Post-conception mating in wild long-tailed macaques (Macaca fascicularis): characterization, endocrine correlates and functional significance

In many anthropoid primates, mating activity is not restricted to the ovarian cycle but also occurs during pregnancy. Although it has been suggested that the main function of this post-conception mating is to confuse paternity, studies showing whether or not male primates can distinguish between the fertile phase of the conception cycle (FPCC) and the period of peak post-conception mating (peak PCM) are almost non-existent. Here, we examine whether the pattern of female sexual traits (specific sexual behaviors, sexual swelling) and female attractiveness to males differ between FPCC and peak PCM in 6 wild female long-tailed macaques. We also use fecal hormone analysis to investigate whether female traits during peak PCM are related to changes in female sex hormones. All females exhibited a distinct period of heightened mating activity around days 45-60 of gestation. During peak PCM, swelling size and frequency of female solicitations (but not reaching back) were significantly correlated with changes in the estrogen to progestogen ratio. Swelling size, frequency of female sexual behaviors and copulations and proportion of male-initiated copulations and ejaculations were not significantly different between FPCC and peak PCM. Although males spent significantly less time consorting females during peak PCM, all (particularly low-ranking and non-resident males) invested heavily in terms of reproductive costs associated with mate-guarding and mating during pregnancy. We conclude that post-conception mating in wild long-tailed macaques is not merely a by-product of endocrine changes and devoid of adaptive function. Our results more strongly support the hypothesis that it may form part of a female reproductive strategy to confuse paternity, which appears to apply particularly to low-ranking and extra-group males.     

Female sexual behavior and sexual swelling size as potential cues for males to discern the female fertile phase in free-ranging Barbary macaques (Macaca sylvanus) of Gibraltar

Although female catarrhine primates show cyclic changes in sexual behavior and sexual swellings, the value of these sexual signals in providing information to males about timing of the fertile phase is largely unclear. Recently, we have shown that in Barbary macaques, males receive information from females which enables them to discern the fertile phase and to focus their reproductive effort accordingly. Here, we investigate the nature of the cues being used by examining female sexual behavior and the size of sexual swelling as potential indicators of the fertile phase. We collected behavioral data and quantified swelling size using digital images of 11 females of the Gibraltar Barbary macaque population and related the data to the time of ovulation and the fertile phase as determined from fecal hormone analysis. We found that rates of female sexual behaviors were not correlated with female estrogen levels and did not significantly differ between the fertile and non-fertile phases of the cycle. In contrast, swelling size was significantly correlated with female estrogen levels and increased predictably towards ovulation with size being maximal during the fertile phase. Moreover, frequencies of male ejaculatory copulations showed a strong positive correlation with swelling size and highest rates were found during maximum swelling. Our data provide strong evidence that female Barbary macaques honestly signal the probability of fertility through sexual swelling and that males apparently use this information to time their mating activities. Honest advertising of the fertile phase might be part of a female strategy to manipulate male mating behavior for their own advantage, such as ensure fertilization with high quality sperm or influence paternity outcome.     

The Role of Courtship Behavior and Size in Mate Preference in the Sex‐Role‐Reversed Gulf Pipefish,Syngnathus scovelli

In sex‐role‐reversed species, sexual selection acts more strongly on females than on males, a situation that can result in the evolution of secondary sexual traits in females and strong mating preferences in males. While some research exploring mating preferences in sex‐role‐reversed species has been conducted, overall, this topic remains relatively unexplored. The Gulf pipefish, Syngnathus scovelli, is a highly polyandrous pipefish species. Sexual selection is significantly stronger in females than in males, which has led to the evolution of both morphological and behavioral female secondary sexual traits. However, because males gestate the offspring in specialized pouches and make a substantial investment in embryos during development, females may also benefit from being choosy. The goal of this study was to examine both male and female mating preferences in this species. We found that male mating preference was significantly associated with female courtship behavior. Larger females were also able to maintain these behaviors for longer intervals than smaller females. No evidence of female mating preference in regard to male size was observed but the data suggest that male behaviors may be providing positive reinforcement to courting females. This research provides further insight into how mate preferences vary among sex‐role‐reversed species.     

