A new experimental model for the investigation of sequential hermaphroditism.

The stunning sexual transformation commonly triggered by age, size or social context in some fishes is one of the best examples of phenotypic plasticity thus far described. To date our understanding of this process is dominated by studies on a handful of subtropical and tropical teleosts, often in wild settings. Here we have established the protogynous New Zealand spotty wrasse, Notolabrus celidotus, as a temperate model for the experimental investigation of sex change. Captive fish were induced to change sex using aromatase inhibition or manipulation of social groups. Complete female-to-male transition occurred over 60 days in both cases and time-series sampling was used to quantify changes in hormone production, gene expression and gonadal cellular anatomy. Early-stage decreases in plasma 17ß-estradiol (E2) concentrations or gonadal aromatase (cyp19a1a) expression were not detected in spotty wrasse, despite these being commonly associated with the onset of sex change in subtropical and tropical protogynous (female-to-male) hermaphrodites. In contrast, expression of the masculinising factor amh (anti-Müllerian hormone) increased during early sex change, implying a potential role as a proximate trigger for masculinisation. Collectively, these data provide a foundation for the spotty wrasse as a temperate teleost model to study sex change and cell fate in vertebrates.

Methyl farnesoate regulatory mechanisms underlying photoperiod-dependent sex determination in the freshwater crustacean Daphnia magna.

Freshwater zooplankton Daphnia magna has been widely used in ecotoxicology studies. During the last 20 years, it has been demonstrated that the topical application of juvenile hormone (JH) or JH analogs to mother daphnids induce male offspring production. Based on this finding, an in vivo screening validation method for chemicals with JH agonistic effect has developed. Although this screening system successfully identified a number of JH-like chemicals, molecular mechanisms underlying the male sex-determining process remain largely unknown. To address this issue, we established a reliable male- or female-producing system using Daphnia pulex WTN6 strain by changing the rearing photoperiod. Taking advantage of this rearing system, we successfully found several factors involving male sex determination such as ionotropic glutamate receptors, protein kinase C and pantothenate. Here, we used two D. magna strains that can also control the production of female or male offspring by photoperiod differences as model species for ecotoxicology studies. We demonstrated that either treatment of antagonist of ionotropic glutamate receptors or inhibitor of protein kinase C strongly suppressed male offspring production even under male-producing conditions. Moreover, we revealed that male sex-determining processes are likely diverged between D. magna and D. pulex based on the current experiment. This study provides a fine experimental method for in vivo screening not only JH agonists but also JH antagonists. Moreover, using daphnids with photoperiod-dependent sex determination manner will hugely contribute to understanding the mode-of-action of JH in daphnids.

A threshold dosage of estrogen for male-to-female sex reversal in the Glandirana rugosa frog.

Steroid hormones play very important roles in gonadal differentiation in many vertebrate species. Previously, we have determined a threshold dosage of testosterone (T) to induce female-to-male sex reversal in Glandirana rugosa frogs. Genetic females formed a mixture of testis and ovary, the so-called ovotestis, when tadpoles of G. rugosa were reared in water containing the dosage of T, which enabled us to detect primary changes in the histology of the masculinizing gonads. In this study, we determined a threshold dosage of estradiol-17ß (E2) to cause male-to-female sex reversal in this frog. We observed first signs of histological changes in the ovotestes, when tadpoles were reared in water containing the dosage of E2. Ovotestes were significantly larger than wild-type testes in size. By E2 treatment, male germ cells degenerated in the feminizing testis leading to their final disappearance. In parallel, oocytes appeared in the medulla of the ovotestis and later in the cortex as well. Quantitative polymerase chain reaction analysis revealed that the expression of sex-related genes involved in testis formation was significantly decreased in the ovotestis. In addition, immuno-positive signals of CYP17 that is involved in testis differentiation in this frog disappeared in the medulla first and then in the cortex. These results suggested that oocytes expanded in the feminizing gonad (ovary) contemporaneously with male germ cell disappearance. Primary changes in the histology of the gonads during male-to-female sex reversal occurred in the medulla and later in the cortex. This direction was opposite to that observed during female-to-male sex reversal in the G. rugosa frog.

