Bill Color Preferences of Zebra Finches

Bill color varies with age and sex in zebra finches. Among birds of similar age and condition, males' bills tend to be redder and darker than those of females, but there is overlap in the phenotypic expression of the sexes. The bills of young birds are paler and less red than those of older birds. There is also interindividual variation within age and sex class. Experiments were performed to measure heterosexual and isosexual (= same sex) preferences of finches. Females preferred to associate with males with the reddest, brightest bills; they even preferred males whose bills were exaggerated through color applications of non-toxic marking pen. Males preferred to associate with females with bill colors in the middle of the phenotypic range. Females thus have “directional” preferences for male bill color, whereas male preference is “stabilizing” with regard to female bill color. In isosexual tests, neither sex showed a consistent preference for particular bill colors. Both sexes, however, displayed a tendency toward individual variability in preference. Bill color appears to be more important in heterosexual than in isosexual interactions. Several authors have recently suggested that organisms prefer brightly colored mates because bright coloration indicates superior physical condition. Results reported here do not support this hypothesis. Alternative functional explanations for the observed preferences are that bill color signals mating status, age or reproductive value. None of these appears to be a cogent explanation for the trends. Preferences do not appear to result from sexual imprinting. The possibility that the preferences are aesthetic and non-functional is discussed.     

Sexually dimorphic mate preference in Japan

Lonely hearts advertisements (LHA) published in Japan were examined in a comparative study on sexually dimorphic mate preference. I analyzed 944 LHA written by Japanese (730 by males and 214 by females) seeking short-term relationships and 780 LHA (577 by males and 203 by females) seeking long-term relationships. Some universal patterns of mate preference were confirmed and others were not. Female advertisers in both categories sought more traits than they offered; they also sought more traits than male advertisers. Males tended to offer their financial and social status, and females tended to seek those traits. More females requested family commitment than males. While there was no sex difference in offering and seeking physical appearance and health, females tended to request photographs of their potential mates. Males were more likely than females to be willing to accept children from previous relationships, although there was no significant difference in refusing such children. More females seeking long-term mates requested family commitment than females seeking short-term mates. In both males and females, more advertisers seeking long-term mates offered family commitment than advertisers seeking short-term mates. Some predictions for contingent preference were also examined. One prediction confirmed was that females offering physical appearance and health sought more traits than those not doing so. However, males offering financial and social status did not make higher demands than those who did not, which does not support one prediction. This paper was presented in a meeting of a team research project on "Mating systems, mate choice, and evolution by sexual selection in humans" by the International Research Center for Japanese Studies. I appreciate Professor Takeru Akazawa and other members inviting me to the project. Ryo Oda obtained his Ph.D. from the University of Tokyo for the study of lemur vocal communication. He is a lecturer at Nagoya Institute of Technology, and his current work focuses on the evolution of human behavior and language.     

Size-dependent response to conspecific mating calls by male crickets.

Male sexual displays provide females with information that is crucial to their reproductive decisions. That same information is available to eavesdroppers, with potential consequences for both signaller and receiver. We present empirical evidence for size-dependent responses to intersexual communication by conspecific rivals. Acoustic features of a male house cricket's (Acheta domesticus) mating call are positively associated with its size, with females preferring the calls of larger males. In order to investigate whether conspecific males make use of the information content of mating calls, we examined their phonotactic responses to call recordings that differ in attractiveness to females. Males of all sizes exhibited positive phonotaxis, with smaller males showing a clear preference for female-preferred calls. Smaller males were also less likely to seek contact with the speaker playing their chosen call. We discuss possible explanations for this size-dependent male behaviour.     

Male-Biased Sex Ratios in Offspring of Attractive Males in the Guppy

The attractiveness hypothesis predicts that females produce offspring with male-biased sex ratios when they mate with attractive males because their male offspring will inherit the paternal sexual attractiveness and may have high reproductive success. In this study, we examined the effect of the attractiveness of the male guppy Poecilia reticulata in terms of the conspicuousness of its orange spot patterns, important criteria affecting female choice in this species, on the offspring sex ratios. We found that food-manipulation treatment altered the conspicuousness of the orange spot patterns in a full-sibling male pair. When females were presented to these males, they showed a greater mate preference for males having brighter orange spots than for those having duller orange spots. Subsequently, half of the females were mated with the preferred males and the remaining females were mated with the less preferred males. When the females exhibited a greater preference for their mates, their offspring sex ratios were more male biased. These results appear to be consistent with the prediction of the attractiveness hypothesis. In the guppy, as male sexual attractiveness is heritable, the male-biased sex ratios of the broods of attractive males may be adaptive.     

