Sex-role reversal revisited: choosy females and ornamented, competitive males in a pipefish

In the pipefish Syngnathus typhle sex roles are reversed, thatis, females compete more intensely than males over mates. However,competition over mates among individuals of one sex does notnecessarily prevent members of that same sex from being choosy,and choosiness in the other sex does not prevent competitionwithin it. In an experiment we allowed a female pipefish tochoose freely between two males, after which we released themales and let the three interact. Comparisons with earlier resultsshow that both sexes courted partners and competed with consexuals.However, females courted more often than did males, and courtshipwas more frequent in treatments involving large individualsthan in treatments with small individuals. Males competed amongthemselves for access to mates but for a shorter duration thanfemales in the same situation. Males displayed an ornament towardsfemales but not to males during mating competition. Females,however, used their ornament in both contexts. Females did notalways mate with the male of their previously made choice, whichwe interpret as females being constrained by male-male competition,male motivation to mate, or both. Thus, in this sex-role reversedspecies, mate choice in the more competitive sex may be circumventedand even overruled by mate competition and mating willingnessin the least competitive sex. Hence, sex roles should not beconsidered as sexes being either choosy or competitive but ratherthat males and females may exhibit different combinations ofchoice and competition.     

配偶选择中“听众效应”及鸣唱对雌性灰文鸟行为的影响

配偶选择是性选择研究核心问题之一。雌性通过选择高质量的雄性配偶获得直接利益,如资源、营养和保护等,也可以通过获得高质量雄性提高后代的适合度。配偶选择研究对于研究性选择机制和进化均具有重要意义。目前,对配偶选择的研究主要集中在影响配偶选择的因素及雌性"听众效应"中雄性-雄性竞争方面。鸣唱对配偶选择的影响和雄性"听众效应"中雌性-雌性竞争的研究对于探索鸟类配偶选择中信号交流、调整的方式及选择策略均具有重要意义。以灰文鸟为对象,研究了雄性鸣唱对雌性配偶选择的影响及雄性"听众效应"对雌性灰文鸟同性竞争行为的影响进行了探讨。实验一利用双向选择装置,以配偶鸣唱(求偶鸣唱或非求偶鸣唱)和非配偶鸣唱(求偶鸣唱或非求偶鸣唱)对雌鸟进行刺激,观察雌鸟对两端鸣唱的偏爱状况。实验二主要观察雌鸟之间在无听众、听众为熟悉的雄性和听众为配偶条件下的竞争行为。结果表明,雌性灰文鸟大多偏爱配偶鸣唱,相对于配偶的非求偶鸣唱更偏爱非配偶的求偶鸣唱。求偶鸣唱比非求偶鸣唱更具有吸引力,求偶鸣唱更能刺激雌性灰文鸟配偶选择的积极性,这种积极要付出更多的时间和资源,但雌鸟可以通过选择更高质量的雄性配偶获益。在配偶雄性作为听众条件下雌鸟攻击行为最高,显著高于熟悉雄性为听众的条件下,并且两者都显著高于无听众条件下雌鸟的攻击行为。雌性灰文鸟会基于不同"听众"而对雌-雌竞争行为做出适当调整。上述研究结果对于深入理解鸟类的性选择行为机制具有重要帮助作用。     

An intimidating ornament in a female pipefish

A sexually selected signal may serve a dual function being bothattractive to mates and deterring rivals. Presently, there arefew unambiguous demonstrations of an ornament functioning inboth a mate choice and mate competition context and none regardingfemale ornaments. We have shown earlier that a temporary ornament,a striped pattern, in a sex-role reversed female pipefish, Syngnathustyphle, attracts males. Here we show that this ornament alsointimidates rival females: in one experiment a male could interactwith either 1 or 2 females. Latency until copulation was longerwhen 2, rather than 1, females were present. Moreover, when2 females were present, competition lasted longer and time untilmating took place increased when females displayed their ornamentsmore equally. In another experiment, a focal female could see1 stimulus female and 1 stimulus male, the latter 2 being unawareof each other. The ornament of the stimulus female was manipulated,either strengthened by being painted black or left unalteredby being sham-painted. As a result, focal females experiencingblack-painted stimulus females decreased courtship as well ascompetitive activities compared with focal females seeing sham-paintedfemales. Moreover, focal females seeing black-painted femalesdisplayed less of their own ornament compared with controls.This decrease was due to a decrease in display toward malesrather than to stimulus females. Thus, this female ornamentindeed has a dual function, attracting mates and deterring rivals.In addition, the social costs invoked by this intimidating effecton rivals may help to maintain signal honesty.     