Multiple Paternity in Polyandrous Barn Owls (Tyto alba)

In polyandrous species females produce successive clutches with several males. Female barn owls (Tyto alba) often desert their offspring and mate to produce a 2^nd annual brood with a second male. We tested whether copulating during chick rearing at the 1^st annual brood increases the male''s likelihood to obtain paternity at the 2^nd annual breeding attempt of his female mate in case she deserts their brood to produce a second brood with a different male. Using molecular paternity analyses we found that 2 out of 26 (8%) second annual broods of deserting females contained in total 6 extra-pair young out of 15 nestlings. These young were all sired by the male with whom the female had produced the 1^st annual brood. In contrast, none of the 49 1^st annual breeding attempts (219 offspring) and of the 20 2^nd annual breeding attempts (93 offspring) of non-deserting females contained extra-pair young. We suggest that female desertion can select male counter-strategies to increase paternity and hence individual fitness. Alternatively, females may copulate with the 1^st male to derive genetic benefits, since he is usually of higher quality than the 2^nd male which is commonly a yearling individual.     

Mating speed and the interplay between female and male courtship responses inDrosophila melanogaster (Diptera: Drosophilidae)

The objective of this study was to compare measures of general activity and sexual behavior for various genotypes within a strain of Drosophila melanogaster, which had known differences in mating speed. Three inbred lines of D. melanogaster differed significantly in mating speed when tested in female-choice and in single-pair experiments. Analyses of locomotor activity and sexual activity of females and males revealed no significant differences between the inbred lines. An analysis of the interplay between female and male courtship behaviors enabled the examination of signal-response differences between the inbred lines. The inbred lines with intermediate and slow mean mating speed showed a decreased number of significant transitions between female and male behavioral responses. This decrease was more severe in the slow mating line. Further, the intermediate- and slow-mating females and males displayed courtship responses toward signals of the opposite sex that were different from those of the fastmating line. Models of the relationship between behavioral activity and mating speed in Drosophila are discussed and a different explanation for variation in mating speed among the three inbred lines is considered.     

Relationship between sexual interactions and the timing of the fertile phase in captive female Japanese macaques (Macaca fuscata)

Japanese macaques live in multi‐male/multi‐female social groups in which competition between males, female mate choice, and alternative male mating strategies are important determinants of mating and reproductive success. However, the extent to which adult males rely on female behavior to make their mating decisions as well as the effect of social rank on mating success are not clear as results are inconclusive, varying from study to study. In this study, we combined behavioral and endocrine data of 14 female Japanese macaques to examine the relationship between ovarian cycle phase and frequency of sexual behaviors, and to investigate how social rank influences sexual behavior in this species. We found that there was no increase in female proceptive behaviors during the fertile phase of the ovarian cycle, suggesting that female behaviors did not clearly signal the probability of conception. In spite of that, the frequencies of ejaculatory copulations were highest during this phase, indicating that the attractivity of females increased significantly during the period with higher probability of conception. Males, and especially the highest ranking male, were able to discriminate females nearing ovulation and to concentrate their mating effort, implying that the timing of ovulation was not concealed from them. The α male seemed able to monopolize most female matings, which is probably due in part to the low number of females simultaneously ovulating and to the limited number of inconspicuous places that the lower ranking males have to mate with females and avoid α male aggression. All together, these results suggest that different males may have access to different signals of ovulation and/or are differentially restrained as to how they can act on that information. The exact nature of the estrogen‐related cues males use to recognize female reproductive status, and to what extent males use them warrants further investigation. Am. J. Primatol. 71:868–879, 2009. © 2009 Wiley‐Liss, Inc.     