Modulation of sexual signalling by immune challenged male mealworm beetles (Tenebrio molitor, L.): evidence for terminal investment and dishonesty

Organisms partition resources into life-history traits in order to maximise fitness over their expected lifespan. For the males of many species fitness is determined by qualitative and quantitative aspects of costly sexual signals: The notion that epigamic traits are costly forms the cornerstone of those theories that propose parasites drive sexual selection. Consequently studies examining this notion assume sexual signalling is honest (i.e. driven by cost) when they seek to identify correlations or causal links between male immune function and attractiveness. We demonstrate that immune challenged males of the mealworm beetle, Tenebrio molitor, increased their investment in epigamic pheromone signals: these males became significantly more attractive to females whilst increasing the activity of a key immune effector system. In other words males increase terminal reproductive effort (invest in attractiveness) in response to a survival threat (immune insult). Consequently the signal preferred by the female is dishonest when considering the male's condition.     

Male mate choice in the gynogenetic–sexual complex of crucian carp,<Emphasis Type="Italic"> Carassius auratus</Emphasis>

The asexual all-female Japanese crucian carp, Carassius auratus langsdorfii (Teleostei: Cypriniformes), reproduces gynogenetically, relying on the sperm of males of the sexual "host," C. auratus subspp. Theoretically, frequency-dependent mating preference of males to conspecific females can lead to the coexistence of asexual and sexual fish, if all else is equal. Our specific questions are whether males prefer conspecific females over asexual females and whether individuals show dominance hierarchies that potentially cause frequency-dependent mating preference. In an individual choice experiment, a tank was partitioned into three compartments with the middle one for a single male and the two outer ones for a sexual and an asexual female. The males of C. auratus bürgeri demonstrated a significant preference for ovulated conspecific females over ovulated asexual females. In contrast, in a group mating experiment, a single experimental tank included two males, a sexual female, and an asexual female together, and males chased and mated with both asexual and sexual females equally. Male mate preference was weak in group mating, which is typical in natural populations. Males and females of crucian carp showed no apparent agonistic behavior to each other in the group mating experiment. This is different from other gynogenetic complexes with the dominance hierarchy of males showing strong frequency-dependent mating preference (e.g., Poeciliopsis). We conclude that male mate preference is unlikely to be a strong frequency-dependent force maintaining the coexistence of asexual–sexual complexes of Japanese crucian carp. Received in revised form: 5 February 2001 Electronic Publication     

Tail Length and Mutual Mate Choice in Bearded Tits (Panurus biarmicus)

Direct sexual selection via mutual mate choice can result in both sexes showing conspicuous traits. We experimentally tested whether this hypothesis can explain tail length in the bearded tit (Panurus biarmicus). In this species, both sexes have a long, graduated tail. Males have, however, a longer tail than females, suggesting perhaps that females are choosier than males in selecting mates. We used two choice set‐ups for each sex: shortened vs. control tail individuals and elongated vs. control tail individuals. We found that direct sexual selection seems to operate differently in the two sexes. In both set‐ups, females spent more time with the male with the longest tail, and they also showed sexual display behaviour only towards these males. Males spent more time with control than with short‐tailed females, but they did not discriminate between control and long‐tailed females. Moreover, males displayed preference towards both short‐ and long‐tailed females. Thus, females preferred long‐tailed males, whereas males did not always prefer long‐tailed females. Our study suggests that mutual mate choice has played a role in the evolution of long tails in bearded tits. It also suggests that the sexual dimorphism in tail length has evolved because mate choice exerts a stronger sexual selection pressure on males than on females.     