Sequential mate encounters: female but not male body size influences female remating behavior

Whether and how individuals choose sequentially among matesis an important but largely neglected aspect in sexual selectionstudies. Here, we explore female remating behavior in the cellarspider Pholcus phalangioides. We focus on body size as one ofthe most important traits involved in mate choice. Large andsmall females (n = 216) were double mated with large or smallmales in all eight possible combinations. All females copulatedwhen virgin, but only 82% accepted a second male. The chanceof a female remating was not significantly predicted by thebody size of the second or first male or by the size differencebetween the two. In contrast, a previous study demonstrateda male size effect in that larger males monopolized femalesuntil egg laying when two males of different sizes were present.We suggest that sequential encounters are more common undernatural conditions than male monopolization of females becauseestimates of concurrent multiple paternity together with observationsin a natural population do not favor mate guarding as the predominantmating strategy in this species. It follows from our study thatthe intensity of sexual selection on male size may be greatlyoverestimated when using a competitive laboratory setting fora species in which females generally encounter mates in a sequentialfashion. Female remating probability was significantly predictedby female size, with large females remating with higher probabilitythan small females. Thus, when mating with large females, malesmay gain higher fertilization success through increased femalefecundity but also face a higher sperm competition risk.     

Sexual behavior in brown capuchins ( Cebus apella )

We observed sexual behavior patterns in two captive groups of Cebus apella.We obtained data on intersexual solicitations and intersexual competition. The length of proceptivity cycles by females averaged 18.8 ± 1.2 days; this corresponds with published reports of physiological measures of ovulatory cycles. Females initiated sexual interactions with males significantly more than males initiated interactions with females, and female solicitations increased in frequency over the duration of displayed periods of proceptivity. In contrast, male solicitations of females were infrequent and did not change significantly throughout female proceptive phases. Each female solicited the same male throughout a given proceptive phase. We observed no evidence of male-male or female-female competition. Males seem to respond to female sexual behavior directed toward them, rather than initiating sexual interactions themselves. Even so, male sexual interactions with females followed only a small proportion of solicitations.     

Unexpected male choosiness for mates in a spider

Sexual selection theory traditionally considers choosiness for mates to be negatively related to intra-sexual competition. Males were classically considered to be the competing, but not the choosy, sex. However, evidence of male choosiness is now accumulating. Male choosiness is expected to increase with an individual's competitive ability, and to decrease as intra-sexual competition increases. However, such predictions have never been tested in field conditions. Here, we explore male mate choice in a spider by studying size-assortative pairing in two natural sites that strongly differ in the level of male-male competition. Unexpectedly, our results demonstrate that mate choice shifts from opportunism to high selectivity as competition between males increases. Males experiencing weak competition did not exhibit size-related mating preferences. By contrast, when competition was intense we found strong size-assortative pairing due to male choice: while larger, more competitive males preferentially paired with larger, more fecund females, smaller males chose smaller females. Thus, we show that mating preferences of males vary with their competitive ability. The distinct preferences exhibited by males of different sizes seem to be an adaptive response to the lower reproductive opportunities arising from increased competition between males.     