The Administration of Cortisol Induces Female-to-Male Sex Change in the Protogynous Orange-Spotted Grouper, Epinephelus coioides.

In this study, we injected cortisol into the protogynous orange-spotted grouper (Epinephelus coioides) to investigate the role of this hormone in sex change. Following injection, we evaluated gonadal changes, serum levels of steroid hormones, and sex-related gene expression during the processes of cortisol-induced sex change and cortisol withdrawal in the orange-spotted grouper. Cortisol treatment caused the degeneration of oocytes and induced sex change in a dose-dependent manner. Over the long-term, we observed a significant increase in serum 11-ketotestosterone (11-KT) levels in all cortisol-treated groups, although levels of 17ß-estradiol did not change significantly. Consistent with the elevation of serum 11-KT levels, the expression of genes related to testicular development was also significantly up-regulated in the cortisol-treated groups. Based on our results, we propose that cortisol may trigger masculinization by inducing the synthesis of 11-KT and by directly activating the expression of sex-related genes. Furthermore, we found that cortisol-induced sex change was not permanent and could be reversed after the withdrawal of cortisol treatment.

A suggested bisphenol A metabolite (MBP) interfered with reproductive organ development in the chicken embryo while a human-relevant mixture of phthalate monoesters had no such effects.

Bisphenol A (BPA) and phthalate diesters are ubiquitous environmental contaminants. While these compounds have been reported as reproductive toxicants, their effects may partially be attributed to metabolites. The aim of this study was to examine reproductive organ development in chicken embryos exposed to the BPA metabolite, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP; 100 µg/g egg) or a human-relevant mixture of 4 phthalate monoesters (85 µg/g egg). The mixture was designed within the EU project EDC-MixRisk based upon a negative association with anogenital distance in boys at 21 months of age in a Swedish pregnancy cohort. Chicken embryos were exposed in ovo from an initial stage of gonad differentiation (embryonic day 4) and dissected two days prior to anticipated hatching (embryonic day 19). No discernible effects were noted on reproductive organs in embryos exposed to the mixture. MBP-treated males exhibited retention of Müllerian ducts and feminization of the left testicle, while MBP-administered females displayed a diminished the left ovary. In the left testicle of MBP-treated males, mRNA expression of female-associated genes was upregulated while the testicular marker gene SOX9 was downregulated, corroborating a feminizing effect by MBP. Our results demonstrate that MBP, but not the phthalate monoester mixture, disrupts both male and female reproductive organ development in an avian embryo model.

Transgenic Medaka Identify Embryonic Periods Sensitive to Disruption of Sex Determination.

Gonadal development in medaka (Oryzias latipes) is dependent on the synergy between estrogens and androgens. Disruption of steroid hormone levels can lead to ovo-testis. To determine the sensitive windows for hormonally induced sex reversal in medaka, we developed a novel 42sp50-GFP_ChgH-GFP transgenic medaka line, allowing the identification of female gonadal tissue by fluorescence present in developing oocytes. Germinal transgenesis resulted in a stable line exhibiting a strong green fluorescent protein signal constitutively in the ovaries and in the liver in response to estrogens. The sensitivity of this line to disruption of sex determination following 16-d chronic exposures was in the nanograms per liter range. To identify the developmental period sensitive to exogenous agents, fry were exposed to 24-h pulses of high concentrations of 17ß-estradiol (E2) or 5α-dihydrotestosterone (DHT) at various time points between days postfertilization (dpf) 0 and 12. Evaluation of phenotype followed by genotyping at 16 dpf revealed sensitivity to E2 between 1 and 8 dpf as well as 2 periods of susceptibility to DHT between 0 and 1 dpf and 4 and 8 dpf. No phenotypic sex reversal was detected after exposure to DHT or E2 on 11 or 12 dpf. The observed effects persisted to at least 24 dpf. The identified sensitive embryonic time periods for disruption of sex determination will aid future research on sex determination and the development of screening assays using early embryonic life stages. Environ Toxicol Chem 2020;39:842-851. © 2020 SETAC.

