Significant Male Biased Sexual Size Dimorphism in Leptobrachium leishanensis

Sexual size dimorphism(SSD) is a widespread phenomenon among animals, and whose evolution and maintenance has been a central topic in evolutionary biology since Darwin's time. SSD varies in direction among the major taxonomic groups of animals and even within the same groups. In anurans, female biased SSD is the rule in many lineages, whereas male biased SSD is a rare phenomenon. In this paper, we analyze whether SSD exists inLeptobrachium leishanensis by comparing morphological characteristics between the sexes. Our results show that all six morphological characteristics measured are significantly different between the sexes. Males are significantly larger than females, indicating that the male biased SSD of this species is apparent. The size of the nuptial spines, a special secondary sex trait of males, is significantly and positively correlated with body size. We suggest that the resource defense polygyny mating system and parental care behavior may be explanations for the evolution of male biased SSD and nuptial spine development in this species.     

Implications of Male and Female Contributions to Sexual Size Dimorphism for Inferring Behavior in the Hominin Fossil Record

Sexual dimorphism is commonly used to directly infer or support reconstructions of social behavior in early hominins. This is often done by comparing the magnitude of sexual size dimorphism to that seen in extant primates and extrapolating a likely social behavior. Such comparisons are of limited value, though, allowing only the inference of strong male–male competition when dimorphism is strong. Recent studies have begun to focus on the selective factors that impact female body size, and thereby size dimorphism. Considerations of changes in male and female size in the fossil record potentially allow insight into the meaning of changes in sexual dimorphism through time. To illustrate, I compare estimates of body mass dimorphism for four hominin taxa to assess changes in male and female size. Assuming that early Homo represents a single taxon, sexual size dimorphism increased in early Homo through an increase in male size, but was subsequently reduced through an increase in female size in Homo erectus. This would imply a significant increase in sexual selection acting on males in early Homo. An increase in female size with a loss of dimorphism in Homo erectus would imply a simultaneous shift in female optimal body size through selection for increased female fecundity, and/or an increase in female resource abundance, coupled with a shift in selection acting on male size. Although none of these inferences are certain, the exercise illustrates the potential for considering how dimorphism changes through time, rather than simply focusing on the magnitude of size dimorphism in isolation.     

Testosterone Affects Neural Gene Expression Differently in Male and Female Juncos: A Role for Hormones in Mediating Sexual Dimorphism and Conflict

Despite sharing much of their genomes, males and females are often highly dimorphic, reflecting at least in part the resolution of sexual conflict in response to sexually antagonistic selection. Sexual dimorphism arises owing to sex differences in gene expression, and steroid hormones are often invoked as a proximate cause of sexual dimorphism. Experimental elevation of androgens can modify behavior, physiology, and gene expression, but knowledge of the role of hormones remains incomplete, including how the sexes differ in gene expression in response to hormones. We addressed these questions in a bird species with a long history of behavioral endocrinological and ecological study, the dark-eyed junco (Junco hyemalis), using a custom microarray. Focusing on two brain regions involved in sexually dimorphic behavior and regulation of hormone secretion, we identified 651 genes that differed in expression by sex in medial amygdala and 611 in hypothalamus. Additionally, we treated individuals of each sex with testosterone implants and identified many genes that may be related to previously identified phenotypic effects of testosterone treatment. Some of these genes relate to previously identified effects of testosterone-treatment and suggest that the multiple effects of testosterone may be mediated by modifying the expression of a small number of genes. Notably, testosterone-treatment tended to alter expression of different genes in each sex: only 4 of the 527 genes identified as significant in one sex or the other were significantly differentially expressed in both sexes. Hormonally regulated gene expression is a key mechanism underlying sexual dimorphism, and our study identifies specific genes that may mediate some of these processes.     