Patterns of fluctuating asymmetry in sexual ornaments predict female choice

Extravagant secondary sexual characters are assumed to have arisen and be maintained by sexual selection. While traits like horns, antlers and spurs can be ascribed to intrasexual competition, other traits such as extravagant feather ornaments, displays and pheromones have to be ascribed to mate choice. A number of studies have tested whether females exert selection on the size of male ornaments, but only some of these have recorded female preferences for the most extravagantly ornamented males. Here I demonstrate that female choice can be directly predicted from the relationship between the degree of fluctuating asymmetry and the size of a secondary sexual character. Fluctuating asymmetry is an epigenetic measure of the ability of individuals to cope with stress, and it occurs when an individual is unable to undergo identical development of an otherwise bilaterally symmetric trait on both sides of its body. There is a negative relationship between the degree of fluctuating asymmetry and the absolute size of an ornament in those bird species with a female preference for the largest male sex trait, while there is a flat or U-shaped relationship among species without a female preference. These results suggest that females prefer exaggerated secondary sexual characters if they reliably demonstrate the ability of males to cope with genetic and environmental stress. Some species may demonstrate a flat or U-shaped relationship between the degree of fluctuating asymmetry and the absolute size of an ornament because (i) the genetic variance in viability signalled by the secondary sex trait has been depleted; (ii) the secondary sex trait is not particularly costly and therefore does not demonstrate condition dependence; or because (iii) the sex traits can be considered arbitrary traits rather than characters reflecting good genes.     

The Function of Male Agonistic Displays in Ursine Colobus Monkeys (Colobus vellerosus): Male Competition,Female Mate Choice or Sexual Coercion?

Male agonistic displays may allow males to assess competitors, females to assess mates, or could be directed at cycling females to sexually coerce them. We analysed the display output of 26 male ursine colobus monkeys (Colobus vellerosus) in four groups over 13‐mo at the Boabeng‐Fiema Monkey Sanctuary, Ghana. Display indices (including three behaviours, loud calls, stiff‐legs, and jump‐displays) were calculated for males in each group. Males vary in their expression of these behaviours suggesting they are sexually selected signals. We investigated the target of displays and whether display indices varied in relation to male dominance rank, eviction of other males, copulation rate, and proceptive behaviours received from females, to assess the primary function of these behaviours. Male displays decreased in vigour over time and were targeted to other groups and males. High‐ranking males displayed more than low‐ranking males. Alpha male display indices correlated with the number of other males evicted from the group. Display rates were generally higher when cycling females were present in the group. However, neither male display index nor rank correlated with copulation rates. Alpha and non‐alpha males gave cycling females equal rates of sexual solicitations; likewise cycling females showed no difference in the rates of proceptive behaviours directed towards alpha and non‐alpha males. Females mated promiscuously and did not seem to base mating decisions on male display output, although data on female hormones is needed to determine if they mate with strongly displaying males more in the periovulatory period. The male–male competition hypothesis received the greatest support, with some support for the female mate choice hypothesis. Although behaviours that appeared sexually coercive were observed, the function of male displays did not seem to be sexual coercion. Displays were rarely directed at females and males that displayed more did not have greater mating success.     

Juvenile infection and male display: testing the bright male hypothesis across individual life histories

Current tests of the bright male hypothesis focus on assaysof adult disease resistance and their relation to male traitdevelopment and female choice. We suggest that if parasiteshave significant harmful effects on juvenile stages of a host,then females selecting males that effectively signal juvenileparasite resistance may gain a significant "good genes" benefit.Currently, there is no information on juvenile and adult infectionor resistance in the same male and whether adult male displayssignal juvenile parasite resistance. In the present study, wemeasure infection of the ectoparasitic louse, Myrsidea ptilonorhynchi,in individual male satin bowerbirds (Ptilonorhynchus violaceus)both as juveniles and nine or more years later as adults. Wetest hypotheses that examine the role of juvenile parasite infectionin mediating sexual selection. We found that (1) juvenile infectionis higher than adult infection in the same individuals, (2)adult males able to hold display sites have lower juvenile infection,and (3) juvenile and adult infection in the same individualsare not significantly correlated. In addition, comparisons amonga larger set of individuals from a single year show that bloodand ectoparasite infections are highly correlated, and bothdecrease with male age and are inversely related to male courtshipsuccess. These results, combined with the evidence that femalesmate exclusively with bower-holding males support the hypothesisthat females use adult male display traits to identify maleswith a high level of juvenile disease resistance. We suggestthat effective tests of the bright male hypothesis should include(1) assessment of infection resistance in both subadult andadult life history stages, (2) tests of whether differencesin age-specific resistance are indicated in adult male displays,and (3) tests to determine if females attend to these traitsin mate choice. Although these requirements increase the difficultyof testing the bright male hypothesis, they are necessary fora more accurate assessment of the effects of parasites on maledisplay and female choice.     