Estrogen-induced ovarian development is time-limited during the temperature-dependent sex determination of the American alligator.

Many reptiles, including the American alligator, exhibit temperature-dependent sex determination (TSD), whose thermo-sensitive period for the female alligator begins at stages-15 and ends at stage-24. Estrogen signaling plays a central role in TSD, which can be overridden by an estrogen-exposure during the thermo-sensitive period. As some environmental contaminants are estrogenic, there is growing concern about their effects on the sex ratio and reproductive health of TSD-species. It is crucial to identify the timing of gonadal commitment to either ovary or testis for a better understanding of TSD and estrogen-signals. In the current study, eggs were exposed to 5 µg/g egg of 17ß-estradiol (E2) or vehicle ethanol alone at three developmental stages-22, 24, and 26 at a male-promoting temperature, which produced 81% testis in all controls. E2-exposure at stages-22 and 24 induced more ovaries than the control group, whereas the exposure at stage-26 did not induce the same outcome. These results indicated that there is a critical commitment in the testicular development between the developmental stage 24 (100% ovary in E2 Exposure) and 26 (39% ovary with E2). Based on these results, we estimated a pivotal stage as stage-25.28. Thus, a gonadal commitment to testis could be later than a known temperature-sensitive period for promoting male in TSD.

Developmental basis for flower sex determination and effects of cytokinin on sex determination in Plukenetia volubilis (Euphorbiaceae).

KEY MESSAGE: Cytokinin might be an important factor to regulate floral sex at the very early stage of flower development in sacha inchi. Sacha inchi (Plukenetia volubilis, Euphorbiaceae) is characterized by having female and male flowers in a thyrse with particular differences. The mechanisms involved in the development of unisexual flowers are very poorly understood. In this study, the inflorescence and flower development of P. volubilis were investigated using light microscopy and scanning electron microscopy. We also investigated the effects of cytokinin on flower sex determination by exogenous application of 6-benzyladenine (BA) in P. volubilis. The floral development of P. volubilis was divided into eight stages, and the first morphological divergence between the male and female flowers was found to occur at stage 3. Both female and male flowers can be structurally distinguished by differences in the shape and size of the flower apex after sepal primordia initiation. There are no traces of gynoecia in male flowers or of androecia in female flowers. Exogenous application of BA effectively induced gynoecium primordia initiation and female flower development, especially at the early flower developmental stages. We propose that flower sex is determined earlier and probably occurs before flower initiation, either prior to or at inflorescence development due to the difference in the position of the female and male primordia in the inflorescence and in the time of the female and male primordia being initiated. The influence of cytokinin on female primordia during flower development in P. volubilis strongly suggests a feminization role for cytokinin in sex determination. These results indicate that cytokinin could modify the fate of the apical meristem of male flower and promote the formation of carpel primordia in P. volubilis.

An estradiol-17ß/miRNA-26a/cyp19a1a regulatory feedback loop in the protogynous hermaphroditic fish, Epinephelus coioides.

Cyp19a1a is a key gene responsible for the production of estradiol-17ß (E2), the main functional estrogen and a major downstream regulator of reproduction in teleost fish. It is widely known that CYP19 gene expression, aromatase activity, and E2 production can influence gonadal differentiation and sex reversal in teleost fish, but the feedback mechanisms whereby E2 regulates cyp19a1a remain poorly understood, especially regarding the potential roles of endogenous small RNA molecules (miRNAs). Here, we identified miR-26a-5p as a regulatory factor of its predicted target gene (cyp19a1a). In vitro and in vivo studies showed that miR-26a-5p can decrease cyp19a1a expression. Furthermore, high doses of E2 act as a repressor of miR-26a-5p. This study proposes a regulatory feedback loop whereby E2 regulates cyp19a1a through miR-26a-5p, and suggests that this positive feedback is an important aspect of the control of E2 production.

