Sexual Selection Pressures Research Articles

Sexual Selection on Non-Ornamental Traits Is Underpinned by Evidence of Genetic Constraints on Sex-Biased Expression in Dusky Pipefish.

Species lacking distinct secondary sex characteristics, such as differences in size or morphology, are often thought to experience lower levels of sex-specific selection in comparison to highly sexually dimorphic organisms. However, monomorphism in classic visible traits could be a result of genetic or physiological constraints that prevent the sexes from reaching divergent fitness optima. Additionally, biochemical and molecular work have revealed a variety of less easily observed phenotypes that nonetheless exhibit profound dimorphism. Sex-specific selection could act on these more subtle, less visible, traits. We investigate sex-specific selection in the polygynandrous dusky pipefish (Syngnathus floridae), which lacks distinct secondary sexual characteristics such as size, colour and morphological dimorphism. Using experimental breeding populations, we revealed that although males and females have similar opportunities for sexual selection, only males experience significant sexual selection pressures on body size. We also investigated patterns of sex-biased and sex-specific gene expression in gonads, livers and gills, and tested whether genes with highly divergent expression patterns between the sexes are more likely to be tissue-specific, and therefore relieved of genetic constraints. Sex bias in gene expression was widespread, although the reproductive organs had the most sex-biased and sex-specific genes. Sex-specific selection on gene expression in gills was primarily related to immune response, whereas the liver and gonads had a wide variety of cellular processes, as well as reproductive proteins, showing sex-biased expression. These sex-biased genes showed higher organ-specificity in their expression patterns, suggesting that pleiotropic constraints might have historically impacted the evolution of sex-specific expression patterns. Altogether, we find evidence for ongoing and historical sex-specific selection in the dusky pipefish.

Females increase reproductive investment when mated to less sexually attractive males in a serially monogamous fish

Reproductive investment decision is an integral part of life-history theory. Differential allocation hypothesis predicts that females should increase investment when mated to high-quality males, conversely, reproductive compensation hypothesis predicts that females should increase investment when mated to low-quality males. Empirical research dominantly focuses on polygamous species and rarely on serially monogamous species. So, the question remains: which hypothesis does serially monogamous species fit? And if it fits reproductive compensation hypothesis, do females only compensate once or continuously for multiple times when mating to low-quality males? Here, we used a serially monogamous fish, the lined seahorse (Hippocampus erectus), to investigate the reproductive investment pattern of females in relation to male quality (measured by sexual attractiveness). We found that females allocated more resources into eggs when they mated to less-sexually-attractive males, indicating the investment pattern of lined seahorse falls in with the prediction of reproductive compensation hypothesis. This finding may imply that the sex role of seahorses is reversed, and female is the side imposed on a greater sexual selection pressure. On this basis, we compared the investment difference of females in two consecutive breeding events when mated to less-sexually-attractive males. We found that females allocated less resources into eggs in the second breeding than in the first one. Females reduced their reproductive compensation in the second breeding, which may be attributed to the improvement in the quality (e.g., paternal care ability) of their mates after the first breeding, thus eliminating the need for them to invest more in the second breeding.

Natural variation in sexual traits and gene expression between selfing and outcrossing Arabidopsis lyrata suggests sexual selection at work.

Flowering plants show significant diversity in sexual strategies, profoundly impacting the evolution of sexual traits and associated genes. Sexual selection is one of the primary evolutionary forces driving sexual trait variation, particularly evident during pollen-pistil interactions, where pollen grains compete for fertilization and females select mating partners. Multiple mating may intensify competition among pollen donors for siring, while in contrast, self-fertilization reduces sire-sire competition, relaxing the sexual selection pressure. Traits involved in male-male competition and female choice are well described, and molecular mechanisms underlying pollen development and pollen-pistil interactions have been extensively studied in the model species Arabidopsis thaliana. However, whether these molecular mechanisms are involved in sexual selection in nature remains unclear. To address this gap, we measured intrinsic pollen performance and its interaction with female choice, and investigated the associated gene expression patterns in a selfing and an outcrossing population of Arabidopsis lyrata. We found that pollen germination and pollen tube growth were significantly higher in outcrossers than selfers, and this difference was accompanied by changes in expression of genes involved in vesicle transport and cytoskeleton. Outcrosser mother plants showed a negative impact on pollen tube growth compared to selfer mother plants, together with a difference of expression for genes involved in auxin and stress response, suggesting a potential mechanism for female choice through molecular crosstalk at the post-pollination stage. Our study provides insight on the impact of sexual selection on the evolution of sexual gene expression in plants.