Dangerous love? Predation risk does not affect female mate choice in blue‐black grassquits

Predation risk may be an important factor affecting female mate choice. Hypothetically, females could choose extravagantly ornamented males that survive in high predation risk environments. However, this decision could be different if choosing a conspicuous male under high predation risk is costly for females or results in reduced offspring survival. In such contexts, females could become indifferent to male quality or prefer inconspicuous males. We tested this idea using captive blue‐black grassquits (Volatinia jacarina, Linnaeus, 1766), a species in which males perform conspicuous leap displays coupled with songs during the breeding season, which presumably subjects females and offspring to higher predation risk. Females were placed in an arena with speakers on opposite sides emitting male courtship songs. One speaker emitted songs at a high rate (proxy for a conspicuous male) while the other speaker broadcast songs at a low rate (proxy for a less conspicuous male). While the female evaluated the two male songs, a third speaker emitted vocalizations characterizing three levels of risk: adult predator, nest predator, and no‐risk control. Females showed no preference for either male stimuli across the predation risk treatments. This lack of preference relative to frequency of male vocal displays suggests that leap‐song frequency is not used by females during mate choice. We suggest that in addition to its role in courtship, male grassquit displays also signal status to other males when competing for territories. Thus, we propose that predation risk does not directly influence blue‐black grassquit intersexual selection and that females in this species may exercise indirect mate choice, choosing social mates based on male ability to establish and defend a territory, and relying secondarily upon other aspects of male display attributes, such as its visual components.     

Female mate choice and male–male competition in Tonkean macaques: Who decides?

The theory of sexual selection predicts that females should be discriminatory in the choice of sexual partners. Females can express their choice in two ways. In direct mate choice, they show preferences for certain partners. In indirect mate choice, they select partners by displaying sexually attractive traits, thus eliciting contest competition between males. We focused on a primate species in which females advertise the timing of their ovulation and studied the balance between these two choice strategies. We tested predictions related to three hypotheses about direct and indirect female choice, namely the best‐male, graded‐signal and weak‐selectivity hypotheses. We investigated the sexual and agonistic interactions occurring during oestrous periods in five captive groups of Tonkean macaques (Macaca tonkeana). The results showed that dominant males used mate guarding to monopolise sexual access to parous females that were in the fertile stage of their reproductive cycle, while lower‐ranking males monitored only nulliparous females. The distribution of sexual presentations indicated that females accepted different types of partners, supporting the weak‐selectivity hypothesis regarding direct mate choice. The analysis of behavioural sequences revealed that mate‐guarding males used mild coercive behaviours to prevent females from mating with other males at conception time. The distribution of mounts showed that females mainly mated with dominant males, which leads us to argue that the best‐male hypothesis provides the most parsimonious explanation regarding indirect mate choice in Tonkean macaques. At the individual level, it may be concluded that male competitive strategies prevented females from exercising direct mate choice. At the evolutionary level, however, female sexual advertising and thus indirect choice promoted competition between males. The outcome is that indirect mate choice appears more important than direct mate choice in female Tonkean macaques.     

Mate choice based on static versus dynamic secondary sexual traits in the dark-eyed junco

Some secondary sexual traits (SSTs) such as structural characteristicsare semi-permanent or static, while others, such as courtshipdisplay, are more labile or dynamic. In this paper we reportresults from two experiments designed to test the relative attractivenessto female dark-eyed juncos (Junco hyemalis, Passeriformes, Aves)of a relatively static plumage trait, the amount of white inthe tail, and a relatively dynamic behavioral trait, courtshipintensity. The experiments derived from a study showing that femalejuncos prefer males that court more vigorously. We asked whether femalesalso base their preferences on plumage traits and how they respond whenpresented with a choice between attractive traits that are eitherstatic (plumage) or dynamic (courtship) in nature. In the firstexperiment we presented males to females in paired mate-choicetrials and found that males enhanced with more white in theirtails were more attractive to females than controls with unenhancedtails. Females spent more time with enhanced males and directedmore sexual displays toward them. In the second experiment we testedwhether females preferred males with enhanced tails (a staticSST) or males with enhanced hormone-mediated courtship behavior(a dynamic SST). In this experiment females did not demonstratea consensus preference for either the static or the dynamictrait. Instead, some females preferred the male whose courtshipperformance was enhanced with testosterone, while others preferredthe male with an enhanced tail. We conclude that both kindsof traits are important in junco mate choice, but that somefemales apparently weigh static traits more heavily than dynamicones, while other females use opposite weightings.     

