Honest Signal Of Male Quality Research Articles

Sexual selection for single song repertoires.

Despite birdsong being one of the most studied models of sexual selection, how it operates in birds that sing only one song remains poorly understood. A recent study using a big data approach reveals a novel aspect of song that may potentially function as an honest signal of male quality and a way to maintain listener attention.

A vocalization in male Japanese bush warblers in response to both predators and conspecific females

AbstractMale Japanese bush warblers (Cettia diphone) produce not only typical songs but also long, conspicuous vocalizations (continuous songs) during the breeding season. In my preliminary observations, male warblers produced continuous songs in response to both the appearance of a predator and the calls of conspecific females. Although predator‐elicited vocalizations by males have been studied in some species, there are no known cases in which an acoustically identical vocalization is also triggered in response to conspecific females. Here, I examined whether these continuous songs triggered in response to predators and females were acoustically similar. In field experiments, I presented dummies of a Eurasian sparrowhawk and a female warbler before (April) and after (June) female arrival at the breeding ground. Before female arrival, 11.1% of males responded with continuous songs to each of the hawk and female presentations; after female arrival, the respective values were 27.6% and 48.3%. Thus, more males responded to the model presentations with continuous songs after female arrival. There was no difference in the acoustic characteristics of the continuous songs between the two models. The males approached the female model more intensively than the hawk model. These findings do not support the hypothesis that the song functions as an alarm or predator deterrent. The function of these continuous songs remains unclear, but this study is the first to show an example where males produce the same vocalization in response to both predators and conspecific females. The continuous song contains a trill‐like structure, which can be considered a performance‐related song trait. Therefore, the continuous song may possibly be an honest signal of male quality for females. Further studies are required to understand the function of this novel vocalization, particularly the effects of female breeding stage on male singing activity and the female response to the songs.

Display activity and foraging costs of a frugivorous lekking bird

Sexual success of males in lek breeding systems is often determined by display activities that require high energetic costs and may represent honest signals of male quality to females. In this context, manakins (Aves, Pipridae) evolved behavioral, morphological, and physiological adaptations that enable complex display maneuvers, and a high rate of fruit ingestion is needed to cope with the energetic costs of lekking activities. We examined the relationship between different displays (rolled-snaps, flights-down, and snap-jumps) and fruit consumption (a proxy for energy intake) by White-bearded Manakin males (Manacus manacus). We conducted a fruit supplementation experiment and recorded male displays in 23 arenas on 5 leks in southeastern Brazil. The flight-down was the display most related to fruit consumption (and energy refueling) by males of the White-bearded Manakin. This display seems to be decisive to the mating success of Manacus males; once inside a lek area, females are driven to display arenas by flights-down of males as an obligatory stage before copulation. This study opens a promising avenue for further field experiments designed to test how local food resources differentially impact display behavior among males in leks.

To compete or not to compete: bushcricket song plasticity reveals male body condition and rival distance

Males of several animals, including insects, use acoustic signals to attract a sexually receptive conspecific partner. In the orthopteran chorusing genus Poecilimon (Tettigoniidae), male signalling as well as female preference can be related to male body condition and to the social environment. Song is thought to be an honest signal of male quality, and song characteristics are therefore often important for sexual and social selection. At the same time, signal expression is plastic and this plasticity depends on the quality of the individual signaller, the acoustic components preferred by females and rivals' body condition and proximity. Using the bushcricket species Poecilimon ampliatus as a model, we investigated how both internal (body condition) and external (level of competition) factors affected the expression of temporal song characteristics. We show that both factors significantly affected acoustic signalling activity: when competing against light rivals, heavy males adjusted the characteristics of their songs to different social conditions. However, light males competing against a heavy rival showed less plasticity in their acoustic signals across social conditions. During the most escalated competition, heavier males increased their acoustic signal investment up to the maximum level, signalling with longer verses and higher duty cycles, in comparison to all other treatments. Body condition and the social environment affected male acoustic signal activity, which suggests that these factors mediate the allocation of resources for signalling and different strategies adopted in competition. The adaptive plasticity of acoustic signals in this species raises new questions about the potential role that this process could play in natural choruses, where more than two competitors are signalling simultaneously.

