Variation In Male Song Research Articles

Is female mate choice repeatable across males with nearly identical songs?

Individual-specific mate preferences are thought to be widespread, but they are still poorly understood in terms of mechanisms and function. Earlier work on a songbird (the zebra finch, Taeniopygia guttata ) showed predominantly individual-specific mate preferences and signs of behavioural incompatibility with certain partners. However, the phenotypic target of preference or aversion remains unclear. A previous study suggested that female preferences may be related to variation in male song. Male zebra finches have individually distinct songs and together with individual-specific female song preferences they could function according to a ‘key–lock principle’. Here we report on a preregistered study in which we tested the hypothesis that individual females respond to males with highly similar songs in a similar way. We selected 18 duos of males with nearly identical songs and released them with females in communal breeding aviaries. We scored female preference as the female's responsiveness to male courtship and confirmed that females indeed had strong individual-specific mate preferences. However, female responsiveness scores were not positively correlated across males closely matched for their song, thereby rejecting the idea of a song-based ‘key–lock principle’ as an explanation for the observed individual-specific preferences. We suggest researchers should focus on details of the interactions between potential partners to elucidate the cause of behavioural incompatibility. • Individual-specific mate preferences are common but poorly understood. • Mate preferences differ strongly between individual female zebra finches. • Individual males differ strikingly in their songs. • Females respond differently to males with exceptionally similar songs. • Song traits are hence not the target of individual-specific preferences.

Song characters as reliable indicators of male reproductive quality in the Savannah Sparrow (Passerculus sandwichensis)

Bird song may provide female birds with signals of male quality. To investigate this potential for sexual selection via female choice, we assessed the relationships between male song variation and male mating and reproductive success of the Savannah Sparrow (Passerculus sandwichensis (J.F. Gmelin, 1789)) over 3 years (2001–2003) in a population of Savannah Sparrows near London, Ontario, Canada. We measured song rate, as well as temporal and frequency attributes of song structure, as possible predictors of male quality, and then related these measures to attributes of male reproductive performance (mating and breeding success and territory size of males). We found significant correlations between male reproductive performance and several song features, such that the combined effects of two trill sections could potentially play an important role: males possessing such songs arrived and paired earlier and had higher fledging success. The results suggested that the trill segments of the song may signal important aspects of male quality. Possible reasons for significant roles of such songs in open-habitat birds are discussed.

Behavioural response of a migratory songbird to geographic variation in song and morphology.

IntroductionSexually selected traits contribute substantially to evolutionary diversification, for example by promoting assortative mating. The contributing traits and their relevance for reproductive isolation differ between species. In birds, sexually selected acoustic and visual signals often undergo geographic divergence. Clines in these phenotypes may be used by both sexes in the context of sexual selection and territoriality. The ways conspecifics respond to geographic variation in phenotypes can give insights to possible behavioural barriers, but these may depend on migratory behaviour. We studied a migratory songbird, the Stonechat, and tested its responsiveness to geographic variation in male song and morphology. The traits are acquired differently, with possible implications for population divergence. Song can evolve quickly through cultural transmission, and thus may contribute more to the establishment of geographic variation than inherited morphological traits. We first quantified the diversity of song traits from different populations. We then tested the responses of free-living Stonechats of both sexes to male phenotype with playbacks and decoys, representing local and foreign stimuli derived from a range of distances from the local population.ResultsBoth sexes discriminated consistently between stimuli from different populations, responding more strongly to acoustic and morphological traits of local than foreign stimuli. Time to approach increased, and time spent close to the stimuli and number of tail flips decreased consistently with geographic distance of the stimulus from the local population. Discriminatory response behaviour was more consistent for acoustic than for morphological traits. Song traits of the local population differed significantly from those of other populations.ConclusionsEvaluating an individual’s perception of geographic variation in sexually selected traits is a crucial first step for understanding reproductive isolation mechanisms. We have demonstrated that in both sexes of Stonechats the responsiveness to acoustic and visual signals decreased with increasing geographic distance of stimulus origin. These findings confirm consistent, fine discrimination for both learned song and inherited morphological traits in these migratory birds. Maintenance or further divergence in phenotypic traits could lead to assortative mating, reproductive isolation, and potentially speciation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-014-0085-6) contains supplementary material, which is available to authorized users.