Blouch: Bayesian Linear Ornstein-Uhlenbeck Models for Comparative Hypotheses.

Relationships among species in the tree of life can complicate comparative methods and testing adaptive hypotheses. Models based on the Ornstein-Uhlenbeck process permit hypotheses about adaptation to be tested by allowing traits to either evolve towards fixed adaptive optima (e.g., regimes or niches) or track continuously changing optima that can be influenced by other traits. These models allow estimation of the effects of both adaptation and phylogenetic inertia - resistance to adaptation due to any source - on trait evolution, an approach known as the "adaptation-inertia" framework. However, previous applications of this framework, and most approaches suggested to deal with the issue of species non-independence, are based on a maximum likelihood approach and thus it is difficult to include information based on prior biological knowledge in the analysis, which can affect resulting inferences. Here I present Blouch, (Bayesian Linear Ornstein-Uhlenbeck Models for Comparative Hypotheses), which fits allometric and adaptive models of continuous trait evolution in a Bayesian framework based on fixed or continuous predictors and incorporates measurement error. I first briefly discuss the models implemented in Blouch, and then the new applications for these models provided by a Bayesian framework. This includes the advantages of assigning biologically meaningful priors when compared to non-Bayesian approaches, allowing for varying effects (intercepts and slopes), and multilevel modeling. Validations on simulated data show good performance in recovering the true evolutionary parameters for all models. To demonstrate the workflow of Blouch on an empirical dataset, I test the hypothesis that the relatively larger antlers of larger bodied deer are the result of more intense sexual selection that comes along with their tendency to live in larger breeding groups. While results show that larger bodied deer that live in larger breeding groups have relatively larger antlers, deer living in the smallest groups appear to have a different and steeper scaling pattern of antler size to body size than other groups. These results are contrary to previous findings and may argue that a different type of sexual selection or other selective pressures govern optimum antler size in the smallest breeding groups.

Evolution of species recognition when ecology and sexual selection favor signal stasis.

The process of reproductive character displacement involves divergence and/or the narrowing of variance in traits involved in species recognition, driven by interactions between taxa. However, stabilizing sexual selection may favor stasis and species similarity in these same traits if signals are optimized for transmission through the prevailing environment. Further, sexual selection may promote increased variability within species to facilitate individual recognition. Here we ask how the conflicting selection pressures of species recognition and sexual selection are resolved in a genus of Himalayan birds that sing exceptionally similar songs. We experimentally show that small differences in two traits (note shape and peak frequency) are both necessary and sufficient for species recognition. Song frequency shows remarkable clinal variation along the Himalayan elevational gradient, being most divergent where species co-occur, the classic signature of reproductive character displacement. Note shape shows no such clinal variation but varies more between individuals of an allopatric species than it does among individuals within species that co-occur. We argue that the different note shapes experience similar transmission constraints, and differences produced through species interactions spread back through the entire species range. Our results imply that reproductive character displacement is likely to be common.

Filling the gaps in ecology of tropical tiger beetles (Coleoptera: Cicindelidae): first quantitative data of sexual dimorphism in semi-arboreal Therates from the Philippine biodiversity hotspot.

Sexual dimorphism, driven by sexual selection, leads to varied morphological distinctions in male and female insects, providing insights into selection pressures across species. However, research on the morphometric variability within specific taxa of tiger beetles (Coleoptera: Cicindelidae), particularly arboreal and semi-arboreal species, remains very limited. We investigate sexual dimorphism in six semi-arboreal Therates tiger beetle taxa from the Philippines, focusing on morphological traits. We employed morphometric measurements and multivariate analyses to reveal patterns of sexual dimorphism between sexes within the taxa. Our results indicate significant sexual dimorphism in elytra width, with females consistently displaying broader elytra, potentially enhancing fecundity. Notable sexual size dimorphism was observed in Therates fulvipennis bidentatus and T. coracinus coracinus, suggesting heightened sexual selection pressures on male body size. Ecological factors, mating behavior, and female mate choice might contribute to the observed morphological variation. These findings emphasize the need for further studies to comprehend mating dynamics, mate choice, and ecological influences on morphological variations in semi-arboreal and arboreal tiger beetles.

Surviving the serenade: how conflicting selection pressures shape the early stages of sexual signal diversification.

