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Background Many studies of birds have indicated that offspring sex ratios can vary with environmental and parental traits. On the basis of long-term research, we first evaluated the possible influence of parental age difference and brood characteristics on offspring sex and fitness in multi-brooded Blackbirds Turdus merula. Methodology The study was conducted in the city-centre Stefan Żeromski Park in Szczecin, NW Poland, where the local population of Blackbirds has been studied since 1996. Data on the offspring sex and fitness were collected in five years, 2005–2007 and 2016–2017. During the breeding season we inspected the study area to locate the pairs’ territories and to track their nests and clutches. Results We found that the overall sex ratio did not differ statistically from 50:50, but that younger females bonded with older mates did tend to produce more sons, probably because of the greater fitness of male descendants. Accordingly, the sons’ breeding success increased with the father’s age, but this relationship was close to non-linear, which may indicate that the transgenerational effect of paternal senescence could negatively affect progeny fitness despite the high-quality of older fathers. Older females mated with younger males produced more daughters, which could have been due to the lesser attractiveness of the males and the mothers’ poorer condition caused by accelerated senescence. We found that neither offspring hatching sequence nor hatching date or clutch sequence were significant for sex determination. Conclusions We consider that in our Blackbird population, parental age could make a more significant contribution to shaping offspring sex and reproductive success.

Background. Many studies of birds have indicated that offspring sex ratios can vary with environmental and parental traits. On the basis of long-term research, we first evaluated the possible influence of parental age difference and brood characteristics on offspring sex and fitness in multi-brooded Blackbirds Turdus merula. Methodology. The study was conducted in the city-centre Stefan eromski Park in Szczecin, NW Poland, where the local population of Blackbirds has been studied since 1996. Data on the offspring sex and fitness were collected in five years, 2005-2007 and 2016-2017. During the breeding season we inspected the study area to locate the pairs' territories and to track their nests and clutches. Results. We found that the overall sex ratio did not differ statistically from 50:50, but that younger females bonded with older mates did tend to produce more sons, probably because of the greater fitness of male descendants. Accordingly, the sons' breeding success increased with the father's age, but this relationship was close to nonlinear, which may indicate that the transgenerational effect of paternal senescence could negatively affect progeny fitness despite the high-quality of older fathers. Older females mated with younger males produced more daughters, which could have been due to the lesser attractiveness of the males and the mothers' poorer condition caused by accelerated senescence. Wefound that neither offspring hatching sequence nor hatching date or clutch sequence were significant for sex determination. Conclusions. We consider that in our Blackbird population, parental age could make a more significant contribution to shaping offspring sex and reproductive success. [ABSTRACT FROM AUTHOR]

Pre-maturation social experiences may affect post-maturation reproductive strategies of females, including mating preferences and investment in offspring. Whether pre-maturation social experiences affect other aspects of females' reproductive strategies, including the number of accepted males and post-copulatory decisions, is still an open question. To address this question, we performed laboratory experiments using the highly polyandrous cricket Teleogryllus commodus. Previous studies showed that juvenile females reared in an acoustic environment with male calls of different rates (MIX) are more responsive to highly attractive calls than females reared in an environment with male calls of only high calling rates (HIGH). We exposed juvenile females to the same two acoustic environments (MIX and HIGH) and estimated the number of accepted males, time of spermatophore retention, and offspring quality. We found that the acoustic environment did not change the number of accepted males, indicating that the higher responsiveness shown in a previous study does not translate into high degree of polyandry. An increased number of mates reduced offspring quality, suggesting that polyandry is costly to females. Finally, when compared with females of the HIGH group, females of the MIX group retained spermatophores for shorter periods and produced higher quality offspring if mated with highly attractive males. This finding suggests that both the pre-maturation acoustic environment and the quality of the mates found by the adult females determine their post-copulatory decisions and eventually offspring quality. Taken together, our results indicate that both the pre- and post-mating strategies of females are subject to socially cued plasticity. Significance statement: There is increasing evidence that pre-maturation experiences affect mating decisions of females after maturity, making them more or less selective. Both the pre-maturation social environment and the quality of potential mates found by an adult female may determine the number and quality of accepted males, which in turn may influence offspring quality. We experimentally tested this hypothesis using a highly polyandrous cricket species and showed that the pre-maturation acoustic environment does not affect the number and attractiveness of males accepted by the females. However, offspring quality was determined by an interaction between the pre-maturation acoustic environment and attractiveness of males accepted by the females. This result provides a link between the pre- and post-maturation social experience of a female and the quality of her offspring. [ABSTRACT FROM AUTHOR]