The impact of traits offered in personal advertisements on response rates

The number of responses to personal advertisements can be a good source of information about preferences within the human mate market. From an analysis of responses to 551 advertisements placed by males in a local Lower Silesian (Poland) newspaper and 617 placed by females, we assessed which particular traits influenced the “hit rate” (the number of responses), using the Generalized Linear Model (GLM) with the number of responses as the dependent variable and traits offered by advertisers such as age, education level, place of residence, marital status, height, weight, offered resources, and attractiveness as the independent variables. The traits that appeared to influence the hit rate for advertisements placed by males were, in order of importance, education level, age, height, and resources offered, all of which were positively correlated with the hit rate. In contrast, certain traits advertised by females such as weight, height, education, and stated age were all negatively correlated with the hit rate. Resources offered by men had only a small positive effect and the advertising of general attractiveness by women had no effect at all on the hit rate, suggesting that respondents to personal advertisements rely much more on relatively objective traits, such as achieved education, male height, and female weight, than on those traits which are more open to subjective error or manipulation.     

Context‐dependent female preference for multiple ornaments in the bearded reedling

While it is well established that females prefer to mate with well‐ornamented males, the influence of perceptive and cognitive processes on the expression of female mate choice is still poorly known. It has been suggested that the female perception of a male's attractiveness is not absolute, but depends on the other males with which he is compared that have been previously encountered (comparative evaluation). We investigated whether mate preference in bearded reedlings (Panurus biarmicus) is dependent on or independent of social context in relation to two different traits: beard and tail lengths. Each female had a choice between two to three males with different modifications of beard and tail. For each female, three different experiments were conducted (one binary and two trinary tests). We found that when females are presented with options that vary antagonistically with respect to two ornaments (binary test), some individuals prefer one trait while others the other trait. This indicates that in our bearded reedlings population exists a mate preference polymorphisms. Moreover, we found that the presence of a third stimulus, irrespective of the initial preference, reduced the strength of the initial preference – what we can call a “preference dilution effect.” Our results suggest that the female's choice may be constrained by her cognitive abilities when she is simultaneously presented with several options varying for two uncorrelated traits.     

Evolved gender differences in mate preferences: Evidence from personal advertisements

Evolutionary theorists have posited that contemporary men and women may differ in their specific psychological mechanisms having to do with mate selection because different strategies would have benefitted men versus women in our distant ancestral past. From these theorized gender differences in mating strategies, several hypotheses were generated and subsequently tested in the current study using a large sample of personal advertisements (N = 1111). The results were generally supportive of evolutionary predictions: men were more likely than women to offer financial resources and honesty/ sincerity, and to seek attractiveness, appealing body shape, and a photograph in selecting a potential mate; women were more likely than men to offer an appealing body shape and to seek financial resources, qualities likely to lead to resource acquisition, and honesty/sincerity in potential mates. Women were also more likely than men to seek male friendship and/or companionship and to offer greater involvement only after the establishment of such friendship, whereas men more frequently than women made explicit requests for a sexual relationship. In general, men sought potential mates who were younger than themselves, a trend which became more pronounced among older advertisers. Women generally sought mates who were older than themselves, a trend which decreased slightly with the age of the advertiser. Results are discussed with regard to implications for hypothesized gender differences in evolved psychological mechanisms.     

Do male mealworm beetles, <Emphasis Type="Italic">Tenebrio molitor</Emphasis>, sustain the honesty of pheromone signals under immune challenge?

Immune function is potentially costly and traded-off against the expression of sexual signals, thus, making sexual advertisement a condition-dependent and honest indicator of current immunocompetence. We conducted a series of laboratory experiments using mature mealworm beetles, Tenebrio molitor, to examine whether an immunological challenge (nylon implant(s), microbial lipopolysacharides, microlatex beads) could affect the attractiveness of male pheromones or male’s survival in ad libitum and ‘water-only’ food regimes or whether pheromones signal more long-term qualities of males. We treated another set of newly-emerged males with a single nylon implant and gave first ad libitum food but later only water. We used several immune challengers and feeding regimes to examine if the expected trade-off between immune function and sexual signaling would be expressed differently depending on the resource level and the type of the immune challenge. None of the treatments affected the female preference for male pheromones or the male longevity except for the acute mortality caused by two-implant treatments. However, males lost less body mass when immune challenged and given an opportunity to feed. We conclude that females seem to prefer certain males, and the effect of immune challenge in males cannot systematically override these preferences.     