Female Preference for Sympatric vs. Allopatric Male Throat Color Morphs in the Mesquite Lizard (Sceloporus grammicus) Species Complex

Color polymorphic sexual signals are often associated with alternative reproductive behaviors within populations, and the number, frequency, or type of morphs present often vary among populations. When these differences lead to assortative mating by population, the study of such polymorphic taxa may shed light on speciation mechanisms. We studied two populations of a lizard with polymorphic throat color, an important sexual signal. Males in one population exhibit orange, yellow, or blue throats; whereas males in the other exhibit orange, yellow, or white throats. We assessed female behavior when choosing between allopatric and sympatric males. We asked whether females discriminated more when the allopatric male was of an unfamiliar morph than when the allopatric male was similar in coloration to the sympatric male. We found that female rejection of allopatric males relative to sympatric males was more pronounced when males in a pair were more different in throat color. Our findings may help illuminate how behavioral responses to color morph differences between populations with polymorphic sexual signals contribute to reproductive isolation.     

Sociosexual behavioral patterns involving nulliparous female orangutans (Pongo sp.) reflect unique challenges during the adolescent period

The primate adolescent period is characterized by a series of changes in physiology, behavior, and social relationships. Orangutans have the slowest life history and the longest period of dependency of all primates. As members of a semisolitary species with high levels of sexual coercion, adolescent female orangutans face a unique combination of challenges when achieving independence from their mother. This study examined the mating behavior of adolescent female orangutans and compared it with that of adult females to assess whether mating behavior reflects distinct strategies at these different points in the life cycle. Data were collected in Gunung Palung National Park on the island of Borneo over 20 years. Mating events from adolescent (n = 19) and adult females (n = 26) were scored and compared. Adolescent female mating events had significantly higher mating scores (indicating more proceptivity) than those of adult females (β = 1.948, p = .001). Adolescent females also engaged in elaborate sociosexual interactions with different flanged males, behaviors that were never observed during mating events of adult females. These interactions involved characteristic behavior on the part of both the adolescent females and the flanged males. Given these findings and the documentation of similar accounts of adolescent female–flanged male mating from the island of Sumatra, we propose that adolescent female orangutans display distinctive behavioral repertoires throughout the genus Pongo which serves to overcome male ambivalence toward nulliparous females, establish familiarity, and evaluate coercive tendencies in flanged males. We suggest that these behavioral patterns are an integral part of female social development in a female philopatric, but highly dispersed species where consistent social support is absent after ranging independence is achieved.     

Female behavioral strategies during consortship in Tibetan macaques (Macaca thibetana)

Consortship has been defined as a temporary association between an adult male and an estrous/receptive female. It has been considered as male mating strategies to improve male mating success and potential reproductive success. However, the female roles have been more or less neglected, and thus, less is known about female behavioral strategies during the consortship periods. In this study, during the two consecutive mating seasons, we collected behavioral data of free‐ranging Tibetan macaques (Macaca thibetana) habituated in Mt. Huangshan, China, to investigate female behaviors when she was consorted by an adult male. The results showed that (a) females were more likely to approach and exhibit sexual solicitation to their consorting males during the consorted period, and females also exhibited less approach to their nonconsorting males; (b) females exhibited strong responses (either departed distantly or formed affiliative relationships with their consorting male partner) when their consorting males mated with rival females or showed sexual motivation toward rival females; (c) female preferences were positively correlated to the duration of consortships and the frequencies of ejaculation copulations, independent of the social ranks of their consorting male partners. Our results suggested that female strategies played much more important roles in forming and maintaining consortship than previously assumed. It provides new insight into understanding female adaptive strategies to male strategies by forming consortships in multimale–multifemale primate species when males could not identify female''s fertile phase accurately.     