Continent-wide patterns of divergence in acoustic and morphological traits in the House Wren species complex

ABSTRACT Phenotypic traits are important for assessing differences between populations, especially in groups with poorly resolved taxonomy. One such group, the House Wren complex, presents extensive taxonomic controversy and is thought to comprise many independent evolutionary units. Although the songs and morphological features of House Wrens (Troglodytes aedon) show extensive variation, differences between populations have not been quantified. We assessed variation in acoustic and morphometric traits within this complex and compared patterns of variation with currently recognized subspecies boundaries. First, we compared songs and morphology among eight recognized subspecies (T. a. aedon, T. a. parkmanii, T. a. cahooni, T. a. brunneicollis, T. a. nitidus, T. a. musculus, T. a. beani, and T. a. rufescens), controlling for significant effects of latitude. Second, we used variation in male song, a trait with an important role in mate choice and male–male competition, to assess divergence among subspecies. ...

Multivariate sexual selection in a rapidly evolving speciation phenotype

Estimating the fitness surface of rapidly evolving secondary sexual traits can elucidate the origins of sexual isolation and thus speciation. Evidence suggests that sexual selection is highly complex in nature, often acting on multivariate sexual characters that sometimes include non-heritable components of variation, thus presenting a challenge for predicting patterns of sexual trait evolution. Laupala crickets have undergone an explosive species radiation marked by divergence in male courtship song and associated female preferences, yet patterns of sexual selection that might explain this diversification remain unknown. We used female phonotaxis trials to estimate the fitness surface for acoustic characters within one population of Laupala cerasina, a species with marked geographical variation in male song and female preferences. Results suggested significant directional sexual selection on three major song traits, while canonical rotation of the matrix of nonlinear selection coefficients (γ) revealed the presence of significant convex (stabilizing) sexual selection along combinations of characters. Analysis of song variation within and among males indicated significantly higher repeatability along the canonical axis of greatest stabilizing selection than along the axis of greatest linear selection. These results are largely consistent with patterns of song divergence that characterize speciation and suggest that different song characters have the potential to indicate distinct information to females during courtship.

Male Song Variation and Female Mate Choice in the Golden-Winged Warbler

Abstract. We investigated the distinctiveness of males' song and the relationship between song variables and females' mate choice in the Golden-winged Warbler (Vermivora chrysoptera). We recorded the songs of 23 males and quantified them to examine performance-related traits and specific song content. We carried out discriminant function analysis to compare variation within and among males for characteristics of both song types I and II. We used microsatellite DNA to identify the parents of 62 nestlings from 17 nests. By assigning paternity to males in our population we could examine relationships between females' choice and variation in males' song by comparing characteristics of within- and extra-pair sires. While we were able to discriminate statistically between individual males' songs, we found no significant differences in song variables between the within- and extra-pair males at a given nest. Therefore, female Golden-winged Warblers do not appear to be using these differences in song in choosing a...

Female Lincoln's sparrows modulate their behavior in response to variation in male song quality

Sexually reproducing organisms should mate with the highest quality individuals that they can. When female songbirds choose a mate, they are thought to use several aspects of male song that reflect his quality. Under resource-limited environmental conditions, male Lincoln's sparrows (Melospiza lincolnii) vary among one another in several aspects of song quality, including song length, song complexity, and trill performance. In a 2-pronged approach, we tested whether variation in song quality of male Lincoln's sparrows influences the behavior of females that are in a reproductive-like state. Over two trials, we exposed females to songs from the high and low ends of the distribution of naturally occurring song quality variation and found a higher level of behavioral activity in females exposed to high-quality songs, especially when they had first been exposed to low-quality songs. We also examined female phonotaxis toward antiphonally played songs with experimentally elevated and reduced trill performance and found that females moved preferentially toward the songs with elevated trill performance. Contrary to most studies investigating the behavioral responses of wild, female songbirds to variation in male song, we obtained our results without administering exogenous estradiol, which can artificially perturb the female's physiology. Our results demonstrate that the behavior of female Lincoln's sparrows is modulated by the quality of male songs to which they are exposed and that trill performance plays a significant role in this behavioral modulation. Furthermore, as the order of song quality presentation matters, it appears that recent song experience also influences female behavior.

