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Where dramatic sexual displays are involved in attracting a mate, individuals can enhance their performances by manipulating their physical environment. Typically, individuals alter their environment either in preparation for a performance by creating a "stage" or during the display itself by using discrete objects as "props." We examined an unusual case of performative manipulation of an entire stage by male Albert's lyrebirds (Menura alberti) during their complex song and dance displays. We found that males from throughout the species' range shake the entangled forest vegetation of their display platforms, creating a highly conspicuous and stereotypical movement external to their bodies. This "stage shaking" is performed in two different rhythms, with the second rhythm an isochronous beat that matches the beat of the coinciding vocalizations. Our results provide evidence that stage shaking is an integral, and thus likely functional, component of male Albert's lyrebird sexual displays and so highlight an intriguing but poorly understood facet of complex communication. [ABSTRACT FROM AUTHOR]

The postulates of developmental instability–sexual selection hypothesis is intensely debated among evolutionary biologists, wherein despite a large amount of empirical data, evidence for or against it has been largely inconclusive. A key assumption of this hypothesis is that animals assess symmetry in potential mates as an indicator of genetic quality (developmental stability), and consequently use this information to discriminate against those with higher asymmetries while choosing mates. However, the perceptional basis that must underlie such discriminatory behavior (is symmetry a signal or is symmetry signaled) is not clearly defined. It is also argued that since asymmetry levels in natural populations are very low, the low signal‐to‐noise ratio would make accurate assessment of symmetry both difficult and costly. Rather than attempting to validate this hypothesis or even as to whether animals assess mate symmetry, this review simply aims to examine the plausibility that animals perceive symmetry (directly or indirectly) and consequently discriminate against asymmetric mates in response to perceived irregularities during courtship. For this, we review mate choice and courtship literature to identify potential sensory cues that might advertise asymmetry or lead to discrimination of asymmetric individuals. Although signaling associated with mate choice is commonly multimodal, previous studies on asymmetry have mainly focused on visual perception. In the light of a recent study (Vijendravarma et al., 2022, Proceedings of the National Academy of Sciences of the United States of America, 119, e2116136119), this review attempts to balance this bias by emphasizing on non‐visual perception of asymmetry. In conclusion, we discuss the methodological challenges associated with testing the role of multimodal cues in detecting mate asymmetry, and highlight the importance of considering ecological, behavioral, and evolutionary aspects of animals while interpreting empirical data that test such hypothesis. [ABSTRACT FROM AUTHOR]

Many animals use extended phenotypes to attract mates, but the availability of suitable resources in the environment can affect the size and form of these signals, with unknown consequences for honest signalling. In some populations of the great bowerbird, Ptilonorhynchus nuchalis, males arrange decorations by size, with smaller decorations placed closer to the bower entrance than larger decorations. This may create a more even background pattern from the female's viewpoint within the bower than if decorations were arranged randomly. Males show consistent, individual variation in the size-distance gradient, which could reflect variation among males in the cognitive skills needed to arrange decorations. We examined whether individual consistency in gradient characteristics is related to a male's skill at decoration arrangement or the types of decorations at bowers. We paired 18 males and switched bower decorations between pairs. We measured gradient characteristics before switching and 4 and 8 days after switching. Gradient characteristics after switching were related to those of the bower from which decorations were received, not to those of the male's own bower before switching. Gradient characteristics were also related to the types of decorations received, including bones and snail shells. These results suggest that variation among males in the size-distance gradient is explained by differences in the availability of decorations at bowers, not the cognitive skills required to arrange decorations. Although variation in gradient characteristics could indicate the male's ability to locate and transport particular decorations, it could also reflect local availability of objects, with no relationship to male quality.

Many animals use extended phenotypes to attract mates, but the availability of suitable resources in the environment can affect the size and form of these signals, with unknown consequences for honest signalling. In some populations of the great bowerbird, Ptilonorhynchus nuchalis, males arrange decorations by size, with smaller decorations placed closer to the bower entrance than larger decorations. This may create a more even background pattern from the female's viewpoint within the bower than if decorations were arranged randomly. Males show consistent, individual variation in the size-distance gradient, which could reflect variation among males in the cognitive skills needed to arrange decorations. We examined whether individual consistency in gradient characteristics is related to a male's skill at decoration arrangement or the types of decorations at bowers. We paired 18 males and switched bower decorations between pairs. We measured gradient characteristics before switching and 4 and 8 days after switching. Gradient characteristics after switching were related to those of the bower from which decorations were received, not to those of the male's own bower before switching. Gradient characteristics were also related to the types of decorations received, including bones and snail shells. These results suggest that variation among males in the size-distance gradient is explained by differences in the availability of decorations at bowers, not the cognitive skills required to arrange decorations. Although variation in gradient characteristics could indicate the male's ability to locate and transport particular decorations, it could also reflect local availability of objects, with no relationship to male quality.

