The biology of Marchantia polymorpha subsp. ruderalis Bischl. & Boissel. Dub in nature.

Introduction: Though used as the model liverwort in culture for several decades, the biology of Marchantia polymorpha subsp. ruderalis in nature has never been documented in detail in a single account. Methods: Here we synthesize routine field observations documented with hundreds of images of M. ruderalis colonies (or groups) showing sex differentiation over 3 years on two populations of M. ruderalis after major heathland fires in 2020. Results: Initial post-fire establishment is from airborne spores rather than a spore bank but thereafter spread is via gemmae which have less exacting germination requirements. Young sporelings are highly gemmiferous but gemmae production becomes less frequent after sex organ formation. Over the course of a year there are up to three waves of carpocephalum production with the overwhelming majority of antheridiophores appearing 2-3 months ahead of the archegoniophores though no differences in growth rates were apparent between male and female thalli. Spermatozoids are produced almost continuously throughout the year, whilst sporophyte maturation is restricted to the summer months. Discussion: Because of the asynchrony between antheridiophore and archegoniophore production a 1:1 sex ratio is only apparent over this period. The spring months see an excess of males with more females in the summer. An almost 100% fertilization rate, with fertilization distances of up to 19 m far exceeding those in all other bryophytes, is attributed to vast spermatozoid production for most of the year, dispersal on surface oil films between thalli and highly effective intra-thallus spermatozoid transport via the pegged-rhizoid water-conducting system. Archegoniophores do develop on female-only populations but have shorter stalks than those where fertilization has occurred. Eventual disappearance post fires is attributed to a fall in topsoil nutrient levels preventing new sporeling establishment and competition from Ceratodon purpureus and Polytrichum spp. A major drought in the summer of 2022 almost wiped out the heathland Marchantia populations but all the other bryophytes survived.

Successive stamen movement in Saxifraga candelabrum is responsive to weather and pollinator visits.

BACKGROUND: Successive stamen movement is a complex plant behavior involving successive uplift of stamens and pollen release, which plays a role in reducing sexual interference, increasing pollen deposition and promoting pollen export. Although reported from several taxa, studies on whether the movement can be influenced by abiotic and biotic factors are scarce. METHODS: In this study, we here for the first time described a pattern of successive stamen movement in Saxifraga candelabrum (Saxifragaceae). We then compared the rates of stamen movement in S. candelabrum under different weather and varying pollinator visits. Pollen packaging and presentation schedule of S. candelabrum were also investigated. RESULTS: The results showed that the number of stamens bent per day in sunny days was significantly higher than overcast and rain. Flowers that receive more pollinator visits (control treatment) had significantly higher number of stamen movement than those that received fewer (removal treatment) and none (bagging treatment). Throughout the staminate phase of a flower, there was a progressive increase in both pollen quantity of individual stamens and pollen presentation during each day. CONCLUSION: Our research demonstrates that successive stamen movement in S. candelabrum was accelerated by favorable weather and increased pollinator visits, which may promote pollen export. Moreover, incremental pollen packaging is likely an adaptation to seasonal regularity in variations of sex ratio resulting from protandry.

Effect of the COVID-19 pandemic on Vogt-Koyanagi-Harada disease.

To determine the disease prevalence rate and clinical characteristics of Vogt-Koyanagi-Harada (VKH) disease among new patients before and after the declaration of a state of emergency (April 7, 2020) in Japan. New patients and patients with newly diagnosed VKH disease were categorized into "Before" and "After" groups based on the initial visit. The prevalence rate, sex ratio, and age of patients newly diagnosed with VKH were compared between the groups. Best-corrected visual acuity (BCVA) and recurrence rates were compared among 59 patients observed for > 12 months after receiving pulse steroid therapy. For reference, we also examined the prevalence rate of patients newly diagnosed with acute angle closure (AAC) in the Before and After groups. The prevalence rates of VKH disease among newly diagnosed patients (P < 0.05) or patients with AAC (P < 0.001) were significantly higher in the After group. No significant differences in sex ratio or age of VKH disease were observed in both groups. BCVA and recurrence rates showed no significant differences. The COVID-19 pandemic increased the prevalence of VKH disease among new patients compared with that of AAC. However, the clinical features of VKH disease were unlikely affected by the COVID-19 pandemic.