Plumage Coverage is Related to Body Condition and Ectoparasitism in Blue-black Grassquits

Females may prefer elaborate sexual ornaments in males as these can be costly and may honestly indicate male viability. We used a wild population of the Blue-black Grassquit (Volatinia jacarina) in central Brazil to test whether more ornamented males have lower parasite loads (parasite-mediated sexual selection) and/or better body condition (condition-dependent sexual selection) compared with less ornamented males. We predicted that blue-black plumage coverage should be positively correlated to body condition (weight/tarsus) and negatively correlated to parasite load (Mallophaga lice). We found that blue-black plumage coverage of grassquit males was positively related to body condition score and negatively related to ectoparasite load. However, body condition was not correlated with ectoparasite load in these males. Our data are consistent with the hypothesis of sexual selection mediated by parasites as well as with the hypothesis of sexual selection mediated by body condition, indicating that nuptial plumage coverage can be an honest signal of male quality in Blue-black Grassquits, and could thus be used by females during mate choice.

Sexual signaling under predation: attractive moths take the greater risks

Individuals often have to balance the costs of risky behavior against the potential benefits they may gain from it. This trade-off is especially obvious in the interplay between natural and sexual selection because traits for mate attraction may attract predators as well. In the lesser wax moth Achroia grisella, ultrasonic sexual signaling comes with such a risk because calling for mates also attracts predatory bats. Attractive males should behave more cautiously than unattractive males under such circumstances, as they can expect more future mating opportunities and therefore have more to lose (the so-called asset protection principle). Contrary to these predictions, we found that pulse pair rate and peak amplitude, 2 song components attractive to females, correlated negatively with the duration of a silence response which is displayed when courtship song is experimentally overlayed with the search signal of a predator, the greater horseshoe bat. More attractive males thus recommence singing sooner than less attractive males. Although this is not in line with the asset protection principle, we discuss 3 different ways in which these distinct behavioral differences might be explained: 1) attractive males are in better condition and thus can more easily evade predators, 2) attractive signals are costly in terms of reduced life expectancy, and 3) risk-taking may in itself be a sexually selected trait and as such act as an honest signal of male quality.

Is sexual ornamentation an honest signal of male quality in the Chinese grouse (Tetrastes sewerzowi)?

We examined the variation in sexual ornamentation of male Chinese grouse (Tetrastes sewerzowi) in the Gansu Province, China, seeking to identify factors involved in whether ornament size and brightness are honest signals of male quality. Compared to unmated males, mated males had significantly larger and redder combs and, although they did not have significantly larger territories, they defended them more vigorously. Mated males had significantly higher blood carotenoid and testosterone levels, significantly better body condition, and significantly lower parasite loads than unmated males. Our findings are thus consistent with the hypothesis that comb size and color are honest signals of better male quality in the grouse, mediated through lower parasite loads and/or higher testosterone levels.

Dominance is not always an honest signal of male quality, but females may be able to detect the dishonesty

Females prefer dominant males as mating partners in numerous species. Male dominance rank is considered as an honest signal of male quality, because only healthy males in good condition are thought to be able to win fights with other males. Here, we tested whether activation of the immune system influences the success of males in male-male competition and mating in the field cricket, Gryllus integer. We activated the immune system of males with a nylon monofilament (to mimic a parasitoid larva), and arranged fights between male pairs to assess male dominance and associated mating success. Activation of the immune system with nylon monofilament substantially enhanced the fighting success of males during male-male competition but had no effect on mating success. However, sham-manipulation (a wound only) did not have any effect on fighting success although females mated more often with dominant males. Our study suggests that when male crickets meet an apparent survival threat they may behave more dominantly, probably owing to terminal investment. Male success during male-male competition is not always an honest signal of males' quality, but females may be able to detect this dishonesty.

