Starting in the late nineteenth century, the teaching profession became increasingly feminized. This article examines the results of this process, exploring the working and living conditions of rural female primary school teachers with a focus on the experiences of loneliness, harassment, and violence that they suffered in early twentieth-century Sweden. By investigating the public debate on these issues 1900–1940, we found that two main threats to the well-being of female teachers were identified: isolation and the threat of male violence. Male politicians as well as female authors and teachers acknowledged that female teachers faced loneliness, anxiety, and possible threats from violent men. The consequences of these threats were both emotional and practical, but the debate focused to a large extent on practical solutions such as providing the teachers with telephones, guard dogs, or weapons.

Within populations of the amphipod crustaceans Orchestia gammarellus and Orchestia aestuarensis, a proportion of females produce thelygenic (female-only) broods, which often contain intersexual individuals. This phenomenon is associated with the presence of two putative feminizing parasites, the paramyxid Paramarteilia orchestiae and the microsporidian Dictyocoela cavimanum, which frequently co-infect the same host. In order to determine which of the parasites causes feminization, Orchestia were resampled from the type locality of P. orchestiae in France and from another population in the UK. Breeding experiments indicated that female O. gammarellus infected with P. orchestiae produced a significantly higher proportion of female and intersex offspring than uninfected females, even in the absence of D. cavimanum. There was no difference in mortality between infected and uninfected broods, indicating that the paramyxid alters the sex ratio through feminization rather than male-killing. Although D. cavimanum also displays a female-biased prevalence in Orchestia populations, this is due to co-infection with P. orchestiae, indicating that the paramyxid, rather than the microsporidian, is the cause of feminization in these Orchestia populations.

Parasites are detrimental to host fitness and therefore should strongly select for host defence mechanisms. Yet, hosts vary considerably in their observed parasite loads. One notable source of inter-individual variation in parasitism is host sex. Such variation could be caused by the immunomodulatory effects of gonadal steroids. Here we assess the influence of gonadal steroids on the ability of guppies (Poecilia reticulata) to defend themselves against a common and deleterious parasite (Gyrodactylus turnbulli). Adult male guppies underwent 31 days of artificial demasculinization with the androgen receptor-antagonist flutamide, or feminization with a combination of flutamide and the synthetic oestrogen 17 β-estradiol, and their parasite loads were compared over time to untreated males and females. Both demasculinized and feminized male guppies had lower G. turnbulli loads than the untreated males and females, but this effect appeared to be mainly the result of demasculinization, with feminization having no additional measurable effect. Furthermore, demasculinized males, feminized males and untreated females all suffered lower Gyrodactylus-induced mortality than untreated males. Together, these results suggest that androgens reduce the ability of guppies to control parasite loads, and modulate resistance to and survival from infection. We discuss the relevance of these findings for understanding constraints on the evolution of resistance in guppies and other vertebrates.

In this paper, we describe the occurrence of a microsporidian parasite in female-biased populations of an intertidal amphipod, Corophium volutator (Pallas), at mudflat sites in the Bay of Fundy, Canada. Sequence data for the parasite's 16S rDNA indicate that it is a novel microsporidian species. This parasite was found principally in female host gonads, indicating that it might be a vertically transmitted, sex-distorting microparasite. At 4 sites each sampled in early and mid-summer, parasite prevalence varied from 0 to 21%. In the lab, infected mothers gave rise to more female-biased broods, than did uninfected mothers. Infection was not associated with size of females or with lowered survivorship of their young. Surprisingly, infected mothers actually had higher fertility controlling for body length than did uninfected mothers. Taken together, our results suggest that this novel microsporidian is likely a feminizing microparasite and is a contributing factor to local and widespread sex ratio distortion in C. volutator.

