Sexual Ornaments Research Articles

Visual Observation to Identify Sexes in Subspecies of Adult Black Skimmers (Rynchops niger)

Identifying sexes in birds from visual observations could be a useful and inexpensive method. While sexual dichromatism and ornaments are readily used by observers, sexual size dimorphism can also be used to identify sexes in some bird species. This study assessed the applicability of visual observation of size differences to identify sexes in adult Black Skimmers (Rynchops niger). Black Skimmers do not have sexual dichromatism; however, Black Skimmer males are skeletally larger (6.7–31.7% depending on trait) and 33.3–37.5% heavier than females. The study focused on two subspecies: Amazonian (R. n. cinerascens) and South American (R. n. intercedens) Black Skimmers. Sex identified by visually observing size differences was consistent with the sex identified at specimen preparation from examining gonads (RGLMM = 0.996 ± 0.004). The identification of sexes from photographs using visual observation of size had a very high within- (RGLMM = 0.995 ± 0.001) and between- (RGLMM = 0.984 ± 0.002) observer repeatability. Non-invasive methods for identifying sex by visual observation may allow enhanced use of data from photographic datasets, citizen science projects, and surveys using direct observation or images.

The relation between R. A. Fisher's sexy-son hypothesis and W. D. Hamilton's greenbeard effect

AbstractRecent years have seen a growing interest in the overlap between the theories of kin selection and sexual selection. One potential overlap is with regards to whether R. A. Fisher's “sexy-son” hypothesis, concerning the evolution of extravagant sexual ornamentation, may be framed in terms of W. D. Hamilton's greenbeard effect, concerning scenarios in which individuals carry an allele that allows them to recognize and behave differently toward other carriers of the same allele. Specifically, both scenarios involve individuals behaving differently toward social partners who exhibit a phenotypic marker, with linkage disequilibrium between marker and behavior loci ensuring genetic relatedness between actor and recipient at the behavior locus. However, the formal connections between the two theories remain unclear. Here, we develop these connections by: (1) asking what kind of greenbeard is involved in the sexy-son hypothesis; (2) exploring the relationship between the problem of “falsebeards” and the “lek paradox”; (3) investigating whether these two problems may be resolved in analogous ways; and (4) determining whether population structure facilitates both of these evolutionary phenomena. By building this conceptual bridge, we are able to import results from the field of kin selection to sexual selection, and vice versa, yielding new insights into both topics.

Sperm variation in Great Tit males (Parus major) is linked to a haematological health-related trait, but not ornamentation

The phenotype-linked fertility hypothesis (PLFH) proposes that both sexual ornaments and sperm traits are phenotypically plastic and co-affected by environmental factors through individual condition, resulting in a positive correlation between ornament expression and functional fertility. Ornaments may then serve females in the identification of the most fertile males. Despite intense research on the relationship between sexual characters and male ejaculate quality, published results are not consistent with the PLFH. The aim of our study was to test if sperm morphology is associated with sexual ornamentation and several health/condition-dependent traits in Great Tit males (Parus major). We evaluated the association between sperm morphology and two types of ornaments, carotenoid- and melanin-based ventral feather coloration, to evaluate predictions of the PLFH. As surrogates for condition and health/stress status, we used standardized male weight and the peripheral blood heterophil to lymphocyte ratio (H/L). Also, we used the immature erythrocyte frequency as a trait linked to the rate of haematopoiesis, and presumably metabolism and pace of life. Our results support an association of sperm traits with health-related traits: the within-male variability in total sperm length was negatively related to the H/L ratio. This either suggests that birds maintaining low sperm variability may afford to invest more into heterophil production or, in contrast to the PLFH, there could be a trade-off between individual investment in reproduction (ejaculate quality) and the avoidance of long-term physiological stress. Contrary to the predictions of the PLFH we were unable to identify any parameter of sperm morphology associated with either body condition or the expression of male sexual traits. Thus, our study contributes to evidence rejecting the hypothesis of ornamental involvement in fertility selection, while giving weak support to the sperm competition theory.