Ambient temperature-related sex ratio at birth in historical urban populations: the example of the city of Poznan, 1848-1900.

This study examines whether exposure to ambient temperature in nineteenth-century urban space affected the ratio of boys to girls at birth. Furthermore, we investigate the details of temperature effects timing upon sex ratio at birth. The research included 66,009 individual births, aggregated in subsequent months of births for the years 1847-1900, i.e. 33,922 boys and 32,087 girls. The statistical modelling of the probability of a girl being born is based on logistic GAM with penalized splines and automatically selected complexity. Our research emphasizes the significant effect of temperature in the year of conception: the higher the temperature was, the smaller probability of a girl being born was observed. There were also several significant temperature lags before conception and during pregnancy. Our findings indicate that in the past, ambient temperature, similar to psychological stress, hunger, malnutrition, and social and economic factors, influenced the viability of a foetus. Research on the effects of climate on the sex ratio in historical populations may allow for a better understanding of the relationship between environmental factors and reproduction, especially concerning historical populations since due to some cultural limitations, they were more prone to stronger environmental stressors than currently.

Wolbachia affect female mate preference and offspring fitness in a parasitoid wasp.

BACKGROUND: Wolbachia are widespread intracellular bacteria in insects that often have high rates of spread due to their impact on insect reproduction. These bacteria may also affect the mating behavior of their host with impacts on the fitness of host progeny. In this study, we investigated the impact of Wolbachia on a preference for mating with young or old males in the parasitoid wasp Habrobracon hebetor. RESULTS: Our results showed that uninfected females from a tetracycline-treated line preferred to mate with young males, whereas Wolbachia-infected females had no preference. Time to mating was relatively shorter in the infected lines. Regardless of Wolbachia infection status, progeny resulting from matings with young males showed higher fitness than those from crosses with old males, and infected females crossed with infected young males showed the highest performance. CONCLUSION: These results suggest an impact of Wolbachia on female mate preference and offspring fitness although it is unclear how this phenomenon increases Wolbachia transmission of infected wasps. © 2024 Society of Chemical Industry.

The Impact of Lifestyle on the Secondary Sex Ratio: A Review.

The secondary sex ratio (SSR), indicating the ratio of male to female live births, has garnered considerable attention within the realms of reproductive biology and public health. Numerous factors have been posited as potential trendsetters of the SSR. Given the extensive research on the impact of daily behaviors and habits on individuals' reproductive health, there is a plausible suggestion that lifestyle choices may also influence the SSR. By synthesizing the existing literature on the current research field, this comprehensive review indicates that an elevated SSR has been associated with an increased intake of fatty acids and monosaccharides, proper nutrition, higher educational levels, financial prosperity, and favorable housing conditions. On the other hand, a decreased SSR may be linked to undernutrition, socioeconomic disparities, and psychological distress, aligning with the Trivers-Willard hypothesis. Occupational factors, smoking habits, and cultural beliefs could also contribute to trends in the SSR. Our review underscores the significance of considering the aforementioned factors in studies examining the SSR and emphasizes the necessity for further research to unravel the mechanisms underpinning these connections. A more profound comprehension of SSR alterations due to lifestyle holds the potential to adequately develop public health interventions and healthcare strategies to enhance reproductive health and overall well-being.

Developmental Delay and Male-Biased Sex Ratio in esr2b Knockout Zebrafish.