Sexual dimorphism is widespread, but we have a limited understanding of its significance for communities and ecosystems. Several new experiments demonstrate that sexual dimorphism can have far-reaching ecological effects. These results suggest that sexual dimorphism and sexual selection are potent, but largely overlooked components of eco-evolutionary dynamics. [ABSTRACT FROM AUTHOR]

Male-male competition can cause less competitive males to pursue alternative mating strategies or defer reproduction until they are older. For species that display using non-bodily ornaments, male interference can also involve limiting rivals’ access to display materials. I document a novel solution to male interference with external display structures in Great Bowerbirds (Ptilonorhynchus nuchalis). Males build and display at stick structures (‘bowers’), but they frequently destroy other males’ bowers. I show that some males, including young individuals, adapt to this interference by displaying around tree trunks instead of bowers. Tree trunks cannot be destroyed, so males can display at them despite interference. Display rates were higher at tree trunk display sites (‘display trees’) than bowers. Display trees had a basal diameter similar to the width of the front of the bower walls, allowing males to display in a similar manner as at bowers. Bower-owning males stole more experimentally placed decorations from display trees than random trees or bowers; most attempts at bower building by males at display trees were destroyed. Display trees were located closer to bowers than bowers were to each other. Display trees may allow younger and less competitive males to attempt to attract females visiting nearby established bowers and to gain competence in display. [ABSTRACT FROM AUTHOR]

Sexual selection is most often thought of as acting on organismal traits, such as size or color. However, individuals' habitat use may also affect mating success. Here, we show that, in threespine stickleback, nest depth can be a target of sexual selection. In postglacial lakes in British Columbia, male threespine stickleback nest in a narrow range of depths. Prior studies revealed heritable variation in males' preferred nest microhabitat. We surveyed four natural populations, finding that male stickleback with shallower nests were more successful at breeding. Indeed, nest depth was a much stronger predictor of male mating success than more commonly studied targets of sexual selection in stickleback (size, condition, shape, color, infection status). This selection on nest depth means that variance in fitness changed predictably across microhabitats, altering the opportunity for sexual selection to act on other traits. Accordingly, we show that sexual selection on other male traits is strongest where variance in nesting success is highest (at intermediate nest depths in some lakes). We conclude that males' choice of nesting microhabitat is an especially important target of sexual selection, resulting in fine-scale spatial variation in sexual selection on other traits. [ABSTRACT FROM AUTHOR]

In social species, fitness consequences are associated with both individual and social phenotypes. Social selection analysis has quantified the contribution of conspecific social traits to individual fitness. There has been no attempt, however, to apply a social selection approach to quantify the fitness implications of heterospecific social phenotypes. Here, we propose a novel social selection based approach integrating the role of all social interactions at the community level. We extended multilevel selection analysis by including a term accounting for the group phenotype of heterospecifics. We analyzed nest activity as a model social trait common to two species, the lesser kestrel ( Falco naumanni) and jackdaw ( Corvus monedula), nesting in either single- or mixed-species colonies. By recording reproductive outcome as a measure of relative fitness, our results reveal an asymmetric system wherein only jackdaw breeding performance was affected by the activity phenotypes of both conspecific and heterospecific neighbors. Our model incorporating heterospecific social phenotypes is applicable to animal communities where interacting species share a common social trait, thus allowing an assessment of the selection pressure imposed by interspecific interactions in nature. Finally, we discuss the potential role of ecological limitations accounting for random or preferential assortments among interspecific social phenotypes, and the implications of such processes to community evolution. [ABSTRACT FROM AUTHOR]

Many animals use extended phenotypes to attract mates, but the availability of suitable resources in the environment can affect the size and form of these signals, with unknown consequences for honest signalling. In some populations of the great bowerbird, Ptilonorhynchus nuchalis , males arrange decorations by size, with smaller decorations placed closer to the bower entrance than larger decorations. This may create a more even background pattern from the female's viewpoint within the bower than if decorations were arranged randomly. Males show consistent, individual variation in the size–distance gradient, which could reflect variation among males in the cognitive skills needed to arrange decorations. We examined whether individual consistency in gradient characteristics is related to a male's skill at decoration arrangement or the types of decorations at bowers. We paired 18 males and switched bower decorations between pairs. We measured gradient characteristics before switching and 4 and 8 days after switching. Gradient characteristics after switching were related to those of the bower from which decorations were received, not to those of the male's own bower before switching. Gradient characteristics were also related to the types of decorations received, including bones and snail shells. These results suggest that variation among males in the size–distance gradient is explained by differences in the availability of decorations at bowers, not the cognitive skills required to arrange decorations. Although variation in gradient characteristics could indicate the male's ability to locate and transport particular decorations, it could also reflect local availability of objects, with no relationship to male quality. [ABSTRACT FROM AUTHOR]