Indirect mate choice, direct mate choice and species recognition in a bower-building cichlid fish lek

Sexual selection arising through female mate choice typically favours males with larger, brighter and louder signals. A critical challenge in sexual selection research is to determine the degree to which this pattern results from direct mate choice, where females select individual males based on variation in signalling traits, or indirect mate choice, where male competition governs access to reproductively active females. We investigated female mate choice in a lekking Lake Malawi cichlid fish, Hemitilapia oxyrhynchus, in which males build and aggressively defend sand 'bowers'. Similar to previous studies, we found that male reproductive success was positively associated with bower height and centrality on the lek. However, this pattern resulted from males holding these territories encountering more females, and thus their greater success was due to indirect mate choice. Following initial male courtship, an increase in the relative mating success of some males was observed, but this relative increase was unrelated to bower size or position. Crucially, experimentally manipulating bowers to resemble those of a co-occurring species had no appreciable effect on direct choice by females or male spawning success. Together, these results suggest indirect mate choice is the dominant force determining male-mating success in this species, and that bowers are not signals used in direct mate choice by females. We propose that, in this species, bowers have a primary function in intraspecific male competition, with the most competitive males maintaining larger and more central bowers that are favoured by sexual selection due to higher female encounter rates.     

同时而非先后一雌多雄交配增加不同温度下食蚜瓢虫的适合度（英文）

【目的】尽管一雌多雄在瓢虫科中常见,但各研究中获得的数据不足以解释雌虫多次交配和一雌多雄的一般适应性意义或适合度后果。本研究以温度为胁迫因子,旨在评价一雌多雄的某些益处（如增加的适合度）是否可传递给后代。【方法】本研究检测了黄斑盘瓢虫Coelophora saucia (Mulsant) 3种交配处理中的适合度：一雌一雄（与同一雄虫交配5次,1次/d）,先后一雌多雄（与5头不同的雄虫依次交配5次,即每天与新的雄虫交配1次）,以及同时一雌多雄（放进5头雄虫,任由雌虫选择雄虫,交配5次,1次/d）。观察了各交配处理不同温度下（25, 27和 30℃）繁殖力、卵的育性、后代发育和存活。【结果】结果表明,经历一雌多雄然后进行交配选择或竞争的雌性的繁殖能力最强,后代能在更广温度范围内最好地适应发育和存活。但先后一雌多雄交配的雌性与一雌一雄交配的雌性的繁殖能力相似。【结论】结果说明,在无交配选择或雄性竞争的条件下,一雌多雄的益处不明显。这可能是由于在依次射精的雄性间存在精子竞争,或由于雌性的隐性选择。据我们所知,本研究中观察发现的无交配选择时不表现一雌多雄的益处的现象,之前在昆虫中未观察到过。     

Mating preference of female zebrafish, Danio rerio, in relation to male dominance

Mating success tends to be skewed toward dominant males, thoughfemale mate preferences may not always correlate with male dominance.In this study, we investigated the mating preferences of femalezebrafish, Danio rerio, in the absence of male–male competition.We paired females sequentially with males of known dominancerank, using a nested, repeated measures design, with egg productionas a measure of female mate preference. We predicted that femaleswould spawn more frequently and produce larger clutches whenpaired with males of higher dominance rank. We found significantdifferences among females in the size of clutches produced andamong males in the size of clutches received, but these differenceswere independent of male dominance rank. Male body size wasnot related to either dominance rank or clutch size received.These results indicate that females vary clutch size in relationto the males with which they are paired but that they do notfavor dominant males. Thus, male competition may normally overridefemale mate preference in zebrafish.     

