Re: Female Secondary Sex Characteristics
Teodolinda Mattson
A secondary sex characteristic is a physical characteristic of an organism that is related to or derived from its sex, but not directly part of its reproductive system.[1] In humans, these characteristics typically start to appear during puberty. In animals, they can start to appear at sexual maturity.[2][3] In humans, secondary sex characteristics include enlarged breasts and widened hips of females, facial hair and Adam's apples on males, and pubic hair on both.[1][4] In non-human animals, secondary sex characteristics include, for example, the manes of male lions,[3] the bright facial and rump coloration of male mandrills, and horns in many goats and antelopes.
Secondary sex characteristics are particularly evident in the sexually dimorphic phenotypic traits that distinguish the sexes of a species.[5] In evolution, secondary sex characteristics are the product of sexual selection for traits that show fitness, giving an organism an advantage over its rivals in courtship and in aggressive interactions.[6]
Many characteristics are believed to have been established by a positive feedback loop known as the Fisherian runaway produced by the secondary characteristic in one sex and the desire for that characteristic in the other sex. Male birds and fish of many species have brighter coloration or other external ornaments. Differences in size between sexes are also considered secondary sexual characteristics.
The reproductive organs in male or female mammals that are usually identifiable at birth are described as the primary sex characteristics or sex organs. In the male, these are the penis, testes, scrotum. In the female, these are the ovaries, fallopian tubes, uterus, cervix, vagina and vulva. The primary sex organs are different from the secondary sex organs because at maturity they produce gametes, which are haploid male or female germ cells which can unite with another of the opposite sex during sexual reproduction to form a zygote.
The secondary sex characteristics differ in that they will not be identifiable at birth, they will develop as the subject becomes sexually mature. In mammals, these characteristics include breasts in females and greater muscle mass in males. Secondary sexual characteristics have an evolutionary purpose: increase the chance of breeding.[7]
In The Descent of Man and Selection in Relation to Sex, Charles Darwin hypothesized that sexual selection, or competition within a species for mates, can explain observed differences between sexes in many species.[8]
Ronald Fisher, the English biologist, developed a number of ideas concerning secondary characteristics in his 1930 book The Genetical Theory of Natural Selection, including the concept of Fisherian runaway which postulates that the desire for a characteristic in females combined with that characteristic in males can create a positive feedback loop or runaway where the feature becomes hugely amplified. The 1975 handicap principle extends this idea, stating that a peacock's tail, for instance, displays fitness by being a useless impediment that is very hard to fake. Another of Fisher's ideas is the sexy son hypothesis, whereby females will desire to have sons that possess the characteristic that they find sexually attractive in order to maximize the number of grandchildren they produce.[9] An alternative hypothesis is that some of the genes that enable males to develop impressive ornaments or fighting ability may be correlated with fitness markers such as disease resistance or a more efficient metabolism. This idea is known as the good genes hypothesis.[citation needed]
Examples of secondary sex characteristics in non-human animals include manes of male lions[3] and long feathers of male peafowl, the tusks of male narwhals, enlarged proboscises in male elephant seals and proboscis monkeys, the bright facial and rump coloration of male mandrills, horns in many goats and antelopes,[10] and the swollen upper lip and elongated premaxillary and maxillary teeth of male spikethumb frogs.[11] Male fish develop "nuptial tubercles",[12] mainly on their snouts, in the breeding season. These are an honest signal of health, and may assist females in sexual selection for species that use lek mating, such as the roach Rutilus rutilus.[13]
Biologists today distinguish between "male-to-male combat" and "mate choice", usually female choice of male mates. Sexual characteristics due to combat are such things as antlers, horns, and greater size. Characteristics due to mate choice, often referred to as ornaments, include brighter plumage, coloration, and other features that have no immediate purpose for survival or combat.[14]