In nest-building species, offspring survival and reproductive success of parental individuals are strongly influenced by nest quality. Thus, quantifying the influence of abiotic conditions on nest integrity is important to predict the effects of weather variability on the fitness of parental individuals. Here, we investigated how rainfall affects nest integrity and how nest integrity influences males' attractiveness and nest tenure. Our study species was the harvestman Quindina limbata , in which males build mud nests on fallen logs and protect the eggs against predators and fungi. Our data set comprises 12 months of regular inspections of 149 nests in a Costa Rican rainforest. We found that almost 50% of the nests were destroyed by rainfall. The drag force caused by rainfall running on the fallen log surface negatively affected nest integrity. Fungi cover on nests was influenced by an interaction between rainfall and nest position on the fallen log. Irrespective of their body size, males in nests with high integrity received more eggs than males in nests with low integrity. Fungi cover did not influence the number of eggs received by the males. Finally, nest integrity and fungi cover did not affect nest tenure, but males that did not receive eggs for a long time tended to abandon their nests. Considering that intense rainfall occurs all year long in tropical forests, males should build their nests in protected sites that preserve nest structure. Protected sites may keep nest structure better preserved, improve offspring survival, attract more females, and increase males' reproductive success. [ABSTRACT FROM AUTHOR]

Reproductive promiscuity, whereby females are fertilized by extrapair mates, is common. The frequency of extrapair fertilizations (EPFs) depends on at least three sources of variation. First, females may differ in their proneness to being fertilized by extrapair males. Second, males may differ in traits that affect realized promiscuity of females. Third, EPF decisions depend on the combined effects of the identity of social mates. Here, we relied on extensive genetic parentage analysis of the offspring of a socially monogamous bird, the barn swallow, Hirundo rustica , to assess which of the above sources of variation predict the occurrence of EPFs. When we controlled for pair composition and social mate attractiveness, EPFs covaried with morphological and coloration traits of feathers in females. As expected, females mated with highly ornamented, long-tailed males had fewer EPFs. The composition of the breeding pair also accounted for variation in EPFs, implying that the ability of individual males to secure genetic parentage varies between female mates. These results show that females differ in promiscuity, and phenotypic traits of females that are visible to males are associated with promiscuity, potentially serving as cues to prospecting males. Hence, contrary to common interpretations of the negative relationship between male sexual attractiveness and female promiscuity, it can be speculated that larger genetic parentage by highly ornamented males results from their ability to secure the less promiscuous mates rather than from females being less promiscuous when mated to them. Moreover, our study shows that EPFs also depend on the composition of the social pair, as expected if a component of female promiscuity decisions depends on genetic or behavioural compatibility with the social male mate. Our study emphasizes that female promiscuity and its phenotypic correlates, and composition of the social pair, deserve closer attention in studies of sexual selection mediated by EPFs. [ABSTRACT FROM AUTHOR]

Leg-to-body ratio (LBR) predicts evolutionary fitness, and is therefore expected to influence bodily attractiveness. Previous investigations of LBR attractiveness have used a wide variety of stimuli, including line drawings, silhouettes, and computer-generated images based on anthropometric data. In two studies, community samples of heterosexual women from the USA rated the attractiveness of male figures presented as silhouettes and as detailed computer-generated images with three different skin tones (white, black, and an artificial grey). The effects of LBR depended on the image format. In particular, a curve-fitting analysis indicated that the optimally-attractive LBR for silhouettes was fractionally below the baseline, whereas the optima for more detailed computer-generated images was approximately 0.5 s.d. above the baseline and was similar for all three skin-tones. In addition, the participants' sensitivity to changes in the LBR was lowest for the silhouettes and highest for the grey figures. Our results add to evidence that the most attractive LBR is close to, but slightly above, the population mean, and caution that the effects of limb proportions on attractiveness depend on the ecological validity of the figures.