Understanding how the early stages of sexual signal diversification proceed is critically important because these microevolutionary dynamics directly shape species trajectories and impact macroevolutionary patterns. Unfortunately, studying this is challenging because signals involve complex interactions between behavior, morphology, and physiology, much of which can only be measured in real-time. In Hawaii, male Pacific field cricket song attracts both females and a deadly parasitoid fly. Over the past two decades, there has been a marked increase in signal variation in Hawaiian populations of these crickets, including novel male morphs with distinct mating songs. We capitalize on this rare opportunity to track changes in morph composition over time in a population with three novel morphs, investigating how mate and parasitoid attraction (components of sexual and natural selection) may shape signal evolution. We find dramatic fluctuation in morph proportions over the three years of the study, including the arrival and rapid increase of one novel morph. Natural and sexual selection pressures act differently among morphs, with some more attractive to mates and others more protected from parasitism. Collectively, our results suggest that differential protection from parasitism among morphs, rather than mate attraction, aligns with recent patterns of phenotypic change in the wild.

Movement or plasticity: acoustic responses of a torrent frog to stream geophony

Abstract Vocalization is the main form of communication in many animals, including frogs, which commonly emit advertisement calls to attract females and maintain spacing. In noisy environments such as streams, mechanisms to maximize signaling efficiency may include vocal plasticity and/or movement of individuals to quieter sections, but which strategy is used is still uncertain. We investigated the influence of stream geophony on the advertisement call of the torrent frog Hylodes perere in the Atlantic Rainforest, in southeastern Brazil. In a mark-recapture study, we tested if males remain in their territories and thus adjust their advertisement calls to maximize their communication. We ran linear mixed models to verify the relationship of call parameters and stream geophony, body size, and environmental temperature. We found that males remained in the same location across time, increased call intensity in noisier environments, but did not reduce call effort. Males also increased the dominant frequency in these situations, suggesting a modulation in this parameter. Our results indicate that territoriality is an important factor for males to increase call intensity to surpass stream noise instead of repositioning along the stream. However, because call effort was maintained, we suggest that sexual selection is crucial in this system, favoring males that better detect others and adjust their call efficiency. This is the first study to evaluate simultaneously frog movements and adaptations to geophony, which contributes to the investigation of the concomitant environmental and sexual selective pressures in species that communicate in noisy environments.

Widow spiders alter web architecture and attractiveness in response to same-sex competition for prey and mates, and predation risk

Female-female competition in animals has rarely been studied. Responses of females that compete context-dependently for mates and prey, and seek safety from predators, are ideally studied with web-building spiders. Cobwebs possess unique sections for prey capture and safety, which can be quantified. We worked with Steaoda grossa females because their pheromone is known, and adjustments in response to mate competition could be measured. Females exposed to synthetic sex pheromone adjusted their webs, indicating a perception of intra-sexual competition via their sex pheromone. When females sequentially built their webs in settings of low and high intra-sexual competition, they adjusted their webs to increase prey capture and lower predation risk. In settings with strong mate competition, females deposited more contact pheromone components on their webs and accelerated their breakdown to mate-attractant pheromone components, essentially increasing their webs’ attractiveness. We show that females respond to sexual, social and natural selection pressures originating from intra-sexual competition.

On a remarkable sexual dimorphic trait on scales and fins of the old world Cyprinodontiformes (Actinopterygii: Aphaniidae)

AbstractSecondary sexual dimorphism is an interesting and stupendous subject of research study due to the fact that it is a result of sexual selection, mostly attributed to either female mate choice or male–male competition. This study aims to investigate the microscopic characterization of scales and fin rays in several aphaniids (Cyprinodontiformes: Aphaniidae) to find out the possibility of using these structures as secondary sexual dimorphism traits and discuss their taxonomic and evolutionary significance. Herein, the results reveal that (i) male individuals of aphaniid species of the genera Aphanius, Aphaniops and Paraphanius present contact organs in the forms of ctenus‐like structure (in posterior margin of the scales) and spicule‐like structure (in anal fin rays) that show sexual dimorphism of scales and fins; (ii) number, position, size and shape of contact organs provide taxonomic signal to distinguish members of the genus Aphaniops from two other genera; (iii) females of Aphaniops ginaonis also represent contact organs in scales but fewer than males and (iv) as the sexual dimorphism results from different sexual selection pressures acting on males and females, it provides evolutionary signals.