Assessment of Patterns of Fluctuating Asymmetry and Sexual Dimorphism in Carabid Body Shape

The measurement tool most used to estimate developmental stability (DS) is fluctuating asymmetry (FA), which is a measure of the small random deviations that occur between the left and right sides of bilaterally symmetrical traits. In the Biobío Region of Chile, forest plantations are a widely extended phenomenon, which affect 27% of the surface area of the region and which are dominated by the monoculture of Pinus radiata. This study evaluated the presence of FA in the body shape of two populations of Ceroglossus chilensis (Eschscholtz) in two 13-year-old forest plantations (commercial thinning) using insects collected with interception traps. Since the biotic and abiotic components of forest plantations are subject to continual anthropic modifications that affect almost all ecological processes, including population dynamics, community composition, and material and energy flows, these characteristics are reflected in the DS of individuals. The results showed that there was greater precision using geometric morphometrics to detect the presence of asymmetry in plantations due to shape analysis, as proposed by studies in antennal morphology using traditional measures. It should be noted that the populations were exposed to different environments; the population in the Coast Range is more humid, while the Andes Foothills population is in a drier area with drier soils. In spite of this, there was minimum phenotypic variation detected at the population level, which reflected the different environments and may be associated with patterns of environmental phenotypic plasticity.     

Androgen Induction of Male Sexual Behaviors in Female Goldfish

The effectiveness of testosterone (T) and 11-ketotestosterone (K) in inducing male-typical sex behaviors in goldfish was examined by implanting intact adult females with one empty (blank) Silastic implant (B females), one implant containing T or K, or one T and one K implant (T + K females). Behavior of the four female groups was compared to that of untreated males and males containing a blank implant. Male-typical behaviors (coutship, spawning) and associated behavioral changes (increased activity, reduced spontaneous feeding) were assessed 3.5 and 4.5 months after implant in 30-min tests in which the test female or male was allowed to interact with a stimulus female in which sexual receptivity and attractivity had been induced by acute prostaglandin F_2αinjection. Prostaglandin-induced female-typical spawning behavior in the test females and males was also assessed 4.5 months after implant in a 60-min test for female-typical behavior in which the test fish was injected with prostaglandin and placed immediately with a sexually active male. Blood samples 5 months postimplant showed that implants generated physiological levels of T and K. In both tests for male-typical behaviors, K and T + K females exhibited the full suite of behaviors shown by spawning males, e.g., male-typical courtship and spawning, increased swimming activity, and reduced spontaneous feeding. Although behaviors of K and T + K females did not differ, those of T + K females were more often equivalent to those of males and significantly different from those of B females. T females exhibited marginal male-typical behaviors which never differed significantly from those of B females. Androgen-treated females exhibited female-typical; spawning behaviors equivalent to that of males and B females. The results show that adult female goldfish can be behaviorally masculinzed without behavioral defeminization, and suggest that male-typical sex behaviors in goldfish are dependent on K, although other steroids also may be required. The inducible behavioral bisexuality of goldfish, a gonochoristic species, is discussed in terms of the prevalence of hermaphroditism in teleosts.     

Male Microchimerism in the Human Female Brain

In humans, naturally acquired microchimerism has been observed in many tissues and organs. Fetal microchimerism, however, has not been investigated in the human brain. Microchimerism of fetal as well as maternal origin has recently been reported in the mouse brain. In this study, we quantified male DNA in the human female brain as a marker for microchimerism of fetal origin (i.e. acquisition of male DNA by a woman while bearing a male fetus). Targeting the Y-chromosome-specific DYS14 gene, we performed real-time quantitative PCR in autopsied brain from women without clinical or pathologic evidence of neurologic disease (n = 26), or women who had Alzheimer’s disease (n = 33). We report that 63% of the females (37 of 59) tested harbored male microchimerism in the brain. Male microchimerism was present in multiple brain regions. Results also suggested lower prevalence (p = 0.03) and concentration (p = 0.06) of male microchimerism in the brains of women with Alzheimer’s disease than the brains of women without neurologic disease. In conclusion, male microchimerism is frequent and widely distributed in the human female brain.     

Becoming Different But Staying Alike: Patterns of Sexual Size and Shape Dimorphism in Bills of Hummingbirds

Hummingbirds are known for their distinctive patterns of sexual dimorphism, with many species exhibiting sex-related differences in various ecologically-relevant traits, including sex-specific differences in bill shape. It is generally assumed that such patterns are consistent across all hummingbird lineages, yet many taxa remain understudied. In this study we examined patterns of sexual size and sexual shape dimorphism in bills of 32 of 35 species in the monophyletic Mellisugini lineage. We also compared patterns of bill size dimorphism in this group to other hummingbird lineages, using data from 219 hummingbird species. Overall, the presence and degree of sexual size dimorphism was similar across all hummingbird lineages, with the majority of Mellisugini species displaying female-biased sexual size dimorphism, patterns that remain unchanged when analyzed in a phylogenetic context. Surprisingly however, we found that sexual dimorphism in bill shape was nearly absent in the Mellisugini clade, with only 3 of the 32 species examined displaying bill shape dimorphism. Based on observations in other hummingbird lineages, the lack of sexual shape dimorphism in Mellisugini is particularly unusual. We hypothesize that the patterns of sexual size dimorphism observed here may be the consequence of differential selective forces that result from competition for ecological resources. We further propose that an influential mechanism underlying shape dimorphism is competition and niche segregation. Taken together, the evolutionary changes in patterns of sexual shape dimorphism observed in Mellisugini suggest that the evolutionary trends of sexual dimorphism in the Trochilidae are far more dynamic than was previously believed.     

