Duration of courtship effort as a costly signal

We consider a male and a female in a courtship encounter over continuous time. Both parties pay participation costs per unit time. The game ends when either one or other of the parties quits or the female accepts the male as a mate. We assume that there is a binary variable which determines whether the male is a “good” or “bad” type from the female's point of view, according to either his condition or his willingness to care for the young after mating. This variable is not directly observable by the female, but has fitness consequences for her: she gets a positive fitness payoff from mating with a “good” male but a negative fitness payoff from mating with a “bad” male. We assume also that a “good” male has a higher ratio of fitness benefit from mating to fitness cost per unit time of courtship than a “bad” male. We show that, under suitable assumptions, there are evolutionarily stable equilibrium behaviours in which time-extended courtship takes place. A “good” male is willing to court for longer than a “bad” male; in this way the duration of a male's courtship signals his type, and acts as a costly handicap. By not being willing to mate immediately the female achieves a degree of screening because the posterior probability that the male is “good”, conditional on his not having quit the game, increases with the duration of courtship.     

Testosterone control of male courtship in birds

A sequence of behaviours which we call courtship initiates reproduction in a large number of species. In vertebrates, as a component of male sexual behaviour courtship is strongly influenced by testicular androgen. Here I will review some salient issues about the regulation of courtship by testosterone in birds. The first section will briefly summarize the first 100 years of research on this topic. The specific role of testosterone or its oestrogenic metabolites in the control of different components of courtship will be the subject of the second section. Then, I will discuss how behavioural patterns can be recruited into courtship and modified in their structure by testosterone action. In the following section, the role of sexual selection and female choice in shaping the link between testosterone and courtship will be addressed. The problematic nature of the quantitative relationships between testosterone and behaviour will be topic of the fifth section. Finally, I will discuss how courtship traits that are activated by testosterone can be apparently independent of hormone blood concentrations. These issues will be examined in an evolutionary perspective, in an attempt to understand how natural and sexual selection have shaped the links between the hormone and the behaviour.     

Female preference of the gobiid fish Eviota abax in relation to elongation of the first dorsal spine in males

The significance of elongation of the first and second spines of the first dorsal fin in male Eviota abax (Gobiidae) was examined in relation to female preference. Reproductive behavior occurred in three phases: male approach to female home, male leading female to nest, and male entering nest. During each phase, the female either accompanied the male or departed. The ratio of positive female mating responses to males before the elongated male dorsal spines were clipped and thereafter was compared in an aquarium. Females preferred male elongated spines in the first phase of courtship, but not in the second phase . Because females may be more exposed to predators during the second phase, owing to conspicuous male courtship, their greater receptivity to elongated dorsal spines in the first phase may decrease predation pressures during subsequent phases of courtship. Electronic Publication     

Resource-dependent nuptial feeding in Panorpa vulgaris: an honest signal for male quality

In mating systems that are characterized by resource-dependentmale behavior like nuptial feeding, food limitation obviouslyplays a major role in male performance. In Panorpa vulgaris(Mecoptera: Panorpidae), the ability to produce nuptial giftshas major fitness consequences as the number of gifts determinescopulation duration, which then determines the number of eggsfertilized by a given male. In the present study, we are ableto show that males of P. vulgaris were limited in their productionof salivary secretions. The number of saliva secretions maleswere able to produce declined in successive matings. Moreover,males of nutritionally high status produced more gifts thanthose of nutritionally low status. The proximate factor determiningmale saliva secretion was the development of the salivary gland,which in turn depended on the amount of food a male could access.The degree of male mating effort corresponded to the size ofthe salivary gland, yet while absolute investment increasedwith gland size, the relative investment decreased. Mating costsfor males thus depend on nutritional status.     

Female preference for male courtship flashes in Photinus ignitus fireflies

In Photinus fireflies, males produce spontaneous bioluminescentcourtship flashes. Females preferentially respond to particularmale flashes with flashes of their own. This study exploredvariation in female flash responsiveness as a function of maleflash duration, female condition, lantern size, and lanterndistance, as well as the relationship between male characteristicsand spermatophore mass in Photinus ignitus fireflies. We determinedfemale preference by scoring female flash response to simulatedmale flashes and determined variation in overall female flashresponsiveness for laboratory-mated, laboratory-fed, and controlP. ignitus females. Flash duration, lantern size, and body masswere recorded for field-collected males. Males were then matedto determine spermatophore mass. Females exhibited greater preferencefor artificial flashes representing the upper range of conspecificmale flash duration and lantern size as well as flashes producedat a closer distance. Both laboratory-mated and laboratory-fedP. ignitus females showed lower overall responsiveness acrossall flash durations relative to control females that did notmate or feed in the laboratory. Male flash duration predicteda significant proportion of the variation in spermatophore massfor early-season males. These results suggest that female Photinusignitus may prefer long flashes in order to obtain the directbenefit of larger spermatophores and may adjust their overallflash responsiveness as the relative importance of this benefitvarieswith changing female condition.     