Experimental manipulation of the rearing environment influences adult female zebra finch song preferences

In songbirds, sensory and social learning processes in juveniles contribute to variation in male song and female preferences. The developmental stress hypothesis proposes that suboptimal early development affects the costly brain structures involved in male song learning and, as a consequence, song quality. As an extension of this hypothesis we tested in this study whether developmental conditions also modulate female song preference acquisition. We tested song preferences in adult female zebra finches, Taeniopygia guttata, originating from a brood size manipulation experiment that had induced differences in mass, condition, immune response and levels of plasma testosterone at the early nestling stage. During the song-learning phase, juvenile birds were housed in small mixed-treatment groups with unrelated adult male song tutors. Adult females' song preferences were tested in an operant set-up where females could trigger different song playbacks by pecking different response keys. When females could choose between their own and an unfamiliar tutor's song they preferred their tutors' songs independent of experimental brood size. However, when females chose between two unfamiliar songs there was a significant effect of experimental brood size on preference strength: females from small broods showed significantly stronger preferences than those from medium and large broods. Hence, both females' rearing environment and sensory learning processes appear to contribute to variation in the direction and strength of female preference for male mating signals.

Neural orchestration of mate-choice plasticity in songbirds

Females may choose between prospective mates based on signals that reflect male quality. In songbirds, variation in male song can be such a signal. Females can adjust their choosiness according to the prevalence of preferred song, presumably because environmental variation can influence the availability of preferred phenotypes. Studies using induction of the immediate early gene ZENK (also called zif-268, egr-1, NGFI-A, and Krox-24) as an indicator of neuronal activity have revealed that the caudomedial mesopallium (CMM) and caudomedial nidopallium (NCM) of the female auditory forebrain are sensitive to song quality and respond proportionally to the strength of the female’s choosiness. In European starlings (Sturnus vulgaris), long songs are preferred by females and induce higher ZENK expression in the CMM and NCM compared to short songs. Experimentally reducing the perceived prevalence of long songs in the environment reduces this forebrain sensitivity to song length, raising the possibility that the songbird auditory forebrain integrates information about the social environment that enables the female to adjust her choosiness according to the availability of preferred phenotypes. In some songbird species, the noradrenergic system modulates mate-choice behavior, modulates song-induced auditory forebrain activity, and itself is modulated by the prevailing song environment, suggesting a possible role for this system in mediating the effects of social environment on forebrain and behavioral sensitivity to mate-choice cues. The presence of such a system would seem beneficial when the availability of preferred mates varies.

The extent of variation in male song, wing and genital characters among allopatric Drosophila montana populations

Drosophila montana, a species of the Drosophila virilis group, has distributed around the northern hemisphere. Phylogeographic analyses of two North American and one Eurasian population of this species offer a good background for the studies on the extent of variation in phenotypic traits between populations as well as for tracing the selection pressures likely to play a role in character divergence. In the present paper, we studied variation in the male courtship song, wing and genital characters among flies from Colorado (USA), Vancouver (Canada) and Oulanka (Finland) populations. The phenotypic divergence among populations did not coincide with the extent of their genetic divergence, suggesting that the characters are not evolving neutrally. Divergence in phenotypic traits was especially high between the Colorado and Vancouver populations, which are closer to each other in terms of their mtDNA genotypes than they are to the Oulanka population. The males of the Colorado population showed high divergence especially in song traits and the males of the Vancouver population in wing characters. Among the male song traits, two characters known to be under sexual selection and a trait important in species recognition differed clearly between populations, implying a history of directional and/or diversifying rather than balancing selection. The population divergence in wing characters is likely to have been enhanced by natural selection associated with environmental factors, whereas the male genitalia traits may have been influenced by sexual selection and/or sexual conflict.

Response biases in auditory forebrain regions of female songbirds following exposure to sexually relevant variation in male song.

