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Fitness Costs of Sexual Harassment–The Price of Persuasion

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Abstract

Females are often subjected to unwanted mating advances from males. Such advances can be costly to both parties. The short-term costs of harassment to females have been widely explored in the literature; however, few studies have measured the direct fitness costs. Moreover, male costs are seldom considered. Conventional wisdom would lead us to hypothesise that sexual harassment is costly; thus, when males and females are housed together, harassment should reduce foraging, growth and reproductive output and may disrupt social interactions. This study quantified harassment costs in both sexes by observing behavioural responses and long-term effects of unsolicited mating in a controlled setting. Sexually mature guppies were subjected to two housing treatments: equal sex ratios or single-sex groups. The effects of male harassment on males and females were assessed by measuring behaviour, growth rate and the number of offspring produced over a period of 6 mo. Contrary to our expectations, our results indicated no significant differences in foraging and growth rates between mixed- and single-sex shoals for either sex. Moreover, there was no significant difference in fry production between mixed- and all-female shoals. Large males showed higher mortality when housed with females. Both sexes showed a reduction in shoaling when in mixed-sex groups. Thus, there appear to be few direct costs of harassment for females in natural, mixed-sex shoals, but males appear to bear significant harassment costs. The study provides insights into reproductive behaviour and life-history traits.

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... We chose to examine challenges and courtship because these are the two mechanisms which can reveal and reinforce the social structure of a group, such as bison (Hawley 1999;Chase 1982;Barroso et al. 2000;Marstellar et al. 1980;Richards 1974;Rowell 1974). Also, these behaviors cause the most harassment, or are the most likely to cause observable social stress (Creel 2001;Jerry and Brown 2017;Sapolsky 2005;Barroso et al. 2000). We found that high ranking members, of both sexes, tended to challenge more, which is consistent with previous studies (Table 1; Reinhardt 1985;Lott 2003;Barroso et al. 2000). ...
... Furthermore, we found that mature bulls tend to exert more energy running off suitors (75% of the time they ran) than chasing after females (25%) during observation hours, whereas the young bulls spent their energy running after females (89% of the times they ran). The energy spent by the males during breeding may be costlier than the actual harassment experienced by females (Jerry and Brown 2017). However, the harassment is enough to drive females to stay near higher ranking males, and these males rarely need to run after females in many different locations (Lott 2003;Wolff 1998). ...
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Males can maximise their fitness by copulating with as many females as possible. Although this behaviour may have negative consequences for the females involved, females can also benefit from multiple mating. For example, multiple mated female guppies produce more, larger and fitter offspring. It is not clear if these fitness benefits are a direct result of multiple mating, or the product of female choice — either pre or post copulatory — for better quality males. To answer this question, individual virgin female guppies were exposed to different combinations of males: just one male; three males, one at a time; and three males presented simultaneously. Mating activity was more intense in the three-at-a-time treatment but did not differ between the other two. This increased attention did not affect gestation time nor offspring size, but significantly reduced the number of offspring produced. This reveals that male harassment causes a direct reduction in female short-term fitness.
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Attempts by males of the solitary beeAnthophora plumipesPallas (Apoidea: Anthophoridae) to mate with foraging females at flowers of comfrey,Symphytum orientale, were studied. The mating system conformed to scramble competition polygyny. After an initial period of nectar foraging in the morning, males patrolled the comfrey and attempted to copulate with any females they encountered. The majority of females were unreceptive, and were able to reject the male after his initial pounce, which knocked the female to the ground. Females could experience rates of attempted copulation exceeding once every 3s, which significantly reduced their rate of visiting flowers and hence prolonged the period required to provision nest cells. Females responded to male harassment by evasive flight and physical repulsion and also by a more general change in foraging behaviour. Females abandoned flowers on the outer parts of plants frequented by males, and foraged from flowers inside the plant's growth where males did not often venture. Consideration of sugar rewards per flower and handling times suggested that male harassment halved the rate of reward for females from exposed outer flowers. When males were removed from the site, females abandoned the inner flowers and foraged from more profitable outer flowers. When males were released, the original pattern of behaviour was quickly re-established. During poor weather the ability of females to provision cells became marginal, and male harassment could thus have significant consequences for female fitness.
