Prevalence of urinary retention after vaginal delivery: a systematic review and meta- analysis.

INTRODUCTION AND HYPOTHESIS: Postpartum urinary retention requires timely detection and intervention as late detection can lead to long-term voiding dysfunction; however, trends in the prevalence of urinary retention during the postpartum period remain unclear. This systematic review and meta-analysis aimed to estimate the pooled overall prevalence of overt and covert urinary retention in women after vaginal delivery and the difference in prevalence within 4 days after delivery. METHODS: MEDLINE, CINAHL, Ichu-shi web, and J-stage databases were searched up until October 2020. Two researchers screened and included observational studies reporting the prevalence of urinary retention up to 4 days postpartum based on inclusion criteria. The overall prevalence of overt and covert urinary retention was calculated. RESULTS: From 24 studies, the overall overt and covert urinary retention prevalence rates were estimated to be 1% and 13%, respectively. The prevalence of overt urinary retention over time was 2% at 6 h postpartum, 1% at 6-12 h, and 3% from postpartum to 24 h postpartum. The prevalence of covert urinary retention over time was 19% (6 h postpartum), 15% (24 h postpartum), 11% (1 day postpartum), 7% (2 days postpartum), 8% (3 days postpartum), and 0.1% (4 days postpartum). CONCLUSIONS: By postpartum day 4 after vaginal delivery, 14% of women were found to have experienced urinary retention. The highest prevalence was observed at 6 h postpartum, suggesting that urinary retention could be identified at 6 h postpartum.

Occupational stress is associated with job performance among pregnant women in Japan: comparison with similar age group of women.

BACKGROUND: Pregnancy results in physical and psychological changes in women; however, pregnant women hesitate to take a break from work even when they feel the need. Since working while physically ill leads to decreased job performance, it is important to determine the factors that lead to this phenomenon. AIM: To study the occupational stress associated with job performance and absenteeism of pregnant women compared with non-pregnant women. METHODS: In 2019, non-pregnant and pregnant employed women in their 20-40 s in Japan completed an online survey examining job performance (Work Limitation Questionnaire - Short Form), absenteeism, occupational stress (Brief Job Stress Questionnaire), and working situations. RESULTS: Of 918 respondents who met the inclusion criteria, 904 were included in the final analysis (454 non-pregnant and 450 pregnant women). Logistic regression analyses showed that absenteeism was significantly higher for pregnant women. However, for women who were absent, there was no significant difference between non-pregnant and pregnant women. After adjusting for attributes and working conditions, pregnant women had significantly higher (p < .001) work productivity losses than non-pregnant women, but only in the physical tasks domain; their physical stress response was also higher compared to non-pregnant women (p = .048). However, pregnant women reported significantly less interpersonal conflict stress (p < .001) and psychological stress (p = .026), as well as better workplace support as a buffering factor for stress (p = .021), than non-pregnant women. CONCLUSION: Clarifying the physical burden associated with pregnancy and assisting women in coordinating their work duties while considering the physical demands of pregnancy may minimize work productivity losses among pregnant women.

Developing a Prenatal Couple Education Program Focusing on Coparenting for Japanese Couples: A Quasi-Experimental Study.

Having and raising children can be a source of joy for parents. However, the transition to parenthood is associated with a certain degree of strain and stress, and couple relationship quality often declines during the transition. Coparenting, the shared responsibility of childrearing, benefits both parents and children and is an important aspect of the transition to parenthood. In this quasi-experimental study, we aimed to develop a couple education program in Japan that focuses on coparenting among couples expecting their first child. Twenty-one healthy couples voluntarily participated in the intervention group (n = 16) or the control group (n = 5). Couples in each group could voluntarily participate in standard childbirth education classes. The intervention was a couple education program designed to enhance coparenting and consisted of two interactive classes, including discussions within each couple and watching a short video showing an example of childrearing. We collected outcome measures on childrearing, couple relationship, parental mental health, and child adjustment at 1 month and 3 months after childbirth. Multiple regression analysis was performed and showed positive effects of the intervention on childrearing and child adjustment. Being in the intervention group had a significant positive effect on Coparenting Support scores at 1 month after childbirth (ß = 0.457, p < 0.003, R2 = 0.187) and Soothability scores for child adjustment at 3 months after childbirth (ß =0.429, p < 0.006, R2 = 0.157). In conclusion, we have developed the prenatal education program focusing on coparenting for Japanese couples.