The estrogen receptor signaling pathway plays an important role in vertebrate embryonic development and sexual differentiation. There are four major estrogen receptors in zebrafish: esr1, esr2a, esr2b and gper. However, the specific role of different estrogen receptors in zebrafish is not clear. To investigate the role of esr2b in zebrafish development and reproduction, this study utilized TALENs technology to generate an esr2b knockout homozygous zebrafish line. The number of eggs laid by esr2b knockout female zebrafish did not differ significantly from that of wild zebrafish. The embryonic development process of wild-type and esr2b knockout zebrafish was observed, revealing a significant developmental delay in the esr2b knockout zebrafish. Additionally, mortality rates were significantly higher in esr2b knockout zebrafish than in their wild-type counterparts at 24 hpf. The reciprocal cross experiment between esr2b knockout zebrafish and wild-type zebrafish revealed that the absence of esr2b resulted in a decline in the quality of zebrafish oocytes, while having no impact on sperm cells. The knockout of esr2b also led to an abnormal sex ratio in the adult zebrafish population, with a female-to-male ratio of approximately 1:7. The quantitative PCR (qPCR) and in situ hybridization results demonstrated a significant downregulation of cyp19ab1b expression in esr2b knockout embryos compared to wild-type embryos throughout development (at 2 dpf, 3 dpf and 4 dpf). Additionally, the estrogen-mediated induction expression of cyp19ab1b was attenuated, while the estradiol-induced upregulated expression of vtg1 was disrupted. These results suggest that esr2b is involved in regulating zebrafish oocyte development and sex differentiation.

Transformation of meiotic drive into hybrid sterility in Drosophila.

Hybrid male sterility is one of the fastest evolving intrinsic reproductive barriers between recently isolated populations. A leading explanation for the evolution of hybrid male sterility involves genomic conflicts with meiotic drivers in the male germline. There are, however, few examples directly linking meiotic drive to hybrid sterility. Here, we report that the Sex-Ratio chromosome of Drosophila pseudoobscura, which causes X-chromosome drive within the USA subspecies, causes near complete male sterility when moved into the genetic background of the Bogota subspecies. In addition, we show that this new form of sterility is genetically distinct from the sterility of F1 hybrid males in crosses between USA males and Bogota females. Our observations provide a tractable study system where non-cryptic drive within species is transformed into strong hybrid sterility between very young subspecies.

Effects of hazardous chemicals on secondary sex ratio: A comprehensive review.

The secondary sex ratio (SSR), defined as the ratio of male to female offspring at birth, has garnered significant scientific interest due to its potential impact on population dynamics and evolution. In recent years, there has been a growing concern regarding the potential consequences of environmental chemicals on the SSR, given their widespread exposure and potential enduring ramifications on the reproductive system. While SSR serves as an indicator of health, ongoing research and scientific inquiry are being conducted to explore the potential relationship between chemicals and offspring ratio. Although some studies have suggested a possible correlation, others have yielded inconclusive results, indicating that the topic is intricate and still needs to be elucidated. The precise mechanism by which chemical agents exert their influence on the SSR remains ambiguous, with disruption of the endocrine system being a prominent justification. In light of the complex interplay between chemical exposure and SSR, the present review aims to comprehensively examine and synthesize existing scientific literature to gain a deeper understanding of how specific chemical exposures may impact SSR. Insights into chemical hazards that shift SSR patterns or trends could guide prevention strategies, including legislative bans of certain chemicals, to minimize environmental and public health risks.

The evolution of sex roles: The importance of ecology and social environment.

Males and females often have different roles in reproduction, although the origin of these differences has remained controversial. Explaining the enigmatic reversed sex roles where males sacrifice their mating potential and provide full parental care is a particularly long-standing challenge in evolutionary biology. While most studies focused on ecological factors as the drivers of sex roles, recent research highlights the significance of social factors such as the adult sex ratio. To disentangle these propositions, here, we investigate the additive and interactive effects of several ecological and social factors on sex role variation using shorebirds (sandpipers, plovers, and allies) as model organisms that provide the full spectrum of sex role variation including some of the best-known examples of sex-role reversal. Our results consistently show that social factors play a prominent role in driving sex roles. Importantly, we show that reversed sex roles are associated with both male-skewed adult sex ratios and high breeding densities. Furthermore, phylogenetic path analyses provide general support for sex ratios driving sex role variations rather than being a consequence of sex roles. Together, these important results open future research directions by showing that different mating opportunities of males and females play a major role in generating the evolutionary diversity of sex roles, mating system, and parental care.

Female-biased birth sex ratio in a female dispersal primate suggests local resource competition.