Divergent male and female mate preferences do not explain incipient speciation between lizard lineages

Diversification in sexual signals is often taken as evidence for the importance of sexual selection in speciation. However, in order for sexual selection to generate reproductive isolation between populations, both signals and mate preferences must diverge together. Furthermore, assortative mating may result from multiple behavioral mechanisms, including female mate preferences, male mate preferences, and male–male competition; yet their relative contributions are rarely evaluated. Here, we explored the role of mate preferences and male competitive ability as potential barriers to gene flow between 2 divergent lineages of the tawny dragon lizard, Ctenophorus decresii, which differ in male throat coloration. We found stronger behavioral barriers to pairings between southern lineage males and northern lineage females than between northern males and southern females, indicating incomplete and asymmetric behavioral isolating barriers. These results were driven by both male and female mate preferences rather than lineage differences in male competitive ability. Intrasexual selection is therefore unlikely to drive the outcome of secondary contact in C. decresii, despite its widely acknowledged importance in lizards. Our results are consistent with the emerging view that although both male and female mate preferences can diverge alongside sexual signals, speciation is rarely driven by divergent sexual selection alone.     

Sexual signalling in female crested macaques and the evolution of primate fertility signals

ABSTRACT: BACKGROUND: Female signals of fertility have evolved in diverse taxa. Among the most interesting study systems are those of multimale multifemale group-living primates, where females signal fertility to males through multiple signals, and in which there is substantial inter-specific variation in the composition and reliability of such signals. Among the macaques, some species display reliable behavioural and/or anogenital signals while others do not. One cause of this variation may be differences in male competitive regimes: some species show marked sexual dimorphism and reproductive skew, with males fighting for dominance, while others show low dimorphism and skew, with males queuing for dominance. As such, there is variation in the extent to which rank is a reliable proxy for male competitiveness, which may affect the extent to which it is in females' interest to signal ovulation reliably. However, data on ovulatory signals are absent from species at one end of the macaque continuum, where selection has led to high sexual dimorphism and male reproductive skew. Here we present data from 31 cycles of 19 wild female crested macaques, a highly sexually dimorphic species with strong mating skew. We collected measures of ovarian hormone data from faeces, sexual swelling size from digital images, and male and female behaviour. RESULTS: We show that both sexual swelling size and female proceptivity are graded-signals, but relatively reliable indicators of ovulation, with swelling size largest and female proceptive behaviours most frequent around ovulation. Sexual swelling size was also larger in conceptive cycles. Male mating behaviour was well timed to female ovulation, suggesting that males had accurate information about this. CONCLUSION: Though probabilistic, crested macaque ovulatory signals are relatively reliable. We argue that in species where males fight over dominance, male dominance rank is surrogate for competitiveness. Under these circumstances it is in the interest of females to increase paternity concentration and assurance in dominants beyond levels seen in species where such competition is less marked. As such, we suggest that it may be variation in male competitive regimes that leads to the evolution of fertility signalling systems of different reliability.     

Male mate choice in a sexually cannibalistic species: male escapes from hungry females in the praying mantid <Emphasis Type="Italic">Tenodera angustipennis</Emphasis>

While competing males and choosy females may be common in animal mating systems, male choice can evolve under certain conditions. Sexual cannibalism is such a condition because of the high mortality risk for males. In mantids, female body condition is associated with male mate preference, with fat females preferred, due to at least two reasons: females in poor nutritional condition are likely to attack and predate males, and fat females can potentially increase the number of offspring. Thus, the risk of cannibalism and female fecundity can influence male mating behavior. In this study, we attempted to separate these factors by using the praying mantid Tenodera angustipennis to examine whether male preference for fat female mantids was based on avoiding sexual cannibalism (cannibalism avoidance hypothesis) or preference for female fecundity (fecundity preference hypothesis). The feeding regimes were experimentally manipulated to discriminate between the effects of female fecundity and female hunger status on male and female mating behaviors. We found that recently starved females more frequently locomoted toward the male, and that male abdominal bending was less intensive and escape was sooner from recently starved females. These female and male behavioral responses to female hunger condition may reveal male avoidance of dangerous females in this mantid.     