Ontogenetic stage-specific quantitative trait loci contribute to divergence in developmental trajectories of sexually dimorphic fins between medaka populations.

Sexual dimorphism can evolve when males and females differ in phenotypic optima. Genetic constraints can, however, limit the evolution of sexual dimorphism. One possible constraint is derived from alleles expressed in both sexes. Because males and females share most of their genome, shared alleles with different fitness effects between sexes are faced with intralocus sexual conflict. Another potential constraint is derived from genetic correlations between developmental stages. Sexually dimorphic traits are often favoured at adult stages, but selected against as juvenile, so developmental decoupling of traits between ontogenetic stages may be necessary for the evolution of sexual dimorphism in adults. Resolving intralocus conflicts between sexes and ages is therefore a key to the evolution of age-specific expression of sexual dimorphism. We investigated the genetic architecture of divergence in the ontogeny of sexual dimorphism between two populations of the Japanese medaka (Oryzias latipes) that differ in the magnitude of dimorphism in anal and dorsal fin length. Quantitative trait loci (QTL) mapping revealed that few QTL had consistent effects throughout ontogenetic stages and the majority of QTL change the sizes and directions of effects on fin growth rates during ontogeny. We also found that most QTL were sex-specific, suggesting that intralocus sexual conflict is almost resolved. Our results indicate that sex- and age-specific QTL enable the populations to achieve optimal developmental trajectories of sexually dimorphic traits in response to complex natural and sexual selection.

Female mate preference for longer fins in medaka.

Medaka, Oryzias latipes complex, display sexual dimorphisms in anal- and dorsal-fin lengths that suggest that females may prefer males with longer fins. However, female preference for longer anal and/or dorsal fins has not yet been described for the medaka. One reason that previous studies have not investigated this relationship may be because variations in male fin lengths within a single population are too small to experimentally detect female preference. In this study, we artificially crossed individuals from two wild populations (Aomori and Okinawa) that differed in male anal- and dorsal-fin lengths to increase phenotypic variation. We then tested female mate preference using these hybrid males. The results of the mating experiments and stepwise multiple regression analyses indicate that anal- and/or dorsal-fin lengths of the males contributed to female preference (i.e., males with longer anal and/or dorsal fins were less likely to be rejected by females). Variation in male standard length did not affect female preference. The evolution of female preference for longer fins in the medaka species complex may be explained by the "sexy son" hypothesis or the direct benefit hypothesis.

Feasibility and Usability of the Job Adjustment Mobile App for Pregnant Women: Longitudinal Observational Study.