Female Choice Undermines the Emergence of Strong Sexual Isolation between Locally Adapted Populations of Atlantic Mollies (Poecilia mexicana).

Divergent selection between ecologically dissimilar habitats promotes local adaptation, which can lead to reproductive isolation (RI). Populations in the Poecilia mexicana species complex have independently adapted to toxic hydrogen sulfide and show varying degrees of RI. Here, we examined the variation in the mate choice component of prezygotic RI. Mate choice tests across drainages (with stimulus males from another drainage) suggest that specific features of the males coupled with a general female preference for yellow color patterns explain the observed variation. Analyses of male body coloration identified the intensity of yellow fin coloration as a strong candidate to explain this pattern, and common-garden rearing suggested heritable population differences. Male sexual ornamentation apparently evolved differently across sulfide-adapted populations, for example because of differences in natural counterselection via predation. The ubiquitous preference for yellow color ornaments in poeciliid females likely undermines the emergence of strong RI, as female discrimination in favor of own males becomes weaker when yellow fin coloration in the respective sulfide ecotype increases. Our study illustrates the complexity of the (partly non-parallel) pathways to divergence among replicated ecological gradients. We suggest that future work should identify the genomic loci involved in the pattern reported here, making use of the increasing genomic and transcriptomic datasets available for our study system.

Habitat constraints on carotenoid-based coloration in a small euryhaline teleost.

Display of bright and striking color patterns is a widespread way of communication in many animal species. Carotenoid‐based coloration accounts for most of the bright yellow, orange, and red displays in invertebrates, fish, amphibians, reptiles, and birds, being widely considered a signal of individual health. This type of coloration is under the influence of several factors, such as sexual selection, predator pressure, pigment availability, and light transmission. Fish offer numerous examples of visual communication by means of color patterns. We used a small cyprinodontid fish, Aphanius fasciatus (Valenciennes, 1821), as a model species to assess habitat constraints on the color display in male caudal fin. Populations from natural and open/closed artificial habitats were tested for differences in the pigmentation of caudal fins. The most important factors explaining the intensity of coloration were the habitat type and the chlorophyll concentration in the sediment, followed by water turbidity; yellow fins were observed in natural habitats with low chlorophyll concentration and high water turbidity, while orange fins occurred in artificial habitats with high chlorophyll concentration and low turbidity. Furthermore, A. fasciatus in artificial habitats showed a higher somatic and a lower reproductive allotment with respect to natural habitats, according to the existing literature on the species. Furthermore, in closed artificial habitats, where the most intense reddish coloration of caudal fins was observed, a trade‐off between somatic growth and the coloration intensity of a carotenoid‐based sexual ornament has been observed; in these populations, intensity of caudal fin coloration was negatively related to the somatic allotment. Results of this study suggested how both the pigmentation of male's caudal fin and the life history strategies of the species are constrained by habitat characteristics.

Mate sampling influences the intensity of sexual selection and the evolution of costly sexual ornaments

Mate choice includes three steps: (1) a choosing individual encounters potential mates, (2) assesses and processes information about them, and (3) makes a mate decision. During mate searching females can access only a sample of males in the mating pool and need to choose their mates based on limited information. Thus, mate sampling may influence sexual selection promoted by mate choice because it constrains female choice. Using individual-based simulations, we found that both female choosiness and mate sampling influenced the variance in mating success among males and thus the intensity of sexual selection. So that sexual selection is most intense when females are strongly choosy and can sample many males. Moreover, in evolutionary simulations, the rate of evolutionary change and the final size of male ornament increase with increasing mate sampling. However, under stronger natural selection, evolutionary change is slower and leads to smaller ornaments. Empirical data on the potential for sexual selection (Is) for several animal species show a positive correlation between the intensity of sexual selection and an index of mate sampling based on behavioral and ecological traits. Based on the results of our simulations, we predict that males of highly mobile species with long-range sexual signal transmission, which allow females to assess many males, will show greater variance in mating success and will be more ornamented than their relatives not exhibiting these features.