Sex allocation theory predicts that females mated to attractive males produce more sons than females mated to unattractive males. However, previous tests of this hypothesis have obtained mixed results. We suggest that females differ in the traits they find attractive. To test this proposition, we assessed female zebra finches' preferences for males banded with red or green plastic leg bands and then tested the sex allocation pattern of females paired with preferred and non-preferred males. Although most females preferred redbanded males, 34% of females consistently preferred green-banded males. The sex ratio at laying and hatching was not influenced by paternal preferred status. However, the fledging sex ratios differed between females paired with preferred and non-preferred males due to sex-biased chick mortality; sons of females paired with preferred males were born heavier and were more likely to survive than daughters. Our results indicate that female zebra finches show individual variation in their preferences for colour banded males, although females do not seem to adjust the offspring sex ratio in response to their mate's band colour. However, the differential posthatch mortality suggests females may differentially allocate resources into male and female eggs according to their individual mate preferences. [ABSTRACT FROM AUTHOR]

Robust evidence shows that voice quality affects various social interactions, including mate preferences. Previous research found that male voices perceived as attractive are characterized by low voice pitch, lower or sexually typical formants and relatively high breathiness. These features tend to be seen as markers of an individual's quality as a potential mate. Although there are considerable differences between languages in vocal parameters that could influence the perceived attractiveness, the above-mentioned findings rely on research based mainly on participants from European or North American countries. In our study, we therefore tested the main acoustic predictors of vocal attractiveness using two male samples from Cameroon and Namibia. Standardized vocal recordings were then assessed for vocal attractiveness by a panel of female raters from the Czech Republic. Our results show that in the Cameroonian voices, fundamental frequency was strongly negatively associated with perceived vocal attractiveness. In the Namibian sample, however, it was not the fundamental frequency but lower mean formants and harmonics-to-noise ratio that were negatively associated with vocal attractiveness. This pattern may be partly attributed to differences in morphological characteristics such as the body mass index, indicating variation across individual populations. [ABSTRACT FROM AUTHOR]

It is well established that in many avian species, prenatal maternal resource allocation varies both between and within clutches and may affect offspring fitness. Differential allocation of maternal resources, in terms of egg weight and yolk composition, may therefore allow the female to adjust brood reduction and to fine-tune reproductive investment in accordance with the expected fitness returns. The adaptive value of such maternal resource allocation is thought to be context-dependent as well as species-specific. We investigated the effects of female preference for her mate on the allocation of prenatal maternal resources in the budgerigar, Melopsittacus undulatus , a monogamous species of parrot that shows an extreme hatching asynchrony. We assessed mate preferences in a two-way preference test and allowed females two breeding rounds: one with the preferred and one with the non-preferred partner. We found no effect of preference on either latency to lay or clutch size, but females mated with the preferred partner laid eggs that contained significantly more yolk. Their eggs also contained significantly more androstenedione but not testosterone. Our results suggest that in this species, female preference may influence maternal resource allocation, and that the functional roles of each androgen in the yolk should be considered separately. In addition, we found a significant effect of laying order on egg and yolk weight as well as on yolk testosterone and androstenedione levels. These measures, however, did not change linearly with the laying order and render it unlikely that female budgerigars compensate for the extreme hatching asynchrony by adjusting within-clutch allocation of prenatal maternal resources. [ABSTRACT FROM AUTHOR]

Parental attractiveness influences paternal and maternal efforts in a wide range of animals that exhibit biparental care. However, we still lack an understanding concerning the direction of the covariance between attractiveness and parental effort, perhaps because studies typically consider only one or a subset of multiple attractiveness signals. In this study we investigated predictions of four hypotheses about the relationship between attractiveness traits (plumage coloration, song and leap display traits) and parental effort (feeding rates) in a wild population of the blue-black grassquit, Volatinia jacarina , a Neotropical sexually dichromatic bird with biparental care. Paternal effort was negatively correlated with male blue-black coloration (UV chroma) and maternal effort was positively correlated with male provisioning rate. Thus, more attractive males relative to the UV chroma are worse fathers relative to less attractive males in this trait. However, female provisioning rate was positively correlated with another male attractive trait: the blue-black plumage coverage. The song, leap display and other features of male coloration were not associated with either male or female parental effort. Taken together, these results support the parental–mating trade-off hypothesis for paternal behaviour, which predicts that attractive males should invest less in current offspring in order to acquire extrapair matings. Also, our results partially support the positive differential allocation hypothesis: although females invested highly in offspring of males with more blue-black plumage coverage, they did not compensate for the low investment of males with UV-shifted blue-black plumage. We highlight the need for future studies to consider multiple sexual traits in order to investigate the relationship between attractiveness and parental investment. [ABSTRACT FROM AUTHOR]