Extreme polygyny results in intersex differences in age-dependent survival of a highly dimorphic marine mammal.

Developmental differences in vital rates are especially profound in polygamous mating systems. Southern elephant seals (Mirounga leonina) are highly dimorphic and extremely polygynous marine mammals. A demographic model, supported by long-term capture-mark-recapture records, investigated the influence of sex and age on survival in this species. The study revealed clear differences between female and male age-dependent survival rates. Overall juvenile survival estimates were stable around 80-85% for both sexes. However, male survival estimates were 5-10% lower than females in the same age classes until 8 years of age. At this point, male survival decreased rapidly to 50% ± 10% while female estimates remained constant at 80% ± 5%. Different energetic requirements could underpin intersex differences in adult survival. However, the species' strong sexual dimorphism diverges during early juvenile development when sex-specific survival rates were less distinct. Maximizing growth is especially advantageous for males, with size being a major determinant of breeding probability. Maturing males may employ a high-risk high-reward foraging strategy to compensate for extensive sexual selection pressures and sex-specific energetic needs. Our findings suggest sex-specific adult survival is a result of in situ ecological interactions and evolutionary specialization associated with being a highly polygynous marine predator.

Proteome Analysis of Male Accessory Gland Secretions in the Diamondback Moth, Plutella xylostella (Lepidoptera: Plutellidae).

In insects, male accessory gland proteins (ACPs) are important reproductive proteins secreted by male accessory glands (MAGs) of the internal male reproductive system. During mating, ACPs are transferred along with sperms inside female bodies and have a significant impact on the post-mating physiology changes of the females. Under sexual selection pressures, the ACPs exhibit remarkably rapid and divergent evolution and vary from species to species. The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a major insect pest of cruciferous vegetables worldwide. Mating has a profound impact on the females' behavior and physiology in this species. It is still unclear what the ACPs are in this species. In this study, two different proteomic methods were used to identify ACPs in P. xylostella. The proteins of MAGs were compared immediately before and after mating by using a tandem mass tags (TMT) quantitative proteomic analysis. The proteomes of copulatory bursas (CB) in mated females shortly after mating were also analyzed by the shotgun LC-MS/MS technique. In total, we identified 123 putative secreted ACPs. Comparing P. xylostella with other four insect ACPs, trypsins were the only ACPs detected in all insect species. We also identified some new insect ACPs, including proteins with chitin binding Peritrophin-A domain, PMP-22/ EMP/ MP20/ Claudin tight junction domain-containing protein, netrin-1, type II inositol 1,4,5-trisphosphate 5-phosphatase, two spaetzles, allatostatin-CC, and cuticular protein. This is the first time that ACPs have been identified and analyzed in P. xylostella. Our results have provided an important list of putative secreted ACPs, and have set the stage for further exploration of the functions of these putative proteins in P. xylostella reproduction.

Sexual size dimorphism and male reproductive traits vary across populations of a tropical rainforest dung beetle species (Onthophagus babirussa).

Sexual size dimorphism (SSD) arises when natural selection and sexual selection act differently on males and females. Male‐biased SSD is rarer in insects and usually indicates strong sexual selection pressure on male body size in a species. Patterns of SSD can also vary between populations of species that are exposed to different environmental conditions, such as differing resource availability and diversity. Here, we investigate intraspecific variation in SSD as well as relative investment in precopulatory (horn length) and postcopulatory traits (sperm length and testes weight) in a tropical rainforest dung beetle Onthophagus babirussa across Singapore and Peninsular Malaysia. Overall, three out of four populations displayed significant male‐biased SSD, and SSD was greater in populations with smaller overall body size. Average male body size was similar across all populations while female body size was significantly smaller in Singapore, suggesting that the pronounced SSD may also be due to stronger sexual selection on male body size in Singapore populations. All populations showed significant investment in horns as a weapon likely used in male‐male competition, while postcopulatory traits showed no clear scaling relationship with body size, suggesting a higher priority on precopulatory sexual traits in the mating system of this species.

Extra-pair paternity drives plumage colour elaboration in male passerines.