Asymmetries, heterosis, and phenotypic profiles of red junglefowl, White Plymouth Rocks, and F1 and F2 reciprocal crosses.

During the domestication of farm animals, humans have manipulated genetic variation for growth and reproduction through artificial selection. Here, data are presented for growth, reproductive, and behavior traits for the red junglefowl, a line of White Plymouth Rock chickens, and their F1 and F2 reciprocal crosses. Intra- and intergenerational comparisons for growth related traits reflected considerable additive genetic variation. In contrast, those traits associated with reproduction exhibited heterosis. The role of sexual selection was seen in the evolution of prominent secondary sexual ornaments that lend to female choice and male-male competition. The large differences between parental lines in fearfulness to humans were only mitigated slightly in the intercross generations. Whereas, overall F1 generation heterosis was not transferred to the F2, there was developmental stability in the F2, as measured by relative asymmetry of bilateral traits. Through multigenerational analyses between the red junglefowl and the domestic White Plymouth Rocks, we observed plasticity and considerable residual genetic variation. These factors likely facilitated the adaptability of the chicken to a broad range of husbandry practices throughout the world.

Apterous A specifies dorsal wing patterns and sexual traits in butterflies.

Butterflies have evolved different colour patterns on their dorsal and ventral wing surfaces to serve different signalling functions, yet the developmental mechanisms controlling surface-specific patterning are still unknown. Here, we mutate both copies of the transcription factor apterous in Bicyclus anynana butterflies using CRISPR/Cas9 and show that apterous A, expressed dorsally, functions both as a repressor and modifier of ventral wing colour patterns, as well as a promoter of dorsal sexual ornaments in males. We propose that the surface-specific diversification of wing patterns in butterflies proceeded via the co-option of apterous A or its downstream effectors into various gene regulatory networks involved in the differentiation of discrete wing traits. Further, interactions between apterous and sex-specific factors such as doublesex may have contributed to the origin of sexually dimorphic surface-specific patterns. Finally, we discuss the evolution of eyespot number diversity in the family Nymphalidae within the context of developmental constraints due to apterous regulation.

Neglected Patterns of Variation in Phenotypic Plasticity: Age- and Sex-Specific Antipredator Plasticity in a Cichlid Fish.

The ability of organisms to plastically respond to changing environments is well studied. However, variation in phenotypic plasticity during ontogeny is less well understood despite its relevance of being an important source of phenotypic variation in nature. Here, we comprehensively study ontogenetic variation in morphological antipredator plasticity across multiple traits in Pelvicachromis taeniatus, a western African cichlid fish with sexually dimorphic ornamentation. In a split-clutch design, fish were raised under different levels of perceived predation risk (conspecific alarm cues or distilled water). Morphological plasticity varied substantially across ontogeny: it was first observable at an early juvenile stage where alarm cue-exposed fish grew faster. Subsequently, significant plasticity was absent until the onset of sexual maturity. Here, alarm cue-exposed males were larger than control males, which led to deeper bodies, longer dorsal spines, larger caudal peduncles, and increased eye diameters. Sexual ornamentation emerged delayed in alarm cue-exposed males. In later adulthood, the plastic responses receded. Despite small effect sizes, these responses represent putative adaptive plasticity, as they are likely to reduce predation risk. In females, we did not observe any plasticity. In accordance with theory, these results suggest fine-tuned expression of plasticity that potentially increases defenses during vulnerable developmental stages and reproductive output.