Costs of Mate Guarding and Opportunistic Mating Among Wild Male Japanese Macaques

A trade-off relationship between mating and feeding effort is important when considering reproductive strategies of long-lived species. I compared the influence of male sexual activities, female mate-choice behaviors and the daily activity budget on male mating success among males in a group of wild Japanese macaques (Macaca fuscata yakui) on Yakushima Island. The 1st-ranking male, which had immigrated into the troop at this rank, more frequently approached peri-ovulatory females, spent more time grooming peri-ovulatory females and in mounting series and spent less time feeding than subordinate males did. The 1st-ranking male attained the highest mating success as a result of his high expenditure of time and energy in sexual behaviors directed toward peri-ovulatory females. Mating success of subordinate males did not relate to the amount of sexual effort, but instead to the frequency of female approaches, female rush toward males and the number of peri-ovulatory females within the group. The pattern of intermale competition shifted from nearly contest competition to scramble competition as the number of peri-ovulatory females in the group increased. Feeding time of subordinate males did not vary between the days when they copulated and the days when they did not. The findings demonstrate that mate guarding in the 1st-ranking male is a high-cost mating tactic, while opportunistic mating in subordinate males is a low-cost mating tactic. The differences in male mating tactics are probably related to male life history and to the formation of groups with a high socionomic sex ratio.     

Mating increases male's interest in other females: a cognitive study in socially monogamous prairie voles (Microtus ochrogaster)

To determine whether socio-sexual interactions with females influence the male prairie vole's cognitive processing, three groups of males were simultaneously exposed to sensory stimuli of a control and a focal female then tested for their behavioral and neuronal responsiveness to the female cues. From the control female, all males received distal cues. From the focal female, the Unmated males received distal cues, the Unmated-Contact males received all cues but did not mate with her, and the Mated-Contact males received all cues and mated with her. Males were tested for their attentiveness to enclosures holding each female and for their memory of the females’ previous location. Males’ brains were then examined to localize activated regions following exposure to the odor of familiar versus unfamiliar focal females. The Mated-Contact males spent more time in the cage of the control female attending to her enclosure than in the cage of the focal female. Exposure to odors of unfamiliar focal females activated the cingulate cortex of Unmated-Contact males. There was a negative correlation between the level of neuronal activation in the retrosplenial cortex of males that were exposed to the odors of a familiar focal female and their attentiveness to the enclosure of the control female. The data suggest that the effect of socio-sexual interactions with a female on males’ cognition depends on the type of sensory signals males receive from females and how individual males perceive those signals.     

Female Choice or Male Sex Drive? The Advantages of Male Body Size during Mating in Drosophila Melanogaster

The mating success of larger male Drosophila melanogaster in the laboratory and the wild has been traditionally been explained by female choice, even though the reasons are generally hard to reconcile. Female choice can explain this success by virtue of females taking less time to mate with preferred males, but so can the more aggressive or persistent courtships efforts of large males. Since mating is a negotiation between the two sexes, the behaviors of both are likely to interact and influence mating outcomes. Using a series of assays, we explored these negotiations by testing for the relative influence of male behaviors and its effect on influencing female courtship arousal threshold, which is the time taken for females to accept copulation. Our results show that large males indeed have higher copulation success compared to smaller males. Competition between two males or an increasing number of males had no influence on female sexual arousal threshold;—females therefore may have a relatively fixed ‘arousal threshold’ that must be reached before they are ready to mate, and larger males appear to be able to manipulate this threshold sooner. On the other hand, the females’ physiological and behavioral state drastically influences mating; once females have crossed the courtship arousal threshold they take less time to mate and mate indiscriminately with large and small males. Mating quicker with larger males may be misconstrued to be due to female choice; our results suggest that the mating advantage of larger males may be more a result of heightened male activity and relatively less of female choice. Body size per se may not be a trait under selection by female choice, but size likely amplifies male activity and signal outputs in courtship, allowing them to influence female arousal threshold faster.     