Background Identifying the sources of variation in mating interactions between males and females is important because this variation influences the strength and/or the direction of sexual selection that populations experience. While the origins and effects of variation in male attractiveness and ornamentation have received much scrutiny, the causes and consequences of intraspecific variation in females have been relatively overlooked. We used cytogenetic cloning techniques developed for Drosophila melanogaster to create "hemiclonal" males and females with whom we directly observed sexual interaction between individuals of different known genetic backgrounds and measured subsequent reproductive outcomes. Using this approach, we were able to quantify the genetic contribution of each mate to the observed phenotypic variation in biologically important traits including mating speed, copulation duration, and subsequent offspring production, as well as measure the magnitude and direction of intersexual genetic correlation between female choosiness and male attractiveness. Results We found significant additive genetic variation contributing to mating speed that can be attributed to male genetic identity, female genetic identity, but not their interaction. Furthermore we found that phenotypic variation in copulation duration had a significant male-associated genetic component. Female genetic identity and the interaction between male and female genetic identity accounted for a substantial amount of the observed phenotypic variation in egg size. Although previous research predicts a trade-off between egg size and fecundity, this was not evident in our results. We found a strong negative genetic correlation between female choosiness and male attractiveness, a result that suggests a potentially important role for sexually antagonistic alleles in sexual selection processes in our population. Conclusion These results further our understanding of sexual selection because they identify that genetic identity plays a significant role in phenotypic variation in female behaviour and fecundity. This variation may be potentially due to ongoing sexual conflict found between the sexes for interacting phenotypes. Our unexpected observation of a negative correlation between female choosiness and male attractiveness highlights the need for more explicit theoretical models of genetic covariance to investigate the coevolution of female choosiness and male attractiveness. [ABSTRACT FROM AUTHOR]

It is generally thought that attractive male traits are positively correlated with dominance (aggressiveness). However, growing evidence suggests that this is not necessarily the case. We investigated whether calling song, a male mating display used by females to evaluate potential mates in a field cricket ( Gryllus integer), is correlated with aggressiveness. In this species, females prefer males with longer durations of singing time. We measured singing time by measuring song over three continuous days using a custom-designed audio-monitor and assessed aggressiveness by pairing males in agonistic interactions. Our results showed that for males caught in the field, the percentage of time spent singing was negatively correlated with aggressiveness. However, in males that were raised in the laboratory, the percentage of time spent singing was not correlated with aggressiveness. Since calling duration is an attractive male trait in these crickets, our data show that the attractiveness of males can be either negatively related to aggressiveness (field) or unrelated to aggressiveness (lab). Neither of these results fit the traditional view that preferred male mating cues should be positively correlated with dominance (aggressiveness). These results also suggest that measurements of aggressiveness made in the lab do not necessarily correspond with aggressiveness in the field. [ABSTRACT FROM AUTHOR]

Life history theory predicts a trade off between the expression of male sexual traits and the immune system. To test for this trade off, male crickets Teleogryllus commodus were injected with bacterial lipopolysaccharides (LPS) to induce an immune response and their subsequent pre- and post-copulatory sexual attractiveness to virgin and non-virgin females was assessed. Pre-copulatory attractiveness was quantified based on the time taken for males to court and mate with a female. Post-copulatory attractiveness was measured as the time that elapsed between mating and a female interrupting sperm transfer by removing the externally attached spermatophore. We found no difference in pre- or post-copulatory attractiveness between LPS and control males. In contrast, virgin females retained spermatophores for almost twice as long as non-virgins, presumably to enhance fertilization and begin egg-laying. Finally, we note that although LPS is a widely used immune elicitor in insects, its effect might be transitory. After 24 h there was no detectable elevation in haemolymph antibacterial activity of LPS injected crickets compared to that of controls. [ABSTRACT FROM AUTHOR]

