Differential effects of mate competition and mate choice on eastern tiger salamanders

Male tiger salamanders, Ambystoma tigrinum tigrinumare slightly larger in body size and have considerably higher and longer tails than females. To determine how these dimorphic traits affected reproductive performance and success, we conducted breeding trials using 12 males and six females per trial and monitored male-female and male-male interactions. Larger males had an advantage in most aspects of mate competition investigated. Males with higher tails had no advantage in either mate competition or mate choice. Males with longer tails also had no advantage in mate competition but were preferred as mates by females. Larger males interrupted courting males more often than smaller males did. The form of male-male interference was conditional on body size and not on either tail dimension. If the intruder was larger than the courting male, it would shove the female away from the courting male and initiate courtship; if the intruder was smaller, it adopted a female mimicry tactic in which it positioned itself between the courting male and female and performed female behaviours to the courting male while simultaneously courting the female. Our trials indicated that the two components of sexual selection may influence the evolution of different male morphological traits in tiger salamanders. Mate competition may favour increased male body length; mate choice may select for greater male tail length.     

Sexual selection as a side-effect of sexual conflict in the seaweed fly, Coelopa ursina (Diptera: Coelopidae)

The mating system of the seaweed fly involves a premating struggle. When mounted, females violently try to remove the male. In this study 48% of premating struggles resulted in successful rejection of the male, 46% in copulation and 6% were terminated by the male. Large males had a mating advantage. However, contrary to what would be predicted if this sexual selection occurred as a result of active female mate choice, we found a positive association between the duration of premating struggles and male size. A positive association was also found between the duration of premating struggles and male mating success, suggesting that large males may benefit through their superior ability to withstand female rejection. Large females rejected males more easily than small females, suggesting that the premating struggle has not evolved to allow mate assessment by females. We conclude that sexual selection is occurring as a side-effect of the female rejection response, which has probably evolved in order to avoid costs associated with copulation. Nevertheless, a sexual size dimorphism has evolved with males being larger and much more variable in size than females. (c) 1998 The Association for the Study of Animal Behaviour.     

Mate choice and mate competition influence male body size in Japanese medaka

A sexual size dimorphism usually occurs when size-dependent reproductive advantages exist in only one sex. Studies on Japanese medaka, Oryzias latipes, have demonstrated reproductive size advantages in females but not in males, even though males and females are similar in body size. We conducted mate-choice and mate-copying tests in which a female could first associate with, then mate with, either a large (>/=1 sd+X standard length) or a small male (相似文献   

Parental investment, reproductive success and polygyny in the lapwing, Vanellus vanellus

We studied the consequences of monogamy and polygyny for male and female lapwings at a site in northern England between 1993 and 1995. Males and females differed in breeding behaviour, and thus the pattern of reproductive investment: males contributed less time than females to the care of their offspring and more time to mating behaviour. We argue that this has resulted from sexual selection. Reproductive behaviour was similar in monogamous and polygynous individuals of both sexes. Male mating success was related to territory size, with males on the largest territories gaining more females. Polygynous male lapwings reared on average between 58 and 100% more chicks each year than monogamous males because of fewer complete breeding failures; between-year return rates of males to the area were similar. This would result in a strong advantage in terms of lifetime reproductive success for polygynous male lapwings. The seasonal breeding success of polygynous females was marginally, but not significantly, lower than that of monogamous females. Between-year return rates of monogamous and polygynous females were similar. Copyright 1998 The Association for the Study of Animal Behaviour.     

Individual variation in male vocal traits and female mating preferences in Bufo americanus

We investigated the amount of variation in mating behaviour between and within individual male and female American toads, because both sources of trait variation can influence the course of sexual selection. Males varied in all four call parameters investigated (dominant call frequency, pulse rate, call rate and call duration). Individual males lowered the dominant frequency of their call when they interacted vocally with nearby males. Dominant call frequency was more highly correlated with body size in vocally interacting males than in non-interacting males. Pulse rate of calls primarily varied with water temperature. Call rate and call duration showed the most variation of the four call properties, but this variation was unrelated to male morphology or social interactions. Females varied in three aspects of mating behaviour: two measures of pair formation and their preference for dominant frequency of male calls. The body size of paired males varied between females both in pairings initiated by either sex and in pairings initiated only by females. Males chosen by females were usually larger than average, although age and prior breeding experience of females did not affect mate choice. Playback experiments indicated that female preference for calls of low dominant frequency depended on the temporal patterning of alternative calls presented. Each of the four male vocal properties showed significant repeatability, but only one of the three aspects of female mating behaviour was repeatable. We discuss how different degrees of repeatability in sexual traits of males and females may influence the action and detection of sexual selection in this and other species. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.     

