A basic hypothesis is that cultural evolutionary processes sustain differences between groups, these differences have evolutionary relevance and they would not otherwise occur in a system without cultural transmission. The empirical challenge is that groups vary for many reasons, and isolating the causal effects of culture often requires appropriate data and a quasi-experimental approach to analysis. We address this challenge with historical data from the final Soviet census of 1989, and our analysis is an example of the epidemiological approach to identifying cultural variation. We find that the fertility decisions of Armenian, Georgian and Azeri parents living in Soviet-era Russia were significantly more son-biased than those of other ethnic groups in Russia. This bias for sons took the form of differential stopping rules; families with sons stopped having children sooner than families without sons. This finding suggests that the increase in sex ratios at birth in the Caucasus, which began in the 1990s, reflects a cultural preference for sons that predates the end of the Soviet Union. This result also supports one of the key hypotheses of gene–culture coevolution, namely that cultural evolutionary processes can support group-level differences in selection pressures that would not otherwise occur in a system without culture.

Sexual conflict theory has been successfully applied to predict how in non-human animal populations, sex ratios can lead to conflicting reproductive interests of females and males and affect their bargaining positions in resolving such conflicts of interests. Recently this theory has been extended to understand the resolution of sexual conflict in humans, but with mixed success. We argue that an underappreciation of the complex relationship between gender norms and sex ratios has hampered a successful understanding of sexual conflict in humans. In this paper, we review and expand upon existing theory to increase its applicability to humans, where gender norms regulate sex ratio effects on sexual conflict. Gender norms constrain who is on the marriage market and how they are valued, and may affect reproductive decision-making power. Gender norms can also directly affect sex ratios, and we hypothesize that they structure how individuals respond to market value gained or lost through biased sex ratios. Importantly, gender norms are in part a product of women's and men's sometimes conflicting reproductive interests, but these norms are also subject to other evolutionary processes. An integration of sexual conflict theory and cultural evolutionary theory is required to allow for a full understanding of sexual conflict in humans.

Maintaining stable breeding groups of rhesus macaques (Macaca mulatta) can be challenging due to the complex social dynamics and despotic nature of the species. Trauma from aggression is a common problem in rhesus colonies and can cause social disruption, strain veterinary and animal management resources, and potentially affect reproduction. Previous research has shown that increasing the number of non-natal adult males in a breeding group can improve group stability, reduce trauma, and increase reproduction. Here, we used mixed-effects regression models to examine the effects of sex ratio and other factors on trauma and reproduction at the Yerkes National Primate Research Center using a historical dataset made up of four large rhesus groups over an eleven-year period (2003-2013). As expected, sex ratio was a significant predictor for both trauma and reproduction. However, group age since formation was a stronger predictor of trauma frequency and the amount of space available was a slightly better predictor of reproduction than sex ratio or trauma. These results indicate that improving sex ratios can be a viable management strategy to reduce trauma and improve reproduction, particularly when it is difficult to manipulate the group compositions and/or their housing situations. Reducing trauma is a primary goal for rhesus breeding colonies, as it directly impacts the monkeys’ health and psychological well-being. Such improvements are necessary for the ethical treatment and care of the animals themselves, but also to reduce financial burdens and maintain a healthy colony for research purposes.

This article analyses long-term population dynamics—growth, decline, sex- and age-composition—in Chaghadaid-era Central Asia in the context of the ‘Late-medieval Crisis’. It is based on a unique dataset of 630 epitaphs from two East Syriac (‘Nestorian') graveyards in the Semirech'ye region (Northwest Tian Shan, North Kyrgyzstan), boosted by archaeological and osteological evidence from the same graveyards. This epigraphic corpus is truly unique in the sense that this is the only surviving data that allow the undertaking of such a quantitative reconstruction of pre-modern Central Asian demography. A close analysis of the corpus, based on the ‘excess mortality’ method, reveals rapid demographic growth between circa 1270 and 1330, despite frequent short-term mortality crises, caused, most likely, by a combination of environmental and political factors. The population growth came to a sudden halt because of a major plague outbreak in 1338–1339, killing about three-quarters of the local population, and initiating what was known as the Black Death of 1347–1353 in West Eurasia and North Africa. The analysis of sex and age ratios indicates that the local population regime was heavily male-dominated. The plague of 1338–1339 targeted primarily younger women, most likely due to pregnancy-related hazards; conversely, in other crisis years, adult males were more susceptible. The findings of the article are wrapped into the wider context of the ‘Late-medieval Crisis’.