Structurally based plumage coloration is an honest signal of quality in male blue grosbeaks

We investigated the signaling function of blue plumage in maleblue grosbeaks (Guiraca caerulea) to determine if structurallybased coloration may act as a reliable signal of quality toconspecifics. Blue plumage results from the microstructureof feather barbules rather than from pigment granules, andthus it is possible that structurally based plumage ornamentsmay function differently from sexually selected ornamental coloration that is pigment based. The plumage of male blue grosbeaksreflects maximally in the blue-ultraviolet range, so most variationin plumage coloration among males is invisible to human observers.In previous research, we showed that increased area of blueplumage on the body is associated with a shift in the wavelengthof maximum feather reflectance toward the ultraviolet and withhigh intensity of light reflected at that maximum, and thatextreme expression of the male ornament is condition dependent.These observations suggest that blue plumage may be an honestadvertisement of male quality. We tested this hypothesis ina wild population of blue grosbeaks. We quantified male qualityin three broad categories. (1) Physical condition was assessed from subcutaneous fat deposits, ectoparasite load, and bodysize. (2) Territory quality was assessed from territory area,prey abundance, and predation risk. (3) Paternal investmentwas assessed from male feeding rate. We found that the bluestmales have the largest body size, maintain the largest territorieswith the greatest prey abundance, and feed nestlings in thefirst nest of the season at the highest rates. We conclude that structurally based plumage coloration functions as an honest,intraspecific signal of quality.     

Female mate preference based on male orange spot patterns in the feral guppy <Emphasis Type="Italic">Poecilia reticulata</Emphasis> in Japan

It is known that females prefer males with larger and/or brighter orange spots in many populations of the guppy Poecilia reticulata. However, female preference for male orange spots varies among populations and changes within several years when they are introduced into new habitats with different environment. Guppies were introduced into Okinawa, Japan, more than 20 years ago and were subjected to natural and sexual selection for a long period. The female preference for orange spot patterns of males was examined by the dichotomous choice experiment for a feral guppy population of the Hiji River, Okinawa. We chose full-sibling males as a pair of stimulus males that were simultaneously presented to a test female, because sibling males should resemble each other. To create different orange spot patterns between stimulus males, one male of the stimulus male pair was fed carotenoid-supplement food such as algae and another male was fed low-carotenoid food. High-carotenoid-treatment males showed not only brighter coloration of orange spots but also larger spots than other males as a result of this dietary-manipulation. In the dichotomous choice experiment, females preferred the high-carotenoid-treatment males. In addition, logistic regression analysis clarified that brighter coloration of male orange spots was the most important factor for female mate preference. This finding suggests indirect benefits of female preference for male orange spot patterns if the male foraging ability for algae were heritable.     

Song as an honest signal of developmental stress in the zebra finch (Taeniopygia guttata)

In a wide range of bird species, females have been shown to express active preferences for males that sing more complex songs. Current sexual selection theory predicts that for this signal to remain an honest indicator of male quality, it must be associated with an underlying cost of development or maintenance. There has been considerable debate questioning the costs associated with song production and learning. Recently, the nutritional stress hypothesis proposed that song complexity could act as an indicator of early developmental history, since the song control nuclei in the brain are laid down early in life. Here we test the nutritional stress hypothesis, by investigating the effects of dietary stress on the quality of adult song produced. In addition, we tested the effects of elevated corticosterone during development on song production to test its possible involvement in mediating the effects of developmental stress. The results demonstrate that both dietary restriction and elevated corticosterone levels significantly reduced nestling growth rates. In addition, we found that experimentally stressed birds developed songs with significantly shorter song motif duration and reduced complexity. These results provide novel experimental evidence that complex song repertoires may have evolved as honest signals of male quality, by indicating early developmental rearing conditions.     

