Sex-Specific Stress Tolerance in Embryos of Lake Char (Salvelinus umbla)

Salmonid fish have become important models in evolution and ecology, but possible effects of embryo or larval sex are mostly ignored, probably because morphological gonad formation starts only months after hatching and sexual maturation years later. However, recent gene expression studies and first observations in domestic strains suggest that sex-specific life histories could already start at an embryonic stage. Here we test this hypothesis in embryos and larvae of lake char (Salvelinus umbla). We sampled wild char and used their gametes to produce embryos of 40 different families. Embryos were raised singly in a stress or a non-stress environment until a late larval stage (stress was induced by allowing remainders of ovarian fluids to support microbial growth). Genetic markers were then used to sex the fish and reconstruct paternity (N = 1,463, including dead embryos). Primary sex ratio did not differ among families and was about 1:1. Female embryos hatched on average later and showed lower stress tolerance than male embryos. There were significant parental effects on offspring growth and mortality, but the sex differences in embryo performance were not family specific. We conclude that the sexes differ in their life history and susceptibilities to environmental stress already at embryonic stages. Environmental stress during incubation can therefore affect population sex ratio and hence population growth and genetics.

Effects of natural nest temperatures on sex reversal and sex ratios in an Australian alpine skink

Altered climate regimes have the capacity to affect the physiology, development, ecology and behaviour of organisms dramatically, with consequential changes in individual fitness and so the ability of populations to persist under climatic change. More directly, extreme temperatures can directly skew the population sex ratio in some species, with substantial demographic consequences that influence the rate of population decline and recovery rates. In contrast, this is particularly true for species whose sex is determined entirely by temperature (TSD). The recent discovery of sex reversal in species with genotypic sex determination (GSD) due to extreme environmental temperatures in the wild broadens the range of species vulnerable to changing environmental temperatures through an influence on primary sex ratio. Here we document the levels of sex reversal in nests of the Australian alpine three-lined skink (Bassiana duperreyi), a species with sex chromosomes and sex reversal at temperatures below 20 °C and variation in rates of sex reversal with elevation. The frequency of sex reversal in nests of B. duperreyi ranged from 28.6% at the highest, coolest locations to zero at the lowest, warmest locations. Sex reversal in this alpine skink makes it a sensitive indicator of climate change, both in terms of changes in average temperatures and in terms of climatic variability.

P–736 Elevated levels of ambient air pollutants increase the primary sex ratio in human embryos

Study question Are there any associations between ambient outdoor air pollution and the primary sex ratio (PSR)? Summary answer Short-term exposure to increased PM10, PM2.5 and NO2 levels were significantly associated with higher PSR. What is known already PSR estimates represent a backward extrapolation from data based on spontaneous or induced abortions, fetal deaths or live births and are usually male-biased. A recent study, analyzing 3- to 6-day-old embryos derived from assisted reproductive technology (ART) procedures, showed that the sex ratio at conception is unbiased (0.5). Epidemiologic studies of air pollution on secondary (birth) sex ratio showed that higher levels of particulate pollution were associated with increased rates of female birth. However, a direct association between urban levels of air pollutants and PSR has not been reported. Study design, size, duration A retrospective cohort study was carried out to assess the impact of long- or short-term exposure to six ambient outdoor air pollutants (particulate matter, PM10µm and PM2.5µm; SO2; CO; NO2; O3) on PSR (XY/XX) of couples undergoing their first IVF cycle for preimplantation genetic screening (N = 337). Data was from fixed air quality monitoring stations across the city between January 2014 and December 2018. Embryos with sex chromosome abnormalities were excluded from the analysis. Participants/materials, setting, methods Average concentrations of the pollutants for the 90 (long-term exposure) and 15 days (short-term exposure) predating oocyte retrieval represented the exposures of interest. Pollutant levels were categorized into quartiles (Q1 to Q4) and exposure risk was divided into two periods in which average concentrations and confidence intervals for the pollutants were in the upper quartile (Q4 period) or not (Q1-Q3 period). The strength association between exposure risk and PSR was performed through analysis of covariance. Main results and the role of chance The estimated means of PM10, PM2.5, SO2, NO2, O3 and CO for Q1-Q3/Q4 periods were 27.7/39.3, 16.7/23.7, 2.5/3.9, 37.0/46.4, 32.2/45.3 µg/m3 and 0.64/0.87 ppm and 26.3/43.0, 16.0/26.3, 2.4/4.2, 36.5/47.8, 31.7/50.4 µg/m3 and 0.62/0.90 ppm for long- and short-term exposures, respectively. PM10, PM2.5 and NO2 levels in the Q4 period had significantly higher PSR (138.1, 134.0 and 137.6) when compared to Q1-Q3 period (94.4, 98.1 and 96.4) for the short-term exposure (p = 0.0193; p = 0.0439; p = 0.0180, respectively). PM10, PM2.5, SO2, NO2 and CO levels in the Q4 and Q1-Q3 periods for the long-term exposure showed no significant effect on PSR. Contrastingly, O3 levels in the Q4 period had significantly lower PSR (82.6) when compared to Q1-Q3 (115.9) for the long-term exposure (p = 0.0202). A monotonic increase in PSR was observed with increased PM10 concentration in the Q4 period for the short-term exposure (F-ratio: 4.4476; p = 0.0352). Limitations, reasons for caution Some limitations of the study should be underlined, such as its retrospective nature, exposure assessment based on pollutant levels derived from a network average across city sites, and limited extrapolation of the results to the general population. Wider implications of the findings: Our data suggest that short-term exposure to environmental factors could affect the primary sex ratio in polluted seasons or cities. A monotonic effect on PSR in the case of exposure to increasing PM10 levels was identified. Trial registration number Not applicable