Understanding the evolution and maintenance of within-sex reproductive morphs, or alternative reproductive phenotypes (ARPs), requires in depth understanding of the proximate mechanisms that determine ARP expression. Most species express ARPs in complex ecological environments, yet little is know about how different environmental variables collectively affect ARP expression. Here, I investigated the influence of maternal and developmental nutrition and sire phenotype on ARP expression in bulb mites ( Rhizoglyphus robini), where males are either fighters, able to kill other mites, or benign scramblers. In a factorial experiment, females were raised on a rich or a poor diet, and after maturation they were paired to a fighter or a scrambler. Their offspring were put on the rich or poor diet. Females on the rich diet increased investment into eggs when mated to a fighter, but suffered reduced longevity. Females indirectly affected offspring ARP expression as larger eggs developed into larger final instars, which were more likely to develop into a fighter. Final instar size, which also strongly depended on offspring nutrition, was the main cue for morph development: a switch point, or size threshold, existed where development switched from one phenotype to the other. Sire phenotype affected offspring phenotype, but only if offspring were on the poor diet, indicating a gene by environment interaction. Overall, the results revealed that complex environmental effects can underlie ARP expression, with differential maternal investment potentially amplifying genetic effects on offspring morphology. These effects can therefore play an important role in understanding how selection affects ARP expression and, like quantitative genetics models for continuous traits, should be incorporated into models of threshold traits. [ABSTRACT FROM AUTHOR]

If sexually selected traits reveal a male's heterozygosity or condition to females, then such traits should exhibit declines with inbreeding. We tested this by examining the effect of inbreeding on advertisement calling in male crickets Teleogryllus commodus. We investigated the effect of one generation of full-sibling mating on calling effort and fine-scale call structure. Inbreeding reduced calling effort but had no effect on call structure. We then compared the attractiveness of inbred and outbred calls in the field by monitoring how many wild females were attracted to each call type. From the field data, we conducted a selection analysis to identify the major axes of linear and nonlinear multivariate sexual selection on call structure. A comparison of multivariate attractiveness of inbred and outbred calls along each major axis of selection revealed no difference in attractiveness. Our results suggest that inbred male calls have a fine-scale structure that is no less attractive to females than that of outbred calls. However, because inbred males call less often, and female T. commodus prefer males with a higher calling effort, inbred males will suffer reductions in mating success. Females who base mate choice on call rate are therefore using a signal correlated with male heterozygosity and/or condition. [ABSTRACT FROM AUTHOR]

Sex allocation theory predicts that female birds with high-quality mates will benefit from producing more sons, since sons will inherit their father's superior traits and enjoy a great reproductive success, whereas females with low-quality mates will benefit from producing more daughters, since the variance in reproductive success among daughters is typically lower. The male attractiveness hypothesis may apply to extra-pair paternity (EPP) because socially monogamous females routinely mate with higher quality males outside the pair bond. We test these predictions using the Tibetan ground tit ( Pseudopodoces humilis), a sexually monomorphic, socially monogamous, facultatively cooperative breeder. There was greater variation in actual reproductive success among males than females due to EPP. An excess of sons was detected for bi-parental (i.e., non-cooperative) broods wherein EPP was mainly sired by bi-parental males. The pattern was attributed to male-biased sex ratios produced for both EPP and within-pair offspring within the same broods. The reason for the latter case might be a random allocation of more offspring to sons by the potentially EPP-exposed females that have an inability to control fertilization by specific males. In cooperative broods where EPP mostly resulted from within-group helpers of presumed low-quality, as indicated by their failure in acquiring a social mate, there was a non-significant tendency for EPP offspring to be daughters and for within-pair offspring in the same broods to be unbiased. These results support the EPP-related male attractiveness hypothesis especially in terms of the overproduction of sons. Offspring produced through quasi-parasitism was unbiased towards either sex, suggesting a weak female choiceness with respect to the quality of host males. [ABSTRACT FROM AUTHOR]