In resource defence polygyny, where males defend resources that females use for reproduction, the resource characteristics preferred by the two sexes are expected to match. We tested this expectation by comparing the shell characteristics preferred by males and females in the shell-brooding cichlid fish Lamprologus callipterus . In this species, males attract females by collecting and defending shells within which females breed. We added shells to males' nests and found that females were more likely to occupy large shells but made no distinction between new, smooth shells and old shells coated with mineral deposits. In contrast, when we placed additional shells adjacent to males' nests, males were more likely to retrieve shells covered in mineral deposits but showed no significant preference for large shells over small shells. Furthermore, many shells in males' nests were smaller than the smallest shell that females used for breeding. The discrepancy between male and female preferences suggests that empty shells in L. callipterus nests may have additional functions, beyond serving as breeding substrate. We discuss the possibility that shells may also be extended phenotype signals analogous to the decorations of a bower. [ABSTRACT FROM AUTHOR]

Nests are built by a wide variety of animals as functional receptacles for developing eggs and offspring, and they play a critical role in the reproductive biology of many species. Traditionally, research on the ecology and evolution of nest building and construction behaviour has focused primarily on birds, and avian studies have dominated the literature. However, as researchers working on non-bird models have realised the importance of nest construction in evolutionary ecology, the number of studies published on the nesting behaviour of nonbird taxa has increased. An analysis of the literature reveals that fish have become major models for studying many aspects of nest building behaviour, but whereas studies of fish nest building behaviour frequently cite classical and contemporary bird studies, the findings of recent fish nesting research appears to be slower to be recognised by bird biologists. Further analysis reveals that this citation bias may arise because of the tendency of nest building studies to be published in taxon-specific, often local journals, and this may be especially the case for bird-focused studies. In this review, I summarise the recent literature on fish nesting behaviour, focusing on aspects that should be of mutual interest to fish and bird biologists. I hope that the review may be used by bird biologists to identify complementary and insightful nest-building research in fish, and that researchers with interests in the nest-building behaviour of animals across the taxonomic spectrum might use the review to focus on questions of mutual and general importance and interest. [ABSTRACT FROM AUTHOR]

Purpose-built nests for rearing offspring have important fitness consequences. Nests not only provide a protective environment for developing young but also in some species can serve as important signalling devices that reveal crucial information about the quality of the builder. Nesting behaviour and nest structure are often adjusted to suit local environmental conditions. An important question is what happens when conditions are altered as a result of anthropogenic activities. Human-induced eutrophication is an insidious, global problem. Here, we investigated experimentally the impact of algal blooms on nest construction in a fish: the three-spined stickleback, Gasterosteus aculeatus. We found that males took longer to complete their nests under algal conditions. Completed nests were also smaller and possessed wider nest entrances. Together, our results suggest that human-induced algal blooms can have profound effects on nesting behaviour and nest construction, with implications for both offspring survival and the utility of nests as extended phenotypic signals. [Copyright &y& Elsevier]

To be useful as mate choice cues, behavioural traits have to be performed consistently within individuals. This may also be true for nest construction, which, in addition to influencing offspring survival, can also function as an extended phenotype of the builder. We tested whether choice of a nesting resource and subsequent nest-building performance are repeatable traits in the sand goby, Pomatoschistus minutus, a small marine fish with paternal egg care and female mating preferences that are influenced by male nest-building behaviour. When given a choice between three different-sized nesting resources (flowerpots), males, on average, preferred medium-sized nesting resources, with larger males preferring larger nests than smaller individuals. At the individual level, the choice of nesting resources was so variable between consecutive trials that choice behaviour was not repeatable. Furthermore, nest building, measured as the amount of sand piled on top of the nesting resource, was highly repeatable when males were free to choose their nest, but had only a low repeatability when males had just a single option. In neither case was the size of the nest entrance repeatable between consecutive rounds of nest building. These results highlight the context-dependent signal value of extended phenotypes. In particular, reliability of nest-building behaviour as a signal seems to be influenced by the male''s opportunity to choose the object it uses for nesting. [Copyright &y& Elsevier]

Interactions between the components of a multiple-signal sexual display can be complex, and previous work has shown that alteration of one component can lead to changed investment in either the altered or other display components. Extended phenotype signals (nonbody structures that carry a signalling function) provide an ideal means to manipulate signal quality in a noninvasive manner, to investigate investment patterns in display components. We made three predictions as to how males might alter investment in display components in response to artificial enhancement of an extended phenotype signal, and tested those predictions using three-spined sticklebacks, Gasterosteus aculeatus. The addition of brightly coloured ornaments (threads) to the nests of male sticklebacks led to increased investment in both courtship of females and nest construction. In a field experiment, males offered coloured threads spent increased time engaged in interactions with females, and in the laboratory, they built nests that were neater and more compact (better quality), relative to males offered dull threads. Our findings support a hypothesis based on resource budgeting, and suggest that resources saved by having an artificially enhanced nest are reallocated to other courtship behaviours. The study provides a framework for investigating the interaction between signal components, and demonstrates that manipulation of extended phenotype signals can provide insight into the ways in which animals balance investment in interacting signal components in sexual displays. [ABSTRACT FROM AUTHOR]