Testosterone causes pleiotropic effects on cleanerfish behaviour.

Mathematical modelling regarding evolutionary theory typically assumes that optimal strategies are not constrained through mechanistic processes. In contrast, recent studies on brain anatomy and neurobiology suggest that flexibility in social behaviour is rather constrained by the physiological state of the social decision-making network. Changing its state may yield selective advantages in some social contexts but neutral or even detrimental effects in others. Here we provide field evidence for such physiological trade-offs. We subjected wild female cleaner wrasse to injections of testosterone or of saline solution (control) and then observed both intraspecific interactions and interspecific cleaning behaviour with other reef fish, referred to as clients. Testosterone-treated females intensified intraspecific social interactions, showing more aggression towards smaller females and tendencies of increased aggressive and affiliative contacts with dominant males. Such testosterone-mediated changes fit the hypothesis that an increase in testosterone mediates female's focus on status in this protogynous hermaphrodite species, where females eventually change sex to become males. Moreover, we also identified other effects on interspecific social interactions: testosterone-treated females interacted less with client reef fishes and hence obtained less food. Most importantly, they selectively reduced service quality for species that were less likely to punish after being cheated. Overall, our findings suggest that testosterone causes pleiotropic effects on intra and interspecific social behaviour by broadly influencing female cleaners' decision-making.

Induction of Gonadal Development in Protogynous Grouper with Orally Delivered FSH DNA.

The availability of sexually mature fish often dictates the success of its captive breeding. In this study, we induced reproductive development in juvenile protogynous tiger grouper through oral administration of a plasmid (p) containing an engineered follicle-stimulating hormone (FSH). An expression construct (pcDNA3.1) was designed to express a single-chain FSH consisting of giant grouper FSH ß-subunit and glycoprotein subunit-α (CGα), linked by the carboxy-terminal peptide (CTP) sequence from the human chorionic gonadotropin (hCG). Single oral delivery of pFSH encapsulated in liposome and chitosan to tiger grouper yielded a significant increase in plasma FSH protein level after 4 days. Weekly pFSH feeding of juvenile tiger groupers for 8 weeks stimulated ovarian development as indicated by a significant increase in oocyte diameter and progression of oocytes to cortical alveolar stage. As the pFSH treatment progressed from 20 to 38 weeks, female to male sex change was initiated, characterized by oocyte regression, proliferation of spermatogonial cells, and occurrence of spermatogenic cysts. It was also associated with significantly lower mRNA expression of steroidogenic genes (cyp11b, cyp19a1a, and foxl2) and basal plasma levels of sex steroid hormones 17ß-estradiol (E2), testosterone (T), and 11-ketotestosterone (11KT). Results suggest that pFSH stimulates ovarian development up to cortical alveolar stage and then initiates sex change in tiger grouper. These findings significantly contribute to our knowledge on the role of FSH in the development of protogynous hermaphroditic fish. This study is the first to demonstrate induction of reproductive development in fish through oral delivery of plasmid gonadotropin.

Genetic control of male production in Daphnia pulex.

Daphnia normally reproduce by cyclical parthenogenesis, with offspring sex being determined by environmental cues. However, some females have lost the ability to produce males. Our results demonstrate that this loss of male-producing ability is controlled by a dominant allele at a single locus. We identified the locus by comparing whole-genome sequences of 67 nonmale-producing (NMP) and 100 male-producing (MP) clones from 5 Daphnia pulex populations, revealing 132 NMP-linked SNPs and 59 NMP-linked indels within a single 1.1-Mb nonrecombining region on chromosome I. These markers include 7 nonsynonymous mutations, all of which are located within one unannotated protein-coding gene (gene 8960). Within this single gene, all of the marker-linked NMP haplotypes from different populations form a monophyletic clade, suggesting a single origin of the NMP phenotype, with the NMP haplotype originating by introgression from a sister species, Daphnia pulicaria Methyl farnesoate (MF) is the innate juvenile hormone in daphnids, which induces the production of males and whose inhibition results in female-only production. Gene 8960 is sensitive to treatment by MF in MP clones, but such responsiveness is greatly reduced in NMP clones. Thus, we hypothesize that gene 8960 is located downstream of the MF-signaling pathway in D. pulex, with the NMP phenotype being caused by expression change of gene 8960.