Testosterone Affects Song Modulation during Simulated Territorial Intrusions in Male Black Redstarts (Phoenicurus ochruros)

Although it has been suggested that testosterone plays an important role in resource allocation for competitive behavior, details of the interplay between testosterone, territorial aggression and signal plasticity are largely unknown. Therefore, we investigated if testosterone acts specifically on signals that communicate the motivation or ability of individuals to engage in competitive situations in a natural context. We studied the black redstart, a territorial songbird species, during two different life-cycle stages, the early breeding phase in spring and the non-breeding phase in fall. Male territory holders were implanted with the androgen receptor blocker flutamide (Flut) and the aromatase inhibitor letrozole (Let) to inhibit the action of testosterone and its estrogenic metabolites. Controls received a placebo treatment. Three days after implantation birds were challenged with a simulated territorial intrusion (STI). Song was recorded before, during and after the challenge. In spring, both treatment groups increased the number of elements sung in parts of their song in response to the STI. However, Flut/Let-implanted males reacted to the STI with a decreased maximum acoustic frequency of one song part, while placebo-implanted males did not. Instead, placebo-implanted males sang the atonal part of their song with a broader frequency range. Furthermore, placebo-, but not Flut/Let-implanted males, sang shorter songs with shorter pauses between parts in the STIs. During simulated intrusions in fall, when testosterone levels are naturally low in this species, males of both treatment groups sang similar to Flut/Let-implanted males during breeding. The results suggest that song sung during a territorial encounter is of higher competitive value than song sung in an undisturbed situation and may, therefore, convey information about the motivation or quality of the territory holder. We conclude that testosterone facilitates context-dependent changes in song structures that may be honest signals of male quality in black redstarts.

Song repertoire size correlates with measures of body size in Eurasian blackbirds

In most oscine bird species males possess a repertoire of different song patterns. The size of these repertoires is assumed to serve as an honest signal of male quality. The Eurasian blackbird’s (Turdus merula) song contains a large repertoire of different element types with a flexible song organisation. Here we investigated whether repertoire size in Eurasian blackbirds correlates with measures of body size, namely length of wing, 8th primary, beak and tarsus. So far, very few studies have investigated species with large repertoires and a flexible song organisation in this context. We found positive correlations, meaning that larger males had larger repertoires. Larger males may have better fighting abilities and, thus, advantages in territorial defence. Larger structural body size may also reflect better conditions during early development. Therefore, under the assumption that body size is linked to overall male quality, our results are in accordance with the hypothesis that repertoire size represents an honest signal in Eurasian blackbirds that has evolved in response to sexual selection.

Expression patterns of mineralocorticoid and glucocorticoid receptors in Bengalese finch (Lonchura striata var. domestica) brain suggest a relationship between stress hormones and song-system development

Much evidence suggests that song traits function as an honest signal of male quality during mate choice in songbirds. Because songbirds learn vocalizations during the juvenile stage, development of the song system and song traits is affected by stressful conditions. However, it remains unknown how stressful conditions affect later song traits during development. To explore the relationship between glucocorticoids and song-system development, we performed in situ hybridization analysis of the glucocorticoid and mineralocorticoid receptors in juvenile and adult brains. The glucocorticoid receptor showed weak expression in song nuclei and strong expression in the hypothalamus, whereas the mineralocorticoid receptor showed strong song-nuclei-related expression. Thus, it appears that glucocorticoids are involved in song development directly by binding to receptors in song nuclei or indirectly by regulating sex hormones through hypothalamic hormones.

Parental care does not vary with age‐dependent plumage in male Saffron Finches Sicalis flaveola

The status signalling hypothesis states that conspicuous male plumage varies among males and serves as an honest signal of male quality and competitive ability. We expected immature‐plumaged males of the Saffron Finch Sicalis flaveola to feed their incubating mates and nestlings and remove faecal sacs at lower rates than those of mature‐plumaged males. We also predicted that females paired with immature‐plumaged males would compensate for their mates’ lower contribution. We found no differences in either feeding rates or sanitation rates between immature‐ and mature‐plumaged males. Similarly, females mated to immature‐ and mature‐plumaged males fed nestlings at equivalent rates. Apparently, male plumage colour and age are not reliable signals of the ability of a male Saffron Finch to provide for his mate and offspring.

Does song repertoire size in Common Blackbirds play a role in an intra-sexual context?

Bird song is thought to have a function in both inter- and intra-sexual contexts with song complexity serving as an honest signal of male quality. Theory predicts that males use repertoire sizes to estimate rivals’ fighting ability. Here we tested whether element repertoire size plays a role in an intra-sexual context in the Common Blackbird Turdus merula, a songbird with a large repertoire. In a territory intrusion playback experiment, we broadcast Common Blackbird song with different element repertoire sizes to territorial males. The test birds did not respond differently to the different repertoire sizes. This was also the case when we considered the test birds’ own repertoire sizes in the analysis. Thus, we found no evidence for the hypothesis that males use repertoire size for estimating rivals’ fighting force. However, this does not exclude the possibility that repertoire size plays a role in different intra-sexual contexts in Common Blackbirds. In the discussion, we address alternative scenarios.