Polyandrous females discriminate against previous mates

In most animal species, particularly those in which females engage in polyandry, mate choice is a sequential process in which a female must choose to mate or not to mate with each male encountered. Although a number of theoretical and empirical investigations have examined the effects of sequential mate choice on the operation of sexual selection, how females respond to solicitation by previous mates has received little attention. Here, we report the results of a study carried out on the polyandrous pseudoscorpion, Cordylochernes scorpioides, that assessed the sexual receptivity of once-mated females presented after a lapse of 1.5 hr or 48 hr with either their first mate or a different male. Females exhibited a high level of receptivity to new males, irrespective of intermating interval. By contrast, time between matings exerted a strong effect on female receptivity to previous mates. After a lapse of 48 hr, females did not differ significantly in their receptivity toward previous mates and different males, whereas at 1.5 hr after first mating, females were almost invariably unreceptive to males from whom they had previously accepted sperm. This result could not be attributed to male size or mating experience or to male sexual receptivity. Indeed, males were as willing to transfer sperm to a previous mate as they were to a new female. This difference between males and females in their propensity to remate with the same individual may reflect a conflict between the sexes, with males seeking to minimize postcopulatory sexual selection and females actively keeping open the opportunity for sperm competition and female choice of sperm by discriminating against previous mates.     

The paternally expressed gene Peg3 regulates sexual experience-dependent preferences for estrous odors.

Sexual experience has marked and long-lasting effects on male behavior in mammals, regulating traits such as the anticipation and display of sexual behavior, aggression, and olfaction. The authors conducted urine preference, habituation-dishabituation, and partner choice tests with sexually experienced and naive male mice and found that wild-type males acquire adaptively significant preferences for the odors of receptive, estrous females with sexual experience, and that these preferences are matched by changes in main olfactory system responses involving the piriform cortex, as indicated by c-Fos expression. The authors also report that these experiential effects are disrupted in male mice carrying a knockout of the imprinted gene Peg3. This paternally expressed gene regulates maternal care and offspring development, but the authors here report that Peg3 mutant males suffer a complex olfactory deficit that affects estrous odor preferences and the responses of the main olfactory system to such odors. Peg3 appears to have evolved to regulate the experience-dependent preference for receptive females, an adaptive trait that would enhance male reproductive success and so potentially increase paternal transmission of this paternally expressed gene. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Assortative mating and female clutch investment in black grouse

Variation in female behaviour has only recently received attention in studies of sexual selection. It has been suggested that females may invest differentially in their offspring in relation to the quality of their mate. This may lead to females that mate with high-quality and/or attractive males laying larger clutches. Females may also differ in their ability to choose between males. For example, females in good physical condition may make better choices. If physical condition and clutch size are positively correlated, this hypothesis could also produce a relationship between male attractiveness and female clutch size. We found, in lekking black grouse, Tetrao tetrix, that females mated to the highest ranked males laid the largest clutches. Furthermore we found, regardless of female age, a positive relationship between a measure of female condition and male rank but not between female condition and her clutch size. In addition, females in good condition visited a larger number of different male territories, and old females produced the largest clutches. Our results suggest two mechanisms to explain our findings. First, females in good physical condition tend to mate with the top males, suggesting an assortative mating pattern. Second, females mating with the highest ranked males lay larger clutches as a consequence of their choice. In general, our result calls for caution in evaluating studies that look at the consequences of mate choice. It may be that differences in female quality produce effects that may be wrongly interpreted as male quality effects. (c) 1998 The Association for the Study of Animal Behaviour.     

Information asymmetries among males: implications for fertilization success in the thirteen-lined ground squirrel

The classical view of mammalian mating competition focuses on combat and threat. By contrast, field studies have revealed that male mating success in some species is more strongly determined by mate location ability than by physical dominance. In thirteen-lined ground squirrels, competition in locating oestrous females is exacerbated by sperm competition that favours the first male to mate with a female. We used a female-removal experiment to identify the distinguishing characteristics of males that were the first at finding and mating with females. Each focal female was observed the day before she entered oestrus; the identities of males that made contact with her and the locations of their interactions were recorded. The following morning the females were temporarily removed, and we monitored male search behaviour in their absence. Males that arrived first were those that had spent more time with the female the previous day relative to their rivals. Time invested the day before, in turn, was highly correlated with male search persistence and familiarity with the female's likely whereabouts. These results demonstrate that differential fertilization success can arise from information asymmetries among males: the advantaged individuals are those that have greater a priori knowledge of the reproductive state and spatial locations of prospective mates than rivals.     