P-736 Elevated levels of ambient air pollutants increase the primary sex ratio in human embryos

Study question Are there any associations between ambient outdoor air pollution and the primary sex ratio (PSR)? Summary answer Short-term exposure to increased PM10, PM2.5 and NO2 levels were significantly associated with higher PSR. What is known already PSR estimates represent a backward extrapolation from data based on spontaneous or induced abortions, fetal deaths or live births and are usually male-biased. A recent study, analyzing 3- to 6-day-old embryos derived from assisted reproductive technology (ART) procedures, showed that the sex ratio at conception is unbiased (0.5). Epidemiologic studies of air pollution on secondary (birth) sex ratio showed that higher levels of particulate pollution were associated with increased rates of female birth. However, a direct association between urban levels of air pollutants and PSR has not been reported. Study design, size, duration A retrospective cohort study was carried out to assess the impact of long- or short-term exposure to six ambient outdoor air pollutants (particulate matter, PM10µm and PM2.5µm; SO2; CO; NO2; O3) on PSR (XY/XX) of couples undergoing their first IVF cycle for preimplantation genetic screening (N = 337). Data was from fixed air quality monitoring stations across the city between January 2014 and December 2018. Embryos with sex chromosome abnormalities were excluded from the analysis. Participants/materials, setting, methods Average concentrations of the pollutants for the 90 (long-term exposure) and 15 days (short-term exposure) predating oocyte retrieval represented the exposures of interest. Pollutant levels were categorized into quartiles (Q1 to Q4) and exposure risk was divided into two periods in which average concentrations and confidence intervals for the pollutants were in the upper quartile (Q4 period) or not (Q1-Q3 period). The strength association between exposure risk and PSR was performed through analysis of covariance. Main results and the role of chance The estimated means of PM10, PM2.5, SO2, NO2, O3 and CO for Q1-Q3/Q4 periods were 27.7/39.3, 16.7/23.7, 2.5/3.9, 37.0/46.4, 32.2/45.3 µg/m3 and 0.64/0.87 ppm and 26.3/43.0, 16.0/26.3, 2.4/4.2, 36.5/47.8, 31.7/50.4 µg/m3 and 0.62/0.90 ppm for long- and short-term exposures, respectively. PM10, PM2.5 and NO2 levels in the Q4 period had significantly higher PSR (138.1, 134.0 and 137.6) when compared to Q1-Q3 period (94.4, 98.1 and 96.4) for the short-term exposure (p = 0.0193; p = 0.0439; p = 0.0180, respectively). PM10, PM2.5, SO2, NO2 and CO levels in the Q4 and Q1-Q3 periods for the long-term exposure showed no significant effect on PSR. Contrastingly, O3 levels in the Q4 period had significantly lower PSR (82.6) when compared to Q1-Q3 (115.9) for the long-term exposure (p = 0.0202). A monotonic increase in PSR was observed with increased PM10 concentration in the Q4 period for the short-term exposure (F-ratio: 4.4476; p = 0.0352). Limitations, reasons for caution Some limitations of the study should be underlined, such as its retrospective nature, exposure assessment based on pollutant levels derived from a network average across city sites, and limited extrapolation of the results to the general population. Wider implications of the findings Our data suggest that short-term exposure to environmental factors could affect the primary sex ratio in polluted seasons or cities. A monotonic effect on PSR in the case of exposure to increasing PM10 levels was identified. Trial registration number Not applicable