The population dynamics of the stout reef octopus, Octopus insularis fished with longlines of pots in mid-shelf waters of north-eastern Brazil was studied based on fishermen's logbooks and onboard monthly fishing trips from September 2009 to August 2010. Specimens marked with oxytetracycline kept in tanks for up to 21 days provided evidence of the daily deposition of growth increments in the lateral wall of the upper beaks. Sampled specimens weighed 50–1280 g and had 43–172 daily growth increments. Compared with congeneric species from higher latitudes, O. insularis grows faster and has a shorter longevity in the north-eastern Brazil tropical environment. Total catches and catch-per-unit effort were substantially higher in the dry season, with less wind and cooler temperatures. The presence of larger specimens was seasonal, correlated with the chlorophyll-a levels recorded six months earlier. The year-round presence of mature females and males, spawned females, and egg masses attached to the pots, were considered evidence of migration of small and young specimens from coastal areas towards the 20–40 m depth range for reproduction. Annual landings attained ~200 tonnes (2005–2010). Although recent landing statistics are missing, fishermen interviewed in 2021 claimed that the fishery was still profitable. It is suggested that, despite the lack of management, the fast growth, year-round reproduction and limited market for this relatively small octopus, prevented the fishery from collapse and reinforces the current view of the high resilience of cephalopod fisheries.

We investigate how changes in the sex ratio induced by World War II affected the bargaining patterns of Italian men in the marriage market. Marriage data from the first wave of the Italian Household Longitudinal Survey (1997) are matched with newly digitized information on war casualties coming from the Italian National Bureau of Statistics. We find that men in post-war marriages were better off in terms of their spouse's education, this gain amounting to about half a year of schooling. By considering heterogeneity across provinces, we find that the effects were more pronounced in rural provinces, mountainous provinces, and provinces with a higher share of population employed in agriculture. This result suggests that in these provinces the war caused a more fundamental change in marriage patterns compared to urban, lower-lying, and less agricultural provinces where marriage markets might have been more flexible to begin with.

Empirical evidence suggests that close to 100 million women are “missing” worldwide. We revisit the empirical evidence for China, the country with the most missing women. Nearly ten million girls born in the 1980s and 1990s who were “missing” according to earlier census data can be found again in the 2010 population census. We discuss two possible explanations for the re-emergence of these formerly missing girls: the delayed registration of girls owing to economic reasons, and the response to amendments to the Chinese Statistics Law in 2009 and policy changes in the 2010 population census. Using the most recent statistics, we document patterns of the underreporting of women over time and across regions as well as explore the basic determinants of underreporting of women. Important policy challenges remain. For the unregistered children, the lack of access to public services will increase their vulnerability and adversely affect their quality of life.

Estuaries and saltmarshes play a fundamental role in the life cycle of many crab species. Diverse studies show that temperature and salinity modulate abundance, size frequency distribution (SFD), sex ratio and growth in crustaceans. These population parameters are usually challenging to estimate due to the high environmental variability of estuaries. Monthly samples of the estuarine crab Hemigrapsus crenulatus were taken from October 2003 to October 2004 (except July 2004) in the Tubul estuary, central Chile. We quantified temporal changes in abundance, size distribution, sex ratio and monthly growth through the annual cycle. A total of 1025 individuals were collected. Sizes ranged from 7.72–33.51 mm carapace length (CL) with a growth rate ranging between 2.13–30.5% mm CL mo−1. Size and growth rates were greater in spring-summer, suggesting a faster growth of younger crabs correlated with increasing sea temperatures in the austral summer. Overall, sex ratio was 1.75:1 in favour of males. Modal analysis identified at least seven cohorts cohabiting throughout the annual cycle. Growth parameters for males and females were the following, respectively: L∞ = 33.6 and 29.6, k = 0.69 and 0.91, t0 = –0.39 and −0.28. Changes in size distribution suggested a recruitment period during autumn and winter seasons when there are lower salinities and temperature fluctuations stresses. Generalized linear models indicated that sea temperature, salinity and chlorophyll were the environmental variables that better predicted the annual patterns in the population structure.