The elaborate ornamental plumage displayed by birds has largely been attributed to sexual selection, whereby the greater success of ornamented males in attaining mates drives a rapid elaboration of those ornaments. Indeed, plumage elaboration tends to be greatest in species with a high variance in reproductive success such as polygynous mating systems. Even among socially monogamous species, many males are extremely colourful. In their now-classic study, Møller and Birkhead (1994) suggested that increased variance in reproductive success afforded by extra-pair paternity should intensify sexual selection pressure and thus an elaboration of male plumage and sexual dichromatism, but the relatively few measures of extra-pair paternity at the time prevented a rigorous test of this hypothesis. In the nearly three decades since that paper's publication, hundreds of studies have been published on rates of extra-pair paternity and more objective measures of plumage colouration have been developed, allowing for a large-scale comparative test of Møller and Birkhead's (1994) hypothesis. Using an analysis of 186 socially monogamous passerine species with estimates of extra-pair paternity, our phylogenetically controlled analysis confirms Møller and Birkhead's (1994) early work, demonstrating that rates of extra-pair paternity are positively associated with male, but not female, colouration and with the extent of sexual dichromatism. Plumage evolution is complex and multifaceted, driven by phylogenetic, ecological, and social factors, but our analysis confirms a key role of extra-pair mate choice in driving the evolution of ornamental traits.

Differences in sex ratio, tail autotomy, body size and body condition between suburban and forest populations of the cuban endemic lizard Anolis homolechis

Although growing evidence suggests that natural and sexual selection pressures may differ between natural and urban habitats, their consequences in terms of morphological differentiation, extent of sexual dimorphism and sex ratio remain poorly studied. Anolis lizards are an ideal model to study the phenotypic effects of urbanization, as they are well known for the existence of ecomorphs adapted to particular microhabitats. However, so far most studies of urban populations of anoles have considered invasive species and largely focused on males. Here, we compared morphological differentiation, sexual dimorphism and sex ratio between suburban and forest populations of the native A. homolechis, in western Cuba, based on large sample size (n > 800) and a balanced nested design. Overall, both male and female individuals from suburban populations were larger and in better body condition than individuals from forest populations. In addition, evidence of caudal autotomy was more than twice more frequent in suburban populations compared to forest ones, with no sex effect. Habitat type and season of the year had additive effects on sex ratios, with a significant excess of males in suburban habitats and during the non-reproductive season. Accordingly, the extent of sexual dimorphism in size was more pronounced in suburban populations compared to forest ones. Our results suggest that the shape and direction of natural selection may differ between urban and natural populations of anoles.

An Overview of Interlocation Sexual Shape Dimorphism in Caquetaia kraussi (Perciformes: Cichlidae): A Geometric Morphometric Approach

C. kraussii is an endemic fish species from Colombia and Venezuela and represents a valuable food resource for local human communities. Due to its economic importance, the management and captive breeding of this species are of special interest. However, the anatomical similarities between sexes have been a problem for visual identification. It is also important to indicate that C. kraussii has cryptic morphological behavior between sexes, a topic that has been one of the main problems for the implementation of management plans. The following research studied individuals from three different localities along the Canal del Dique, Bolívar Department in Colombia, in which the body shape of C. kraussii was analyzed using geometric morphometric analysis. The analyses detected the presence of intralocality sexual dimorphism in two of the three localities analyzed, showing a low morphological variability among males, presenting conserved body shape, as well as a greater morphological disparity among females. This sexual shape dimorphism may be associated with the environmental variation among different locations. These results suggest the presence of two evolutionary forces acting asymmetrically between the sexes of C. kraussii, with males mostly subject to sexual selection pressure, while females are mainly subject to environmental pressures.

Parasite defensive limb movements enhance acoustic signal attraction in male little torrent frogs.

Many animals rely on complex signals that target multiple senses to attract mates and repel rivals. These multimodal displays can however also attract unintended receivers, which can be an important driver of signal complexity. Despite being taxonomically widespread, we often lack insight into how multimodal signals evolve from unimodal signals and in particular what roles unintended eavesdroppers play. Here, we assess whether the physical movements of parasite defense behavior increase the complexity and attractiveness of an acoustic sexual signal in the little torrent frog (Amolops torrentis). Calling males of this species often display limb movements in order to defend against blood-sucking parasites such as frog-biting midges that eavesdrop on their acoustic signal. Through mate choice tests we show that some of these midge-evoked movements influence female preference for acoustic signals. Our data suggest that midge-induced movements may be incorporated into a sexual display, targeting both hearing and vision in the intended receiver. Females may play an important role in incorporating these multiple components because they prefer signals which combine multiple modalities. Our results thus help to understand the relationship between natural and sexual selection pressure operating on signalers and how in turn this may influence multimodal signal evolution.

