Can Xenobiotics Alter the Sex Ratio of Crocodilians in the Wild?
All crocodilians exhibit temperature-dependent sex determination without sex chromosomes. This temperature dependency can be overridden by exposure to estrogen via estrogen receptor 1. Thus, the sex ratio of crocodilian species is vulnerable to estrogenic xenobiotics. Multiple investigations of the mechanism and effects of xenobiotics in crocodilian species have been conducted since the early 1990s. This review focuses on the impact of xenobiotics on sex determination rather than gonadal functions in crocodilians. The thermosensitive and estrogen-sensitive periods that commit the bipotential gonad to develop as an ovary en...
Source: Sexual Development - June 23, 2021 Category: Biology Source Type: research
Erectile Dysfunction in Men on the Rise: Is There a Link with Endocrine Disrupting Chemicals?
Erectile dysfunction (ED) is one of the most prevalent chronic conditions affecting men. ED can arise from disruptions during development, affecting the patterning of erectile tissues in the penis and/or disruptions in adulthood that impact sexual stimuli, neural pathways, molecular changes, and endocrine signalling that are required to drive erection. Sexual stimulation activates the parasympathetic system which causes nerve terminals in the penis to release nitric oxide (NO). As a result, the penile blood vessels dilate, allowing the penis to engorge with blood. This expansion subsequently compresses the veins surroundin...
Source: Sexual Development - June 16, 2021 Category: Biology Source Type: research
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Source: Sexual Development - June 15, 2021 Category: Biology Source Type: research
Sexual Development and the Environment: Conclusions from 40 Years of Theory
In this review, we consider the insight that has been gained through theoretical examination of environmental sex determination (ESD) and thermolability – how theory has progressed our understanding of the ecological and evolutionary dynamics associated with ESD, the transitional pathways between different modes of sex determination, and the underlying mechanisms. Following decades of theory on the adaptive benefits of ESD, several hypotheses seem promising. These hypotheses focus on the importance ofdifferential fitness (sex-specific effects of temperature on fitness) in generating selection for ESD, but highlight alter...
Source: Sexual Development - June 15, 2021 Category: Biology Source Type: research
Environmental Cues and Mechanisms Underpinning Sex Change in Fish
Fishes are the only vertebrates that undergo sex change during their lifetime, but even within this group, a unique reproductive strategy is displayed by only 1.5% of the teleosts. This lability in alternating sexual fate is the result of the simultaneous suppression and activation of opposing male and female networks. Here, we provide a brief review summarizing recent advances in our understanding of the environmental cues that trigger sex change and their perception, integration, and translation into molecular cascades that convert the sex of an individual. We particularly focus on molecular events underpinning the compl...
Source: Sexual Development - June 10, 2021 Category: Biology Source Type: research
Temperature-Induced Sex Reversal in Reptiles: Prevalence, Discovery, and Evolutionary Implications
Sex reversal is the process by which an individual develops a phenotypic sex that is discordant with its chromosomal or genotypic sex. It occurs in many lineages of ectothermic vertebrates, such as fish, amphibians, and at least one agamid and one scincid reptile species. Sex reversal is usually triggered by an environmental cue that alters the genetically determined process of sexual differentiation, but it can also be caused by exposure to exogenous chemicals, hormones, or pollutants. Despite the occurrence of both temperature-dependent sex determination (TSD) and genetic sex determination (GSD) broadly among reptiles, o...
Source: Sexual Development - June 10, 2021 Category: Biology Source Type: research
< b > < i > Podocnemis expansa < /i > < /b > Turtles Hint to a Unifying Explanation for the Evolution of Temperature-Dependent Sex Determination in Long-Lived and Short-Lived Vertebrates
The adaptive significance of temperature-dependent sex determination (TSD) remains elusive for many long-lived reptiles. Various hypotheses proposed potential ecological drivers of TSD. The Charnov-Bull ’77 model remains the most robust and explains the maintenance of TSD in short-lived vertebrates, where sex ratios correlate with seasonal temperatures within years that confer sex-specific fitness (colder springs produce females who grow larger and gain in fecundity, whereas warmer summers produc e males who mature at smaller size). Yet, evidence of fitness differentials correlated with incubation temperature is scarce f...
Source: Sexual Development - May 18, 2021 Category: Biology Source Type: research
Sex Differentiation in Amphibians: Effect of Temperature and Its Influence on Sex Reversal
The role of environmental factors in sexual differentiation in amphibians is not new. The effect of hormones or hormone-like compounds is widely demonstrated. However, the effect of temperature has traditionally been regarded as something anecdotal that occurs in extreme situations and not as a factor to be considered. The data currently available reveal a different situation. Sexual differentiation in some amphibian species can be altered even by small changes in temperature. On the other hand, although not proven, it is possible that temperature is related to the appearance of sex-reversed individuals in natural populati...
