Robust evidence for bisexual orientation among men.

The question whether some men have a bisexual orientation-that is, whether they are substantially sexually aroused and attracted to both sexes-has remained controversial among both scientists and laypersons. Skeptics believe that male sexual orientation can only be homosexual or heterosexual, and that bisexual identification reflects nonsexual concerns, such as a desire to deemphasize homosexuality. Although most bisexual-identified men report that they are attracted to both men and women, self-report data cannot refute these claims. Patterns of physiological (genital) arousal to male and female erotic stimuli can provide compelling evidence for male sexual orientation. (In contrast, most women provide similar physiological responses to male and female stimuli.) We investigated whether men who self-report bisexual feelings tend to produce bisexual arousal patterns. Prior studies of this issue have been small, used potentially invalid statistical tests, and produced inconsistent findings. We combined nearly all previously published data (from eight previous studies in the United States, United Kingdom, and Canada), yielding a sample of 474 to 588 men (depending on analysis). All participants were cisgender males. Highly robust results showed that bisexual-identified men's genital and subjective arousal patterns were more bisexual than were those who identified as exclusively heterosexual or homosexual. These findings support the view that male sexual orientation contains a range, from heterosexuality, to bisexuality, to homosexuality.

Patterns of Genital Sexual Arousal in Transgender Men.

Most men show genital sexual arousal to one preferred gender. Most women show genital arousal to both genders, regardless of their sexual preferences. There is limited knowledge of whether this difference is driven by biological sex or gender identity. Transgender individuals, whose birth sex and gender identity are incongruent, provide a unique opportunity to address this question. We tested whether the genital responses of 25 (female-to-male) transgender men followed their female birth sex or male gender identity. Depending on their surgical status, arousal was assessed with penile gauges or vaginal plethysmographs. Transgender men's sexual arousal showed both male-typical and female-typical patterns. Across measures, they responded more strongly to their preferred gender than to the other gender, similar to (but not entirely like) 145 cisgender (nontransgender) men. However, they still responded to both genders, similar to 178 cisgender women. In birth-assigned women, both gender identity and biological sex may influence sexual-arousal patterns.

Sexual Orientation, Sexual Arousal, and Finger Length Ratios in Women.

In general, women show physiological sexual arousal to both sexes. However, compared with heterosexual women, homosexual women are more aroused to their preferred sex, a pattern typically found in men. We hypothesized that homosexual women's male-typical arousal is due to their sex-atypical masculinization during prenatal development. We measured the sexual responses of 199 women (including 67 homosexual women) via their genital arousal and pupil dilation to female and male sexual stimuli. Our main marker of masculinization was the ratio of the index to ring finger, which we expected to be lower (a masculine pattern) in homosexual women due to increased levels of prenatal androgens. We further measured observer- and self-ratings of psychological masculinity-femininity as possible proxies of prenatal androgenization. Homosexual women responded more strongly to female stimuli than male stimuli and therefore had more male-typical sexual responses than heterosexual women. However, they did not have more male-typical digit ratios, even though this difference became stronger if analyses were restricted to white participants. Still, variation in women's digit ratios did not account for the link between their sexual orientation and their male-typical sexual responses. Furthermore, homosexual women reported and displayed more masculinity than heterosexual women, but their masculinity was not associated with their male-typical sexual arousal. Thus, women's sexual and behavioral traits, and potential anatomical traits, are possibly masculinized at different stages of gestation.

Gender Nonconformity of Identical Twins with Discordant Sexual Orientations: Evidence from Video Recordings.

Gender nonconformity (femininity in males, masculinity in females) is more common in non-heterosexual (bisexual and homosexual) than heterosexual individuals. In the past research (Watts, Holmes, Raines, Orbell, & Rieger, 2018b), identical twins discordant for sexual orientation were perceived more similar in their gender nonconformity than unrelated heterosexual and non-heterosexual people. Yet, these perceptions were based on photographs, which do not contain all aspects of gender nonconformity, such as movement and sound. This could have led to an underestimation of observable difference within twin pairs. We examined evaluations of video recordings from adult identical twins with discordant sexual orientations (eight male pairs, 11 female pairs). These twins were a small subset of those who participated in Watts et al. (2018b). Non-heterosexual twins were rated as significantly more gender nonconforming than their heterosexual co-twins, but only when males and females were combined. Their difference was smaller than the analogous difference between identical twins who were concordant heterosexual (three male pairs, three female pairs) and, unrelated to them, identical twins who were concordant non-heterosexual (six male pairs, two female pairs). These patterns were partially confirmed with twins' self-reported gender nonconformity. Shared influences possibly made twins from discordant pairs somewhat similar in their gender nonconformity, even if non-shared factors differentiated their sexual orientations.