Experimental intraperitoneal Taenia crassiceps cysticercosis in mice exhibits distinct genetical, immunological and endocrinological features possibly resulting from the complex interactive network of their physiological systems. Very notable is the tendency of parasites to grow faster in hosts of the female sex. It is also remarkable in the feminization process that the infection induces in chronically infected male mice, characterized by their estrogenization, deandrogenization and loss of sexual and aggressive patterns of behaviour. The proto-oncogene c-fos is a sex steroid-regulated transcription factor gene, expressed basally and upon stimulation by many organisms. In the CNS of rodents, c-fos is found expressed in association to sexual stimulation and to various immunological and stressful events. Hence, we suspected that changes in c-fos expression in the brain could be involved in the feminization of the infected male mice. Indeed, it was found that c-fos expression increased at different times during infection in the hypothalamus, hippocampus, less so in the preoptic area and cortex, and not in several other organs. The significant and distinctive regional changes of c-fos in the CNS of infected mice indicate that the brain of the host senses intraperitoneal cysticercosis and may also announce its active participation in the regulation of the host–parasite relationship. Possibly, the host's CNS activity is involved in the network that regulates the estrogenization and deandrogenization observed in the chronically infected male mice, as well as in the behavioural and immunological peculiarities observed in this parasitic infection.

Parasitic sex ratio distorters were artificially transferred within and between crustacean host species in order to study the effects of parasitism on host fitness and sex determination and to investigate parasite–host specificity. Implantation of Nosema sp. to uninfected strains of its Gammarus duebeni host resulted in an active parasite infection in the gonad of recipient females and subsequent transovarial parasite transmission. The young of artificially infected females were feminized by the parasite, demonstrating that Nosema sp. is a cause of sex ratio distortion in its host. In contrast, we were unable to cross-infect Armadillidium vulgare with the feminizing microsporidian from G. duebeni or to cross-infect G. duebeni with the feminizing bacterium Wolbachia sp. from A. vulgare.

Historically, studies of the role of endogenous hormones in developmental differentiation of the sexes have suggested that mammalian sexual differentiation is mediated primarily by testicular androgens, and that exposure to androgens in early life leads to a male brain as defined by neuroanatomy and behavior. The female brain has been assumed to develop via a hormonal default mechanism, in the absence of androgen or other hormones. Ovarian hormones have significant effects on the development of a sexually dimorphic cortical structure, the corpus callosum, which is larger in male than in female rats. In the females, removal of the ovaries as late as Day 16 increases the cross-sectional area of the adult corpus callosum. Treatment with low-dose estradiol starting on Day 25 inhibits this effect. Female callosa are also enlarged by a combination of daily postnatal handling and exogenous testosterone administered prior to Day 8. The effects of androgen treatment are expressed early in development, with males and testosterone-treated females having larger callosa than control females as early as Day 30. The effects of ovariectomy do not appear until after Day 55. These findings are more consistent with other evidence of a later sensitive period for ovarian feminization as compared to androgenic masculinization.

The aquaculture production of all-female triploid (sterile) populations is recognized as being of potential advantage for many species of fish where sexual maturation is not desired. All-female triploids have been produced by inducing triploidy in eggs that had been fertilized with monosex female sperm. However, monosex stocks to produce this type of sperm are currently available only for a limited number of economically important species. To circumvent this problem, an alternative method would be the direct fertilization of tripoid embryos. In Pacific salmon, pressure shocks applied shortly after fertilization have consistently resulted in high yields of tripoids, and feminization by direct estrogen treatment has also been shown to be highly effective if applied shortly after hatching. In this study, coho salmon eggs were made triploid by a pressure shock of 633 kg/cm2 for 4 min, applied 20 min after fertilization and incubation at 10 °C. Some of the resulting embryos were then feminized with estradiol-17β in single 2-hour immersion treatments at 400 μg/liter, administered 1 and 8 days after hatching. Six months later, when the fish were juveniles, analysis of the DNA content of erythrocytes by flow cytometry revealed a 100% induction of triploidy, while histological examination of the gonads showed 82% females, which were completely devoid of oocyte development and thus genetically sterile. These manipulations reduced survival during early stages of development but survival became stable later. Together, these results suggest that the production of sterile fish by direct feminization of induced triploids could be of particular advantage for those species in which all-female stocks are yet not available or difficult to obtain.