Abstract: The Caribbean fruit fly, Anastrepha suspensa (Loew), like many polyphagous tephritids, exhibits a lek polygyny mating system, and juvenile hormone levels and adult diet are known to have important positive effects on male sexual success. Among the potential components of this success are male lek tenure and female response to the sexual signals of lekking males. Male A. suspensa where submitted to four different treatments: (M+P+) application of juvenile hormone analog, methoprene (M) and sugar and hydrolyzed yeast as adult food; (M+P−) application of M and sugar as adult food; (M−P+) no application of M and sugar and hydrolyzed yeast as adult food; and (M−P−) no application of M and sugar as adult food. M+P+ males initiated and participated more in aggregations, mated more frequently, and occupied the lek centers more often. They also had fewer unsuccessful mounting attempts than males in all the other treatments. M+P+ males also emitted pheromones and acoustically signaled more often and attracted more females than males in other treatments. Male sexual performance was improved due to methoprene, protein supply, and the interaction of methoprene and protein for most of the parameters. Since the success of the sterile insect technique (SIT), a commonly employed technique to control pest tephritids, requires the release of males that can form leks, engage in agonistic sexual interactions, and attract females, these positive effects of protein and methoprene may substantially improve SIT programs. [Copyright &y& Elsevier]

The extent to which females differ in their mating preferences has important consequences for the evolution of male sexual traits; yet, the way in which female mating preferences vary remains largely unexplored in most animal taxa. Even less is known about the implications of this variation to female fitness. Here, we examine the degree of between-female agreement in the mating preferences of the cockroach, Nauphoeta cinerea, and relate this variation to differences in female reproduction. Using a repeated-measures design, we mated a series of males sequentially to 5 different females. We found that females were largely in agreement in their mating preferences with a significant, albeit low (0.094 ± 0.061), repeatability of male attractiveness as assessed by different females. This is surprising given that females experienced a consistent reduction in offspring production when mating to more experienced males and suggests that females have a limited ability to detect male mating history. This cost may, in part, be offset by a longer gestation time when mating with more experienced males, which is known to extend female longevity in this species. There appears to be good reason for females to agree in their mate choice in this species. Across males, we found a significant negative correlation between male attractiveness and gestation time, suggesting that females actively discriminate against males that accelerate gestation. We discuss the implications of our findings to the operation of sexual selection in N. cinerea. [ABSTRACT FROM PUBLISHER]

Theoretical and empirical evidence suggests that avian females are able to manipulate the offspring sex ratio at birth. Although mating with an attractive male may induce females to skew the sex ratio toward males, the balance between the benefits of producing attractive sons and the costs of competing with other females for mates could vary with female age, a possibility that had not been previously explored. In this paper we increment experimentally the attractiveness of males of the polygynous spotless starling (Sturnus unicolor) by adding green plants to their nests, a trait involved in courtship, and look for female age-differential effects on offspring primary sex ratio. Young and middle aged females produced more sons in experimental than in control nests, as expected, but old females showed the opposite tendency. To explain this novel result, we speculate that older females are limited to produce the most costly sex because the physiological drawbacks imposed by ageing reduce their ability to compete with younger ones for the non-shareable resources offered by males. We discuss that this evolutionary scenario may be widespread in avian polygynous systems. [ABSTRACT FROM AUTHOR]

Finding reliable ways of assessing female mate choice is an essential prerequisite to understanding variation in female preferences and its impact on sexual selection. The zebra finch, Taeniopgyia guttata, is a classic avian model species for investigating mate choice and sexual selection, but to date virtually all work has been carried out using domesticated birds, and there are inconsistencies in the findings between studies. We tested three different methods for measuring female preferences in this species using both wild and domesticated birds. The first method was a traditional two-way mate choice chamber, where we measured the time spent with each male. The second method was a no-choice chamber where a single male and female were placed in the same cage for 5min, such that the pair could physically interact, and the female''s sexual response was recorded. The third method was an aviary set-up, comprising eight birds (four males and four females), and we recorded the number of pair-bonding behaviours observed over a 24-h period. In the aviary, we found that birds formed pair bonds almost exclusively with their own type (wild males paired with wild females, and domestic males paired with domestic females). In the two-way choice chamber, this assortative mating preference was only shown by domestic females, and in the no-choice test, only wild females showed this assortative mating preference. We discuss the possible reasons for these differences between mate choice tests and make recommendations for future studies on mate choice. [Copyright &y& Elsevier]