Group living may entail local resource competition (LRC) which can be reduced if the birth sex ratio (BSR) is biased towards members of the dispersing sex who leave the group and no longer compete locally with kin. In primates, the predicted relationship between dispersal and BSR is generally supported although data for female dispersal species are rare and primarily available from captivity. Here, we present BSR data for Phayre's leaf monkeys (Trachypithecus phayrei crepusculus) at the Phu Khieo Wildlife Sanctuary, Thailand (N = 104). In this population, nearly all natal females dispersed, while natal males stayed or formed new groups nearby. The slower reproductive rate in larger groups suggests that food can be a limiting resource. In accordance with LRC, significantly more females than males were born (BSR 0.404 males/all births) thus reducing future competition with kin. This bias was similar in 2-year-olds (no sex-differential mortality). It became stronger in adults, supporting our impression of particularly fierce competition among males. To better evaluate the importance of BSR, more studies should report sex ratios throughout the life span, and more data for female dispersal primates need to be collected, ideally for multiple groups of different sizes and for several years.

Sex Ratio at Birth after Concurrent Events of Earthquakes and the COVID-19 Pandemic in Croatia.

The sex ratio at birth (ratio of males to females) has been known to be affected by exogenous shocks such as wars, pollution, natural catastrophes, economic crises, and others. Among these stressful events, both earthquakes and the COVID-19 pandemic have been reported to lower the sex ratio at birth. In this article, a rather unusual situation of two episodes of simultaneous events of COVID-19 lockdown and earthquakes approximately nine months apart (March and December of 2020) is investigated to assess whether they were associated with a bias in sex ratio at birth 3-5 months later (in utero loss) and 9 months later (loss at conception) in Croatia. The monthly time series of sex ratio at birth, total number of births, and total number of both male and female births from January 2010 to December 2021 were analyzed. Seasonally adjusted autoregressive moving-average models were used to estimate the functional form of the time series from January 2010 to February 2020. These results were used to predict the future values of the series until December 2021 and to compare them with the actual values. For all series used, there was no indication of deviation from the values predicted by the models, neither for 3-5 months nor for 9 months after the COVID-19 lockdown and earthquake events. The possible mechanisms of the absence of bias, such as the threshold of the stressful events and its localized reach, as well as the statistical methods employed, are discussed.

Maternal hepatitis B status and Sex at birth: A cross-sectional study in a Ghanaian population.

Maternal carrier status of hepatitis B has been associated with excess sons while maternal immunity to it has been associated with excess daughters at birth. However, the proportion of males at birth (sex ratio) is relatively low in Sub-Saharan Africa despite the relatively high prevalence of hepatitis B. However, no known study has tested this hypothesis in the Ghanaian population; hence the aim of the study. The study was cross-sectional between January and September 2023 at the Tamale Central Maternal and Child Health unit. The study involved 380 mothers of whom mothers with daughters (MD) were 145 (38.2 %) while the rest were mothers with sons (MS). The mothers were aged between 18 and 43 years and were sampled within one week of delivery to singleton births. Maternal venous blood samples were collected and tested for hepatitis B surface antigen (HBsAg), surface antibody (HBsAb), envelop antigen (HBeAg) envelope antibody (HBeAb) and core antibody (HBcAb) using immunochromatographic technique and total testosterone (TT), using ELISA. There was no significant difference in the serum total testosterone level between MD and MS (0.32 ± 0.13 vs 0.32 ± 0.27, P = 0.991). Moreover, while the mothers were seropositive for HBsAg (10.5 %), HBsAb (35.5 %), HBeAg (0.0 %), HBeAb (5.3 %) and HBcAb (11.8 %), there was no significant association between sex at birth and maternal hepatitis B status for HBsAg (ꭓ2: 0.531, P = 0.472), HBsAb (ꭓ2: 2.655, P = 0.140), HBeAb (ꭓ2: 0.251, P = 0.633) and HBcAb (ꭓ2: 0.101, P = 1.000). Maternal hepatitis B status may not be associated with the offspring sex at birth in the studied population from Ghana.

Sex allocation is color morph-specific and associated with fledging condition in a wild bird.