Gender Nonconformity of Bisexual Men and Women.

The degree to which bisexual-identified individuals are distinct from either heterosexual or homosexual individuals in their sexual orientation is an ongoing debate. We examined potential differences between these groups with respect to a strong correlate of sexual orientation, gender nonconformity (femininity in males, masculinity in females). Across pooled data, we compared self-reports of childhood gender nonconformity (n = 919) and adulthood gender nonconformity (n = 1265) and observer ratings of adulthood gender nonconformity (n = 915) between sexual orientations. Most analyses suggested a steady increase in gender nonconformity from exclusively heterosexual to exclusively homosexual. However, in some analyses, bisexual men were closer to homosexual men than to heterosexual men in their gender nonconformity. The intermediate status of bisexual people in gender nonconformity was not due to the sample having a mixture of very gender-conforming and very gender-nonconforming individuals. In total, men and women with bisexual orientations appeared neither like heterosexual nor homosexual individuals, at least with respect to their gender-related traits.

Correction to: Finger Length Ratios of Identical Twins with Discordant Sexual Orientations.

Readers should note that the confidence intervals for the effect of sexual orientation on 2D:4D in the left hand of female twins are incorrectly reported in Table 1 of this article. In particular, the upper limit of the confidence intervals is missing a minus sign.

Finger Length Ratios of Identical Twins with Discordant Sexual Orientations.

A proposed marker of prenatal androgen exposure is the ratio of the index finger to ring finger (2D:4D). Within each sex, this ratio may be lower for those who were exposed to higher levels of androgens and become attracted to women, as compared to those who were exposed to lower levels of androgens and become attracted to men. We examined these patterns in identical twins with discordant sexual orientations. Because these twins are genetically identical, differences in prenatal androgen exposure, as reflected in their different finger length ratios, might contribute to their discordance. For 18 female twin pairs, non-straight (bisexual or lesbian) twins had significantly lower, or more masculinized, 2D:4D ratios than their straight co-twins, but only in the left hand. For 14 male pairs, non-straight twins had, contrary to our prediction, more masculinized finger length ratios than straight co-twins, but this difference was not significant. A reanalysis of present and previous data (Hall & Love, 2003; Hiraishi, Sasaki, Shikishima, & Ando, 2012) suggested that these patterns were robust. Furthermore, males had more masculinized 2D:4D ratios than females. This sex difference did not vary by sexual orientation.

Pupil Dilation to Explicit and Non-Explicit Sexual Stimuli.

Pupil dilation to explicit sexual stimuli (footage of naked and aroused men or women) can elicit sex and sexual orientation differences in sexual response. If similar patterns were replicated with non-explicit sexual stimuli (footage of dressed men and women), then pupil dilation could be indicative of automatic sexual response in fully noninvasive designs. We examined this in 325 men and women with varied sexual orientations to determine whether dilation patterns to non-explicit sexual stimuli resembled those to explicit sexual stimuli depicting the same sex or other sex. Sexual orientation differences in pupil dilation to non-explicit sexual stimuli mirrored those to explicit sexual stimuli. However, the relationship of dilation to non-explicit sexual stimuli with dilation to corresponding explicit sexual stimuli was modest, and effect magnitudes were smaller with non-explicit sexual stimuli than explicit sexual stimuli. The prediction that sexual orientation differences in pupil dilation are larger in men than in women was confirmed with explicit sexual stimuli but not with non-explicit sexual stimuli.

The effect of sexual orientation on voice acoustic properties.