Infanticide as Sexual Conflict: Coevolution of Male Strategies and Female Counterstrategies

One of the earliest recognized forms of sexual conflict was infanticide by males, which imposes serious costs on female reproductive success. Here I review two bodies of evidence addressing coevolved strategies of males and females. The original sexual selection hypothesis arguing that infanticide improves male mating success by accelerating the return of females to fertilizable condition has been generally supported in some taxa—notably, some primates, carnivores, rodents, and cetaceans—but not in other taxa. One result of recent research has been to implicate other selective benefits of infanticide by males in various taxa from insects to birds to mammals, such as acquisition of breeding status or improvement of the female breeding condition. In some cases, however, the adaptive significance of male infanticide remains obscure. The second body of data I review is arguably the most important result of recent research: clarifying the possible female counterstrategies to infanticide. These potential counterstrategies span diverse biological systems, ranging from sexual behavior (e.g., polyandrous mating), to physiology (e.g., the Bruce effect), to individual behavior (e.g., maternal aggression), to social strategies (e.g., association with coalitionary defenders of either sex). Although much remains to be studied, these current data provide compelling evidence of sexually antagonistic coevolution surrounding the phenomenon of infanticide.At its most elemental level, infanticide is the killing of a newborn individual by a conspecific. With the growing appreciation of its biological significance, however, infanticide came to be defined more broadly as any “behavior that makes a direct and significant contribution to the immediate death of an embryo or newly hatched or born member of the performer’s own species” (Mock 1984, p. 4) or “any form of lethal curtailment of parental investment in offspring brought about by conspecifics” (Hrdy and Hausfater 1984, p. xv). These definitions highlight the heterogeneous and variable nature of the phenomenon, which can be perpetrated by either sex, by parents or other kin, by individuals unrelated to the victim, in a wide variety of social and mating systems, under a range of seasonal or aseasonal breeding regimes, and across diverse taxa straddling vertebrates and invertebrates.One adaptive form of infanticide—the killing of infants by unrelated males—is arguably the archetype of sexual conflict. In 450 BCE, Herodotus not only documented the behavior among Egyptian cats, but explained it as a male “trick” to obtain sexual access to females otherwise preoccupied with maternal duties (Delibes et al. 2012). Among the myriad ideas inaugurating sociobiology in the 1970s, the hypothesis that infanticide is a male strategy that improves reproductive success at the expense of female fitness (Hrdy 1974) constituted one of the first demonstrations of the “battle of the sexes” theory developed by Williams (1966) and Trivers (1972). Partly because of the controversy surrounding the appearance of this hypothesis (Rees 2009), however, subsequent research focused more on male strategy than on the other party in this sexual dialectic, the female. Thus, field and laboratory research has helped to establish its many forms and conditional occurrence, describe its distribution across taxa, and clarify its adaptive significance, but it is only relatively recently that female counterstrategies have become the subjects of rigorous study, even though their potential importance was grasped early on (Hrdy 1979).In this article, I review selected aspects of this body of data and analysis. My focus is on nonparental male infanticide targeting dependent young—in mammals, nursing individuals—as opposed to older, weaned offspring, the killing of which is variably rendered “juvenilicide,” “pedicide,” or “filicide” (e.g., Agoramoorthy and Mohnot 1988; Palombit 2014, in press).     