Factors Affecting the Ratio of Female to Male of Pinewood Nematodes Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle

The pinewood nematode Bursaphelenchus xylophilus (B. xylophilus) is responsible for a devastating disease of pine forests. Its pathogenicity is closely related to the numbers of individual B. xylophilus. The ratio of female to male (sex ratio) is key to understanding population change in this species. The sex ratio of B. xylophilus varies widely, but it is unclear how it is affected by environmental changes. The sex ratios of nematodes, isolated from different samples in the wild, varied between 0.93 and 2.20. Under laboratory conditions, maternal age and the population did not affect the sex ratio of progeny. A change from good to poor nutritional status was associated with a reduction of the sex ratio of progeny from 1.85 to 1.41, which was speculated to result from a change in the primary sex ratio. Thus, B. xylophilus effectively maintains the sex ratio with maternal age and population changes but adjusts the sex ratio of progeny on the basis of the changes in nutrition.

Do Covariances Between Maternal Behavior and Embryonic Physiology Drive Sex-Ratio Evolution Under Environmental Sex Determination?

Fisherian sex-ratio theory predicts sexual species should have a balanced primary sex ratio. However, organisms with environmental sex determination (ESD) are particularly vulnerable to experiencing skewed sex ratios when environmental conditions vary. Theoretical work has modeled sex-ratio dynamics for animals with ESD with regard to 2 traits predicted to be responsive to sex-ratio selection: 1) maternal oviposition behavior and 2) sensitivity of embryonic sex determination to environmental conditions, and much research has since focused on how these traits influence offspring sex ratios. However, relatively few studies have provided estimates of univariate quantitative genetic parameters for these 2 traits, and the existence of phenotypic or genetic covariances among these traits has not been assessed. Here, we leverage studies on 3 species of reptiles (2 turtle species and a lizard) with temperature-dependent sex determination (TSD) to assess phenotypic covariances between measures of maternal oviposition behavior and thermal sensitivity of the sex-determining pathway. These studies quantified maternal behaviors that relate to nest temperature and sex ratio of offspring incubated under controlled conditions. A positive covariance between these traits would enhance the efficiency of sex-ratio selection when primary sex ratio is unbalanced. However, we detected no such covariance between measures of these categories of traits in the 3 study species. These results suggest that maternal oviposition behavior and thermal sensitivity of sex determination in embryos might evolve independently. Such information is critical to understand how animals with TSD will respond to rapidly changing environments that induce sex-ratio selection.

SEX RATIO IN ARUNACHAL PRADESH: A CASE STUDY

In India, we compute the sex ratio in terms of number of females per thousand males. Among the various components of population composition, sex composition holds a prime place in the context of demographic composition of any region. The balance between the two sexes affects the social and economic relationship within a community. In developed countries, where nursing facilities and medical care are developed, the male mortality rate is higher than the female mortality rate at all ages. But in less developed countries, more females die in comparison to the males. The most desirable and theoretically expected primary sex ratio genetically is 50:50. Arunachal Pradesh in India which is dominated by scheduled tribes [66.78%of total population], despite being an egalitarian society has been experiencing a high sex ratio in tribal society. This paper, therefore, seeks to examine the feature and trend as well as the overall pattern and factors responsible for high sex ratio in Arunachal Pradesh.