Inter- and Intraspecific Variation in Sex Hormone-Induced Sex-Reversal in Medaka, Oryzias latipes and Oryzias sakaizumii.

We compared sex-reversal ratios induced by 17α-methyltestosterone (MT) and 17ß-estradiol (E2) exposure in two inbred medaka strains: Hd-rR derived from Oryzias latipes and HNI-II from O. sakaizumii. All MT exposures (0.2-25 ng mL-1) induced complete XX sex-reversal in HNI-II. Although MT exposure at 0.2 ng mL-1 induced XX sex-reversal at > 95% in Hd-rR, other concentrations tested caused XX sex-reversal at lower frequencies (<50%). MT exposure at 1, 5, and 25 ng mL-1 induced XY sex-reversal in Hd-rR, but not in HNI-II. In Hd-rR, E2 exposure induced XY sex-reversal at > 10 ng mL-1, and in all fish feminization occurred 500 ng mL-1. In HNI-II, E2 induced XY sex-reversal at 50 and 250 ng mL-1, but only at rates below 20%. To clarify whether the strain differences in sex hormone-induced sex-reversal are characteristic of each species, we examined the effects of MT and E2 exposure on sex differentiation in five and two additional strains or wild stocks/populations of O. latipes and O. sakaizumii, respectively. MT exposure induced low XX and high XY sex-reversal rates in O. latipes, except in the Shizuoka population, but the trend was reversed in O. sakaizumii. Furthermore, E2-induced XY sex-reversal rates varied intraspecifically in O. latipes. Our results demonstrated that sensitivity to MT and E2 varied within O. latipes species. To evaluate the ecological impacts of environmental chemicals using medaka, it is important to define not only the species, but the strains, stocks, and populations to obtain accurate results.

The co-administration of estradiol/17α-methyltestosterone leads to male fate in the protogynous orange-spotted grouper, Epinephelus coioides.

Estrogen plays a pivotal role in the sex differentiation of teleosts, whereas the precise function of androgens is more controversial. In this study, orange-spotted grouper (Epinephelus coioides) fry were treated with letrozole (an aromatase inhibitor, AI), 17α-methyltestosterone (MT), or MT and 17ß-estradiol (E2) simultaneously, during the period of gonadal formation and sex differentiation. MT feeding at 50 days after hatching resulted in gonadal dysgenesis, which could be rescued by E2 supplementation. Different doses of AI treatment led to different phenotypes: undifferentiated gonads were maintained in the AI group fed a low dose (5 mg/kg diet), whereas female-to-male sex reversal was observed in the AI group fed a high dose (100 mg/kg diet). MT and MT + E2 treatment could induce female-to-male sex reversal during sex differentiation (90 days after hatching). The expression of female pathway genes was suppressed, while the expression of genes in the male pathway was up-regulated in the MT + E2 group. Consistent with the expression of sex-related genes, the serum 11- ketotestosterone level was also upregulated in MT and MT + E2 group. Finally, we examined the expression of male-specific mark (DMRT1) and proliferating cell nuclear antigen in MT and MT + E2 induced sex reversal, and the result indicated that male germ cells and somatic cells may origin from the gonium and proliferative somatic cells surrounding the efferent duct, respectively. Overall, our data suggested that estrogen acts as a natural inducer of female differentiation, and that the co-administration of estrogen and androgen during sex differentiation leads to a male sex fate in the protogynous orange-spotted grouper.

Expression profiles of dmrts and foxls during gonadal development and sex reversal induced by 17α-methyltestosterone in the orange-spotted grouper.