Introduction: Previous research has investigated sexual orientation differences in the acoustic properties of individuals' voices, often theorizing that homosexuals of both sexes would have voice properties mirroring those of heterosexuals of the opposite sex. Findings were mixed, but many of these studies have methodological limitations including small sample sizes, use of recited passages instead of natural speech, or grouping bisexual and homosexual participants together for analyses. Methods: To address these shortcomings, the present study examined a wide range of acoustic properties in the natural voices of 142 men and 175 women of varying sexual orientations, with sexual orientation treated as a continuous variable throughout. Results: Homosexual men had less breathy voices (as indicated by a lower harmonics-to-noise ratio) and, contrary to our prediction, a lower voice pitch and narrower pitch range than heterosexual men. Homosexual women had lower F4 formant frequency (vocal tract resonance or so-called overtone) in overall vowel production, and rougher voices (measured via jitter and spectral tilt) than heterosexual women. For those sexual orientation differences that were statistically significant, bisexuals were in-between heterosexuals and homosexuals. No sexual orientation differences were found in formants F1-F3, cepstral peak prominence, shimmer, or speech rate in either sex. Discussion: Recommendations for future "natural voice" investigations are outlined.

Restorative function of offshore longline mussel farms with ecological benefits for commercial crustacean species.

Offshore ocean aquaculture is expanding globally to meet the growing demand for sustainable food production. At the United Kingdom's largest longline mussel farm, we assessed the potential for the farm to improve the habitat suitability for commercially important crustaceans. Modelled distribution patterns (GAM & GLM) predicted the low complexity seabed beneath the mussel farm was 34-94 % less suitable for European lobster (Homarus gammarus) and brown crab (Cancer pagurus) than nearby rocky reefs. The mussel farm operations, however, contributed large amounts of living mussels and shell material to the seabed. Acoustic telemetry revealed that H.gammarus remained within the farm for between 2 and 283 days using both the farm anchors and areas of seabed dominated by fallen mussels for refuge. In contrast, C. pagurus movements showed no affinity to either the farm infrastructure or benthic habitat under the farm. Stable isotope analysis indicated a high dietary niche overlap in C. pagurus and H. gammarus (67.8 and 84.6 %) between the mussel farm (mixed muddy sediment) and nearby rocky reef. Our mixed-methods suggest that the mussel farm augments structural complexity on the seabed providing refuge and similar feeding opportunities for lobster and crab as their typical habitat on rocky reefs. Longline mussel farms can deliver profound biodiversity-positive effects through biogenic augmentation of degraded habitat for commercial species and potential for co-benefits to local fisheries.

Phenomics enables measurement of complex responses of developing animals to global environmental drivers.

Phenomics offers technological advances for high-dimensional phenotyping, facilitating rapid, high-throughput assessment of physiological performance and has proven invaluable in global research challenges including drug discovery and food security. However, this rapidly growing discipline has remained largely inaccessible to the increasingly urgent challenge of assessing organismal functional sensitivity to global change drivers. Here, we investigate the response of an ecologically important marine invertebrate to multiple environmental drivers using Energy Proxy Traits (EPTs), a new approach for measuring complex phenotypes captured on video as a spectrum of energy levels across different temporal frequencies in fluctuating pixel values. We imaged three developmental stages of the common prawn Palaemon serratus at different salinities and temperatures, and measured EPTs and heart rate, a major proxy of physiological performance in ectotherms present across stages. Significant interactions were detected between temperature, developmental stage and salinity in frequency-specific energy levels. Despite cardiac activity being a significant contributor to the EPT spectra, treatment interactions were different from those observed on EPTs, highlighting additional phenotypic drivers of EPTs. Elevated temperature resulted in a shift of the EPT spectra towards higher frequency signals, indicating a reallocation of resources within the phenome. Using a non-linear dimensionality reduction, we interrogated the responses of EPT spectra in high-dimensional space. We discovered complex developmental-stage specific sensitivities, highlighting both the complexity of phenotypic responses, and the limits of using univariate approaches with pre-selected traits to assess responses to multiple global environmental drivers. EPTs are a high-dimensional, transferrable method of phenotyping, and are therefore highly relevant to addressing the current limitations of traditional methods of phenotyping applied to assessing biological sensitivity to drivers of global change. We predict that EPTs will become an important tool for indiscriminate phenotyping, transferrable between species, developmental stages and experimental designs.

Stability and Change in Sexual Orientation and Genital Arousal over Time.