Reexamination of Sexual Dimorphism and Female Reproduction in the Many-Lined Sun Skink Eutropis multifasciata from China

We reexamined sexual dimorphism and female reproduction in the Many-Lined Sun Skink Eutropis multifasciata from Hainan,China. Our data confirm that adults are sexually dimorphic in body size and shape,with males being the larger sex and larger in head size but shorter in abdomen length than females of the same snoutvent length(SVL). The rate at which head width increased with SVL was greater in males as opposed to the previous conclusion that the rate does not differ between the sexes. Maternal size was the main determinant of reproductive investment,with larger females generally producing more,as well as larger,offspring. Females produced up to nine offspring per litter as opposed to the previously reported 2–7. Most females gave birth between March and August,a time period approximately four months longer than that(May–June) reported previously. Females with a higher fecundity tended to produce smaller offspring as opposed to the previous conclusion that females do not tradeoff offspring size against number. Litter size,neonate mass and litter mass remained remarkably constant among years,and litter mass was more tightly related to female body size than litter size or neonate mass. Smaller females could produce relatively heavier litters without a concomitant reduction in postpartum body condition.     

Male Sexual Signals and Female Choice in Drosophila grimshawi (Diptera: Drosophilidae)

Sexual selection and sexual signaling have been prominent topics in recent behavioral studies, but limited data have led to controversy regarding these topics. For example, the Hawaiian Drosophila are often cited as examples in which female choice has resulted in the evolution of elaborate male courtship signals, but relatively few data exist to test these claims adequately. We studied D. grimshawi, a lek-forming Hawaiian Drosophila, to determine whether there was evidence for female choice without male competition and to elucidate the possible cues females use to discriminate. Male mating success was found to be nonrandom and males that courted females intensely and deposited many pheromone-containing streaks on the substrate were the most successful. Hence, multiple cues seem to be involved in male mating success in this species. Some males performed only one display, however, and may represent an alternate male mating tactic. The protein content of the adult male diet significantly influenced the level of pheromone streak deposition, and thus, foraging environment may affect the outcome of sexual selection.     

Sexual Selection in the Water Spider: Female Choice and Male–Male Competition

The water spider Argyroneta aquatica is the only spider spending its whole life under water, and one of the few spider species in which males are larger than females. Previous studies indicated that males can cannibalize females, which is uncommon among spiders. Here we aimed to further test for a potential influence of sexual selection on male body size. We examined the importance of female choice by testing whether females prefer the larger of two simultaneously presented males as mating partners. Further, we examined the influence of male–male competition by comparing the fighting behaviour between large and small males when alone or when together with a female, and we determined the outcome of fights. We found that females approach and choose large males as mating partners, despite the risk of male cannibalism. Additionally, males intensively compete for females, and large males clearly win against smaller ones. Hence sexual selection seems to be important for the evolution of the peculiar sexual size dimorphism of water spiders, as large size is beneficial for males in both the intra‐ and intersexual context. Previous studies have suggested an important role of natural selection in the sex‐specific body size of water spiders, but natural and sexual selection mechanisms apparently work in the same direction, favouring large male size.     

RESEARCH PAPER: Multiple Sexual Ornamentation Signals Male Quality and Predicts Female Preference in Minnows

Sexual ornamentation often consists of multiple components. Different sexual signals may indicate different aspects of mate quality or reflect quality in different time scales. On the other hand, same signals can have a dual function and are used both in male–male competition and courtship. Many fish species are capable of rapidly altering their colouration (ephemeral colour changes), but this capability is usually ignored in sexual selection studies. Here, we used experimentally manipulated social environments to study the ephemeral colour changes in multicomponent sexual signals of male minnows (Phoxinus phoxinus) during male–male competition and female choice. We found that the dominant males courted the females more actively and had redder and/or darker skin colouration than the subordinate males. Furthermore, darkness difference between subordinate and dominant males increased in the presence of female, which suggests that the male–male competition may increase the honesty of signalling and thus facilitate female choice. In support of this hypothesis, females had a strong behavioural preference towards the more colourful males, which may indicate female choice. As colourful males often had a higher social status than paler individuals, it is possible that females base their preference on male status, not only the colouration per se. In any case, our results suggest that sexual ornamentation of male minnows may signal status, courting activity and superior quality of the males and that these signals may have a dual function in both male–male competition and female choice. Females preferred different ornamental traits (dark and red colour patterns) relatively equally, indicating that mate choice is based on multiple cues.     