Melanin-based color polymorphism is predicted to evolve and maintain through differential fitness of morphs in different environments, and several empirical studies indicate that life history strategies, physiology, and behavior vary among color morphs. Sex allocation theory predicts that parents should adjust their sex allocation based on differential costs of raising sons and daughters, and therefore, color morphs are expected to modify their brood sex ratio decisions. In color polymorphic tawny owls (Strix aluco), the pheomelanistic brown morph is associated with higher energy requirements, faster growth, and higher parental effort than the gray morph. As hypothesized, we find that brown tawny owl mothers produced more daughters in early broods and more males in late broods, whereas gray mothers did the opposite. At fledging, daughters of early broods and of brown mothers were heavier than those of late broods or gray mothers. Hence, larger and more costly daughters appeared to benefit more than males from being born to brown mothers early in the season. Brown mothers breeding later in the season produced more cheap sons, while gray mothers face fewer challenges under limited resources and favor daughters. These findings suggest that environmental conditions influence brood sex allocation strategies of genetically determined color morphs differently.

Temperature regulates sex determination and growth in the paralichthid flatfish California halibut.

California halibut (Paralichthys californicus) is a candidate species for aquaculture and stock enhancement. These applications rely on sex control, either to maximize the production of faster growing females or to match sex ratios in the wild. Other paralichthids exhibit temperature-dependent sex determination (TSD), but the presence and pattern of TSD is not well defined in California halibut. Juvenile California halibut were cultured at three distinct temperatures (15°C, 19°C, and 23°C) through the developmental period presumed to be thermosensitive based on findings from congeners. Sex ratios were quantified in each treatment using phenotypic sex identification techniques applied early (molecular biomarkers; 51-100 mm total length [TL]) and late (visual examination of the gonads; ≥100 mm TL) in the juvenile phase. Both techniques indicated similar sex determination trends at each temperature, with overall sex ratios assessed as 49.9% male at 15°C, 74.5% male at 19°C, and 98.2% male at 23°C. Growth rates were highest at 23°C and lowest at 15°C, with intrinsically fast- and slow-growing individuals at all temperatures. At 15°C and 19°C, females comprised a higher proportion among the fast growers than they did among the slow growers. These data show that California halibut exhibit TSD, with temperatures of 19°C and 23°C masculinizing fish while 15°C appears to produce a 1:1 sex ratio. This study will help optimize sex ratios and growth in hatcheries through thermal manipulation. Furthermore, the developed biomolecular tools and identified temperature thresholds will be important in future work to understand the influence of global warming on wild population demographics.

Biological and environmental factors influencing reproductive performance in ICR mice, Mus musculus.

BACKGROUND: Since strain names and breeding facilities of ICR mice used in 37 reproductive toxicity studies have changed from 1990 to 2022 in our laboratory, biological and environmental factors that affect reproductive parameters were investigated in control mice to examine the validity of the background data. METHODS: Litter size and sex ratio were measured at birth [postnatal day (PND) 0], while offspring body weight was measured on PND 0 and 21 during the lactation. The relationships between biological and environmental factors and reproductive parameters were assessed with multiple regression analysis using stepwise regression as an explanatory variable selection strategy. The biological factors of litter size at birth, secondary sex ratio (male%), body weight (g) at birth and strain name, and environmental factors of facilities (room), temperature/humidity, and bedding materials were used as explanatory variables, and reproductive parameters of litter size at birth, secondary sex ratio (male%), body weight (g) at birth, and survival index (%) of offspring at PND 21 were used as response variables. RESULTS: No significant effects were indicated in litter size and sex ratio (male %) with any biological and environmental factors. Male and female offspring weights were significantly affected by strain names. No significant effects were indicated in the survival index (%) at PND 21 in both sexes with any biological and environmental factors. CONCLUSIONS: Litter size and sex ratio in this report are sufficient as background data throughout the period because no significant variables of biological and environmental factors affected litter size and gender composition.

Altered Sex Ratio at Birth with Maternal Exposure to Dioxins in Vietnamese Infants.

