction that, the costs of the defence being equal and the gain in fitness increasing with litter size, the intensity of maternal defence of the young should increase with their number.     

The function of male aggressive displays towards females in mountain gorillas

In groups ofGorilla g. beringei, male aggression towards females regularly takes the form of male display. This paper examines male display towards females in two Karisoke study groups (Group 5 and Group BM) in 1989, a period when none of the females were new immigrants. Results are based on 259 hr of focal observations and 121 hr ofad libitum observations on male behaviors towards females. The goal is to see if the data are compatible with four non-mutually exclusive hypotheses to explain male displays towards females: (1) demonstration of male fighting abilities to influence female long term residence decision; (2) decrease potential competitive inequities between females; (3) provision to females of an occasion to confirm their subordinance to a male; and (4) short term influence on mating. First, male-female proximity was tested against proportion of male displays, to rule out the possibility that males display towards females simply because they happen to be close by. There was no association between proximity and male display. Dominant males were responsible for a higher proportion of displays than subordinate males. This is consistent with the idea that males display to demonstrate their fighting abilities, or their qualities as protector, since dominant males are the ones offering long term protection against infanticide and predators. Females that were in a position to transfer did not receive a higher proportion of male display, however. Long term resident dominant females received a higher proportion of displays from the dominant males, which is consistent with the idea that males attempt to decrease potential competitive inequities between females. There was an association between female appeasement reactions and male displays, which suggests that males display to create occasions for the females to confirm their subordinance to them. Estrous females did not receive a higher proportion of male displays, and there was no association between male display and copulation, suggesting that male displays are not a form of courtship aggression aimed at influencing mating in the short term.     

Failure to find sex differences in testosterone activated aggression in two strains of rats

The effect of testosterone (testosterone propionate: TP) on intraspecific aggression in males and females of two strains of rats—WEzob and S3—was examined. Pairs of these rats, gonadectomized and treated either with oil or with testosterone propionate (TP), were tested in three different combinations: OIL against OIL, OIL against TP, and TP against TP-treated animals. Subsequently the effects of TP treatment of the subject and for the opponents interaction with sex and strain on the occurrence of diverse social + aggression behavioral parameters were determined. The results of the S3 strain indicate that testosterone treatment of either the subject or the opponent stimulates aggression in both males and females. No sex difference could be determined with respect to the incidence of aggression. In the WEzob strain a stimulatory effect of TP was shown in females but not in males. The absence of a clear stimulatory effect of TP in WEzob males in terms of changes in the total time spent on aggression, however, could wrongly suggest that TP does not affect aggression in these animals. The possibility of TP having an effect on these males in terms of increasing the intensity of fighting is discussed.     

The group-level consequences of sexual conflict in multigroup populations

In typical sexual conflict scenarios, males best equipped to exploit females are favored locally over more prudent males, despite reducing female fitness. However, local advantage is not the only relevant form of selection. In multigroup populations, groups with less sexual conflict will contribute more offspring to the next generation than higher conflict groups, countering the local advantage of harmful males. Here, we varied male aggression within- and between-groups in a laboratory population of water striders and measured resulting differences in local population growth over a period of three weeks. The overall pool fitness (i.e., adults produced) of less aggressive pools exceeded that of high aggression pools by a factor of three, with the high aggression pools essentially experiencing no population growth over the course of the study. When comparing the fitness of individuals across groups, aggression appeared to be under stabilizing selection in the multigroup population. The use of contextual analysis revealed that overall stabilizing selection was a product of selection favoring aggression within groups, but selected against it at the group-level. Therefore, this report provides further evidence to show that what evolves in the total population is not merely an extension of within-group dynamics.     

Factors driving extreme sexual size dimorphism of a sit-and-wait predator under low density

Sexual size dimorphism is often a likely outcome of the interplay between natural selection and sexual selection, with female size dictated primarily by natural selection that maximizes fecundity and male size by sexual selection that maximizes reproductive opportunities. Attention to male fitness has focused heavily on direct male-male conflict selecting for superior male size and/or fighting ability, although male reproductive traits vary immensely among animals. An alternative, advanced by Michael Ghiselin, posits highly mobile dwarf males as a strategy for finding relatively immobile females in low-density populations. Adult male crab spiders Misumena vatia , sit-and-wait predators, are strikingly smaller, much more active, and relatively longer-legged than their females. This size difference results largely from males having two fewer instars than females, which simultaneously results in marked protandry. Populations of M. vatia often were small and of low density, with a female-biased sex ratio and an operational sex ratio that changed strikingly over the season. Sexual selection through scramble competition (locating the female first) should favour this suite of characters in males of low-density populations. Although direct male-male contests favoured large males, the low densities of adult males and the dispersed, relatively immobile females led to low levels of direct intrasexual contest. Females exaggerated the problem of males in finding them by providing few cues to their presence, a pattern consistent with indirect mate choice. In addition to favouring high mobility, scramble competition favoured males that selected flowers attracting many prey, the sites most often occupied by females.     