Article
Four species of poeciliid fish occur sympatrically in the drainage trenches of Georgetown, British Guiana: they are Poecilia vivipara Bloch and Schneider, P. (=-Lebistes) reticulata Peters, P.(= Micropoecilia) picta Regan, and P. (= Micropoecilia) parae Eigenmann. /// Vier Poeciliiden-Arten leben sympatrisch in den Entwässerungsgräben von Georgetown, Britisch Guiana: Poecilia vivipara Bloch und Schneider, P. (= Lebistes) reticulata Peters, P. (=Micropoecilia) picta Regan und P. (= Micropoecilia) parae Eigenmann.
Article
Alpine accentors and dunnocks bred in polygynandrous groups in which two or more unrelated males shared two or more females. In both species, a female solicited actively to both alpha and subordinate males whereas an alpha male attempted to guard the female to monopolize paternity. Females combated the restrictions imposed by alpha male guarding by increasing their solicitation rate to males who had gained less mating access. Males increased their copulation rate in response, but alpha males ignored more of the offers. In both species, even when a female mated with both alpha and beta males she often gained just one male’s help with chick feeding. Under these conditions, alpha male alpine accentors reduced their amount of help with a decreased mating share, whereas beta males did not. In dunnocks, however, neither alpha nor beta males reduced their help provided a critical share of the matings was exceeded. As predicted if females attempted to maximize male help, female alpine accentors preferred to give more matings to the alpha male while female dunnocks preferred alpha and beta equally. There was no evidence for either species that alpha males sired fitter offspring; within broods of mixed paternity, there was no difference in the weights of chicks sired by alpha versus subordinate males. Female dunnocks competed with other females by territory defence whereas female alpine accentors had overlapping ranges and competed directly for male attention, increasing their solicitation rate to the alpha male if other females in the group were fertile. We suggest that the extraordinarily high rates of solicitation by females, refusal by males and copulation rates (up to a thousand per clutch) in the two species are the outcome of sexual conflict over the control of mating.
Article
Where males can increase their mating success by harassing females until they accept copulation, harassing tactics can be expected to evolve to a point where they have costs to the longevity of both sexes. By experimentally manipulating the sex ratio in captive groups of tsetse flies Glossina morsitans morsitans, we demonstrated that the longevity of females declines where sex ratios are biased toward males, while the longevity of males declines where the sex ratio is biased toward females. Neither irradiation of males nor prevention of copulation by blocking or damaging the external male genitalia increased the longevity of females caged with them, suggesting that female longevity was reduced by the physical aspects of male harassment rather than by components of the ejaculate
Male guppies in wild Trinidadian populations devote a large proportion of their time to pursuing females, and females, as a result, are frequent targets of sneaky mating attempts. In this paper we demonstrate a cost, in terms of lost feeding opportunities, to these female recipients of sexual harassment. An experiment in pools of a Trinidadian stream manipulated sex ratio and fish density within the ranges naturally occurring in the system. We found that sexual harassment (from males) led to a 25% decrease in foraging beyond that which occurred as a result of female competition. Because the fecundity of female fish is a product of their feeding success, reductions in food intake have potentially serious fitness consequences.
Article
This book describes the sexual behavior of guppies and examines how mate choice by females leads to the evolution of the conspicuous colors and the courtship displays for which guppies are widely recognized. The author shows that female guppies prefer males with bright color patterns, especially those with orange spots, and that the mating preferences of females lead to sexual selection on both color patterns and courtship displays of males. Houde's work addresses a number of areas that are of interest in sexual selection, including the remarkable degree of plasticity and evolutionary lability of sexual behavior in guppies, geographic variation in mating preferences, possible mechanisms for the evolution of female mating preferences, and the role of sexual selection in speciation. In conclusion, the author explores the implications of her findings for behavioral ecologists who study sexual selection in other species.
Article
Competition among females over resources may have consequences for their resource budgets and thereby the resource allocation between growth and reproduction. In addition, the consequences of female–female interactions may differ for dominant and subordinate individuals, with the dominant ones being at an advantage. In this study, we investigated the consequences of female–female competition in guppies by manipulating the competitive environment of females. We found that large guppy females dominated smaller females and that interactions between females likely are costly because females exposed to competition grew less. These females compensated by growing at a higher rate when no longer subjected to competition. The higher growth rate might in turn be the cause of the reduced reproductive effort in the more competitive treatments. Furthermore, interactions were more costly for females when they were in the subordinate role than in the dominant role, because the reduction in growth and reproductive effort was highest in females exposed to larger competitors. Whether there was a differential allocation of resources into growth and reproduction depending on dominance status needs further investigation. However, in general, smaller females had a higher growth rate than larger females, independent of competitive level. We also found a negative relationship between reproduction and growth in all treatments, indicating a cost of reproduction.