Longitudinal work suggests that sexual orientation can change over time in men and women. These studies, however, may be susceptible to the bias of self-report. The current study therefore examined self-reported sexual orientation in addition to an objective correlate: genital arousal to erotic videos showing males or females. For 52 men (19 heterosexual, 19 bisexual, 14 homosexual) and 67 women (31 heterosexual, 18 bisexual, 18 homosexual), these measures were taken twice, with approximately 1 year between sessions. For self-reported sexual orientation, women reported lower relative stability (weaker correlation) than men over time, even though women did not change more overall (no stronger mean difference) than men between sessions. Bisexual individuals reported lower relative stability and more mean change than heterosexual and homosexual individuals. For genital arousal, across all groups, response patterns were correlated over time to a similar extent and showed little difference between sessions. Moreover, change in self-reported sexual orientation did not correspond with the change in genital arousal, regardless of sex. Perhaps self-reports overestimate changes in sexual orientation, since these changes were not reflected in physiological sexual response.

Sex Differences in Sexual Arousal and Finger Length Ratio.

Most men show sexual arousal to one, preferred sex, whereas most women respond to both sexes, regardless of their sexual orientation. A different research program indicates that men have lower second-to-fourth finger length ratios (2D:4D) than women, possibly because men are exposed to higher levels of androgens during prenatal development. We hypothesized that sex differences in sexual arousal patterns are influenced by prenatal androgen exposure and would thus be explained by sex differences in 2D:4D. We measured the sexual response patterns of 139 men and 179 women via genital arousal and pupil dilation to erotic videos, in addition to their 2D:4D. Compared to women, men showed stronger responses to one sex over the other, although this pattern was clearer in genital arousal than pupil dilation. Men also had lower 2D:4D than women. However, there was no evidence that sex differences in sexual arousal related to sex differences in 2D:4D. Thus, whichever factor explains sex differences in sexual arousal patterns may not be reflected in 2D:4D.

The relationship between finger length ratio, masculinity, and sexual orientation in women: A correlational study.

Homosexual women are, on average, more masculine in their appearance and behavior than heterosexual women. We hypothesized that their masculinity was influenced by exposure to elevated levels of prenatal androgen during early development. We recruited 199 women (including 67 homosexual women) and measured their masculinity via self-report and observer ratings. Our measure of prenatal androgen exposure was the ratio of the index to ring finger (2D:4D), which is hypothesized to be lower in women exposed to elevated levels of androgens during prenatal development. Homosexual women were substantially more masculine than heterosexual women in both self-report and observer ratings. However, homosexual women neither had more male-typical finger length ratios, nor did their finger length ratios relate to their masculinity in any predicted direction. Thus, we found no evidence that increased prenatal androgen exposure influenced masculinity in homosexual women.

In vitro avian bioaccessibility of metals adsorbed to microplastic pellets.

Microplastics are known to be associated with co-contaminants, but little is understood about the mechanisms by which these chemicals are transferred from ingested plastic to organisms. This study simulates marine avian gastric conditions in vitro to examine the bioaccessibility of authigenic metals (Fe, Mn) and trace metals (Co, Pb) that have been acquired by polyethylene microplastic pellets from their environment. Specifically, different categories of pellet were collected from beaches in Cornwall, southwest England, and exposed to an acidified saline solution of pepsin (pH âˆ¼ 2.5) at 40 °C over a period of 168 h with extracted metal and residual metal (available to dilute aqua regia) analysed by ICP-MS. For Fe, Mn and Co, kinetic profiles consisted of a relatively rapid initial period of mobilisation followed by a more gradual approach to quasi-equilibrium, with data defined by a diffusion model and median rate constants ranging from about 0.0002 (µg L-1)-1 h-1 for Fe to about 7 (µg L-1)-1 h-1 for Co. Mobilisation of Pb was more complex, with evidence of secondary maxima and re-adsorption of the metal to the progressively modified pellet surface. At the end of the time-courses, maximum total concentrations were 38.9, 0.81, 0.014 and 0.10 µg g-1 for Fe, Mn, Co and Pb, respectively, with maximum respective percentage bioaccessibilities of around 60, 80, 50 and 80. When compared with toxicity reference values for seabirds, the significance of metals acquired by microplastics from the environment and exposed to avian digestive conditions is deemed to be low, but studies of a wider range of plastics and metal associations (e.g. as additives) are required for a more comprehensive risk assessment.