If male sexual signalling is honest because it captures genetic variation in condition then traits that are important mate choice cues should be disproportionately affected by inbreeding relative to other traits. To test this, we investigated the effect of brother–sister mating on advertisement calling by male field crickets Teleogryllus commodus. We quantified the effect of one generation of inbreeding on nightly calling effort and five finer-scale aspects of call structure that have been shown to influence attractiveness. We also quantified inbreeding depression on six life history traits and one morphological trait. Inbreeding significantly reduced hatching success, nymph survival and adult lifespan but had no detectable effect on hatching rate, developmental rate or adult body mass. The effect of inbreeding on sexually selected traits was equivocal. There was no decline in calling effort (seconds of sound production/night) by inbred males, but there were highly significant changes in three of five finer-scale call parameters. Sexually selected traits clearly vary in their susceptibility to inbreeding depression. [ABSTRACT FROM AUTHOR]

The androgen concentration in birds’ eggs varies with laying order, breeding conditions, and mate attractiveness. In passerine birds, mate attractiveness depends upon song quality. The aim of our study was to evaluate the effect of one criterion used by females to assess male song quality that is to say the presence of sexually attractive phrases on yolk androgen deposition. Twenty-five female Canaries were assigned to three experimental groups; in the first group, the females were allowed to hear songs made up with attractive phrases; in the second group, they were allowed to hear songs made up with non-attractive phrases; and in the control group, the females could not hear any song. Our results show that females allowed to hear songs with attractive phrases deposit significantly higher amounts of androgens (mostly testosterone) in their eggs than females without acoustical stimulation. The females exposed to songs with non-attractive phrases had androgen amounts halfway between the two other groups. This suggests that when females are paired with mates able to sing attractive phrases they can allocate more androgens in their eggs during the pre-laying period. [Copyright &y& Elsevier]

Recently, a number of studies have found adaptive brood sex ratio (BSR) manipulation in birds. The reason for such manipulations is thought to be the different reproductive value of male and female nestlings. Several studies have found that parental quality and food supply can affect BSR, however results are sometimes inconsistent between species and populations. We investigated BSR patterns in a Hungarian population of Collared Flycatchers (Ficedula albicollis) and compared the results with those obtained in a previous study of the same species in Sweden. We found two significant differences. First, the male forehead patch size, a heritable, sexually selected trait, affected the brood sex ratio in the Swedish population, but not in our Hungarian study population. This difference might be a consequence of the different information content of the forehead patch size in the two populations. Second, a seasonal shift in BSR (more sons late in the season) was observed in the Hungarian, but not in the Swedish population. [ABSTRACT FROM AUTHOR]

It has been suggested that the amount of maternal testosterone allocated into the eggs might be implicated in the process of sex determination. However, recent findings on the effect that female social rank has on the level of egg testosterone suggest that reported associations between male-biased sex ratios and yolk testosterone may represent an indirect hormonal effect mediated by the interdependence among maternal hormones, female social rank, and sex ratio. Here, we report the results of a field experiment in which we manipulated the circulating levels of testosterone in female spotless starlings (Sturnus unicolor) before egg formation. Focal females were controlled in subsequent years to explore possible delayed effects of hormone manipulation on primary sex ratio and social status that could persist because of permanent hormonal change or through hormone-dominance interactions. The results indicate that testosterone-implanted females (T-females) produced significantly more sons than control females (C-females) in the year in which they were manipulated. These differences in offspring sex ratio between T- and C-females persisted in the next 3 years, although no additional hormone treatments were given. These results were not mediated by an eventual effect of testosterone treatment on the quality of the females'' mates. A similar proportion of T- and C-females acquired a nest box and bred either in the manipulation year or in Year 1 after manipulation, but T-females tended to be more successful in acquiring a nest box than C-females in Years 2 and 3 after manipulation. These results suggest that added testosterone had a direct role on the acquisition and maintenance of high social rank. Delayed effects of testosterone on primary sex ratio might have been caused by altered endogenous production of T-females. Alternatively, the maintenance of sex ratio differences between T- and C-females long after having being implanted might be attributed to the positive effect that enhanced social rank of T-females has on their circulating testosterone levels. [Copyright &y& Elsevier]