Article
Sexual conflict can lead to individuals evolving behaviours to circumvent preferences of the opposite sex. For example, females have been shown to adjust their behaviours depending on the risk of sexual harassment. In the present study we investigated the effects of sexual harassment in sailfin mollies, Poecilia latipinna, on both females and males depending on the level of male presence to which they were exposed. We exposed females to four levels of male presence (which we assumed to be correlated with intensity of sexual harassment): (1) no harassment (four females); (2) low male presence (one male with three females); (3) moderate male presence (two males with two females); and (4) high male presence (three males with one female). We measured sexual harassment as male sexual behaviours received by the females. The cost of sexual harassment on both males and females was measured as the overall change in body condition after being exposed to a particular treatment. There were three major results. (1) Sexual harassment caused a decrease in male body condition; this is one of the first studies to examine the cost of sexual harassment for males. (2) There are direct negative effects of sexual harassment on female fitness. (3) Male sexual behaviours are not additive, suggesting that there is some nonlinear relationship between the number of males in a population and the degree of harassment females are subjected to. We demonstrate that the social environment can have a direct effect on the body condition of the individuals within that particular environment. (C) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd.
Article
Competition with individuals of the same sex may affect reproduction, and the effect may depend on own competitive ability. We exposed individual guppy (Poecilia reticulata) females either to larger females, smaller females or held them alone for five weeks. All replicates had visual access to a sexually mature mate. At the end of the experiment, there were no significant differences in daily growth or mass between the three treatments. However, females held alone had a higher reproductive output (in terms of ovary weight and GSI) than females held with either larger or smaller companions. This was mainly caused by a higher number of fully developed eggs in the ovaries of these females. The total number of eggs (including all stages) did not differ between the treatments. We suggest that the 'extra' energy not used in reproduction in the competitive treatments might have been spent on interactions between the females. In guppies socialising with other females seems to impose a cost on female reproduction.
Article
Females of many species receive male attention that re ects a conn ict between the sexes over reproduction. Here we demonstrate that female saill n mollies (Poecilia latipinna) suffer such a cost via a reduction of their feeding time in the presence of males. Female sail n mollies spend signi cantly more time feeding when accompanied by an Amazon molly (P. formosa) or a sail n molly female than when accompanied by a male saill n molly. Furthermore, we show that male sexual harassment is size dependent and that small males impose a greater cost on females.
Article
We examined male–male competition in guppies (Poecilia reticulata) to test for evidence of hierarchy formation and any subsequent effects on male mating success by comparing the interactions of pairs of males that were siblings and life-long tank mates with those of unrelated pairs that had never met. These pairs of males were first observed in the absence of a female; then a female was added to gauge the effects of the initial male–male interactions on male sexual behaviour. The unfamiliar/unrelated pairs engaged in significantly more aggressive interactions such as physical contacts, nipping and chasing than the familiar/related pairs. Based on several previous studies, we suggest that familiarity played a greater role than relatedness in the differences in behaviour that we observed. Our results suggest that, in some circumstances, more aggressive males may have more mating opportunities than less aggressive males. Our results also indicate that males adjust their aggressive and courtship behaviours to the perceived intensity of competition for mates, based on the number of mature males in their rearing tanks. We suggest that male–male competition for mating opportunities may play a more important role in the guppy mating system than previously thought.
Article
Male sexual harassment has been demonstrated to result in high costs for females. Male mosquitofish are amongst the most ardent in the animal kingdom and sexual harassment can halve female foraging efficiency. Female mosquitofish have been found to vary their shoaling behaviour when harassed by a male, approaching other males to promote male–male interactions or reducing the distance to another female to dilute male disturbance. The present study tested two predictions about female counterstrategies. As the dilution effect increases with group size, a harassed female was expected to prefer joining a larger group. She should also benefit from joining larger females since males are known to prefer larger mates. When given a choice between a group of two and a group of four females, females harassed by a male spent significantly more time near the larger group. Harassed females also preferred a shoal consisting of larger females over one consisting of smaller females, but no such preferences were observed in the absence of a male. In addition to influencing the individual decision whether to shoal or not, the presence of a harassing male appears to affect group choice. In these fish, sexual harassment might be a powerful factor in shaping both the structure and the composition of shoals.