Female choice via indicator traits easily evolves in the face of recombination and migration

Species that exist in heterogeneous environments experience selection for specialization that is opposed by the homogenizing forces of migration and recombination. Migration tends to reduce associations between alleles and habitats, whereas recombination tends to break down associations among loci. The idea that heterogeneity should favor the evolution of isolating mechanisms has motivated evolutionary studies of reduced migration, habitat preference, and assortative mating. However, costly female choice of high-quality males can also evolve in heterogeneous populations and is not hindered by either recombination or migration. When information on male fitness is available through indicator traits, female choice based on these traits increases associations between female choice alleles and locally adapted alleles. Not only does female choice evolve in a heterogeneous environment, it acts to enhance the level of genetic variation and is thus self-reinforcing. The amount of female choice at equilibrium depends on how well mixed the habitats are, how much information on male genotype is available, and how different the habitats are. Female choice reaches the highest levels for intermediate levels of heterogeneity, because at such levels of heterogeneity there is both a high risk and high cost of mismating.     

Male courtship attractiveness and paternity success in Photinus greeni fireflies

Although female mate choice and male sperm competition have separately attracted much attention, few studies have addressed how precopulatory and postcopulatory episodes of sexual selection might interact to drive the evolution of male traits. In Photinus fireflies, females preferentially respond to males based on their bioluminescent courtship signals, and females gain direct benefits through male nuptial gifts acquired during multiple matings over several nights. We experimentally manipulated matings of P. greeni fireflies to test the hypothesis that postcopulatory paternity success might be biased toward males that are more attractive during courtship interactions. We first measured male courtship attractiveness to individual females using field behavioral assays. Females were then assigned to two double-mating treatments: (1) least attractive second male-females were first mated with their most attractive male, followed by their least attractive male, or (2) most attractive second male-females mated with males in reverse order. Larval offspring produced by each female following these double matings were genotyped using random amplified polymorphic DNA (RAPD) markers, and male paternity was determined. Contrary to prediction, firefly males that were more attractive to females based on their bioluminescent courtship displays subsequently showed significantly lower paternity, reflecting possible male trade-offs or sexual conflict. Differences in male paternity were not related to male body condition, testes or accessory gland mass, or to variation in female spermathecal size. Additionally, this study suggests that changes in phenotypic selection gradients may occur during different reproductive stages. These results indicate that it is crucial for future studies on sexual selection in polyandrous species to integrate both precopulatory and postcopulatory episodes to fully understand the evolution of male traits.     

Phenotypic correlates of male reproductive success in western gorillas

Sexual selection is thought to drive the evolution of sexually dimorphic traits that increase male reproductive success. Despite a large degree of sexual dimorphism among haplorhine primates, phenotypic traits that may influence the reproductive success of males are largely unstudied due to long life spans and the difficulties in quantifying such traits non-invasively. Here we employ digital photogrammetry of body length and crest size, as well as ranking of the gluteal muscle size, to test whether these sexually dimorphic traits are associated with long-term measures of male reproductive success in western gorillas. Among 19 adult male gorillas monitored for up to 12.5 years, we found that all three phenotypic traits were positively correlated with the average number of mates per male, but only crest size and gluteal muscle size were significantly correlated with offspring survival and the annual rate of siring offspring that survive to weaning age. We discuss why such sexually dimorphic traits might be under ongoing selection in gorillas and other species.     

Courtship as an honest indicator of male parental quality in the bicolor damselfish, Stegastes partitus

Previous work on the bicolor damselfish, a species with exclusivemale parental care of eggs, suggested that female mate choicewas based on male characteristics. The aims of this study wereto determine whether females discriminate among potential mateson the basis of courtship and, if so, to determine whether courtshipserves as an indicator of male parental quality. Observationsmade over two reproductive cycles showed that courtship ratesand mating success of individual males are positively correlatedand that males begin courting several days before females beginlaying eggs. Experimental manipulations showed that a male'scourtship rate is indicative of the subsequent egg survivalfrom his nest. We suggest that observed differences betweenmales in their courtship rates and parental ability may be aresult of differences in their energy reserves. These resultsdemonstrate the operation of honest advertising and lend supportto adaptive models of sexual selection. [Behav Ecol 1991;2:295–300]     