Sexual conflict and speciation

We review the significance of two forms of sexual conflict (different evolutionary interests of the two sexes) for genetic differentiation of populations and the evolution of reproductive isolation. Conflicting selection on the alleles at a single locus can occur in males and females if the sexes have different optima for a trait, and there are pleiotropic genetic correlations between the sexes for it. There will then be selection for sex limitation and hence sexual dimorphism. This sex limitation could break down in hybrids and reduce their fitness. Pleiotropic genetic correlations between the sexes could also affect the likelihood of mating in interpopulation encounters. Conflict can also occur between (sex-limited) loci that determine behaviour in males and those that determine behaviour in females. Reproductive isolation may occur by rapid coevolution of male trait and female mating preference. This would tend to generate assortative mating on secondary contact, hence promoting speciation. Sexual conflict resulting from sensory exploitation, polyspermy and the cost of mating could result in high levels of interpopulation mating. If females evolve resistance to make pre- and postmating manipulation, males from one population could be more successful with females from the other, because females would have evolved resistance to their own (but not to the allopatric) males. Between-locus sexual conflict could also occur as a result of conflict between males and females of different populations over the production of unfit hybrids. We develop models which show that females are in general selected to resist such matings and males to persist, and this could have a bearing on both the initial level of interpopulation matings and the likelihood that reinforcement will occur. In effect, selection on males usually acts to promote gene flow and to restrict premating isolation, whereas selection on females usually acts in the reverse direction. We review theoretical models relevant to resolution of this conflict. The winning role depends on a balance between the 'value of winning' and 'power' (relating to contest or armament costs): the winning role is likely to correlate with high value of winning and low costs. Sperm-ovum (or sperm-female tract) conflicts (and their plant parallels) are likely to obey the same principles. Males may typically have higher values of winning, but it is difficult to quantify 'power', and females may often be able to resist mating more cheaply than males can force it. We tentatively predict that sexual conflict will typically result in a higher rate of speciation in 'female-win' clades, that females will be responsible for premating isolation through reinforcement, and that 'female-win' populations will be less genetically diverse.     

Female preference for fly song: playback experiments confirm the targets of sexual selection

The courtship song of Drosophila is thought to be involved in sexual selection and species recognition. Because of the mating system of flies, however, directly demonstrating that song influences female preference is difficult. The majority of previous studies have used an experimental design that potentially confounds male and female reactions to song. In D. montana, correlational evidence has suggested that males that produce short sound pulses consisting of a high number of sound cycles (i.e. a high carrier frequency) have a higher mating success than other males. In this study, we played synthetic song that varied in pulse length and carrier frequency to individual females in the laboratory, both alone and in the presence of mute males. We scored female preference via an acceptance posture, 'wing spreading', which the females of this species usually display prior to mounting by a male. Females responded to synthetic song in the absence of males. The presence of mute males significantly increased their overall responsiveness, but the relative effectiveness of the songs did not change, eliminating male reaction to song as a possible confounding factor in the results. The interaction between pulse length and carrier frequency determined the discrimination between song types, with females responding most readily to song consisting of short pulses with a high carrier frequency. Thus, direct examination of female preferences supports the previous studies of male mating success, and confirms female song preference as a likely determinant of male mating success. Copyright 1998 The Association for the Study of Animal Behaviour     

Non-genetic benefits of mate choice: fecundity enhancement and sexy sons

I compared reproductive success (lifetime number of fertilized eggs) as a function of mate choice among females of the stink bug, Nezara viridula L. (Hemiptera: Pentatomidae). 'Choosing' (C) females were placed with one of two males on alternate days. CI females chose between inexperienced males while CR females chose between males previously rejected by CI females. 'Non-choosing' (N) females were placed with the same male every day. Non-choosing NI, NR and NA females encountered, respectively, inexperienced males, previously rejected males, or previously accepted and mated males. Reproductive success was highest for CI females, showing direct selection on mate preferences. Reproductive success did not differ between CR and NR females, indicating that male quality, not the act of choosing a mate, affects fitness. CI females preferred males with longer antennae and their fecundity (lifetime number of eggs) was correlated with male antenna length, consistent with antenna length as an indicator of male ability to transfer nutritive sperm produced in paired harlequin lobes of the testes. Harlequin lobes were smaller in rejected than chosen males. In second-generation mate choice trials, sons of NR females competed well against sons of NA females but not against sons of CI females. This suggests that non-genetic paternal contributions that decline with prior mating account for the attractiveness of sons because sons of CI and NA females shared the same fathers. Sons experiencing mating success came from larger eggs and egg size was greatest for CI females, perhaps as a consequence of paternal nutritional contributions. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.     