Sexual behavior in brown capuchins (Cebus apella)

We observed sexual behavior patterns in two captive groups of Cebus apella.We obtained data on intersexual solicitations and intersexual competition. The length of proceptivity cycles by females averaged 18.8 ± 1.2 days; this corresponds with published reports of physiological measures of ovulatory cycles. Females initiated sexual interactions with males significantly more than males initiated interactions with females, and female solicitations increased in frequency over the duration of displayed periods of proceptivity. In contrast, male solicitations of females were infrequent and did not change significantly throughout female proceptive phases. Each female solicited the same male throughout a given proceptive phase. We observed no evidence of male-male or female-female competition. Males seem to respond to female sexual behavior directed toward them, rather than initiating sexual interactions themselves. Even so, male sexual interactions with females followed only a small proportion of solicitations.     

Female egg dumping and the effect of sex ratio on male egg carrying in a coreid bug

Phyllomorpha laciniata Vill (Heteroptera, Coreidae) is uniqueamong terrestrial insects in that females glue eggs on the backsof other conspecifics. Egg carrying byP. laciniatamales haspreviously been considered as paternal care. We explored femaleoviposition with respect to previous mating experience of femalesand tested whether sex ratio affects male egg-carrying. Thehypothesis that male egg-carrying is a form of paternal carepredicts that a male should always accept eggs after matingwith a female. However, if male egg-carrying is a form of postcopulatorymate guarding rather than paternal care, egg carrying shouldincrease in the presence of other males. When two couples wereplaced together, females laid eggs on the backs of all individualsenclosed, including the backs of other females. However, whena female was accompanied by 2 males, 22 out of 26 females ovipositedon their mating partner. Thus, sexual competition rather thanpaternity alone, affects a male's eagerness to carry eggs. However,even if males sometimes carry their own eggs, females lay eggson the backs of all conspecifics they can easily acquire. Thus,egg carrying in P. laciniata is partially voluntary and partiallythe result of female egg dumping     

Male Ornamentation in a Sex‐Role Reversed Pipefish Corythoichthys haematopterus

Sexual selection theory predicts that mating competition in sex‐role reversed animals acts more strongly on females than males and consequently females are expected to develop secondary sexual traits. However, in a sex‐role reversed pipefish Corythoichthys haematopterus (family: Syngnathidae), only males develop an ornamental trait on the thorax, consisting of approx. 3–5 speckles alternated by lateral stripes of brilliant light blue and orange. To understand the function of this male ornament, we examined whether the presence of females affects the expression of this trait, and whether the expression of this trait depends on the male’s physical condition. Individual males were reared in a tank for a month in four different conditions: in high or low food supply and in the presence or absence of a female. After 1 mo, males in better condition expressed larger and deeper blue and yellow speckles, and males maintained with a female expressed larger and deeper blue speckles than solely reared males. These results indicated that the male ornament functions as a signal conveying information on the phenotypic quality of its holder and that females are potential receivers of this signal. Because C. haematopterus exhibits strict monogamy and competition for a mate occurs only among females, we concluded that the male ornament is not displayed in the context of mating competition but rather it is used as a cue for partner recognition to maintain pair bond.     

Female discrimination thresholds frequently exceed local male display variation: implications for mate choice dynamics and sexual selection

Among the factors that can influence female mate choice decisions is the degree to which females differentiate among similar displays: as differences decrease, females are expected to eventually stop discriminating. This discrimination threshold, in conjunction with the magnitude of male trait variation females regularly encounter while making mate choice decisions, may have important consequences for sexual selection. If local display variation is above the discrimination threshold, female preferences should translate into higher mating success for the more attractive male. But if display variation is frequently below the threshold, the resulting increased pattern of random mating may obscure the existence of female mate choice. I investigated the interplay between female discrimination and male display variation in green treefrogs (Hyla cinerea) and found that call trait differences between nearest neighbour males were frequently smaller than what females are expected to discriminate. This finding has two important consequences for our understanding of sexual selection in the wild: first, low display variation should weaken the strength of selection on male display traits, but the direction of selection should mirror the one predicted from females choice trials. Second, caution is needed when interpreting data on realized mating success in the wild: a pattern of random mating with respect to male display traits does not always mean that female preferences are weak or that conditions are too challenging for females to express their preferences. Rather, insufficient display variation can generate the same pattern.