Female coital orgasm may be an adaptation for preferentially retaining the sperm of males with “good genes.” One indicator of good genes may be physical attractiveness. Accordingly, R. Thornhill, S. W. Gangestad, and R. Comer (1995) found that women mated to more attractive men reported an orgasm during a greater proportion of copulations than did women mated to less attractive men. The current research replicates this finding, with several design variations. We collected self-report data from 388 women residing in the United States or in Germany. Results support the hypothesis that women mated to more attractive men are more likely to report an orgasm at the most recent copulation than are women mated to less attractive men, after statistically controlling for several key variables. Discussion addresses (a) the inability of the present research to specify the causal link between female orgasm and male attractiveness and (b) the proactive nature of female sexuality documented in recent research guided by an evolutionary perspective. [ABSTRACT FROM AUTHOR]

Extra-pair copulations create a potential for sexual conflict in pair-bonding birds. Here we report an experimental study of the bluethroat, Luscinia s. svecica, in which the throat ornament of males was blackened with Nyanzol D in order to reduce their sexual attractiveness and thus increase the sexual conflict over fertilizations. In an earlier study, we showed that males blackened before pairing had a lower success in attracting social mates than controls, whereas males blackened after pairing guarded their mates more intensely and sang less than controls. Here we add behavioural data from one more year on males blackened after pairing and corroborate our previous finding that the manipulation caused males to guard their mates more intensely and advertise less for additional mates. Blackened males did not suffer more intrusions from neighbouring males than did controls. Paternity analyses of the combined data set, using multilocus DNA fingerprinting and microsatellite typing, revealed that blackened males lost significantly more paternity than controls. There was also a tendency for blackened males to show a lower success in achieving extra-pair fertilizations. These results indicate that females have the upper hand in the sexual conflict over fertilizations, as females paired with unattractive males can achieve more extra-pair paternity despite the greater constraint posed by the intensified mate guarding. Still, within the blackened group, there were some indications that males guarding more intensely and singing less had higher paternity than males guarding less and singing more, suggesting a marginal positive effect of guarding for unattractive males. Male mate guarding must nevertheless be considered a best-of-a-bad-job strategy in this species. [ABSTRACT FROM AUTHOR]

• Fish species with comparative female mate choice for multiple male characters. • Male attractiveness depends on the other males to whom he is compared by females. • Test for male nesting strategies associated to female comparative choice. • Males maximize their attractiveness by nesting close to less attractive neighbours. • Positive effect on maintenance of genetic variability of sexually-selected traits. Emerging evidence endorses the idea that comparative instead of rational choice is widespread among species and mating contexts. In a comparative scenario the attractiveness of a male is not absolute but depends on the attractiveness of the other males to whom he is compared by females. Therefore, a male may benefit from the ability to choose the appropriate context that enhances his attractiveness. Here we test for the occurrence of strategic male nesting strategies in the peacock blenny, Salaria pavo , a fish species in which females evaluate potential mates by comparing males. Our results show that the large majority of males choose the context that maximize their attractiveness by nesting close to less attractive neighbours. Overall, we suggest that, in the peacock blenny, comparative, non-directional female choice is associated to strategic male nesting strategies and this scenario may contribute to the maintenance of genetic variability of male sexually-selected traits. [ABSTRACT FROM AUTHOR]

Intralocus sexual conflict arises when the expression of shared alleles at a single locus generates opposite fitness effects in each sex (i.e. sexually antagonistic alleles), preventing each sex from reaching its sex-specific optimum. Despite its importance to reproductive success, the relative contribution of intralocus sexual conflict to male pre- and post-copulatory success is not well-understood. Here, we used a female-limited X-chromosome (FLX) evolution experiment in Drosophila melanogaster to limit the inheritance of the X-chromosome to the matriline, eliminating possible counter-selection in males and allowing the X-chromosome to accumulate female-benefit alleles. After more than 100 generations of FLX evolution, we studied the effect of the evolved X-chromosome on male attractiveness and sperm competitiveness. We found a non-significant increase in attractiveness and decrease in sperm offence ability in males expressing the evolved X-chromosomes, but a significant increase in their ability to avoid displacement by other males' sperm. This is consistent with a trade-off between these traits, perhaps mediated by differences in body size, causing a small net reduction in overall male fitness in the FLX lines. These results indicate that the X-chromosome in D. melanogaster is subject to selection via intralocus sexual conflict in males.