Excess female births (lower sex ratio at birth) associated with paternal exposure to 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD) have been reported in Italy. However, no significant effects of maternal TCDD exposure on the sex ratio were reported. We investigated the effects of maternal TCDD exposure and the toxic equivalent quantity of polychlorinated dibenzo-p-dioxins/dibenzofurans (TEQ-PCDD/Fs) on the sex ratio at birth in 576 Vietnamese infants from three birth cohorts. TCDD and TEQ-PCDD/Fs in breast milk were stratified (low, mild, moderate, and high) as maternal exposure markers. Logistic regression analysis was used to investigate associations between female birth and dioxin exposure groups after adjusting for confounders. In sprayed and unsprayed areas, adjusted odds ratios (ORs) of female birth (reference: low-TCDD group) were 2.11 in the moderate-TCDD group and 2.77 in the high-TCDD group, which were significantly associated with increased TCDD exposure. In sprayed areas, a significantly increased OR in the high-TCDD group was observed. No significant associations, however, were found between having a girl and TEQ-PCDD/F levels. These results suggest that maternal TCDD exposure may alter the sex ratio at birth among Vietnamese residents of areas with high dioxin contamination.

Sex ratio shift after frozen single blastocyst transfer in relation to blastocyst morphology parameters.

The sex ratio shift was observed in peoples who underwent ART treatment. Moreover, there is limited evidence on differences in sex ratio between single frozen-thawed blastocyst morphology, insemination type and transfer days. So further research is needed in this area with regard to factors possibly affecting the sex ratio. Retrospective study based on multicenter including two large assisted reproduction centers in Shanghai and Wuhan in China. A total of 6361 singleton delivery offspring after frozen-thawed blastocyst transfer. Propensity score weighting and logistic regression models were used to estimate the associations between blastocyst morphology grading and child sex ratio. The main outcome measures is singleton sex ratio. In our study, the primary outcome measure was sex ratio which was calculated as the proportion of male newborns among all live births. Higher quality blastocysts resulted in a higher sex ratio than single poor-quality frozen-thawed blastocyst transfer. Among the three blastocyst morphological parameters of trophectoderm (TE), Grade A and B were significantly associated with a higher sex ratio than Grade C. The similar trend was observed in both IVF and ICSI treated subgroups. As compared with expansion (4 + 3), expansion degree 6 achieved a higher sex ratio in overall populations and IVF treated subgroup. Transferring blastocysts of day 6 had the highest sex ratio both in IVF group and ICSI group. A 6.95% higher sex ratio in transferring blastocysts of day 5 in IVF group than those in ICSI group. No significant association between inner cell mass degree and sex ratio was observed. However, as compared with IVF treatment, all morphology parameters achieved the similar or the biased sex ratio favoring female in ICSI treated subgroup. Quality of blastocysts was positively associated with sex ratio. TE score and expansion degree rather than ICM were significantly associated with sex ratio at birth. ICSI treatment promotes the biased sex ratio favoring female.

Diversity and Flight Patterns of Caddisflies (Trichoptera) in an Atlantic Forest Fragment: Implications for Species Conservation in Threatened Ecosystems.

Anthropogenic activities have decimated the Atlantic Forest domain (AF) and increased the pressure on freshwater biota, such as Trichoptera, which is the most affected order by the current insect decline. Adult mobility is crucial for the colonisation of new environments unconnected by water sources. In this article, we describe the assemblage of caddisflies in a preserved AF fragment related to their functional feeding group and provide empirical data on the patterns of horizontal and vertical flight. Adults were collected using white sheet and light attraction traps, placed at different distances and heights from a stream in Pernambuco, Brazil. A total of 2934 specimens of 15 species from five families were collected, mostly collector-filterers. Horizontal flight was limited, with 80% of the abundance concentrated up to 20 m. Vertical stratification was also concentrated at lower heights. A female-biased proportion was observed at higher strata. The richness and abundance of species decreased with increasing distances and heights from the stream. Overall, Chimarra sp. and Macrostemum scharfi were the dominant species. Trichoptera is a key taxon used as a biological indicator of water quality, and here, knowledge on the diversity and flight patterns of adults is expanded. At the risk of intensive pollution of rivers in Atlantic forests, data on the adult dispersal can be incorporated in the assessment of endangerment status and in conservation strategies.

Isolating a culture of son preference among Armenian, Georgian and Azeri Parents in Soviet-era Russia.

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.