BACKGROUND: Working pregnant women often need to adjust their physically demanding jobs for a healthy pregnancy. However, uncertainty about the extent of these adjustments can hinder their effectiveness. To address this, we developed the Job Adjustment mobile app, which allows users to input job and health details to generate a variety of personalized action plans. As this is the first version of the app, assessing its feasibility and usability is crucial. OBJECTIVE: This study aims to verify the feasibility and usability of the Job Adjustment mobile app. METHODS: A longitudinal observational study was conducted on pregnant Japanese women who were allowed to use the app anytime from 12 to 34 weeks of gestation; they received reminder emails every 2 weeks encouraging app use. A questionnaire was administered before app use and at 20 and 32 weeks of gestation. Feasibility was evaluated across 4 domains: implementation, demand, acceptability, and adverse events. Implementation was evaluated based on 3 parameters: dropout rate, initial reminder email receipt rate, and adherence rate (measured as pregnant women who used the app at intervals of 2.5 weeks or less). Demand was measured by intervals between use and intervals between log-in, and participants answered 15 questions to assess acceptability. Adverse events were assessed by analyzing the degree of anxiety related to work. Demographic data were analyzed to determine any statistically significant differences in intervals between uses. Usability was evaluated using the System Usability Scale. RESULTS: The analysis included 66 pregnant women, and 61% (n=40) of them were multipara. The dropout rate, adherence rate, and initial reminder email receipt rate were 18% (13/71), 44% (29/66), and 79% (52/66) respectively. The median intervals between use and intervals between log-in were 2.94 (IQR 2.00-5.13) weeks and 2.28 (IQR 1.81-4.00) weeks, respectively. Overall, 60% (35/58) to 90% (52/58) of the participants responded positively to all 15 questions assessing acceptability, and no anxiety regarding work was recorded. The mean System Usability Scale score was 66.1 points. Multipara women had significantly longer intervals between app use compared to primipara women (P=.01). CONCLUSIONS: The results demonstrated acceptable levels of feasibility and usability of the app. However, the low adherence rates, especially among multipara women, suggest the need for modifications to reduce the time burden of the app. Further research should explore more effective and acceptable intervals between use and timing, involving a larger sample and accounting for diverse characteristics of pregnant women. TRIAL REGISTRATION: UMIN Clinical Trials Registry UMIN000042943; https://tinyurl.com/ydrchfas.

Relationship between low back pain and stress urinary incontinence at 3 months postpartum.

Previous studies have proposed that pelvic misalignment may be associated with stress urinary incontinence through a decrease in the contractile function of the pelvic floor muscles; however, this relationship remains unclear. This study aimed to clarify the relationship between low back pain, an indication of pelvic misalignment, and stress urinary incontinence at 3 months postpartum. We conducted a cross-sectional study of women who gave birth to full-term babies between July 2008 and July 2009. Stress urinary incontinence was defined as urinary leakage when coughing, sneezing, or exercising. Low back pain was defined as pain between the ribs and gluteal sulcus in the preceding 2 months. Of the 228 subjects included in the study, the prevalence of stress urinary incontinence was 22.8% (n = 52). The prevalence of low back pain in the stress urinary incontinence group was significantly higher than that in the non-stress urinary incontinence group (78.8% [n = 41] vs. 57.4% [n = 101]; p = 0.005). Stress urinary incontinence was associated with older age, primiparity, vaginal delivery, and low back pain at 3 months. In conclusion, low back pain was associated with stress urinary incontinence after adjusting for pregnancy and delivery factors, suggesting pelvic misalignment contributes to the development of stress urinary incontinence. We propose that including care for pelvic misalignment in pelvic floor muscle training, the treatment of choice for stress urinary incontinence, could be beneficial.

Prevalence of symptoms of pelvic floor dysfunction and related factors among Japanese female healthcare workers.

OBJECTIVES: Women working in the medical field may be at risk for pelvic floor dysfunction due to high physical activity levels leading to increased abdominal pressure; however, the actual situation remains unknown. This study aimed to clarify the prevalence of symptoms of pelvic floor dysfunction and its associated factors among Japanese women working in the medical field. METHODS: A cross-sectional study was conducted among female employees at a public hospital in Japan from July to August 2020. Participants answered a web-based questionnaire. Three types of symptoms related to pelvic floor dysfunction were assessed based on one or more subscale scores in the Pelvic Floor Distress Inventory-Short Form 20 (PFDI-20). RESULTS: Out of 466 female employees in the hospital, 294 responded (response rate 63.1%). The mean age was 42.8 ± 10.3 years old and 221 (73.5%) were nurses. The prevalence of at least one type of symptom was 63.9%. The prevalence of recto-anal symptoms (45.9%) was highest, followed by lower urinary tract (37.1%) and pelvic organ prolapse symptoms (22.8%). The total PFDI-20 score was associated with constipation (ß = .254), body mass index (ß = .136), and part-time work (ß = .167) after adjusting for other variables. CONCLUSION: This study showed a high prevalence of symptoms related to pelvic floor dysfunction among women working in the medical field. Lifestyle management to prevent constipation and obesity is a promising strategy to improve symptoms of pelvic floor dysfunction.

