Sex reversal in Nile tilapia (Oreochromis niloticus Linnaeus) by androgen immersion

Two experiments were conducted to investigate the efficacy of three androgens applied through immersion treatments on the sex ratio of Nile tilapia (Oreochromis niloticus L.) fry. In experiment 1, 14 days post-hatching (DPH) larvae were exposed to a single immersion treatment in 17α-methyltestosterone (MT), 17α-methyldihydrotestosterone (MDHT) or 17α-ethynyltestosterone (ET) at 200, 600 and 1800 μg L^−1 over 4 h (130 larvae per treatment). In experiment 2, Nile tilapia larvae were exposed to the higher androgen concentration (1800 μg L^−1) applied as either a single immersion (14 DPH) or double immersion (10 and 14 DPH) over 4 h (125 larvae per treatment). Change in sex proportion within each experiment as well as between experiments was analysed by the chi-square test. In experiment 1, MT, MDHT and ET were equally effective in significantly increasing the proportion of males when applied at 1800 μg L^−1 (86.0%, 90.0% and 86.7% respectively). At 200 μg L^−1 none of the androgens altered sex ratio. At 600 μg L^−1, only MDHT slightly, but significantly skewed the sex ratio towards males (73.0%). In experiment 2, a single immersion treatment at 14 DPH (1800 μg L^−1) significantly increased the proportion of males, but at this time the response was significantly hormone dependent (MDHT, 100.0%; MT, 91.6%; ET, 76.9%). When compared with a single immersion, two-immersion treatments significantly increased the proportion of males in the MT-treated group (from 91.6% to 98.3%), decreased the proportion of males in the MDHT group (from 100.0% to 93.4%) and had no significant effect the ET-treated group (change from 76.9% to 82.5%). The overall comparison of the sex ratio among same treatments from different experiments (a single immersion in 1800 μg L^−1) was not significantly different.

The country’s not what it used to be : research participants’ understandings of space, place and identity in rural Victoria

This chapter explores the various ways in which research participants from rural areas located in country Victoria, Australia, construct and reconstruct their understandings of themselves and their rural spaces in terms of place and identity. This chapter draws upon the data of two separate research projects that bought together a variety of researchers and research participants either growing up in, working in, or studying in rural areas.

Age discrimination in the evaluation of job applicants

This study investigated the nature of age discrimination against older job applicants. One hundred fifty-six participants (102 students; 54 organization based) evaluated a hypothetical job applicant's (aged 33–66 years) work-related competences and likelihood of being hired. Applicant age affected hiring decisions for both samples where there was a preference for hiring applicants aged 42–48 years. Applicants at both the older and younger ends of the continuum were less likely to be hired, with the oldest applicants (over 54 years) being the least likely to be hired. Although the applicants' age negatively affected evaluations of their trainability and sociability, the effect of applicant age on hiring evaluations was not mediated by these work-related competencies, suggesting that age discrimination occurs via direct bias against older workers.

Australian women in education : 2012 and still blocked at the pass. Is there a remedy?

Women have been striving for equity and diversity for a long time. Despite enormous changes in Australian women’s lives over the past five decades, there are glaring ‘sticking points’ – in education and social life in general - that are proving resilient to change. This keynote addresses some of these issues and canvasses what might be needed to tackle them.

Emotions in education policy : a social contract analysis of asymmetrical dyads and emotion

Like other academic fields, educational policy is being reviewed for the affective component. Analysis is occurring in two forms: (a) the affects of education policy on education, school leaders, teachers and student learning outcomes and (b) text analysis of specific education policies. This chapter explores the representation of emotions in education policy texts, drawing on a theory of social contracts (Rawolle & Vadeboncoeur, 2003; Yeatman, 1996) as a way to explore what is being conveyed to administrators and teachers. This chapter considers the way in which emotions are represented in education policy, through social contract analysis. Social contracts are underpinned by three underlying conditions: consent to be a part of a contract, points of renegotiation through the duration of the contract and mutual accountability to those involved.

Sex-differences in reasons for non-participation at recruitment : Geelong Osteoporosis Study

Background : Understanding reasons for non-participation in health studies can help guide recruitment strategies and inform researchers about potential sources of bias in their study sample. Whilst there is a paucity of literature regarding this issue, it remains highly plausible that men and women may have varied reasons for declining an invitation to participate in research. We aimed to investigate sex-differences in the reasons for non-participation at baseline of the Geelong Osteoporosis Study (GOS).

Methods : The GOS, a prospective cohort study, randomly recruited men and women aged 20 years and over from a region in south-eastern Australia using Commonwealth electoral rolls (2001–06 and 1993–97, respectively). Reasons for non-participation (n=1,200) were documented during the two recruitment periods. We used the Pearson’s chi squared test to explore differences in the reasons for non-participation between men and women.

Results : Non-participation in the male cohort was greater than in the female cohort (32.9% vs. 22.9%; p<0.001). Overall, there were sex-differences in the reasons provided for non-participation (p<0.001); apparent differences related to time constraints (men 26.3% vs. women 10.4%), frailty/inability to cope with or understand the study (men 18.7% vs. women 30.6%), and reluctance over medical testing (men 1.1% vs women 9.9%). No sex-differences were observed for non-participation related to personal reason/disinterest, and language- or travel-related reasons.