Article
EthoLog is a tool that aids in the transcription and timing of behavior observation sessions—experimental or naturalistic, from video/audio tapes or registering real time. It was created with Visual Basic and runs on Windows (3.x / 9x). The user types the key codes for the predefined behavioral categories, and EthoLog registers their sequence and timing and saves the resulting data in ASCII output files. A sequential analysis matrix can be generated from the sequential data. The output files may be edited, converted to plain text files for printing, or exported to a spreadsheet program, such as MS Excel, for further analyses.
Article
In some mating systems males should benefit from mating with virgin females because of their higher reproductive value. We determined experimentally whether and how males distinguish between virgin and recently mated females in the guppy, Poecilia reticulata, a promiscuous livebearer. In a free-swimming experiment, males showed flexible mating behaviour by adjusting their tactics according to the mating status of the female they encountered, virgin or mated. Males followed, nipped and copulated with virgins more than with mated females, but they performed more sneaky copulations with mated females, possibly because the latter were more reluctant to mate than virgin females. When, in another set of experiments, males received only the visual cues of both virgins and mated females they showed no preference for either, but when they were exposed only to the female olfactory cues, they associated considerably more with the smell of virgin females. These results suggest that male guppies assess female behavioural and olfactory cues to determine female virginity and then use different mating tactics depending on the female's status. It is possible that the changes in male mating behaviour increase male reproductive success.
Article
Sexual conflict occurs when the genetic interests of males and females diverge. Recent evidence supporting the view that male and female genomes are in conflict has now revolutionized the way in which we interpret interactions between the sexes, and suggests that sexual conflict is a potent force in male–female coevolution. Here, we consider the nature of sexual conflict and what distinguishes it from models of coevolution by sexual selection. There are advantages and pitfalls to the various experimental and comparative approaches now used. More precise predictions derived from theory are essential to evaluate much of the empirical data in support of sexually antagonistic coevolution. Equally, there needs to be a mechanistic understanding of the traits underlying sexual conflict to formulate and test these predictions.
Article
Male mosquitofish allocate a large proportion of their time budget to attempting to inseminate unreceptive females. Because females invest considerable time and energy in avoiding unwanted copulations, sexual harassment is expected to conflict with other activities such as foraging. We found that sexual harassment more than halved the foraging efficiency of the female in a task requiring the retrieval of food items scattered on the water surface. The presence of shoalmates relieved the female from harassment and foraging efficiency increased with the number of females in the group. Small males attempted to mate significantly more than large males, causing a greater reduction in the female's foraging efficiency. When several males competed for the same female, the larger, dominant male prevented all the other males from attempting to mate and so had fewer opportunities to attempt copulation. Harassment from solitary males appeared to be more costly, as females foraged more efficiently when chased by a group of males. Because male sexual activity has a large impact on a female's feeding efficiency and possibly on her survival and reproduction, sexual conflict is expected to be important in shaping association patterns of female mosquitofish with conspecifics of both sexes. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour
Article
Among poeciliid fish, male sexual harassment is often intense and is costly for females. In Gambusia holbrooki, sexual harassment can greatly reduce female foraging efficiency when an isolated female is harassed by a single male and these costs are negatively correlated with male length. However, when females are in groups, male harassment is diluted and female foraging efficiency increases. When several males compete for the same female, mating attempts are monopolized by the dominant male and female foraging efficiency also increases. We tested whether females actively vary their schooling behaviour with conspecifics according to the presence of a harassing male. Consistent with the predictions, we found that females swam closer to each other when a male was visible. When chased by a male, females approached a group of males, and when males of different size were available, they preferred to stay close to large males. These results suggest that female schooling behaviour is a flexible strategy and that male sexual harassment may represent an important factor influencing social aggregation in poeciliids.