Size and pairing success in Gammarus duebeni: can females be too big?

The crustacean Gammarus duebeni exhibits precopula mate guarding and size-assortative pairing, in which larger males tend to pair with larger females. Size-assortative pairing may result from sexual selection or natural selection (mechanical or loading constraints limiting the size of female that can be carried by the male). If loading constraints are important, large females should have lower pairing success than females of intermediate size as they will be less likely to encounter sufficiently large males capable of carrying them in precopula. We tested this hypothesis in a laboratory study. Female pairing success was dependent on size; however, the relationship was curvilinear: pairing success increased with size up to a point, but larger females suffered decreased pairing success. This supports the hypothesis that loading constraints play a part in structuring size-assortative pairing in this species. We found no evidence for size-related female resistance in structuring the pattern of pairing. We considered size-related pairing success with regard to environmental sex determination and parasitic sex-ratio distortion in G. duebeni1997 The Association for the Study of Animal BehaviourCopyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour     

Correlates versus predictors of courtship success: courtship song in Drosophila silvestris and D. heteroneura

Males of the picture-winged flies Drosophila silvestris and D. heteroneura produce a sound during courtship wing vibration; successful courtships include more time spent in wing vibration. We clipped male wings to test whether this sound is a necessary signal for the success of male courtship. We tested females in no-choice tests and also in choice tests in which each female was provided with a clipped and normal male simultaneously. We found no differences in the probability of copulation for either species in no-choice tests, and no difference for the choice tests with D. heteroneuraSurprisingly, clipped males were significantly more successful than control males in the choice tests with D. silvestrisThe latencies to copulate did not differ by treatment in any tests. Consequently, the sound produced by courtship wing vibration does not influence male mating success and thus does not meet the most important criterion for being a sexual signal. We propose that the vibration of thoracic muscles, transmitted through the substrate or through the male's forelegs, could provide a sexual signal in these species.1997The Association for the Study of Animal Behaviour     

Male traits, mating tactics and reproductive success in the buff-breasted sandpiper, Tryngites subruficollis

Buff-breasted sandpipers use a variety of mating tactics to acquire mates, including remaining at a single lek for most of the breeding season, attending multiple leks during the season, displaying solitarily or displaying both on leks and solitarily. We found that differences in body size, body condition, fluctuating asymmetry scores, wing coloration, territory location and behaviour (attraction, solicitation and agonistic) did not explain the observed variation in mating tactics used by males. Which males abandoned versus returned to leks was also not related to morphology or behaviour, and there was no tendency for males to join leks that were larger or smaller than the lek they abandoned. These results suggest that male desertion of leks was not dependent on a male's characteristics nor on the size of the lek he was presently attending. Males did join leks with larger males than their previous lek, perhaps to mate with females attracted to these larger 'hotshot' males. Males at both leks and solitary sites successfully mated. Lek tenure did not affect mating success, although lekking males appeared to mate more frequently than solitary males. Courtship disruption and to a lesser extent, female mimicry, were effective at preventing females from mating at leks, and may offer a partial explanation for female mating off leks. Our analysis that combined all males together within a year (regardless of mating tactic) indicated that males that attended leks for longer periods of time and that had fewer wing spots were significantly more likely to mate. Given some evidence that wing spotting declines with age, and that females inspect male underwings during courtship, the latter result suggests that female choice may play some role in determining male success. We suggest that male buff-breasted sandpipers may use alternative mating tactics more readily than males in other 'classic' lek-breeding species because: (1) unpredictable breeding conditions in this species' high arctic breeding range leads to low lek stability, which in turn hinders mate selection mechanisms mediated by male dominance and female choice; and (2) males are not constrained by morphological markings that indicate status or sex. Both characteristics may reduce the reproductive benefits associated with males adopting one mating tactic and result in a sort of scramble competition in which males switch between tactics as local conditions change.Copyright 1998 The Association for the Study of Animal Behaviour     

Females prefer leading males: relative call timing and sexual selection in katydid choruses

Females of several acoustic insects and anurans have recently been shown to orient preferentially to the leading of two identical male calls presented in close succession. We studied this phenomenon via two-choice phonotaxis trials in the neotropical katydid Neoconocephalus spiza and found that females avoided male calls occurring during an interval beginning immediately after the onset of a leading call. This avoidance occurred whether or not the following call was overlapped by the leader, indicating that the mechanism of preference for leading calls may represent a psychoacoustic precedence effect rather than simple call masking. We also found that females preferred leading calls as long as the amplitude of the following call was not more than 2 dB higher than the leader. Under certain circumstances, preferences for leading calls remained when females were presented with a sequence of four calls. Thus, preferences for leading calls probably influence a male's attractiveness and mating success in complex natural choruses: females are expected to orient towards males producing leading calls regardless of call length (and the probability of overlapping a following call), when the leading call is up to 1.5 times as distant as a follower, and when succeeded by multiple followers. We suggest that female preferences for leading male calls represent sensory biases that originated in contexts unrelated to sexual selection. None the less they currently play an important role in sexual selection and influence individual male signalling behaviour, and thus chorus structure. Copyright 1998 The Association for the Study of Animal Behaviour.     