Female preference for the pheromone of males with low fluctuating asymmetry in the Japanese scorpionfly (Panorpa japonica: Mecoptera)

Fluctuating asymmetry (FA) is denned as small, random deviationsfrom perfect bilateral symmetry in a bilaterally symmetricalmorphological trait. The relationship between FA in forewinglength of males and the relative sexual attractiveness of theirpair-formation pheromones was studied experimentally in theJapanese scorpionfly, Panorpa japonica. This is the first studyof the role of FA in pheromonal communication systems, and oneof only a few studies on the relationship between FA and sexualselection. Collectively, the results of four interrelated experimentsreveal that females prefer the pheromone of males of relativelylow FA in forewing length. The experimental manipulation offorewing FA of males by cutting wing lengths did not influencetheir olfactory attractiveness to females. In this case, femaleschose the male with the lowest premanipulation FA. Thus, naturalwing length FA apparently is correlated with inherent differencesbetween males that influence the properties of sex attractantmales produce. Female preference for low-FA males may be adaptiveas a result of material and/or genetic benefits received byfemales.     

Evolution of sexual mimicry in sperm-dependent all-female forms of Poeciliopsis (Pisces: Poeciliidae)

The twofold advantage of all-female reproduction is limited in many asexual lineages because females are sperm-dependent. Males of a related sexual-host species typically prefer conspecific females as mates. According to the “sexual mimicry” hypothesis, an all-female lineage that closely resembles females of the sexual-host species should have enhanced mating success. Examination of mating success in all-female fish of the genus Poeciliopsis supported this hypothesis. The excellent sexual mimicry of some all-female strains could have evolved through mutations within clonal lineages subsequent to their origins as interspecific hybrids. Alternatively, this mimicry may have been “frozen” from variation in the sexual gene pool when new unisexual lineages first arose. To test the latter hypothesis, we examined laboratory synthesized strains of the hybridogenetic fish P. monacha-lucida. The frozen variation hypothesis was supported by the present results.     

Male chimpanzees prefer mating with old females

Cross-cultural studies indicate that women's sexual attractiveness generally peaks before motherhood and declines with age. Cues of female youth are thought to be attractive because humans maintain long-term pair bonds, making reproductive value (i.e. future reproductive potential) particularly important to males. Menopause is believed to exaggerate this preference for youth by limiting women's future fertility. This theory predicts that in species lacking long-term pair bonds and menopause, males should not exhibit a preference for young mates. We tested this prediction by studying male preferences in our closest living relative, the chimpanzee (Pan troglodytes). We show that despite their promiscuous mating system, chimpanzee males, like humans, prefer some females over others. However, in contrast to humans, chimpanzee males prefer older, not younger, females. These data robustly discriminate patterns of male mate choice between humans and chimpanzees. Given that the human lineage evolved from a chimpanzee-like ancestor, they indicate that male preference for youth is a derived human feature, likely adapted from a tendency to form unusually long term mating bonds.     

Sex differences in mortality of Japanese macaques: Twenty-one years of data from the Arashiyama West population

Theorists argue that mortality in male mammals should be higher than that of females, and many studies of primates followed across the life course have found this to be the case. This study examines mortality patterns in the rapidly expanding Arashiyama West (Texas) population of Japanese macaques (Macaca fuscata) and finds that males have a significantly lower median survival age (12.2 years) in comparison to females (20.5 years). Males and females are born in equal proportions, but by adulthood there are 2–5 females to every male. Males are at higher risk of falling victim to infectious diseases and human-related causes of death, and they are more likely to “disappear” from the population, which is inferred to result largely from emigration. There are no significant sex differences in the risks of dying from predation, non-infectious illnesses, neonatal defect, or social stress. Males become more susceptible to mortality than females once they reach sexual maturity, and they remain at greater risk than females until their old age. There is no evidence that one sex or the other is at greater risk of dying as infants, or as juveniles. Comparing males of different age classes, adolescent and adult males are more likely to die and to disappear than are juvenile males. These findings support the “high-risk, high-gain” hypothesis that males are mainly lost to the population because of their risk-taking behaviors after sexual maturity, rather than the “fragile male” hypothesis that males are more vulnerable to mortality during the period of growth and development. Am J Phys Anthropol 102:161–175, 1997 © 1997 Wiley-Liss, Inc.     