Metals and marine microplastics: Adsorption from the environment versus addition during manufacture, exemplified with lead.

There are two means by which metals associate with microplastics in the aquatic environment. Firstly, they may be adsorbed to the plastic surface or hydrogenous-biogenic accumulations thereon, and secondly, they may be present in the polymeric matrix as functional additives or as reaction or recyclate residues. In this study, the relative significance of these associations is evaluated with respect to Pb in beached marine microplastics. Thus, adsorbed Pb was determined in <5 mm, neutrally-coloured polyethylene pellets that contained no detectable Pb added during manufacture by digestion in dilute aqua regia, while the bioaccessibility of this association was evaluated using an avian physiologically-based extraction test (PBET). Here, up to about 0.1 µg g-1 of Pb was adsorbed to the plastic and between about 60 and 70% of the metal was accessible. Lead present as additive or residue was determined by x-ray fluorescence analysis of a wider range of beached plastics (polyolefins and polyvinyl chloride), with a selection of positive samples grated to mm-dimensions and subjected to the PBET. Here, total Pb concentrations up to 40,000 µg g-1 and bioaccessibilities up to 16% were observed, with bioaccessible concentrations exceeding equivalent values for adsorbed Pb by several orders of magnitude. Ingestive exposure to Pb, and potentially other toxic metals, is more important through the presence of additives in historical plastics and recyclate residues in contemporary plastics than from adsorption, and it is recommended that future studies focus more on the environmental impacts and fate of metals bound in this form.

The impact of potting for crustaceans on temperate rocky reef habitats: Implications for management.

Multi-use marine protected areas (MPAs) are increasingly designated towards achieving global conservation targets. To develop effective management, the impact of permitted activities must be understood. Potting for shellfish occurs on temperate rocky reefs globally with impact not fully quantified. This UK-based study used underwater video to quantify (a) benthic condition of rocky reefs, (b) mechanisms of potting interaction and (c) true footprint of potting. Assemblages in static gear areas were more indicative of a healthy reef than those in mixed gear areas. Damage was recorded during pot hauling, but the area of damage was not the entire pot haul path. 25-30% of individuals were damaged (commonly through tissue abrasion) or removed. Notably, damage occurred to some long-lived, slow growing taxa raising concerns over impacts. Potting is more destructive than previously thought and managers must balance ecology with social and economic considerations to determine what level of impact is acceptable.

Bisexual men with bisexual and monosexual genital arousal patterns.

Some research suggests that bisexual-identified men show bisexual genital arousal, whereas other research indicates monosexual arousal: they are aroused to one sex only. These seemingly contradictory findings may be due to the type of men identifying as bisexual and the performed analyses. We examined whether both bisexual and monosexual arousal patterns could co-occur within the same sample. 114 men of different sexual orientations viewed erotic videos of males or females while their penile circumference was measured. On average, bisexual-identified men were more aroused to males than females, and especially if they identified as "bisexual leaning gay." However, also on average, bisexual men showed bisexual arousal, and especially if they were "bisexual leaning straight". Furthermore, there was more variability in the arousal patterns of bisexual-identified men, compared with other men. Based on their physiological sexual arousal, bisexual men appear to be a more diverse group than men who identified as heterosexual or homosexual.

Sexual Arousal Patterns of Identical Twins with Discordant Sexual Orientations.

Genetically identical twins can differ in their self-reported sexual orientations. However, whether the twins' subjective reports reflect valid differences in their sexual orientations is unknown. Measures of sexual orientation, which are free of the limitations of self-report, include genital arousal and pupil dilation while viewing sexual stimuli depicting men or women. We examined these responses in 6 male twin pairs and 9 female twin pairs who reported discordant sexual orientations. Across measures, heterosexual male twins responded more strongly to women than to men. Their homosexual co-twins showed an opposite pattern. Heterosexual female twins responded equally to both sexes, whereas their homosexual co-twins responded somewhat more to women than men. These differences within pairs were similar to differences between unrelated heterosexual and homosexual males and females. Our study provides physiological evidence confirming twins' discordant sexual orientations, thereby supporting the importance of the non-shared environment for the development of sexual orientation and sexual arousal.