Male dance moves that catch a woman's eye.

Male movements serve as courtship signals in many animal species, and may honestly reflect the genotypic and/or phenotypic quality of the individual. Attractive human dance moves, particularly those of males, have been reported to show associations with measures of physical strength, prenatal androgenization and symmetry. Here we use advanced three-dimensional motion-capture technology to identify possible biomechanical differences between women's perceptions of 'good' and 'bad' male dancers. Nineteen males were recorded using the 'Vicon' motion-capture system while dancing to a basic rhythm; controlled stimuli in the form of avatars were then created in the form of 15 s video clips, and rated by 39 females for dance quality. Initial analyses showed that 11 movement variables were significantly positively correlated with perceived dance quality. Linear regression subsequently revealed that three movement measures were key predictors of dance quality; these were variability and amplitude of movements of the neck and trunk, and speed of movements of the right knee. In summary, we have identified specific movements within men's dance that influence women's perceptions of dancing ability. We suggest that such movements may form honest signals of male quality in terms of health, vigour or strength, though this remains to be confirmed.

Negative relationships between cellular immune response, Mhc class II heterozygosity and secondary sexual trait in the montane water vole.

Heterogeneities in immune responsiveness may affect key epidemiological parameters and the dynamics of pathogens. The roles of immunogenetics in these variations remain poorly explored. We analysed the influence of Major histocompatibility complex (Mhc) genes and epigamic traits on the response to phytohaemagglutinin in males from cyclic populations of the montane water vole (Arvicola scherman). Besides, we tested the relevance of lateral scent glands as honest signals of male quality. Our results did not corroborate neither the hypotheses of genome-wide heterozygosity-fitness correlation nor the Mhc heterozygote advantage. We found a negative relationship between Mhc hetetozygosity and response to phytohaemagglutinin, mediated by a specific Mhc homozygous genotype. Our results therefore support the hypothesis of the Arte-Dqa-05 homozygous genotype being a ‘good’ Mhc variant in terms of immunogenetic quality. The development of the scent glands seems to be an honest signal for mate choice as it is negatively correlated with helminth load. The ‘good gene’ hypothesis was not validated as Arte-Dqa-05 homozygous males did not exhibit larger glands. Besides, the negative relationship observed between the size of these glands and the response to phytohaemagglutinin, mainly for Mhc homozygotes, corroborates the immunocompetence handicap hypothesis. The Mhc variants associated with larger glands remain yet to be determined.

Ecstatic display calls of the Adélie penguin honestly predict male condition and breeding success

AbstractThe Adélie penguin (Pygoscelis adeliae) breeds in large, noisy Antarctic colonies and has evolved a communication system of complex intra- and inter-sexual visual and vocal behaviours. The Ecstatic Display Call (EDC) given by males whilst at the breeding colony is composed of introductory beats, short repeated syllables and a climactic long syllable. Here, we show that spectral qualities of the short syllables of the EDC can predict body condition and breeding success and suggest that in addition to its role in territory defence, the EDC may function as an honest signal of male quality for female mate choice. In the short repeated syllables frequency modulation, mean frequency, and pitch were all significantly lower in birds of better condition, with frequency modulation changing concomitantly with changing condition during the breeding season. Furthermore, during the period of mate attraction, a male's frequency modulation predicted both his latency to pair and likelihood of successfully breeding. Due to the long incubation fasts in this species we propose that female Adélie penguins may reliably use frequency modulation of the EDC as a potentially honest signal of early season male condition and the likelihood of a successful breeding outcome.