The study characterized the structure of juveniles and sub-adults of Farfantepenaeus brasiliensis and F. paulensis in the Cananéia-Iguape estuarine lagoon system and its adjacent coastal area by evaluating the period of juvenile recruitment, sex ratio, growth, longevity, natural mortality, and development time until the late juvenile phase. Samples were collected from July 2012 to June 2014. Shrimps were identified by species and sex, and measured (carapace length – CL mm); 889 individuals of F. brasiliensis and 848 of F. paulensis were analysed. Females were more abundant than males for both species. The growth parameters of F. brasiliensis were: CL∞ = 45.5 mm, k = 1.8 year−1 for males and CL∞ = 55.2 mm, k = 1.6 year−1 for females; longevity of 2.52 years (males) and 2.88 years (females); and natural mortality of 1.71 (males) and 1.55 (females). For F. paulensis, the following values were observed: CL∞ = 40.7 mm, k = 2.3 year−1 for males and CL∞ = 56.5 mm, k = 1.9 year−1 for females; longevity of 2.04 years (males) and 2.37 years (females); and natural mortality of 2.39 (males) and 2.05 (females). The juvenile recruitment of both species peaked in January 2014. The development time until late juvenile phase was ~7 months (F. brasiliensis) and ~5 months (F. paulensis). Even though the highest abundance of juveniles did not occur in the closed season, fishing is forbidden in the estuarine area and the migration towards the adult population occurred close to or even during the closed season.

The meadow spittlebug, Philaenus spumarius (L.) (Hemiptera: Aphrophoridae), is the main vector in Europe of the recently detected plant pathogen bacterium Xylella fastidiosa Wells et al. (Xanthomonadales: Xanthomonadaceae). While the ecology of continental populations is well documented, nothing is known about the insular populations of P. spumarius, such as in Corsica, where the bacterium was detected in 2015. Hence, in an epidemiological context, the ecology of P. spumarius has been studied in a maquis landscape in the Ajaccio region between 2017 and 2019. Adults and nymphs were almost exclusively collected on Cistus monspeliensis L. (Cistaceae). However, very few specimens were collected in summer, suggesting a movement of the adults to sheltered habitats. Unfortunately, despite several trapping methods used, the location of adult summer habitat remains unknown for the studied population. It might be tempting to destroy the central plant host of P. spumarius populations. However, as spittlebug nymphs are highly polyphagous on low-growing plant species and as the females can lay eggs in any dead plant tissues, such practice could have limited the impact. Instead, the strong relationship between P. spumarius and C. monspeliensis could be used to monitor spittlebug populations, to limit/concentrate the means of insect control, or in an agronomic context to lure insects away from crops. Maintaining natural arboreal vegetation around agronomic systems could help decrease insect abundance – and potentially, pathogen load – on cultivated species. Such hypotheses need to be further studied by landscape experiments.