Behavioral and Neurogenomic Responses to Acoustic and Visual Sexual Cues are Correlated in Female Torrent Frogs

Diverse a nimal species use multimodal communica tion signals to coordina te reproductive behavior.Despite active research in this field,the brain mechanisms underlying multimodal communication remain poorly understood.Similar to humans and many mammalian species,anurans often produce auditory signals accompanied by conspicuous visual cues(e.g.,vocal sac inflation).In this study,we used video playbacks to determine the role of vocal-sac inflation in little torrent frogs(Amolops torrentis).Then we exposed females to blank,visual,auditory,and audiovisual stimuli and analyzed whole brain tissue gene expression changes using RNAseq.The results showed that both auditory cues(i.e.,male advertisement calls)and visual cues were attractive to female frogs,although auditory cues were more attractive than visual cues.Females preferred simultaneous bimodal cues to unimodal cues.The hierarchical clustering of differentially expressed genes showed a close relationship between neurogenomic states and momentarily expressed sexual signals.We also found that the Gene Ontology terms and KEGG pathways involved in energy metabolism were mostly increased in blank contrast versus visual,acoustic,or audiovisual stimuli,indicating that brain energy use may play an important role in response to these stimuli.In sum,behavioral and neurogenomic responses to acoustic and visual cues are correlated in female little torrent frogs.     

Influence of Female Copulation Calls on Male Sexual Behavior in Captive Macaca fascicularis

We investigated the function of copulation calls—vocalizations by females during mating—in captive groups of long-tailed macaques. We tested predictions of the contest-competition, sperm competition, synchronized orgasms, mate again, alpha-male notification and graded-signal hypotheses. We observed 371 copulations of 36 females wherein the presence or absence of a copulation call was clear. Females call equally often with different males and shortly after ejaculation. Copulation calls occurred equally with copulations with and without ejaculation. Calls did not incite disruptions of the mating. Following calls females mated again, more often than expected, with their mating partner. Both pregnant and fertile females uttered copulation calls. Two females conceived and mated mainly with the alpha male then. We conclude that copulation calls do not incite male contest competition for sexual access to females and that it is unlikely that calls synchronize male and female orgasms. Several hypotheses remain plausible, but not all predictions are borne out unequivocably. This alerts us to the possibility that the calls could have multiple beneficial effects; natural selection might strike a compromise among functions. Investigation of the mate again, sperm competition and alpha-male notification hypotheses, and of hypotheses not tested in our study concerning female breeding overlap and female-female agonism, is required.     

Visual Phenotype Matching: Cues to Paternity Are Present in Rhesus Macaque Faces

The ability to recognize kin and thus behaviourally discriminate between conspecifics based on genetic relatedness is of importance both in acquiring inclusive fitness benefits and to enable optimal inbreeding. In primates, mechanisms allowing recognition of paternal relatives are of particular interest, given that in these mating systems patrilineal information is unlikely to be available via social familiarity. Humans use visual phenotype matching based on facial features to identify their own and other''s close relatives, and recent studies suggest similar abilities may be present in other species. However it is unclear to what extent familial resemblances remain detectable against the background levels of relatedness typically found within demes in the wild – a necessary condition if facial cues are to function in kin recognition under natural conditions. Here, we experimentally investigate whether parent-offspring relationships are discernible in rhesus macaque (Macaca mulatta) faces drawn from a large free-ranging population more representative of the latter scenario, and in which genetic relatedness has been well quantified from pedigrees determined via molecular markers. We used the human visual system as a means of integrating multiple types of facial cue simultaneously, and demonstrate that paternal, as well as maternal, resemblance to both sons and daughters can be detected even by human observers. Experts performed better than participants who lacked previous experience working with nonhuman primates. However the finding that even naïve individuals succeeded at the task underlines the strength of the phenotypic cues present in faces.     

Swarming Behavior, Sexual Dimorphism, and Female Reproductive Status in the Sex Role-Reversed Dance Fly Species Rhamphomyia marginata