Identification of molecular pathways and candidate genes associated with cocks\u2019 comb size trait by genome-wide transcriptome analysis

The comb of the male is an important secondary sexual characteristic. Although quantitative trait loci (QTLs) related to comb size have been identified, molecular mechanisms underlying this trait remain mostly unknown. In this study, RNA sequencing (RNA-seq) was employed to compare whole transcriptomic differences between two groups of Partridge Shank chickens that are divergent in comb sizes. A total of 563 differentially expressed genes (DEGs) were identified, including 277 up-regulated and 286 down-regulated DEGs. According to the animal QTL database, eight DEGs including BMP2 and CHADL matching the reported QTLs were associated with the comb size. Functional annotation analysis revealed that DEGs were involved in cell communication and calcium signaling. Protein-protein interaction network analysis showed that STK32A, PIK3R1, EDN1, HSPA5, and HSPA8 have an impact on comb growth. Moreover, potential alternative splicing events and single nucleotide polymorphisms were also identified. Our data provide a source for identifying genes and pathways with functions critical to comb size and accelerate studies involving molecular mechanisms of this sexual ornament.

Evolving doublesex expression correlates with the origin and diversification of male sexual ornaments in the Drosophila immigrans species group.

Male ornaments and other sex-specific traits present some of the most dramatic examples of evolutionary innovations. Comparative studies of similar but independently evolved traits are particularly important for identifying repeated patterns in the evolution of these traits. Male-specific modifications of the front legs have evolved repeatedly in Drosophilidae and other Diptera. The best understood of these novel structures is the sex comb of Drosophila melanogaster and its close relatives. Here, we examine the evolution of another male foreleg modification, the sex brush, found in the distantly related Drosophila immigrans species group. Similar to the sex comb, we find that the origin of the sex brush correlates with novel, spatially restricted expression of the doublesex (dsx) transcription factor, the primary effector of the Drosophila sex determination pathway. The diversity of Dsx expression patterns in the immigrans species group closely reflects the differences in the presence, position, and size of the sex brush. Together with previous work on sex comb evolution, these observations suggest that tissue-specific activation of dsx expression may be a common mechanism responsible for the evolution of sexual dimorphism and particularly for the origin of novel male-specific ornaments.

Maternal breast and body symmetry in pregnancy and offspring condition.

Fluctuating asymmetry (FA) is hypothesized to reflect the level of an individual's developmental instability, and therefore genetic quality. As a potential signal of biological condition, female body (including breast) symmetry was shown to be perceived as more attractive in mate choice context. If symmetry reflects a woman's genetic quality, it is possible that FA, similarly to other maternal anthropometric cues of biological condition (e.g., body height or waist-to-hip ratio), may be also related to her offspring condition. To test this, breast and body asymmetry was measured in 93 pregnant women in the 1st, 2nd, and 3rd pregnancy trimester. Child's birth weight, length, chest and head circumference, information on the Apgar score, congenital malformations, and birth complications was taken from hospital records. The relationships between offspring birth characteristics and maternal breast FA and body FA were analyzed separately, controlled for a child's sex and maternal weight in pregnancy. Breast asymmetry was not a predictor of a child's neonatal condition assessed from morphological parameters at birth. Asymmetry of maternal non-ornamental body characteristcs, commonly used to assess body FA, correlated negatively with a child's weight, head and chest circumference at birth. A composite asymmetry index of eight body traits, non-sexually selected characteristics, seems to be a better predictor of a woman's ability to invest in fetus during pregnancy than breast asymmetry, sexual ornamentation that is perceived as a signal of a woman's attractiveness and biological condition.

Selection for relative brain size affects context-dependent male preference for, but not discrimination of, female body size in guppies.