Calling is an honest indicator of paternal genetic quality in poison frogs

Several competing hypotheses have been put forward to explain why females of many species mate preferentially with males possessing the most conspicuous signals (e.g., ornaments, displays, or songs). We performed a laboratory experiment using two species of poison frogs, Dendrobates leucomelas and Epipedobates tricolor, to test the hypothesis that male calling performance is an honest indicator of parental quality. Our analyses are based on data from behavioral observations of mating activities of captive-reared individuals (and their offspring) that were housed in terraria for four consecutive breeding seasons. Male mating success increased with male calling rate and chirp duration in both species, suggesting that females preferred males with more elaborate calls. Because calling performance improved with age in D. leucomelas, female poison frogs that prefer males with more elaborate calls in the wild may end up mating with older males that have already proven their ability to survive. Females that mated with good callers obtained higher quality offspring. Eggs fertilized by males with high calling rates and long chirp durations had higher hatching success and produced tadpoles that were more likely to metamorphose into surviving frogs. As a consequence, females that mated with males with high calling performance obtained more surviving offspring per egg, compared to females that mated with poor callers. Collectively, our findings comply with the notion that female poison frogs prefer to mate with good callers because calling performance is a reliable predictor of offspring quality. The possible influence of maternal allocation and reasons for the strong effect size compared to previous studies are discussed.     

Female alternative reproductive behaviors: the effect of female group size on mate assessment and copying

Extensive theoretical and empirical research has focused on male alternative reproductive tactics. In comparison, female alternative tactics have attracted little attention, and further theoretical and empirical research are needed. Using a game theoretical model, we examine female choice alternatives (1) by considering assessment errors in a novel and more realistic manner than done previously, and (2) for the first time, by highlighting the formation of groups of females as an important consequence of copying behavior. We consider two alternatives: direct assessment of male quality by females and female copying of the choice of other females. Assessment and copying are predicted to coexist under a wide variety of circumstances and copying is favored when females make assessment errors, when high-quality males are either common or very rare, and when female fitness declines with the number of other females choosing the same male. We also find that the frequency of copying at equilibrium is predicted to decrease when the presence of other females mating with the same male has a positive effect on female fitness (e.g. through increased male parental effort, decreased predation risk or cooperation among females). Female alternative choice tactics also influence the potential for sexual selection. In our model, when the frequency of copying females is low, the potential for sexual selection can be higher than in the absence of female copying. However, contrary to previous theory, we find that as copying females become more common than assessing females, the potential for sexual selection will be low as more females copy the mate choice of other copiers without assessment.     

Female tail wagging enhances sexual performance in male goats

Preference testing has shown that sexually experienced male goats choose females that are tail wagging, a behavior that may function as both attractivity and proceptivity, over those that are not. We hypothesized that exposure to females expressing high rates of tail wagging would arouse males, increasing sexual performance. Tail wagging rate could be manipulated because we have shown previously that flutamide treatment increases the frequency of tail wagging in estrous goats. Sexually experienced males observed different stimuli for 10 min before a 20 min sexual performance test (SPT). The stimuli were an empty pen (MT), or groups of three females that were all estrous (E), non-estrous (NE), estrous + flutamide (E_F) or non-estrous + flutamide (NE_F). During the stimulus observation period, tail wagging was recorded. During SPT, frequencies and latencies of sexual behaviors were recorded. E_F females displayed the most tail wagging. Viewing E_F females before SPT increased the number of ejaculations attained by males and decreased the latencies to first and second ejaculation, as well as the inter-ejaculatory interval. Viewing estrous females (E and E_F) before SPT decreased the latency to first mount, as compared to non-estrous females (NE and NE_F). We conclude that male goats are sexually aroused by tail wagging. This study and previous work demonstrate that tail wagging functions as both attractivity and proceptivity in goats.     

Menstrual cycle phases and female receptivity to a courtship solicitation: an evaluation in a nightclub

Previous research has demonstrated that female behaviors toward men or sexual interest are different across the menstrual cycle. However, women's receptivity to an explicit courtship solicitation still remained in question. In a field experiment, 20-year-old women were approached by 20-year-old male confederates in nightclubs and solicited to dance during the period when slow songs were played. A survey was administered to the women in order to obtain information about the number of days since the onset of previous menses. It was found that women in their fertile phase agreed more favorably to the dance request than women in their luteal phase or in their menstrual phase.     