Cuticular lipids and odors induce sex-specific behaviors in the male cricket Gryllus bimaculatus

Male crickets display sex-specific (e.g., mating and agonistic) behaviors towards conspecific individuals. One of the key signals for these behaviors is the chemical substance on the cricket body surface. In the present study, we analyzed female and male cuticular substances in behavioral assays. Antennal contact stimulation using female forewings elicited a mating behavior in males, while that using male forewings elicited an agonistic behavior in males. Thin-layer-chromatographic and other techniques analysis showed that saturated cuticular lipids were present in both female and male cuticles and that unsaturated lipids were present only in the male cuticle. Filter papers soaked with saturated or unsaturated cuticular lipids were applied to antennae of male crickets. Males showed mating behavior in response to stimulation with saturated lipids from both females and males but showed avoidance behavior in response to stimulation with male unsaturated lipids. Because cuticular lipids did not induce agonistic behavior in males, we collected odors from male crickets and found that these odors induced agonistic behavior in males. Therefore, we concluded that the key signals for mating, avoidance and agonistic behaviors of male crickets are comprised of at least three different components, saturated and unsaturated cuticular lipids and male odors, respectively.     

Functional significance of behavioral,morphological, and endocrine correlates across the ovarian cycle in semifree ranging female Tonkean macaques

The role of sexual displays in mating strategies and their reliability in indicating the time of ovulation has given rise to multiple explanations in nonhuman primates. In order to discriminate among hypotheses, socio-sexual behaviors were recorded in a semifree ranging group of Tonkean macaques (Macaca tonkeana), together with sexual skin swelling volumes and measurements of urinary concentrations of estrone conjugates and pregnanediol glucuronide. A clear preovulatory peak of urinary estrogen levels occurred 2 days before a defined rise in pregnanediol glucuronide concentrations, indicating that both hormones pointed out the female's ovulatory period. The concept of estrus rightly could be applied to female Tonkean macaques since fluctuations in estrogen levels correlated with cyclic changes in genital swelling sizes and rates of female behavioral attractivity and proceptivity. Males proved to be capable of recognizing the optimal conception period as judged from the occurrence of maximal rates of following behavior, serial matings, and ejaculations during the peri-ovulatory phase. During this time, males succeeded in maintaining exclusive and enduring associations with females. However, consortships occurred precociously, with males starting to affiliate with females, follow, and mount them 1 week before the presumed time of ovulation. These long-lasting consortships appear to be a consequence of the female extended follicular phase. This presumably sexually selected character allowed females to extend conspicuous sexual displays: genital swelling and utterance of an estrous call, which might attract males' attention and arouse them. With regard to female mating tactics, the combination of reliably indicating the time of ovulation to the male and durable periods of competitor exclusion led to reject explanations assuming manipulation about paternity or long-lasting intermale competition incitement in Tonkean macaques. Competition for mates between females also turned out to be an irrelevant factor as it was very low in the species. We conclude that the main function of sexual displays is to herald the approach of ovulation toward available mates. Am. J. Primatol. 46:285–309, 1998. © 1998 Wiley-Liss, Inc.     

A comparison of the mating behavior of adolescent and adult female rhesus macaques (Macaca mulatta)