In many species of songbirds, individual variation between the songs of competing males is correlated with female behavioral preferences. The neural mechanisms of song based female preference in songbirds are not known. Working with female European starlings (Sturnus vulgaris), we used immunocytochemistry for ZENK protein to localize forebrain regions that respond to sexually relevant variation in conspecific male song. The number of ZENK-ir cells in ventral caudo-medial neostriatum [NCMv] was significantly higher in females exposed to longer songs than in those exposed to shorter songs, whereas variation in the total duration of song exposure yielded no significant differences in ZENK expression. ZENK expression in caudo-medial ventral hyperstriatum [cmHV] was uniformly high in all subjects, and did not vary significantly among the three groups. These results suggest that subregions of NCM in female starlings are tuned to variation in male song length, or to song features correlated therewith. Female starlings exhibit robust behavioral preferences for longer over shorter male songs (Gentner and Hulse; Anim Behav 59:443-458, 2000). Therefore, the results of this study strongly implicate NCM in at least a portion of the perceptual processes underlying the complex natural behavior of female choice.

Songs and Sexual Responses of Female White-Crowned Sparrows (Zonotrichia Leucophrys) From a Mixed-Dialect Population

Abstract Some researchers have suggested that female songbirds mate with males singing local song types in preference to males singing dialects from more distant populations. Such behaviour might promote genetic isolation among dialect populations. We studied captive female white-crowned sparrows (Zonotrichia leucophrys) from a population in which two song types were equally common, as a model for behaviour at dialect boundaries. Subjects were captured as adults, and the song type of the mate of each was known. Treated with estradiol, females gave sexual displays in response to playback of conspecific male song. As a group, they solicited no more strongly to either local song type, suggesting that males singing either local song type should be able to attract mates. Individuals solicited no more strongly to their mate's song type than to the other local song type. This suggests that strength of response of captive females to song playback may not accurately reflect the behaviour of free-living individuals. Subjects were also treated with testosterone to induce singing. Individuals sang their mates' song type more often than expected by chance. Given that female white-crowned sparrows in this population do not consistently choose mates of one song type, we develop the argument that females learn, for performance, the song type of their first mate. However, the type of song learned for performance appears unlikely to restrict their subsequent mate choice decisions. Our results suggest that female white-crowned sparrows do not base their choice of mates on dialectal variation in male song, and that it is unlikely that mate choice decisions based on song dialect promote the genetic isolation of dialect populations.

Genetic variation in male song and female song preference in the grasshopper Chorthippus brunneus (Orthoptera: Acrididae)

Abstract. Males of Chorthippus brunneus, the common field grasshopper, produce a species-specific song during courtship to which receptive females may respond by stridulation. The signal and the preference for the signal are part of a sexual signal-receiver system which must be co-adapted if males and females are to recognize each other. Evolution of this system will depend on the extent of genetic variation in male and female components and their genetic control. Two experiments using divergent artificial selection were performed to test for the presence of genetic variation in the male signal (mean syllable length of the calling song) and in female preference for that signal. Two generations of selection were performed on male mean syllable length. A response occurred after only one generation of selection, resulting in a significant difference between the two divergent lines. Similarly, selection on female acoustic preference for mean syllable length, tested using artificially created calling songs, resulted in an immediate and significant response to selection. The difference between the lines declined somewhat in later generations.

Variation in male song and female preference within a population of Ephippiger ephippiger (Orthoptera: Tettigoniidae)

Species-specific patterns of insect calling song are commonly assumed to show low variability. In the bushcricket Ephippiger ephippiger, male song shows large geographical variation in syllable number, and females strongly prefer song typical of their own population. Here it is shown that there is also large variation in syllable number within a population of E. ephippiger. Two factors associated with this variability were identified: eclosion sequence (which was positively correlated with mean male syllable number) and male-male interactions (with chorusing males producing more variable song than those singing in isolation). Similar variability was not evident in female preference as females did not show significant heterogeneity when offered a choice of recorded songs representing the main syllable types from the population, nor did overall preference vary amongst the main song types. A variety of factors, including genetic variability, developmental plasticity, male interactions and weak female preferences, could be responsible for this phenotypic variability.