Parasitoids can be used as biological agents of pest control. Anagyrus saccharicola Timberlake (Hymenoptera: Encyrtidae) is a parasitoid of the pink sugarcane mealybug Saccharicoccus sacchari (Cockerell) (Hemiptera: Pseudococcidae). Although this mealybug is present in all sugarcane-producing countries, there is limited information regarding this pest and its parasitoid. Aiming to elucidate information on bioecological parameters of A. saccharicola, were evaluated the survival of parasitoid females and males at three temperatures, the host preference of the parasitoid, and the fecundity and longevity of the host. In addition, the parasitism rate of A. saccharicola was estimated based on three factors, feeding, mating, and time. Survival was evaluated at 20, 25, and 30°C. Host preference was conducted on 15-, 20-, and 30-day-old mealybugs. And the parasitism rate was evaluated in fed and unfed, mated and unmated parasitoids and with 24 h and newly emerged. The temperature of 20°C was the most favorable for parasitoid survival. Parasitism occurred at all evaluated ages of the mealybug; however, the preference was for those that were 30-days-old. The parasitized mealybugs longevity was approximately 8 additional days after parasitization, and non-parasitized mealybugs lived for an additional 20 days for mealybugs aged 30 and 20 days at the outset of the tests, and a further 13 days for the 15 days. Feeding and mating after 24 h of emergence resulted in a higher parasitism rate. These findings can contribute to more efficient rearing of A. saccharicola and in the planning of the biological control of S. sacchari in the integrated pest management programs.

The temperature-dependent development of Apanteles hemara (Nixon), a larval endoparasitoid of the devastating amaranth pest Spoladea recurvalis (F.) was studied in the laboratory at six constant temperatures (10, 15, 20, 25, 30 and 35 °C), a photoperiod of 12L:12D and a relative humidity of 60–70%. Developmental time decreased significantly with increasing temperature within the range of 15–30 °C. The parasitoid's pupal mortality, successful parasitism rate, adult emergence rate and longevity, sex ratio and fecundity were affected by temperature. The population of A. hemara failed to develop at 10 and 35 °C. The development threshold (Tmin) and the thermal constant (K) were calculated by the linear model while the lethal temperature (Tmax) was determined by the Lactin-1 model. The estimated values of Tmin, Tmax and K by the two models were 10.3 °C, 35.0 °C and 185.18 DD respectively for the total immature development. The estimated value of the optimum temperature using the Taylor model was 30.8 °C. This is the first study to report on the effect of temperature on the developmental parameters of A. hemara giving an insight into its biology. The implications of these findings for the use of A. hemara in biological control are discussed.

The sex ratio question has been an area of growing interest in population dynamics, especially in developing countries with respect to the issue of missing women, but few studies have examined this in sub-Saharan Africa. Both at birth and in the general population, sex ratios follow an expected demographic pattern in the absence of the interference of historical events affecting either males or females in a population. In Zambia, an unexpected demographic pattern of sex ratios is exhibited in census and survey data. This study used data from censuses and surveys conducted from 1969 to 2014 to examine variations in sex ratios in the Zambian population. It was found that sex ratio imbalances were largely due to data deficiencies due to age misreporting and under-enumeration. A consistent under-enumeration of young adult males in the 20–34 years age group was found. A systematic pattern of high sex ratios, above 100, for ages 40+ was found, represented by synthetic cohorts traceable from the 1969 census, progressing to the 2000 census and phased out in the 2010 census. Extremely high adult male mortality was found in 2010 in the 35–59 years age group, primarily attributable to HIV/AIDS. Understanding the demographic pattern of sex ratios in a population is relevant for policies to improve the quality of data collection systems, and socioeconomic development planning, for the young age group population, which is prone under-enumeration.

A survey of Antarctic toothfish (Dissostichus mawsoni) was conducted in the northern Ross Sea region during the winter of 2016 to document the timing and location of spawning activity, to collect biological information about reproductive status during the spawning season and to look for temporal signals in biological data from D. mawsoni that may indicate a spawning migration of mature toothfish from the continental slope region to the northern Ross Sea region. The 58 day survey showed that spawning of D. mawsoni began on some seamounts by early July. No changes were detected between winter and summer in length, age, sex ratio or condition factor distributions for D. mawsoni in the northern Ross Sea as hypothesized following a spawning migration from the slope to the northern Ross Sea region. These results suggest that the distribution of D. mawsoni in the Ross Sea is mainly accomplished through ontogenetic migration and not annual return spawning migrations.