Understanding what drives animal decisions is fundamental in evolutionary biology, and mate choice decisions are arguably some of the most important in any individual's life. As cognitive ability can impact decision making, elucidating the link between mate choice and cognitive ability is necessary to fully understand mate choice. To experimentally study this link, we used guppies (Poecilia reticulata) artificially selected for divergence in relative brain size and with previously demonstrated differences in cognitive ability. A previous test in our female guppy selection lines demonstrated the impact of brain size and cognitive ability on information processing during female mate choice decisions. Here, we evaluated the effect of brain size and cognitive ability on male mate choice decisions. Specifically, we investigated the preference of large-brained, small-brained and non-selected guppy males for female body size, a key indicator of female fecundity in this species. For this, male preference was quantified in dichotomous choice tests when presented with dyads of females with small, medium and large body size differences. All types of males showed a preference for larger females but no effect of brain size was found in the ability to discriminate between differently sized females. However, we found that non-selected and large-brained males, but not small-brained males, showed a context-dependent preference for larger females depending on the difference in female size. Our results have two important implications. First, they provide further evidence that male mate choice also occurs in a species in which secondary sexual ornamentation is present only in males. Second, they show that brain size and cognitive ability have important effects on individual variation in mating preference and sexually selected traits.

Phd-Dissertation Reviews in Ornithology (2016–2017 Academic Year)

Oxidative stress is the imbalance between the antioxidant capacity of an organism and the production of free radicals that can damage important biomolecules (lipids, proteins or DNA), affecting cellular senescence. Environmental conditions experienced by organisms can exert a strong influence on the development and expression of their phenotype, especially during early development and reproduction, which may determine access to territories, fecundity and survival. On the other hand, understanding the relationship between oxidative status and telomere dynamics -regions of non-coding DNA whose function is to stabilize the structure of chromosomes and with a fundamental role in ageing- is essential to fully appraise the mechanisms underlying the life-histories determined by the existing trade-offs between reproduction, maintenance and growth. Thus, the main objective of this thesis is to determine, from an ecological-evolutionary point of view, the role of oxidative stress in relation to the different life-histories developed by the birds, analyzing the influence of the nesting environment and the intrinsic and external factors affecting individuals during early development and reproduction. We have studied the physiological adaptations, in relation to oxidative stress, to the different trade-offs that birds face during their life cycle. The Pied Flycatcher (Ficedula hypoleuca) has been used as the study model. The study areas are located in the Sierra de Guadarrama, one in Montes de Valsaín (Segovia), where there are 570 nest boxes, and another one in Lozoya (Madrid), with 100 nest boxes. Both experimental and observational studies have been carried out to analyze the influence of nesting environment and nest-dwelling ectoparasites on nestlings and parental individuals, the costs derived from the reproductive investment and the maintenance of sexual ornaments, the factors affecting the redox status in the early life and the relationships between reproduction, oxidative stress and ageing. Films of nests have been made to analyze parental care and, in all cases, blood samples have been taken from all individuals (adults and nestlings), for analysis of oxidative and biochemical parameters (oxidative damage, antioxidants, triglycerides, uric acid), sex (only in nestlings) and measures of telomeres (adults). In addition, photographs of adult plumage ornaments have been taken to analyze them as a sign of individual quality. This thesis contributes to verify the strong implication of the oxidative state in the trade-offs that sustain life-histories of birds. On the one hand, this thesis shows that the presence of old material in the nest does not affect all populations of ectoparasites equally, questioning the general idea that nest reuse is linked to higher infestations, with consequences on reproductive success and nestling growth. In addition, it is shown how the method to reduce ectoparasite loads of the nest can have uncontrolled effects on birds, which may lead to underestimation of the potential consequences of the presence of such ectoparasites on their avian hosts. We found experimental evidences of negative effects of ectoparasite loads on the oxidative status of adult females and developing chicks, which could have consequences on future survival and reproduction. This study also shows the associations between different components of the oxidative status of developing chicks and various environmental and intrinsic factors, which is essential to understand the importance of oxidative stress in the formation of the phenotype. On the other hand, it is suggested that different achromatic features of plumage can signal the individual capacity to cope with oxidative stress and the importance of the different phases of the reproductive cycle is emphasized to understand the role of oxidative stress as cost and constraint in reproduction. Finally, it is evidenced how the oxidative status is related with telomeres shortening (conseque