A comprehensive overview of the effects of urbanisation on sexual selection and sexual traits.

ABSTRACTUrbanisation can affect mating opportunities and thereby alter inter‐ and intra‐sexual selection pressures on sexual traits. Biotic and abiotic urban conditions can influence an individual's success in pre‐ and post‐copulatory mating, for example through impacts on mate attraction and mate preference, fertilisation success, resource competition or rival interactions. Divergent sexual selection pressures can lead to differences in behavioural, physiological, morphological or life‐history traits between urban and non‐urban populations, ultimately driving adaptation and speciation. Most studies on urban sexual selection and mating interactions report differences between urban and non‐urban populations or correlations between sexual traits and factors associated with increased urbanisation, such as pollution, food availability and risk of predation and parasitism. Here we review the literature on sexual selection and sexual traits in relation to urbanisation or urban‐associated conditions. We provide an extensive list of abiotic and biotic factors that can influence processes involved in mating interactions, such as signal production and transmission, mate choice and mating opportunities. We discuss all relevant data through the lens of two, non‐mutually exclusive theories on sexual selection, namely indicator and sensory models. Where possible, we indicate whether these models provide the same or different predictions regarding urban‐adapted sexual signals and describe different experimental designs that can be useful for the different models as well as to investigate the drivers of sexual selection. We argue that we lack a good understanding of: (i) the factors driving urban sexual selection; (ii) whether reported changes in traits result in adaptive benefits; and (iii) whether these changes reflect a short‐term ecological, or long‐term evolutionary response. We highlight that urbanisation provides a unique opportunity to study the process and outcomes of sexual selection, but that this requires a highly integrative approach combining experimental and observational work.

The ecological function of insect egg micropyles

Abstract Insect egg micropyles are openings through the chorion allowing sperm entry for fertilisation. Micropyles are diverse structures showing remarkable variation in number, spatial arrangement and physical structure across extant insect orders. Despite being almost ubiquitous across insects, they have received little attention. As key morphological features of an immobile life stage, it is plausible that part of the diversity exhibited by micropyles is adaptive, supporting other egg structures during embryo development. So, while egg fertilization is the primary function of micropyles, they could aid embryo development and be shaped by natural, as well as sexual selection. Here I first used ancestral reconstruction to investigate micropyle presence, number and variation in primitive insects. Then, I used phylogenetic comparative analyses to explore the ecological function of micropyle number. I hypothesised that micropyle number correlated with (1) aeropyle presence facilitating oxygen exchange; (2) aquatic oviposition supporting development in water and is influenced by (3) critical bioclimatic variables. Across 24 hexapod orders, the most likely ancestral state was one or two micropyles, interspecific variation was high and intraspecific variation was low. Mean micropyle number ranged from zero in Entognatha, Strepsiptera and Thysanoptera to 120 in Panstrongylus geniculatus, Hemiptera, and over 100 on average for Apidae, Hymenoptera. Micropyle number was strongly positively related to (1) egg size, with larger eggs having more micropyles; (2) the presence of aeropyles; (3) annual precipitation, with eggs developing in habitats with low annual precipitation exhibiting fewer micropyles; and (4) negatively related to micropyle width, insect eggs having fewer larger micropyles or numerous smaller ones. However, aquatic oviposition did not affect micropyle number. Overall these findings point to an adaptive ecological function of egg micropyles in addition to their primary fertilisation function. This is consistent with the hypothesis that micropyles aid embryo survival, and so this almost‐ubiquitous trait across insects is shaped by sexual and natural selection pressures during this critical life stage. Read the free Plain Language Summary for this article on the Journal blog.

Females and Males Sing Distinctly Different Songs in a Temperate Zone Songbird

Female song is widespread across songbirds, especially in tropical and subtropical species, in which females sing for resource defence, competition with intruders and mutual mate-guarding. We compared songs of males and females, produced spontaneously in a wild population of the Plain Laughingthrush Pterorhinus davidi, a songbird endemic to temperate China. We found that both sexes sing in this species and the number of notes within a song differed significantly between the two sexes. Females generally produced a longer first note than downstream notes; however, males sang in more variable frequencies than females. Males and females also differed significantly in song duration, pace and note structure. Sex-specific songs may indicate different functions and social and/or sexual selective pressures. Further studies are required to determine the functions of female song in this temperate zone passerine bird.