Associations between Coparenting Relationships and Maternal Depressive Symptoms and Negative Bonding to Infant.

Maternal mental illnesses during early postpartum may be caused by lack of the coparenting relationship parents share and cooperate regarding child-rearing. This study clarifies the association of the coparenting relationship and negative mental health of mothers at one and three months after childbirth. This study conducted a secondary analysis of data from an intervention study wherein 24 mothers rearing their first child with a cohabitant (husband/partner) participated. Maternal mental health was evaluated using the Edinburgh Postnatal Depression Scale to determine postpartum depressive symptoms and the Mother-to-Infant Bonding Scale to assess negative bonding. Mothers' average age was 31.5 ± 4.2 years old. All mothers were not working during the research period. The prevalence of postpartum depression and bonding disorder were approximately 13% and 21%, respectively. A better coparenting relationship was associated with lower postpartum depressive symptoms at both one month (ß = -0.617, p = 0.002) and three months (ß = -0.709, p < 0.01) postpartum. In contrast, no association was found between a coparenting relationship and negative bonding. The results indicate that the coparenting relationship may possibly prevent maternal depression during the early postpartum period.

Factors Associated With the Work Productivity of Japanese Working Pregnant Women: A Cross-Sectional Study.

OBJECTIVES: Working pregnant women experience physical and psychosocial changes, which are associated with two aspects of work productivity: presenteeism and absenteeism. We examined the factors that affect these two aspects. METHODS: This cross-sectional study was conducted in April to May 2019 through an online survey. Participants were 450 working women who were pregnant for the first time. RESULTS: Occupational stress (job overload sß: 0.14, suitable jobs sß: 0.16); physical conditions, such as pregnancy complications (sß: 0.32) and gestational period (sß: 0.18); and adjustment status in the workplace due to pregnancy, such as pregnancy disclosure (sß: 0.11) and pregnancy discrimination (sß: 0.18), were related to presenteeism. Meanwhile, pregnancy complications were the only factor associated with absenteeism (sß: 0.32; all P < 0.05). CONCLUSIONS: In addition to physical condition support, support for psychosocial conditions in the workplace is required.

Longitudinal study of physical activity using an accelerometer in Japanese pregnant women.

AIM: To describe the characteristics of objectively measured physical activity (PA) during the 2nd and 3rd trimesters of pregnancy using a accelerometer. METHODS: This was a longitudinal observational study wherein PA in pregnant women in the 2nd and 3rd trimesters was measured for seven consecutive days using a accelerometer (Silmee W10, TDK, Japan). RESULTS: A total of 34 primiparous women were examined. There was no statistically significant difference in the amount of PA during the 2nd and 3rd trimesters of pregnancy. Sub-group analysis demonstrated that PA in the full-time housewife group increased significantly from the 2nd to the 3rd trimester, while total PA and moderate and vigorous PA of the stopped-working group, decreased significantly over that time. There was no difference in the PA of the currently working group between trimesters. In the full-time housewife group, the amount of PA for each hour significantly increased at 12:00, 18:00, and 22:00 hr. In the currently working group, the amount of PA for each hour significantly increased at 9:00, 10:00, and 16:00 hr. In the stopped-working group, the amount of PA for each hour significantly decreased at 7:00, 8:00, and 18:00 hr. CONCLUSION: Objective measurements using an accelerometer did not identify any significant changes in PA during the different trimesters of pregnancy. Sub-group analysis revealed clear patterns in PA change correlating with different lifestyles during pregnancy. Future research may enable the development of personalized health guidance by identifying the relationship between PA and pregnancy outcomes.