The orange-spotted grouper, Epinephelus coioides, is a marine protogynous hermaphrodite fish of commercial importance. There are many examples of sex change species among marine fish, but the molecular basis for the sex change is still unknown. Gonadal expression patterns of the dmrts and foxls genes in E. coioides have pointed to sexual dimorphism in this species and it has been shown that mRNA levels of dmrts and foxls to vary significantly during reproduction cycles. The steroid 17α-methyltestosterone was used to induce sex reversal in these fish, during which dmrts and foxls levels changed significantly and subsequently reverted to normal when 17α-methyltestosterone was withdrawn. Interestingly, the expression of dmrt2b and dmrt3 was not affected by this steroid. We speculate that the role of foxl2 in reproduction may be conserved via regulation of early differentiation of the ovary by the hypothalamus-pituitary-gonad axis, and dmrt2 may have a significant role in premature ovarian differentiation and maintenance in E. coioides. dmrt1 and foxl3 played a role in the development of the testes and are believed to be potential male regulatory genes.

Effects of exposure to BPF on development and sexual differentiation during early life stages of zebrafish (Danio rerio).

Bisphenol F (BPF) has become a predominant bisphenol contaminant in recent years. It has significant estrogenic properties in both in vivo and in vitro studies. We have previously studied the disrupting mechanisms of BPF on the hypothalamic-pituitary-gonadal axis of adult zebrafish. However, the effects of BPF exposure on development and sexual differentiation of zebrafish embryos/larvae remain unclear. To determine the effects of BPF on the critical stage of sex differentiation in zebrafish, zebrafish embryos/larvae were exposed to 1, 10, 100, and 1000 µg/L BPF from fertilization to 60 days post-fertilization (dpf). Developmental malformations were induced by exposure to BPF from 2 h post-fertilization (hpf), with a LC50 of 10,030 µg/L at 96 hpf and 9391 µg/L at 120 hpf. Long-term exposure during sex differentiation tended to result in a female sex ratio bias. Histological analyses at 60 dpf indicated that the development of ovo-testes and immature ovaries was induced by 100 and 1000 µg/L BPF. Homogenate testosterone levels decreased and 17ß-estradiol levels increased in zebrafish in a concentration-dependent manner. BPF exposure suppressed gene expression of double sex, Mab3-related transcription factor 1(dmrt1), fushi tarazu factor 1d (ff1d), sry-box containing gene 9a (sox9a) and anti-Mullerian hormone (amh); induced expression of the forkhead box L2 transcription factor (foxl2), leading to increased expression of aromatase (cyp19a1a), which promoted production of estrogens, and further caused phenotypic feminization of zebrafish. These results suggest that developmental exposure to BPF has adverse effects on sexual differentiation, and the results were useful for a BPF risk assessment.

Investigation of the potential endocrine effect of nitrate in zebrafish Danio rerio and brown trout Salmo trutta.

Nitrate has the potential to affect steroid production. Nitrate concentrations in streams in agricultural areas may exceed concentrations showing effects in laboratory studies. The effects of nitrate and/or nitrite on endocrine relevant endpoints were tested in zebrafish and brown trout. Zebrafish were exposed in two experiments to nitrate (8.8 to 89 mg NO3-/L) and nitrite (3.6 to 19 mg NO2-/L) during the period of sexual differentiation and sex ratios were determined. Vitellogenin concentrations were determined in the second experiment. The sex ratio was unaffected by the exposure to nitrate and nitrite. Vitellogenin concentrations were slightly elevated in males (but not females) in all of the groups exposed to nitrate. Juvenile brown trout were exposed to 5.7, 14, and 31 mg NO3-/L for 8 days and vitellogenin levels in liver were determined. Vitellogenin concentrations in the females were not affected by exposure, but in the males, there was an overall statistically significant effect of exposure to nitrate with the group exposed to 5.7 mg NO3-/L showing a trend of higher vitellogenin concentrations than the control group; levels in the males of the groups exposed to 14 and 31 mg NO3-/L were not statistically different from those of the control group. In conclusion, some marginal effect of nitrate in male fish on endocrine activity was observed but the present results for zebrafish, using environmentally relevant concentrations, do not define nitrate and nitrite as endocrine disrupting chemicals according to the generally accepted WHO/IPCS definition because no adverse effects (altered sex ratios) were demonstrated.