Female sexual swelling size, timing of ovulation, and male behavior in wild West African chimpanzees

Conspicuous swellings of the perineal skin can be observed in females of many catharrine primate species particularly during the middle stages of the ovarian cycle. The functional significance of this trait remains poorly understood. Recently, two hypotheses, the "reliable indicator" hypothesis and the "graded signal" hypothesis that take into account not only the pattern but also the exaggerated size of sexual swellings, have gained attention. Here we test several predictions made by these hypotheses by combining (i) direct size measures (from video captures) of female sexual swellings with (ii) urinary hormone data to indicate timing of ovulation through enzyme immunoassay measurements of estrone conjugates and pregnanediol glucuronide (PdG) and (iii) behavioral observations of male mating efforts throughout 36 ovulatory cycles in 12 wild chimpanzees. We are able to show that (i) even within the traditionally defined maximum swelling period, further slight increases in swelling size indicate approaching ovulation, and (ii) that male mating interest changes according to the changes in swelling size. Furthermore, absolute swelling size during the periovulatory period increases and the alpha male associates more with females as the number of cycles to conception decreases. Finally, when having the choice between several "maximally" tumescent females, the alpha male prefers the female that is in the fertile phase of her cycle rather than that with the biggest swelling at that time. Thus, most of our findings are in line with the predictions of the graded signal hypothesis while none of them would support the reliable indicator hypothesis.     

Male courtship song frequency as an indicator of male genetic quality in an insect species,Drosophila montana.

Most theoretical models on evolution of male secondary sexual characters and female preferences for these characters suggest that the male characters evolve in response to female preferences that may themselves evolve in response to direct or indirect benefits of choice. In Drosophila montana (a species of the D. virilis group), females use male song in their mate choice, preferring males that produce songs with short sound pulses and a high carrier frequency. We demonstrate here that the females get indirect benefits from their choice: in our data the frequency of the male song correlated with the survival rate of the male''s progeny from egg to adulthood (indirect benefit for the female), but not with the fecundity of his mating partner (no direct benefit for the female). Male wing centroid asymmetry did not correlate with male wing song characters, nor with female egg production nor the fitness of her progeny, suggesting that fluctuating asymmetry in male wings does not play a major role in sexual signalling. The fact that the male song gives the female information on the male''s condition/genetic quality in D. montana suggests that in this species the evolution of female preferences for male song characters could have evolved through condition-dependent viability selection presented in some ''good genes'' models.     

Sequential search and the influence of male quality on female mating decisions

 The patterns of phenotypic association between mated males and females depend on the decision rules that individuals employ during search for a mate. We generalize the sequential search rule and examine how the shape of the function that relates a male character to the benefit of a mating decision influences the threshold value of the male trait that induces females to terminate search. If the fitness function is linear the optimal threshold value of a male character increases with the slope of the function. The phenotypic threshold criterion declines, all else being equal, if the fitness function is made more concave (or less convex) by an increase of the risk of the function. The expression of the trait in females has no effect on the optimal threshold value of a male character if the fitness function is linear and phenotypic values combine additively to influence the benefit of a mating decision; the phenotypic threshold criterion is ubiquitous among females. A convex fitness function induces females with high trait values to adopt a relatively high phenotypic threshold criterion, whereas a concave fitness function induces such females to adopt a low threshold value for the male trait. Thus, linear, convex and concave fitness functions effect random, assortative and disassortative combinations of phenotypes among mated individuals, respectively. Changes of female search behavior induced by changes of the distribution of a male character similarly depend on the shape of the fitness function. A variance-preserving increase of male trait values produces a relatively small increase of the threshold criterion for the male character if the fitness function is concave, relative to conditions in which the fitness function is either linear or convex. Our results suggest that a sequential search rule can in principle induce the kinds of mating patterns observed in nature and that the phenotypic association between mated individuals is likely to depend on how a male character translates into fitness, the distribution of the trait among males and attributes of searching females. Received: 20 September 1997 / Revised version: 13 August 1998     

Female and male visually based mate preferences are consistent with reproductive isolation between populations of the Lake Malawi endemic Labeotropheus fuelleborni

Sexual selection via female mate choice is thought to have played a key role in the speciation of haplochromine cichlids, but a dominant role for visual signals in such processes has lately been called into question. In addition, the possible role of male mating preferences in haplochromine speciation has been little studied. We studied patterns of both female and male mate choice, based exclusively on visual signals, in order to evaluate potential reproductive isolation between two populations of the Lake Malawi haplochromine Labeotropheus fuelleborni. In the first experiment, females were allowed to choose between two males, one from the same population and the other allopatric with respect to the female. Females in this experiment responded more frequently to males from their own population. Similarly, the males in these trials displayed more frequently when presented with females of their own population. In the second experiment, a female was allowed to choose between two males, either both from her own population or both allopatric. In these trials, both males and females from the Katale population interacted significantly more frequently in settings in which all three individuals were from the same population (same-population trios), and those from the Chipoka population showed a similar trend. Thus, patterns in both male and female courtship behavior suggest that visual signals contribute to at least incipient reproductive isolation between populations of L. fuelleborni [Current Zoology 56 (1): 65-72 2010].