Density-dependent selection on horn phenotype in Soay sheep

In the naturally regulated population of Soay sheep (Ovis aries L.) on Hirta (St Kilda), 12% of males and 24% of females have scurred horns. This trait reduces the competitive ability of males in the mating season but is associated with higher overwinter survival rates in both sexes (Moorcroft et al. 1996). In this paper, we show that scurred females also show higher conception rates and weaning rates than non-scurred ones, and that these differences are associated with heavier maternal body weight as well as higher birth weights of offspring. Selection pressures favouring scurredness in females vary with population density and are generally more pronounced among younger animals than adults. We discuss these results with reference to recent suggestions that temporal fluctuation in selection pressures may help to maintain genetic diversity within populations. We suggest that selection against scurredness operating through male mating success is opposed by selection favouring this trait, operating through the breeding success of females and the survival of both sexes.     

Sex roles and sexual selection

Sexual selection has been portrayed as acting predominantly on males who compete with each other over copulatory access to females; selection was considered to be driven by females choosing between males at the pre- or postcopulatory level. However, a broader view of sexual selection is now emerging. Examining male discrimination between females and female-female competition has been beneficial in identifying factors influencing the direction and strength of sexual selection. Furthermore, consideration of processes such as sexual coercion or genetic incompatibility, which indirectly influence an individual's set of copulation partners, gamete set or their offspring success, has helped to clarify the ways in which sexual selection may operate. Moreover, there is increasing evidence that not all copulations translate directly to paternity and that paternity does not necessarily translate into successful offspring. Postcopulatory and postfertilization mechanisms that influence not only paternity share but offspring recruitment now require further consideration. The benefits to each sex of copulating with particular partners or with more than one partner remains an area of debate. More carefully designed studies which eliminate alternative possibilities or quantify the relative importance of different selective pressures will also benefit from considering that not all copulations function solely to inseminate or receive sperm. It is also now clear that not all individuals of one sex follow the same strategy. Examining the variation between individuals in reproductive behaviour, fertilization success and offspring success will be important in establishing the selective pressures and mechanisms underlying the operation of sexual selection. (c) 1998 The Association for the Study of Animal Behaviour.     

Effects of olfactory cues on sexual behavior in the brown lemming, Lemmus trimucronatus..

Tested 3 groups of 12 female lemmings each to determine the effects of odor familiarity on measures of reproductive behavior. A familiar odor (FO) group was exposed to the bedding of a particular male for 1 wk, then tested with that male. A 2nd female group (unfamiliar odor; UO) was exposed to the bedding of a male for 1 wk, then tested with a different male. A 3rd group (control; CO) was not exposed to male bedding prior to being tested with a male. The FO females engaged in higher frequencies of contact social behaviors than did UO and CO females. Males with FO females ejaculated more frequently than did the males with UO and CO females. Latencies to first display of sexual behaviors (female:lordosis; male:mount, thrust, and ejaculation) were lower for FO pairs. Results suggest that previous exposure of females to the odor of a given male facilitates sexual behaviors when such females are later paired with that male. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of novelty on the reproductive behavior of male Japanese quail (Coturnix coturnix japonica).

In Exp I, 8 sexually deprived male Japanese quail were exposed to 1 of 7 female Japanese quail until they satisfied a 20-min sexual satiation criterion. The female was then replaced with a novel female or was allowed to remain in the test cage undisturbed. Introduction of the novel female did not reinvigorate sexual behavior above levels observed when the female was allowed to remain undisturbed. In Exp II, with 9 males and 15 females, males that were not sexually deprived were tested in the presence of 2 females. During experimental tests, 1 of the females was novel and the other was familiar. During control tests, both of the females were familiar. The presence of a novel female increased overall levels of male sexual behavior and also increased the number of males engaged in reproductive behavior. However, the enhanced sexual behavior was not differentially directed toward the novel or familiar female. Implications of these findings for the mating system of Japanese quail and for studies of the role of novelty in sexual behavior are discussed. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)