Acceptability and Feasibility of a Sedentary Behavior Reduction Program during Pregnancy: A Semi-Experimental Study.

Physical activity (PA) during pregnancy is associated with maternal benefits. Therefore, innovative strategies that promote PA are needed. This study investigated the acceptability and feasibility of a sedentary behavior (SB) reduction program during pregnancy. The study employed a semi-experimental research design using historical control subjects. The intervention group program consisted of individual face-to-face guidance, automatic alerts during SB from wearable devices, and self-monitoring of SB patterns, from 20 gestation weeks to delivery. PA and SB, assessed using a wearable device, were compared with those of the control group at 24-27 (T1) and 32-35 (T2) weeks of gestation. In 56 women, the mean wearing time was 90.2 days in the intervention phase. The response rate to automatic SB alerts was 55.5% at T1 and 63.0% at T2. Self-monitoring more than twice or thrice a week was 77.8% at T1 and 59.3% at T2. There was no significant difference in the cumulative SB time at T2 between the two groups (F = 2.31, p = 0.132). This program appears to be acceptable and feasible for pregnant women; however, SB reduction effect of the intervention remains unclear. Improvements to increase the response rate to automatic SB alerts and the frequency of self-monitoring are needed.

Genome-wide association study of self-reported food reactions in Japanese identifies shrimp and peach specific loci in the HLA-DR/DQ gene region.

Food allergy is an increasingly important health problem in the world. Several genome-wide association studies (GWAS) focused on European ancestry samples have identified food allergy-specific loci in the HLA class II region. We conducted GWAS of self-reported reactivity with common foods using the data from 11011 Japanese women and identified shrimp and peach allergy-specific loci in the HLA-DR/DQ gene region tagged by rs74995702 (P = 6.30 × 10-17, OR = 1.91) and rs28359884 (P = 2.3 × 10-12, OR = 1.80), respectively. After HLA imputation using a Japanese population-specific reference, the most strongly associated haplotype was HLA-DRB1*04:05-HLA-DQB1*04:01 for shrimp allergy (P = 3.92 × 10-19, OR = 1.99) and HLA-DRB1*09:01-HLA-DQB1*03:03 for peach allergy (P = 1.15 × 10-7, OR = 1.68). Additionally, both allergies' associated variants were eQTLs for several HLA genes, with HLA-DQA2 the single eQTL gene shared between the two traits. Our study suggests that allergy to certain foods may be related to genetic differences that tag both HLA alleles having particular epitope binding specificities as well as variants modulating expression of particular HLA genes. Investigating this further could increase our understanding of food allergy aetiology and potentially lead to better therapeutic strategies for allergen immunotherapies.

Genome-wide association study in Japanese females identifies fifteen novel skin-related trait associations.

Skin trait variation impacts quality-of-life, especially for females from the viewpoint of beauty. To investigate genetic variation related to these traits, we conducted a GWAS of various skin phenotypes in 11,311 Japanese women and identified associations for age-spots, freckles, double eyelids, straight/curly hair, eyebrow thickness, hairiness, and sweating. In silico annotation with RoadMap Epigenomics epigenetic state maps and colocalization analysis of GWAS and GTEx Project eQTL signals provided information about tissue specificity, candidate causal variants, and functional target genes. Novel signals for skin-spot traits neighboured AKAP1/MSI2 (rs17833789; P = 2.2 × 10-9), BNC2 (rs10810635; P = 2.1 × 10-22), HSPA12A (rs12259842; P = 7.1 × 10-11), PPARGC1B (rs251468; P = 1.3 × 10-21), and RAB11FIP2 (rs10444039; P = 5.6 × 10-21). HSPA12A SNPs were the only protein-coding gene eQTLs identified across skin-spot loci. Double edged eyelid analysis identified that a signal around EMX2 (rs12570134; P = 8.2 × 10-15) was also associated with expression of EMX2 and the antisense-RNA gene EMX2OS in brain putamen basal ganglia tissue. A known hair morphology signal in EDAR was associated with both eyebrow thickness (rs3827760; P = 1.7 × 10-9) and straight/curly hair (rs260643; P = 1.6 × 10-103). Excessive hairiness signals' top SNPs were also eQTLs for TBX15 (rs984225; P = 1.6 × 10-8), BCL2 (rs7226979; P = 7.3 × 10-11), and GCC2 and LIMS1 (rs6542772; P = 2.2 × 10-9). For excessive sweating, top variants in two signals in chr2:28.82-29.05 Mb (rs56089836; P = 1.7 × 10-11) were eQTLs for either PPP1CB or PLB1, while a top chr16:48.26-48.45 Mb locus SNP was a known ABCC11 missense variant (rs6500380; P = 6.8 × 10-10). In total, we identified twelve loci containing sixteen association signals, of which fifteen were novel. These findings will help dermatologic researchers better understand the genetic underpinnings of skin-related phenotypic variation in human populations.