Potential Interference of Oil Vehicles on Genital Tubercle Development during the Fetal Period in ICR Mice.

Corn oil, sesame oil, and 10% ethanol in corn oil are commonly used as dosing vehicles in toxicology studies. Since these vegetable oils contain bioactive compounds, it is important for toxicology studies to characterize the toxicities of the dosing vehicles themselves. It has been recently proposed that the width of the genital tubercle (GT), the dorsal-ventral length (D-V length) of the GT, and urethral tube closure in mouse fetuses can be used as novel markers for monitoring sexual development in mice. However, how these parameters are influenced by the dosing vehicles themselves remains unclear. Therefore, we evaluated the effects of corn oil, sesame oil, and 10% ethanol in corn oil on GT width, D-V length, and GT morphology in ICR mice. Our results showed that all three vehicles influenced GT width and D-V length, but not GT morphology, suggesting that the effects of dosing vehicles themselves might need to be considered when GT width or D-V length is used as a parameter to evaluate the effects of chemicals on GT development.

Mate choice, sexual selection, and endocrine-disrupting chemicals.

Humans have disproportionately affected the habitat and survival of species through environmental contamination. Important among these anthropogenic influences is the proliferation of organic chemicals, some of which perturb hormone systems, the latter referred to as endocrine-disrupting chemicals (EDCs). EDCs are widespread in the environment and affect all levels of reproduction, including development of reproductive organs, hormone release and regulation through the life cycle, the development of secondary sexual characteristics, and the maturation and maintenance of adult physiology and behavior. However, what is not well-known is how the confluence of EDC actions on the manifestation of morphological and behavioral sexual traits influences mate choice, a process that requires the reciprocal evaluation of and/or acceptance of a sexual partner. Moreover, the outcomes of EDC-induced perturbations are likely to influence sexual selection; yet this has rarely been directly tested. Here, we provide background on the development and manifestation of sexual traits, reproductive competence, and the neurobiology of sexual behavior, and evidence for their perturbation by EDCs. Selection acts on individuals, with the consequences manifest in populations, and we discuss the implications for EDC contamination of these processes, and the future of species.

Feminizing effects of exposure to Corexit-enhanced water-accommodated fraction of crude oil in vitro on sex determination in Alligator mississippiensis.

Deepwater Horizon spilled over 200 million gallons of oil into the waters of the Gulf of Mexico in 2010. In an effort to contain the spill, chemical dispersants were applied to minimize the amount of oil reaching coastal shorelines. However, the biological impacts of chemically-dispersed oil are not well characterized, and there is a particular lack of knowledge concerning sublethal long-term effects of exposure. This study examined potential estrogenic effects of CWAF, Corexit 9500-enhanced water-accommodated fraction of oil, by examining its effect on estrogen receptors and sex determination in the American alligator, Alligator mississippiensis. The alligator exhibits temperature-dependent sex determination which is modulated by estrogen signals, and exposure to 17ß-estradiol (E2) and estrogenic compounds in ovo during the thermosensitive period of embryonic development can induce ovarian development at a male-producing temperature (MPT). CWAF induced transactivation up to 50% of the maximum induction by E2 via alligator estrogen receptors in vitro. To determine potential endocrine-disrupting effects of exposure directly on the gonad, gonad-adrenal-mesonephric (GAM) organ complexes were isolated from embryos one day prior to the thermosensitive period and exposed to E2, CWAF, or medium alone in vitro for 8-16 days at MPT. Both CWAF and E2 exposure induced a significant increase in female ratios. CWAF exposure suppressed GAM mRNA abundances of anti-Müllerian hormone (AMH), sex determining region Y-box 9, and aromatase, whereas E2 exposure suppressed AMH and increased Forkhead box protein L2 mRNA abundances in GAM. These results indicate that the observed endocrine-disrupting effects of CWAF are not solely estrogenically mediated, and further investigations are required.