Sexual differentiation begins during gestation, when the gonads are formed. The general structure and shape of the body and face, as well as sex hormone levels, are similar in preadolescent boys and girls. As puberty begins and sex hormone levels rise, differences appear, though some changes are similar in males and females. Male levels of testosterone directly induce the growth of the genitals, and indirectly (via dihydrotestosterone (DHT)) the prostate. Estradiol and other hormones cause breasts to develop in females. However, fetal or neonatal androgens may modulate later breast development by reducing the capacity of breast tissue to respond to later estrogen.[16][17][18]
Underarm hair and pubic hair are usually considered secondary sex characteristics,[4] but they may also be considered non-secondary sex characteristics because they are features of both sexes following puberty.[19]
In females, breasts are a manifestation of higher levels of estrogen; estrogen also widens the pelvis and increases the amount of body fat in hips, thighs, buttocks, and breasts.[1][4] Estrogen also induces growth of the uterus, proliferation of the endometrium, and menstruation.[1] Female secondary sex characteristics include:
The increased secretion of testosterone from the testes during puberty causes the male secondary sexual characteristics to be manifested.[23] Testosterone directly increases size and mass of muscles, vocal cords, and bones, deepening of the voice, and changing the shape of the face and skeleton.[1] Converted into DHT in the skin, it accelerates growth of androgen-responsive facial and body hair but may slow and eventually stop the growth of head hair.[citation needed] Taller stature is largely a result of later puberty and slower epiphyseal fusion.[citation needed] Overall, male secondary sex characteristics include:
The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.
Nedd8 is a ubiquitin-like protein that covalently conjugates to target proteins through neddylation. In addition to cullin-RING ligases, neddylation also modifies non-cullin proteins to regulate protein activity, stability and localization. However, the roles of NEDD8 remain largely unknown in vivo Here, we found that loss of nedd8 in female zebrafish led to defects in oogenesis, disrupted oocyte maturation and stimulated growth of the breeding tubercles (BTs) on the pectoral fins. The BTs are normally present in males, not females. However, the loss of one copy of ar can partially rescue the phenotypes displayed by nedd8-null female zebrafish. Further assays indicated that Nedd8 conjugates to Ar and Ar is neddylated at lysine 475 and lysine 862. Moreover, Nedd8 conjugation efficiently suppressed Ar transcriptional activity. Lysine 862 (K862) of Ar is the key site modified by neddylation to modulate Ar transcriptional activity. Thus, our results not only demonstrated that Nedd8 modulates ovarian maturation and the maintenance of female secondary sexual characteristics of female zebrafish in vivo, but also indicated that androgen signaling is strictly regulated by nedd8.
Sexual dimorphism often results from hormonally regulated trait differences between the sexes. In sex-role-reversed vertebrates, females often have ornaments used in mating competition that are expected to be under hormonal control. Males of the sex-role-reversed Gulf pipefish (Syngnathus scovelli) develop female-typical traits when they are exposed to estrogens. We aimed to identify genes whose expression levels changed during the development and maintenance of female-specific ornaments. We performed RNA-sequencing on skin and muscle tissue in male Gulf pipefish with and without exposure to estrogen to investigate the transcriptome of the sexually dimorphic ornament of vertical iridescent bands found in females and estrogen-exposed males. We further compared differential gene expression patterns between males and females to generate a list of genes putatively involved in the female secondary sex traits of bands and body depth. A detailed analysis of estrogen-receptor binding sites demonstrates that estrogen-regulated genes tend to have nearby cis-regulatory elements. Our results identified a number of genes that differed between the sexes and confirmed that many of these were estrogen-responsive. These estrogen-regulated genes may be involved in the arrangement of chromatophores for color patterning, as well as in the growth of muscles to achieve the greater body depth typical of females in this species. In addition, anaerobic respiration and adipose tissue could be involved in the rigors of female courtship and mating competition. Overall, this study generates a number of interesting hypotheses regarding the genetic basis of a female ornament in a sex-role-reversed pipefish.
From a biological perspective, puberty is the stage of physical maturation in which an individual becomes physiologically capable of sexual reproduction. The biological changes that occur during puberty include several neurosecretory factors and/or hormones, all of which modulate somatic growth, the development of the sex glands, and their endocrine as well as exocrine secretions.
7fc3f7cf58