Hybrid speciation leads to novel male secondary sexual ornamentation of an Amazonian bird

Hybrid speciation is rare in vertebrates, and reproductive isolation arising from hybridization is infrequently demonstrated. Here, we present evidence supporting a hybrid-speciation event involving the genetic admixture of the snow-capped (Lepidothrix nattereri) and opal-crowned (Lepidothrix iris) manakins of the Amazon basin, leading to the formation of the hybrid species, the golden-crowned manakin (Lepidothrix vilasboasi). We used a genome-wide SNP dataset together with analysis of admixture, population structure, and coalescent modeling to demonstrate that the golden-crowned manakin is genetically an admixture of these species and does not represent a hybrid zone but instead formed through ancient genetic admixture. We used spectrophotometry to quantify the coloration of the species-specific male crown patches. Crown patches are highly reflective white (snow-capped manakin) or iridescent whitish-blue to pink (opal-crowned manakin) in parental species but are a much less reflective yellow in the hybrid species. The brilliant coloration of the parental species results from nanostructural organization of the keratin matrix feather barbs of the crown. However, using electron microscopy, we demonstrate that the structural organization of this matrix is different in the two parental species and that the hybrid species is intermediate. The intermediate nature of the crown barbs, resulting from past admixture appears to have rendered a duller structural coloration. To compensate for reduced brightness, selection apparently resulted in extensive thickening of the carotenoid-laden barb cortex, producing the yellow crown coloration. The evolution of this unique crown-color signal likely culminated in premating isolation of the hybrid species from both parental species.

Experimental stress during molt suggests the evolution of condition-dependent and condition-independent ornaments in the king penguin.

Sexual selection and social selection are two important theories proposed for explaining the evolution of colorful ornamental traits in animals. Understanding signal honesty requires studying how environmental and physiological factors during development influence the showy nature of sexual and social ornaments. We experimentally manipulated physiological stress and immunity status during the molt in adult king penguins (Aptenodytes patagonicus), and studied the consequences of our treatments on colourful ornaments (yellow‐orange and UV beak spots and yellow‐orange auricular feather patches) known to be used in sexual and social contexts in this species. Whereas some ornamental features showed strong condition‐dependence (yellow auricular feather chroma, yellow and UV chroma of the beak), others were condition‐independent and remained highly correlated before and after the molt (auricular patch size and beak UV hue). Our study provides a rare examination of the links between ornament determinism and selection processes in the wild. We highlight the coexistence of ornaments costly to produce that may be honest signals used in mate choice, and ornaments for which honesty may be enforced by social mediation or rely on genetic constraints.

Sex Differences in 20-Hydroxyecdysone Hormone Levels Control Sexual Dimorphism in Bicyclus anynana Wing Patterns.

In contrast to the important role of hormones in the development of sexual traits in vertebrates (Cox RM, Stenquist DS, Calsbeek R. 2009. Testosterone, growth and the evolution of sexual size dimorphism. J Evol Biol. 22(8):1586–1598.), the differentiation of these traits in insects is attributed almost exclusively to cell-autonomous mechanisms controlled by members of the sex determination pathway (Verhulst EC, van de Zande L. 2015. Double nexus – doublesex is the connecting element in sex determination. Brief Funct Genomics 14(6):396–406.), such as doublesex. Although hormones can shape the development of sexual traits in insects, variation in hormone levels are not conclusively known to cause dimorphism in these traits (Prakash A, Monteiro A. 2016. Molecular mechanisms of secondary sexual trait development in insects. Curr Opin Insect Sci. 17:40–48.). Here, we show that butterflies use sex-specific differences in 20-hydroxyecdysone hormone titers to create sexually dimorphic wing ornaments. Females of the dry season (DS) form of Bicyclus anynana display a larger sexual ornament on their wings than males, whereas in the wet season form both sexes have similarly sized ornaments (Prudic KL, Jeon C, Cao H, Monteiro A. 2011. Developmental plasticity in sexual roles of butterfly species drives mutual sexual ornamentation. Science 331(6013):73–75.). High levels of circulating 20-hydroxyecdysone during larval development in DS females and wet season forms cause proliferation of the cells fated to give rise to this wing ornament, and results in sexual dimorphism in the DS forms. This study advances our understanding of how the environment regulates sex-specific patterns of plasticity of sexual ornaments and conclusively shows that hormones can play a role in the development of secondary sexual traits in insects, just like they do in vertebrates.