Male reproductive success and its behavioural correlates in a polygynous mammal,the Galápagos sea lion (Zalophus wollebaeki)

Sexual selection theory predicts competitive males and choosy females. Nevertheless, since molecular marker‐based studies, paternity outside the expected mating patterns has increasingly been described. Even in highly polygynous systems, where paternity is expected to be strongly skewed towards large, dominant males, alternative mating tactics have been suggested. We examined reproductive success in the polygynous Galápagos sea lion (Zalophus wollebaeki). Semiaquatic territoriality allows females to move freely and may lower the degree of polygyny otherwise suggested by both territorial behaviour and strong sexual dimorphism. We assigned paternities with 22 microsatellites and analysed how male reproductive success was related to size, dominance status, intra‐sexual agonistic behaviour, proximity to females, and attendance in the colony. Male behaviour was consistent across two seasons for all parameters under consideration. Attendance was by far the most important determinant of paternal success. Skew in reproductive success towards large, dominant males was weak and dominance status played no role. This appears to be caused by an extremely long reproductive season lasting five or more months, making it difficult for any male to monopolize receptive females. Females seem to choose displaying males that were present in the colony for a long time rather than dominance per se. Sexual dimorphism in Galápagos sea lions may thus be more influenced by selection for fasting than fighting ability. Our data provide further evidence for alternative mating tactics, as several males gained relatively high reproductive success despite short attendance and hardly any involvement in agonistic interactions.     

Higher relatedness mitigates mortality in a nematode with lethal male fighting

According to kin selection theory, individuals show less aggression towards their relatives. Limited dispersal promotes interactions among relatives but also increases competition among them. The evolution of cooperation in viscous populations has been subject of mainly theoretical exploration. We investigated the influence of relatedness on aggression in males of entomopathogenic nematode Steinernema longicaudum that engage in lethal fighting. In a series of in vitro experiments, we found that both competitor male group size and relatedness influence male mortality rates. Higher relatedness led to progressively lower rates of male mortality. In experimentally infected insects, wherein large numbers of males and females interact, the proportion of dead and paralysed (= terminally injured) males was higher when infection was established by infective juveniles originating from a mixture of three lines than in those infected by a single line. The results collectively show that Steinernema longicaudum males recognize their kin and consequently male mortality rates are lower in groups consisting of more related males. Furthermore, this monotonic negative relationship between aggression and relatedness suggests that kin selection benefits are still substantial even under extreme competition. Our experiments also suggest that kin recognition in entomopathogenic nematodes has a genetic basis rather than being strictly based on environmental cues. We discuss our findings within the theoretical context of the evolution of altruistic/cooperative behaviour in structured populations.     

Do female broiler breeder fowl display a preference for broiler breeder or laying strain males in a Y-maze test?

In recent years, the commercial broiler breeder industry has reported problems of male aggression towards females [Millman, S.T., 1999. An investigation into extreme aggressiveness of broiler breeder males. Unpublished PhD Thesis, University of Guelph]. Although this aggression is shown by the males and is apparently a defect in their behaviour [Millman, S.T., Duncan, I.J.H., 2000. Strain differences in aggressiveness of male domestic fowl in response to a male model. Appl. Anim. Behav. Sci. 66, pp. 217-233], it is also possible that it stems in some way from the females. For example, broiler breeder females may not be receptive to male courtship advances, and may avoid males, thus causing frustration in otherwise normal males. The objective of this study was to examine mate preference by broiler breeder females and the effects of sexual experience on preference. A total of 24 mature, broiler breeder females were individually tested in a Y-maze, with females choosing between a broiler breeder male and a laying strain male. Females were tested using male models and tethered live males, both when the females were sexually inexperienced and after they had been housed with broiler breeder or laying strain males for 6 weeks.Females did not display a male-strain preference when tested with models, but sexually experienced females displayed some evidence of a preference for laying strain males in tests with live males, which did not reach statistical significance (P<0.10). Live males were a stronger attractant for sexually experienced females than were models (P<0.005). Individual females tested with the same pair of males showed different preferences, suggesting females used male behaviour as a basis for their choices, and not male morphology.In conclusion, we found no evidence that broiler breeder females inherently discriminate against broiler breeder males.     

The relation between male body size, fighting, and mating success in Dawson's burrowing bee, Amegilla dawsoni (Apidae, Apinae, Anthophorini)

Males of the bee Amegilla dawsoni (Anthophorini) vary greatly in size, with some of the largest individuals as large as the largest females, a rare phenomenon in insects. The occurrence of unusually large males appears to be the product of sexual selection for fighting ability. As predicted from this hypothesis: (1) males regularly competed aggressively to be in the best position to mount sexually receptive, virgin females as they emerged from the ground; (2) larger males usually won fights for potential mates, as demonstrated by the fact that males able to defend sites with an emerging female were larger on average than males they kept at bay; (3) the fighting advantage of large males translated into greater mating success. Males captured while mounted on a female were significantly larger on average than randomly captured matesearching males in two of three populations sampled in 1993. Moreover, males known to mate more than once were consistently larger than single-mating males in the 10 samples taken from four populations examined in 1994. Thus, a large male mating advantage applies across years and among populations, making it potentially advantageous for females of Dawson's burrowing bees to produce large, superior fighting sons about the same size as their daughters.