Conclusions : Improving participation rates in epidemiological studies may require different recruitment strategies for men and women in order to address sex-specific concerns about participating in research.

Utilising self-report data to measure racial discrimination in the labour market

Although economists have developed a series of approaches to modelling the existence of labour market discrimination, rarely is this topic examined by analysing self-report survey data. After reviewing theories and empirical models of labour market discrimination, we examine self-reported experience of discrimination at different stages in the labour market, among three racial groups utilising U.S. data from the 2001-2003 National Survey of American Life. Our findings indicate that African Americans and Caribbean blacks consistently report more experience of discrimination in the labour market than their non-Hispanic white counterparts. At different stages of the labour market, including hiring, termination and promotion, these groups are more likely to report discrimination than non-Hispanic whites. After controlling for social desirability bias and several human capital and socio-demographic covariates, the results remain robust for African Americans. However, the findings for Caribbean blacks were no longer significant after adjusting for social desirability bias. Although self-report data is rarely utilised to assess racial discrimination in labour economics, our study confirms the utility of this approach as demonstrated in similar research from other disciplines. Our results indicate that after adjusting for relevant confounders self-report survey data is a viable approach to estimating racial discrimination in the labour market. Implications of the study and directions for future research are provided.

Gender wage discrimination in rural and urban labour markets of Bangladesh

Female wages in Bangladesh are significantly lower than male wages. This paper quantifies the extent to which discrimination can explain this gender wage gap across the rural and urban labour markets of Bangladesh, using unit record data from the 1999–2000 Labour Force Survey. The gender wage differential is decomposed into a component that can be explained by differences in productive characteristics and a component not explained by observable productive differences, which is attributed to discrimination. An attempt is also made to improve on the standard methodology by implementing a wage-gap decomposition method that accounts for selectivity bias, on top of the usual “explained” and “unexplained” components. Analytical results from this paper show that gender wage differentials are considerably larger in urban areas than in rural areas and a significant portion of this wage differential can be attributed to discrimination against women. The results also show that selectivity bias is an important component of total discrimination.

Sex differences in insect immune function : a consequence of diet choice?

Males often have reduced immune function compared to females but the proximate mechanisms underlying this taxonomically widespread pattern are unclear. Because immune function is resource-dependent and sexes may have different nutritional requirements, we hypothesized that sexual dimorphism in immune function may arise from differential nutrient intake (acquisition hypothesis). To test this hypothesis, we examined patterns of phenoloxidase (PO) activity in relation to nutrient consumption in Queensland fruit flies (Q-flies). In the first experiment, flies were allowed to choose their preferred nutrient intake. Compared with males, female Q-flies had higher PO activity, consumed more calories, and preferred a higher protein:carbohydrate (P:C) diet, suggesting that differential acquisition could explain sex differences. In the second experiment, we restricted flies to one of 12 diets varying in protein and carbohydrate concentrations and mapped PO activity for each sex onto a nutritional landscape. Counter to our hypothesis, females had higher PO activity than males at any given level of nutrient intake. Both carbohydrate and protein intake affected PO activity in females but only protein affected PO activity in males. Our results indicate that sex differences in Q-fly immune function are not solely explained by sex differences in nutrient intake, although nutrition does contribute to the magnitude of these sex differences.

Molecular sex-typing in shorebirds: a review of an essential method for research in evolution, ecology and conservation

Knowing the correct sex of individuals is essential both for research in evolutionary ecology and for practical conservation. Recent molecular advances have produced cheap, quick and reliable methods for sexing birds including chicks, juveniles, immatures and adults. Shorebird researchers have not yet fully utilised these advances. Here we provide an overview of work in this area to date with two objectives: (i) to review the major applications of molecular sexing and findings of shorebird research so far, and (ii) to provide an essential guide on how to carry out molecular sexing using current methods whilst avoiding methodological pitfalls. We encourage shorebird researchers to make better use of molecular sex-typing techniques in studies of conservation, migration, foraging ecology and breeding behaviour.

Molecular determination of sex-ratio in Yellowhammer Emberiza citrinella offspring

Theory predicts skewed offspring sex-ratios in a range of situations in which the economics of producing the two sexes differ. Offspring sex-ratio skews in birds are relatively scarcely observed compared to other taxa. This could be because avian molecular sexing techniques, which allow young birds to be sexed, have only recently become available. Alternatively, birds may be largely constrained from adaptively manipulating the sex-ratio of their offspring. We used a recently-developed molecular sexing technique for birds to sex 420 Yellowhammer Emberiza citrinella offspring from 168 clutches found in Oxfordshire. Clutch sex-ratio of the population did not depart from the expected binomial distribution, and there was no variation in clutch sex-ratio with laying date, breeding attempt, or a variety of habitat variables which were predicted to differentially affect the survival and future reproductive success of offspring of the two sexes. There was no difference in size or growth rate of the sexes and nestling mortality was not sex-biased. Hence, although we can identify possible advantages of manipulating the sex-ratio in this species, it seems not to be used as a breeding strategy. Given the lack of consistent evidence for skewed avian offspring sex-ratios, more experimental work is required to determine whether, and how, birds may adaptively manipulate their offspring sex-ratio.