Coevolutionary arms races between males and females have equipped both sexes with mutually manipulative and defensive adaptations. These adaptations function to benefit individual reproductive interests at the cost of the reproductive interests of oppositesex mates, and arise from evolutionary dynamics such as parental investment (unequal reproductive costs between the sexes) and sexual selection (unequal access to opposite-sex mates). Individuals use these adaptations to hijack others' reproductive systems, psychological states, and behaviors--essentially using other individuals as extended phenotypes of themselves. Such extended phenotypic manipulation of sexual rivals and opposite-sex mates is enacted by humans with the aid of hormones, pheromones, neurotransmitters, emotions, language, mind-altering substances, social institutions, technologies, and ideologies. Furthermore, sexual conflict may be experienced at an individual level when maternal genes and paternal genes are in conflict within an organism. Sexual conflict may be physically and emotionally destructive, but may also be exciting and constructive for relationships. By extending the biological concept of sexual conflict into social and cultural domains, scholars may successfully bridge many of the interdisciplinary gaps that separate the sciences from the humanities. [ABSTRACT FROM AUTHOR]

In a wide range of animal taxa, males build elaborate mating structures to attract females. For instance, some bird species use their nests or display sites as nonbodily ornaments (extended phenotypes) in intersexual communication. Recently, it has been proposed that feather carrying constitutes a postmating sexual display. Here, evidence supporting this hypothesis is presented for a species in which such behavior had not been previously reported, the blue tit Cyanistes caeruleus. In our Mediterranean study populations, males carry feathers to the nest and place them outside the nest cup. Here, we show experimentally and by means of observational data that feather carrying by male blue tits induced their mates to increase their clutch size. In addition, males from ornamented nests fed their offspring at a higher rate than those from nests in which this behavior was not detected. Feather-carrying effort was positively associated with male tarsus length. On the other hand, females paired with males engaging in this activity reduced their feeding rates but obtained direct fitness benefits: Ornamented nests resulted in more fledged young with better body condition than those without feathers carried by males. In summary, this study suggests that male feather-carrying ability constitutes an honest signal of their parental quality and a good predictor of breeding success in these blue tit populations. [ABSTRACT FROM PUBLISHER]

In many animals, sexual selection on male traits results from female mate choice decisions made during a sequence of courtship behaviors. We use a bower-building cichlid fish, Nyassachromis cf. microcephalus, to show how applying standard selection analysis to data on sequential female assessment provides new insights into sexual selection by mate choice. We first show that the cumulative selection differentials confirm previous results suggesting female choice favors males holding large volcano-shaped sand bowers. The sequential assessment analysis reveals these cumulative differentials are the result of selection acting on different bower dimensions during the courtship sequence; females choose to follow males courting from tall bowers, but choose to engage in premating circling with males holding bowers with large diameter platforms. The approach we present extends standard selection analysis by partitioning the variances of increasingly accurate estimates of male reproductive fitness and is applicable to systems in which sequential female assessment drives sexual selection on male traits. [ABSTRACT FROM AUTHOR]

Sexual selection arising through female mate choice typically favours males with larger, brighter and louder signals. A critical challenge in sexual selection research is to determine the degree to which this pattern results from direct mate choice, where females select individual males based on variation in signalling traits, or indirect mate choice, where male competition governs access to reproductively active females. We investigated female mate choice in a lekking Lake Malawi cichlid fish, Hemitilapia oxyrhynchus, in which males build and aggressively defend sand ‘bowers’. Similar to previous studies, we found that male reproductive success was positively associated with bower height and centrality on the lek. However, this pattern resulted from males holding these territories encountering more females, and thus their greater success was due to indirect mate choice. Following initial male courtship, an increase in the relative mating success of some males was observed, but this relative increase was unrelated to bower size or position. Crucially, experimentally manipulating bowers to resemble those of a co-occurring species had no appreciable effect on direct choice by females or male spawning success. Together, these results suggest indirect mate choice is the dominant force determining male-mating success in this species, and that bowers are not signals used in direct mate choice by females. We propose that, in this species, bowers have a primary function in intraspecific male competition, with the most competitive males maintaining larger and more central bowers that are favoured by sexual selection due to higher female encounter rates. [ABSTRACT FROM AUTHOR]