Early Developmental Conditions and Male Attractiveness in Zebra Finches

Traits used in mate choice are often costly to produce or maintain, and thus can reflect an individual’s current condition. Mate choice, however, might not only be influenced by the current condition of a potential partner, but also by the condition it had experienced during its early development which can have strong and long‐lasting effects on various traits. Here we studied the effects of different early developmental conditions, imposed by brood size manipulations (small, medium and large broods), on male attractiveness as measured by female choice experiments in zebra finches (Taeniopygia guttata). In three different experiments, we allowed females to choose between males that had been raised in different experimental brood sizes. In none of the experiments, females showed a significant preference for males which had experienced better developmental conditions, i.e. were raised in the relatively smaller experimental broods. Song rate was higher in males coming from small than large broods, but females did not prefer males that sang more. These results suggest that sexual attractiveness either was not affected by our experimental treatment or that males subsequently had compensated in their overall attractiveness for negative effects of early developmental conditions.     

Male Calling Behavior and Female Choice in the Neotropical Treefrog Hyla microcephala

The effect of stimulus call complexity and calling rate on the vocal responses of males and female mate choice was studied in Hyla microcephala in Panama. Males increased the number of notes in their calls in response to increases in stimulus call complexity during both playback of 1 to 8-note advertisement calls and during natural interactions. However, precise matching of the number of notes in stimuli and responses did not occur consistently. Males also increased calling rates if stimuli were presented above prestimulus rates. Two-stimulus choice experiments demonstrated that females prefer both higher calling rates and greater call complexity, indicating that the ways males change their vocal behavior during interactions increases their attractiveness to potential mates. Tests in which the relative intensity of a high and low rate stimulus was varied indicated that females prefer stimuli with higher total sound energy. In a natural chorus, it is likely that females simply approach males giving the most conspicuous calls.     

Is female preference for male repertoires due to sensory bias?

There are several possible explanations for the female preference for male repertoires in birds. These males are older, and have better territories; thus there are functional reasons for females to prefer these males. However, there is an alternative explanation; females may habituate less quickly to song repertoires than single songs. I tested whether females have a non-functional, sensory bias for male song repertoires, by testing female preference for a repertoire in zebra finches (Taenopygia guttata), a species in which males possess a single stereotyped song. Females chose between a male repertoire of four different phrases created from the song phrase of one individual and that of one of those phrases repeated four times (natural zebra finch song). Females were also given a choice between the above repertoire and a song made from the phrases of four related males (''family'' stimulus). I tested female preference by training females to press a button for presentation of a song stimulus, and counting the number of button presses. Females preferred the song repertoire to a single phrase song, and did not differentiate between the repertoire and song phrases from four males. Evidence from the Estrildidae indicates that having a single song is the ancestral state for zebra finches, so the preference is not ancestral.     

The Best Timing of Mate Search in Armadillidium vulgare (Isopoda,Oniscidea)

Mate choice is mediated by many components with the criteria varying across the animal kingdom. Chemical cues used for mate attractiveness can also reflect mate quality. Regarding the gregarious species Armadillidium vulgare (isopod crustacean), we tested whether individuals can discriminate conspecifics at two different levels (between sex and physiological status) based on olfactory perception. Tested conspecifics were individuals of the same or opposite sex, with the females at different moult stages. We found that the attractiveness of individuals was mediated by short-distance chemical cues and tested individuals were able to discriminate and prefer individuals of the opposite sex. Moreover, male preference to female increased during their moulting status as they matured. Males were particularly more attracted by females with appearing white calcium plates, which corresponds to the beginning of their higher receptivity period. These differences in attractiveness due to sex and physiological status are likely to shape the composition of aggregates and facilitate mate finding and optimize the reproductive success for both males and females. Thus aggregation pheromones could be linked to sex pheromones in terrestrial isopods.     

Time course of androgenic modulation of odor preferences and odor cues in male meadow voles, Microtus pennsylvanicus.

During the breeding season, male meadow voles prefer female over male odors and females prefer male over female odors. Testosterone control of males' odor preferences and production of odors attractive to females differ. A male meadow vole's preference for female versus male odor was still evident 1 week after castration, but not 1 week later. This preference was reinstated in testosterone-treated male voles 2 weeks after the onset of hormone replacement. The attractiveness of male odors to females did not disappear until 3 weeks after castration. The attractiveness of male odors was reinstated 1 week after castrated males were treated with testosterone. The time course for the androgenic modulation of production of odors attractive to females may facilitate breeding. For example, at the end of the breeding season males may emit an odor that is still attractive to females. Similarly, at the beginning of the breeding season males may emit an odor that is attractive to females.