The Trivers–Willard Hypothesis (TWH) states that parents in good conditions bias the sex ratio towards sons and parents in poor conditions bias the sex ratio towards daughters. This study used data from a large nationwide population dataset (N=1,401,851) from the Czech Republic – a modern contemporary society. The study included air pollution and property prices in the TWH estimation, and had a more detailed focus on stillbirths than previous studies. Using official natality microdata from the Czech Statistical Office for years between 1992 and 2010 and data on levels of air pollution in the country over the same period, the study assessed whether the biological and socioeconomic status of mothers and environmental factors affected the sex of children. The results were largely insignificant and not robust across specifications. The presented epidemiological evidence suggests that stillbirths are randomly distributed in the Czech Republic and that the sex ratio is not affected by the socioeconomic status of mothers or by environmental characteristics.

The Chinese white pine beetle Dendroctonus armandi (Coleoptera: Scolytinae) typically displays bivoltinism at altitudes below 1700 m in the Qinling Mountains, China. The periods of host colonization and larval overwintering are two important phases in the life cycle of bark beetles, as it is during these periods that they have to contend with host plant defences and periods of intense cold, respectively. Although during different seasons, the females and males of Chinese white pine beetles show varying tolerances to host plant terpenoids, the sex ratio and survival physiology condition of the two beetle generations are unknown. We investigated the sex ratio of individuals, and also examined the body mass, energy stores, and detoxication enzymes of males and females in each of the two generations in order to determine the overall population stability of each generation. We identified a female-biased sex ratio among adults in both generations. Furthermore, patterns of body mass, energy stores, and detoxication enzymes were found to differ between the two sexes and two seasons. Compared with the males, the females have a larger body mass and higher amounts of stored lipids, which are assumed to be adaptations designed to overcome host resistance and facilitate subsequent oviposition.

The blue shark Prionace glauca is the most abundant species in the artisanal driftnet fishery off the coastal waters of Ivory Coast. The reproductive parameters were investigated with the aim of providing basic information on the reproductive biology for fisheries management. A total of 424 specimens (256 males and 168 females) ranging from 170–330 cm in total length (TL) were sampled between August 2014 and November 2016. Sample for embryonic sex ratio was obtained from 18 litters of 503 individuals (255 males and 248 females). The embryonic sex ratio was not significantly different from 1:1 (χ2 = 0.10, P > 0.05, N = 503). The size at 50% maturity (L50) was 218.1 cm TL for males and 223.3 cm TL for females. The litter size based on the number of embryos varied from 6 to 62, with an average of 30 embryos. Mating started in July whereas ovulation, fertilization and uterine eggs occurred in late October–November. Smallest embryos of 3–5 cm in stretch total length (STL) appeared in uterus from November to January. The embryo size varied widely among months, and well-pigmented embryos were already present in April–May samples, although most of them occurred in August–September, suggesting a gestation period of around 11 months. The absence of neonates in catches, as well as parturition females, does not support a hypothesis that parturition takes place in the Gulf of Guinea.

Coupled with the social practice of female hypergamy, the male surplus within the never-married population means that today's Chinese marriage market is extremely tight in particular for men from a rural background and the least privileged socio-economic categories. Drawing on quantitative data from a survey conducted in 2014–2015, this article sheds light on the situation of single men who are past prime marriage age in three rural districts of Shaanxi particularly affected by this phenomenon. It compares single men's characteristics to those of their married counterparts and offers insights into the heterogeneity of single men with the aim of challenging some commonly accepted assumptions about bachelorhood in rural China. Results suggest a strong internalization of the various characteristics, centred on being able to offer social mobility to a potential wife, that a man is expected to have to be attractive to women in a context where women have more choice in mate selection. We conclude that mate selection is highly marked by class, social norms, social interactions, health, generation and age, and requires the mobilization of certain amounts of individual, social and economic resources. Unwanted bachelorhood would thus be better understood using an intersectional approach rather than mainly in numeric terms.