Dance flies are predaceous insects which often form male mating swarms. In many species males prior to swarming catch an insect prey, which is presented to the female at mating. In Rhamphomyia marginata, females in contrast to males gather to swarm, while males carrying a prey visit swarms for mating. Here I describe the swarming and courtship behavior in R. marginata and provide data on sexual dimorphism and swarming female reproductive status. Females swarm in small clearings in the forests. There was no specific swarm-maker. The swarming period lasted for 2–3 h and peaked around sunset. Identical swarm sites were used each evening and for several years. The mean number of females in swarms (swarm sites with at least one female) was 9.9 ± 9.1 (range, 1–40; n = 107) in 1993 and 7.1 ± 7.0 (range, 1–35; n = 68) in 1994. No obvious competition between females in swarms was observed. The operational sex ratio in swarms was extremely female biased (all swarms, 0.04). Less than one-third of male visits to swarms resulted in mating and males were found more often in larger swarms. Nuptial prey consisted of male midges. Females seem to mate more than once. Swarming females had undeveloped eggs, whereas mated females in swarms had further developed eggs than unmated females. Amount of sperm in the spermatheca was correlated with egg size. Amount of sperm and egg size did not correlate with wet weight, wing length, or wing load, except for egg size and weight. The wing coloration pattern and shape in R. marginata females are unique among dance flies, being greatly enlarged (1.6 times larger than that of males) and bicolored (gray part, 60% of wing area). When females, instead of males, possess extravagant secondary sexual characters, it is predicted from sexual selection theory that females should compete for males and that males should be selective in their choice of partner. A sex-role reversal will evolve when assess to males limit female reproductive success. The dance fly species R. marginata, like Empis borealis, another dance fly species studied earlier and discussed here, seems to fit these predictions.     

Male attractiveness is influenced by UV wavelengths in a newt species but not in its close relative

Background

Functional communication in the UV range has been reported in Invertebrates and all major groups of Vertebrates but Amphibians. Although perception in this wavelength range has been shown in a few species, UV signalling has not been demonstrated in this group. One reason may be that in lentic freshwater habitats, litter decomposition generates dissolved organic carbon that absorbs UV radiation and thus hinders its use for visual signalling. We tested the effect of male UV characteristics on female sexual preference in two newt species that experience contrasting levels of UV water transmission when breeding.

Methodology/Principal Findings

We analysed water spectral characteristics of a sample of breeding ponds in both species. We quantified male ventral coloration and measured male attractiveness under two lighting conditions (UV present, UV absent) using a no-choice female preference design. UV transmission was higher in Lissotriton vulgaris breeding sites. Male UV patterns also differed between experimental males of the two species. We observed a first common peak around 333 nm, higher in L. vulgaris, and a second peak around 397 nm, more frequent and higher in L. helveticus. Male attractiveness was significantly reduced in L. vulgaris when UV was not available but not in L. helveticus. Male attractiveness depended on the hue of the first UV peak in L. vulgaris.

Conclusion/Significance

Our study is the first report of functional UV-based communication in Amphibians. Interestingly, male spectral characteristics and female preferences were consistent with the differences in habitat observed between the two species as L. helveticus often breeds in ponds containing more UV blocking compounds. We discuss the three hypotheses proposed so far for UV signalling in animals (enhanced signal detectability, private communication channel, indicator of individual quality).     

Sexual Dimorphism in the Hindlimb Muscles of the Asiatic Toad(Bufo gargarizans)in Relation to Male Reproductive Success

In many anurans, the forelimb muscles of males are used to grasp females and are often heavier than those of females despite the larger female body size. Such sexual dimorphism in forelimb musculature is thought to result from sexual selection. In addition, the hindlimbs of frogs and toads play an important role in the reproductive process as amplectant males can expel rivals with robust hindlimbs through kicking. In this study, the sexual dimorphism in dry mass for six hindlimb muscles of the Asiatic toad(Bufo gargarizans) was investigated. The results showed that, when controlled for body size, the hindlimb muscle mass of males significantly exceeded that of females for every muscle. The hindlimb muscle mass of amplectant males was also significantly larger than that of non-amplectant males. These results suggested that if strong hindlimb muscles could improve mating success of males, sexual selection would promote the evolution of dimorphism in this character.     

A Lack of Sexual Dimorphism in Width-to-Height Ratio in White European Faces Using 2D Photographs, 3D Scans, and Anthropometry

Facial width-to-height ratio has received a great deal of attention in recent research. Evidence from human skulls suggests that males have a larger relative facial width than females, and that this sexual dimorphism is an honest signal of masculinity, aggression, and related traits. However, evidence that this measure is sexually dimorphic in faces, rather than skulls, is surprisingly weak. We therefore investigated facial width-to-height ratio in three White European samples using three different methods of measurement: 2D photographs, 3D scans, and anthropometry. By measuring the same individuals with multiple methods, we demonstrated high agreement across all measures. However, we found no evidence of sexual dimorphism in the face. In our third study, we also found a link between facial width-to-height ratio and body mass index for both males and females, although this relationship did not account for the lack of dimorphism in our sample. While we showed sufficient power to detect differences between male and female width-to-height ratio, our results failed to support the general hypothesis of sexual dimorphism in the face.