Article
Sexual conflict occurs when individuals of one sex express traits that reduce the fitness of individuals of the other sex. In many poeciliid fish, males harass females for copulations, which is thought to reduce female fitness by lowering foraging efficiency and increasing predation risk, energetic expenditure and the likelihood of disease transmission. Mating may also be costly for males, who often engage in aggressive interactions with other males in addition to expending energy pursuing females. We examined the effects of three operational sex ratios on male behaviour, female fitness and male body condition in the western mosquitofish, Gambusia affinis, during a 10-week experiment. Despite a significant reduction in male harassment, female growth and reproductive success decreased as the proportion of females increased. Results suggest that increases in female density had a strong, negative effect on female fitness, overwhelming any potential costs of male harassment. Aggressive behaviour between males increased and male copulation rate decreased as the proportion of males increased, suggesting that operational sex ratio influences the number of copulations that a male attempts by altering the frequency of agonistic interactions with other males and the number of females available to mate. We did not detect a difference in male body condition between treatments. Sources of female density dependence and consequences of variation in operational sex ratio on male fitness are discussed.
Article
Male harassment of females to gain mating opportunities is a consequence of an evolutionary conflict of interest between the sexes over reproduction and is common among sexually reproducing species. Male Trinidadian guppies Poecilia reticulata spend a large proportion of their time harassing females for copulations and their presence in female social groups has been shown to disrupt female-female social networks and the propensity for females to develop social recognition based on familiarity. In this study, we investigate the behavioural mechanisms that may lead to this disruption of female sociality. Using two experiments, we test the hypothesis that male presence will directly affect social behaviours expressed by females towards other females in the population. In experiment one, we tested for an effect of male presence on female shoaling behaviour and found that, in the presence of a free-swimming male guppy, females spent shorter amounts of time with other females than when in the presence of a free-swimming female guppy. In experiment two, we tested for an effect of male presence on the incidence of aggressive behaviour among female guppies. When males were present in a shoal, females exhibited increased levels of overall aggression towards other females compared with female only shoals. Our work provides direct evidence that the presence of sexually harassing males alters female-female social behaviour, an effect that we expect will be recurrent across taxonomic groups.
Article
Two core ideas in the study of mating systems and sexual selection are (1) the existence of a conflict between the sexes over mating decisions, and (2) that variation in ecological conditions drives the evolution of adaptive mating strategies and the diversification of mating systems. A recent burst of experimental studies of mating behavior and sexual selection in water striders has focused on the interaction of these ideas and led to new insights into the evolutionary ecology of mating systems and sexual selection.
Article
The reproductive effort that a male directs to a familiar female declines over time, suggesting decreasing marginal returns. But is this diminishing returns a function of increasing reproductive costs or decreasing benefits of sustained effort? Here, we use the restoration of male reproductive effort with unfamiliar females to differentiate the role of diminishing returns and lifetime costs of increased reproductive effort of male guppies. We kept males with familiar or unfamiliar females throughout their lives and manipulated their ability to either court or mate with females. We found that increased male reproductive effort with novel mates lead to an immediate trade-off in the form of reduced foraging effort. Further, males able to mate with a series of unfamiliar females had lower lifetime growth, indicating the primary cost of male reproductive effort in guppies arises from copulation rather than courtship. The lifetime growth trade-offs were significant only when males mated with unfamiliar mates, suggesting that male reproductive effort with familiar females declines before it is restricted by physical exhaustion. These findings provide some of the first evidence of longitudinal costs of increased male reproductive effort in a vertebrate.
Article
Female choices of males, and how these choices are influenced by ecological and social factors, have been studied extensively. However, little is known about the effects of age and breeding experience on female mating decisions. We used video techniques to examine female mate choice in guppies based on the area of carotenoid (orange) pigmentation on the body. Females were presented with paired images of males, one ornamented and the other plain. Visual preference for each male was measured. Age-related changes in the criteria of choice were examined by comparing the responses of the same mature but sexually inexperienced 6-mo-old and 12-mo-old females. Effects of breeding experience on female choice were examined by comparing mate preferences of 12-mo-old female virgins with their preferences after they had mated and produced a brood. Female preferences for ornamented males with large areas of carotenoid pigment changed with age but not with mating experience. Six-month-old virgin females preferred ornamented males, whereas 12-mo-old virgin and postpartum females did not differentiate between males based on orange coloration. The results are discussed in light of life-history theory and have important implications for studies of sexual selection as well as for the design of mate-choice studies.