Parasitism affects variation in a male damselfly sexual ornament

Sexually selected ornaments in animals are costly, with parasitism often affecting the degree to which they are expressed. Male Calopteryx splendens damselflies exhibit melanised ‘wing spots’. Those possessing large spots are favoured by females but also have an increased likelihood of being attacked by Calopteryx virgo, a common sympatric competitor. Melanin is used to produce the wing spots, but it is also used in immune defence against parasites that commonly infect damselflies. A total of 261 C. splendens males were collected from 26 Finnish and Latvian populations, of which half were found to be sympatric with C. virgo. It was found that males which originated from populations in which eugregarine parasites were present had smaller wing spots than individuals from parasite-free populations. Contrary to previous studies, the wing spots of C. splendens males in populations sympatric with C. virgo were not found to be smaller than those in allopatric populations. Parasite presence in C. splendens was found to be strongly associated with populations sympatric with C. virgo. The results suggest that the presence of C. virgo may increase rates of parasitism in C. splendens, and show that parasitism is an important additional factor to interspecific aggression in determining variation in the sizes of the wing spots of C. splendens males. These findings highlight a lack of understanding on the determinants of the expression of secondary sexual characters and the processes of how parasitism affects hosts.

Viability and expression of sexual ornaments in the barn swallow Hirundo rustica: a meta-analysis.

Sexual selection results in the evolution of exaggerated secondary sexual characters that can entail a viability cost. However, in species where sexual ornaments honestly reflect individual quality, the viability cost of secondary sexual characters may be overwhelmed by variation in individual quality, leading to expect that individuals with the largest secondary sexual characters show higher, rather than lower viability. Here, we used meta-analyses to test whether such expected positive relationship between sexual ornamentation and viability exists in the barn swallow Hirundo rustica, which is one of the most studied model species of sexual selection under field conditions. We found a mean positive effect size of viability in relation to the expression of secondary sexual characters of 0.181 (CI: 0.084-0.278), indicating that in this species the more ornamented individuals are more viable, and therefore of high quality. Analyses of moderator variables showed similar effects in males and females, the H.r.rustica subspecies rather than others and tail length rather than other secondary sexual characters. Future research emphasis on other subspecies than the European one and secondary sexual characters than tail length may help identify the sources of heterogeneity in effect sizes.

Lifetime reproductive success, selection on lifespan, and multiple sexual ornaments in male European barn swallows.

Natural and sexual selection arise when individual fitness varies according to focal traits. Extra-pair paternities (EPPs) can affect the intensity of selection by influencing variance in fitness among individuals. Studies of selection require that individual fitness is estimated using proxies of lifetime reproductive success (LRS). However, estimating LRS is difficult in large, open populations where EPPs cause reallocation of biological paternity. Here, we used extensive field sampling to estimate LRS in a population of barn swallows (Hirundo rustica) to estimate selection on lifespan and ornamental traits of males. We found selection on lifespan mediated both by within- and extra-pair fertilization success and selection on tail length mediated by within- but not extra-pair fertilization success. In addition, we found selection on tail white spots via extra-pair fertilization success after controlling for selection on other traits. These results were not confounded by factors that hamper studies of LRS, including nonexhaustive sampling of offspring and biased sampling of males. Hence, natural and sexual selection mediated by LRS operates on lifespan, tail length, and size of the tail white spots in barn swallows.