Melanin‐based Feather Colour and Moulting Latitude in a Migratory Songbird

AbstractMelanins are common pigments used for colouration in animal tissue and recent evidence suggests that they may be condition‐dependent signals used in mate choice. We examined the hypothesis that individuals moulting during migration produce relatively dull feathers compared to individuals moulting on the breeding grounds prior to migration because of the costs associated with overlapping these two activities. We estimated both the colour and moulting latitude of melanin‐based feathers in barn swallows (Hirundo rustica). Moulting latitude was inferred from stable‐hydrogen isotope (δD) values of individuals that were known to have bred at the same site the previous year. Contrary to expectations, δD values in feathers suggested that most, if not all, individuals moulted their feathers south of the breeding grounds. Furthermore, we found that males moulting at southern latitudes tended to produce darker, more rufous coloured throat feathers compared to males moulting at more northern latitudes, closer to the breeding grounds. However, we found no such relationship in females. Males could face a trade‐off between growing new but relatively dull feathers before or just after the commencement of migration versus waiting to grow more rufous coloured feathers well into fall migration or on the wintering grounds. We suggest that this trade‐off could produce an honest signal of male quality if only high quality males can afford to migrate large distances on feathers that are greater than a year old.

Male dominance influences pheromone expression, ejaculate quality, and fertilization success in the Australian field cricket, Teleogryllus oceanicus

The outcome of fights between males can often represent an honest signal of male quality and are therefore widely used by females in mate choice. Indeed, female preference for males that win fights has been demonstrated in numerous animal taxa, and many recent studies have focused attention on how subordinate males compensate for this disadvantage through postcopulatory mating strategies, such as increased investment in their ejaculates. Here, using the Australian field cricket, Teleogryllus oceanicus, we show that rather than investing more in postcopulatory strategies, subordinate males invest in an alternative precopulatory mating approach. We find that subordinate males produce ejaculates of lower quality than dominate males and sire less offspring when competing for fertilizations. However, subordinate males upregulate the quantity of a number of cuticular compounds that have previously been shown to increase male mating success. Our results suggest that male reproductive success is likely to result from the interaction of multiple traits in this species. Key words: cuticular hydrocarbons, paternity, social status, sperm quality, Teleogryllus oceanicus. [Behav Ecol]

Phenotypic correlates and survival consequences of male mating success in lek-mating greater prairie-chickens (Tympanuchus cupido)

Female choice and male–male aggression are two modes of sexual selection that can lead to elaboration of male morphological and behavioral traits. In lek-mating species, male mating success is often strongly skewed, and it is puzzling why variation in male traits is still observed given directional female choice. If male traits correlated with reproductive success are honest signals of male quality, there may be survival costs associated with the expression of those traits. In this study, we examined whether morphological, behavioral, and territorial traits are correlated with male mating success and survival in the lek-mating greater prairie-chicken (Tympanuchus cupido). We introduce a novel application of multinomial discrete choice models for analysis of female mate choice behavior. We found that behavioral and territorial attributes showed 6.5 times more variability among males than morphological traits. Both display and aggressive behaviors were strong predictors of male mating success, suggesting that both female choice and male–male aggression were important in determining mating success among male greater prairie-chickens. Moreover, annual survival of male prairie-chickens was independent of mating success and male traits. Females appear to be choosing males based on behavioral traits where large variation exists between males (coefficient of variation >30%). Behavioral traits were the most important factor in determining mating success of male prairie-chickens, but the mechanism underlying this relationship is unknown. In the future, experimental manipulations of male hormones or parasite loads could bridge the proximate mechanisms and ultimate consequences of factors mediating male mating success in lek-mating grouse.

Dawn song of the eastern kingbird: an honest signal of male quality?

To be used as honest signals of quality, phenotypic traits must vary markedly within populations and show repeatable differences between individuals. Eastern kingbirds, Tyrannus tyrannus, sing a distinctive dawn song in the predawn darkness, and one hypothesis for its function is that it serves as an honest signal of male quality that females use during choice of within-pair or extrapair mates. Over a 2-year period, we quantified dawn songs of males to measure between- and within-season repeatability of the timing (start and end time) and length of song bouts, and song rate. We also measured morphological characters to measure repeatability and describe individual differences in body size and plumage quality. All song traits varied considerably among males, start time and song rates were repeatable between years, and all song rates were repeatable within both years. All morphological characters were significantly repeatable between years. Moreover, early singing males were larger and had relatively long flight feathers, and males that sang at high rates had relatively long flight feathers. Early singing males were also paired to the earliest breeding females, and in one year, male song rate was positively correlated with their social mate's clutch size. Relatively long flight feathers in other species are typical of older males and individuals of higher body condition, suggesting that, despite being suboscine passerines with relatively simple and innate songs, eastern kingbirds use song performance as an honest signal of male quality that females may use during mate choice.