Source: Sexual Development - May 17, 2021 Category: Biology Source Type: research
Where the Ends Meet: An Overview of Sex Determination in Atheriniform Fishes
Atheriniform fishes have recently emerged as attractive models for evolutionary, ecological, and molecular/physiological studies on sex determination. Many species in this group have marked temperature-dependent sex determination (TSD) and yet many species also have a sex determinant gene that provides a strong drive for male differentiation. Thus, in these species the 2 forms of sex determination that were once considered to be mutually exclusive, environmental (ESD) and genotypic (GSD) sex determination, can coexist at environmentally relevant conditions. Here, we review the current knowledge on sex determination in athe...
Source: Sexual Development - May 5, 2021 Category: Biology Source Type: research
The Unique Penile Morphology of the Short-Beaked Echidna, < b > < i > Tachyglossus aculeatus < /i > < /b >
This study confirmed that the echidna penis contains many of the same overall structures and morphology as other mammalian penises and a number of features homologous with reptiles. The corpus cavernosum is well supplied with blood, extends up to the base of the glans penis and is primarily responsible for erection. However, the echidna possesses 2 distinct corpora spongiosa separated by a septum, each of which surround the urethra only distal to the initial urethral bifurcation in the glans penis. Together with the bifurcation of the main penile artery, this provides a mechanism by which blood flow could be directed to on...
Source: Sexual Development - April 29, 2021 Category: Biology Source Type: research
Do the Offspring of Sex Reversals Have Higher Sensitivity to Environmental Perturbations?
Sex determination systems in vertebrates vary along a continuum from genetic (GSD) to environmental sex determination (ESD). Individuals that show a sexual phenotype opposite to their genotypic sex are called sex reversals. Aside from genetic elements, temperature, sex steroids, and exogenous chemicals are common factors triggering sex reversal, a phenomenon that may occur even in strict GSD species. In this paper, we review the literature on instances of sex reversal in fish, amphibians, reptiles, birds, and mammals. We focus on the offspring of sex-reversed parents in the instances that they can be produced, and show tha...
Source: Sexual Development - April 28, 2021 Category: Biology Source Type: research
Is Thermal Responsiveness Affected by Maternal Estrogens in Species with Temperature-Dependent Sex Determination?
In species with temperature-dependent sex determination (TSD), incubation temperatures regulate the expression of genes involved in gonadal differentiation and determine whether the gonads develop into ovaries or testes. For most species, natural incubation conditions result in transient exposure to thermal cues for both ovarian and testis development, but how individuals respond to this transient exposure varies and can drive variation in the resulting sex ratios. Here, we argue that variation in the timing to respond to temperature cues, or thermal responsiveness, is a trait needing further study. Recent work in the red-...
Source: Sexual Development - April 26, 2021 Category: Biology Source Type: research
With or Without W? Molecular and Cytogenetic Markers are Not Sufficient for Identification of Environmentally-Induced Sex Reversal in the Bearded Dragon
Transitions from environmental sex determination (ESD) to genotypic sex determination (GSD) require an intermediate step of sex reversal, i.e., the production of individuals with a mismatch between the ancestral genotypic and the phenotypic sex. Among amniotes, the sole well-documented transition in this direction was shown in the laboratory in the central bearded dragon,Pogona vitticeps, where very high incubation temperatures led to the production of females with the male-typical (ZZ) genotype. These sex-reversed females then produced offspring whose sex depended on the incubation temperature. Sex-reversed animals identi...
Source: Sexual Development - March 23, 2021 Category: Biology Source Type: research
Primordial Germ Cell Migration and Histological and Molecular Characterization of Gonadal Differentiation in Pach ón Cavefish < b > < i > Astyanax mexicanus < /i > < /b >
The genetic regulatory network governing vertebrate gonadal differentiation appears less conserved than previously thought. Here, we investigated the gonadal development ofAstyanax mexicanus Pach ón cavefish by looking at primordial germ cells (PGCs) migration and proliferation, gonad histology, and gene expression patterns. We showed that PGCs are first detected at the 80% epiboly stage and then reach the gonadal primordium at 1 day post-fertilization (dpf). However, in contrast to the gen erally described absence of PGCs proliferation during their migration phase, PGCs number in cavefish doubles between early neurula an...
Source: Sexual Development - March 10, 2021 Category: Biology Source Type: research
Adolescent Gynecomastia due to Minimal Androgen Resistance Syndrome: A Case Report and Literature Review
A 14-year-old boy with a 46,XY karyotype and persistent breast-3-stage gynecomastia is reported. The reproductive axis was investigated by standard laboratory methods and the androgen receptor (AR) gene was sequenced. Also, a literature review of phenotypes associated with theAR genetic variant p.Pro392Ser was performed. The boy presented with height in the upper normal range (+1.9 SDS) and normal body mass index ( −0,3 SDS); pubertal development was PH5/G4 (mean testicular volume 15 mL; 0 SDS). Laboratory findings were normal for age and sex, except aromatization index (0.09; reference range 0.03–0.07). Analysis of th...
Source: Sexual Development - March 10, 2021 Category: Biology Source Type: research