This study compares adult and adolescent female rhesus macaques with regard to (1) characteristics of their copulatory partners, (2) their proceptive behaviors, and (3) adult male behaviors toward them during estrus. We conducted focal follows of 24 adolescent and 65 adult free-ranging estrous female rhesus macaques on Cayo Santiago during two mating seasons. Compared to adult females, adolescents presented sexually to males at higher rates; copulated more frequently with rankless young male, and extra-group males; and, in one of two mating seasons, were ignored more frequently by males to whom they presented sexually. Adolescents tended to copulate with ranked, resident males at higher frequencies on days when the operational sex ratio (adult males:estrous adult females) was high. Males directed “muzzle-up” signals to adolescents at lower rates than to adults in one of two mating seasons, although this effect vanished when males who might have fathered adolescent females were excluded from analysis. Adolescents did not differ consistently from adults in strength of the correlation between proximity maintenance (dyadic Hinde's Index) and copulation rate, or in approach rate to males. Adolescent females, relative to adult females, presented sexually more to rankless young males, but did not present more to ranked, resident males. Both proximate (e.g. endocrine) and ultimate (e.g. differential fecundity; female-female mate competition) explanations may account for the reported differences between adult and adolescent female rhesus macaque sexuality.     

Testing for Links Between Female Urine Odor and Male Sexual Behaviors in Japanese Macaques (<Emphasis Type="Italic">Macaca fuscata</Emphasis>)

Urine is involved in sexual communication in New World monkeys and lemurs, but most studies of the role of olfaction in sexual communication in Old World monkeys have focused on vaginal secretions rather than urine. We investigated whether female urine promotes male sexual behaviors (approaches and inspections of genital area) in Japanese macaques (Macaca fuscata). We used a sequential presentation paradigm in behavioral experiments, presenting unfamiliar female urine and control cotton swabs to males living in a social group with cycling females. We tested whether males (N = 3) showed more processing behaviors (licking, sniffing, tasting) toward female urine (22 stimuli per male from prefertile, fertile, and postfertile phases, based on urinary estrone and progesterone conjugate profiles) than control odor (8 stimuli per male). We then compared male sexual behaviors toward resident females pre- and post-exposure to stimuli and in relation to the females’ reproductive status (perifertile, nonfertile, and pregnancy periods, based on fecal estrone and progesterone conjugate profiles). We found that males showed significantly more processing behaviors toward urine stimuli than to controls but that male behavior did not vary across urine samples from prefertile, fertile, and postfertile phases. Exposure to unfamiliar female urine stimuli did not modulate male approaches to and inspections of resident females at any stage of the female reproductive cycle. Although our study is limited by its small sample size, the results suggest that female urine contains compounds that males detect, but we found no evidence that female urine is related to male sexual behaviors.     

Sexual signals and mating patterns in Syngnathidae

Male pregnancy in the family Syngnathidae (pipefishes, seahorses and seadragons) predisposes males to limit female reproductive success; sexual selection may then operate more strongly on females and female sexual signals may evolve (sex-role reversal). A bewildering array of female signals has evolved in Syngnathids, e.g. skin folds, large body size, colouration, markings on the body and elaborate courtship. These female sexual signals do not seem quantitatively or qualitatively different from those that evolve in males in species with conventional sex roles where males provide females or offspring with direct benefits. In several syngnathid species, males also evolve ornaments, females are choosy in addition to being competitive and males compete as well as choosing partners. Thus, sex roles form a continuum, spanning from conventional to reversed within this group of fishes. Cases are presented here suggesting that stronger sexual selection on females may be most extreme in species showing classical polyandry (one male mates with several females, such as many species where males brood their eggs on the trunk), intermediate in polygynandrous species (males and females both mate with more than one partner, as in many species where males brood their eggs on the tail) and least extreme, even exhibiting conventional sex roles, in monogamous species (one male mates solely with one female, as in many seahorses and tropical pipefishes). At the same time caution is needed before unanimously establishing this pattern: first, the connection between mating patterns, strength of sexual selection, sex roles and ornament expression is far from simple and straightforward, and second, knowledge of the actual morphology, ecology and behaviour of most syngnathid species is scanty. Basically only a few Nerophis, Syngnathus and Hippocampus species have been studied in any detail. It is known, however, that this group of fishes exhibits a remarkable variation in sex roles and ornamentation, making them an ideal group for the study of mating patterns, sexual selection and sexually selected signals.