Japanese GWAS identifies variants for bust-size, dysmenorrhea, and menstrual fever that are eQTLs for relevant protein-coding or long non-coding RNAs.

Traits related to primary and secondary sexual characteristics greatly impact females during puberty and day-to-day adult life. Therefore, we performed a GWAS analysis of 11,348 Japanese female volunteers and 22 gynecology-related phenotypic variables, and identified significant associations for bust-size, menstrual pain (dysmenorrhea) severity, and menstrual fever. Bust-size analysis identified significant association signals in CCDC170-ESR1 (rs6557160; P = 1.7 × 10-16) and KCNU1-ZNF703 (rs146992477; P = 6.2 × 10-9) and found that one-third of known European-ancestry associations were also present in Japanese. eQTL data points to CCDC170 and ZNF703 as those signals' functional targets. For menstrual fever, we identified a novel association in OPRM1 (rs17181171; P = 2.0 × 10-8), for which top variants were eQTLs in multiple tissues. A known dysmenorrhea signal near NGF replicated in our data (rs12030576; P = 1.1 × 10-19) and was associated with RP4-663N10.1 expression, a putative lncRNA enhancer of NGF, while a novel dysmenorrhea signal in the IL1 locus (rs80111889; P = 1.9 × 10-16) contained SNPs previously associated with endometriosis, and GWAS SNPs were most significantly associated with IL1A expression. By combining regional imputation with colocalization analysis of GWAS/eQTL signals along with integrated annotation with epigenomic data, this study further refines the sets of candidate causal variants and target genes for these known and novel gynecology-related trait loci.

Inter- and intrapopulation variation in thermal reaction norms for growth rate: evolution of latitudinal compensation in ectotherms with a genetic constraint.

In ectotherms, lower temperatures in high-latitude environments would theoretically reduce the annual growth rates of individuals. If slower growth and resultant smaller body size reduce fitness, individuals in higher latitudes may evolve compensatory responses. Two alternative models of such latitudinal compensation are possible: Model I: thermal reaction norms for growth rates of high-latitude individuals may be horizontally shifted to a lower range of temperatures, or Model II: reaction norms may be vertically shifted so that high-latitude individuals can grow faster across all temperatures. Model I is expected when annual growth rates in the wild are only a function of environmental temperatures, whereas Model II is expected when individuals in higher latitudes can only grow during a shorter period of a year. A variety of mixed strategies of these two models are also possible, and the magnitude of horizontal versus vertical variation in reaction norms among latitudinal populations will be indicative of the importance of "temperature" versus "seasonality" in the evolution of latitudinal compensation. However, the form of latitudinal compensation may be affected by possible genetic constraints due to the genetic architecture of reaction norms. In this study, we examine the inter- and intrapopulation variations in thermal reaction norms for growth rate of the medaka fish Oryzias latipes. Common-environment experiments revealed that average reaction norms differed primarily in elevation among latitudinal populations in a manner consistent with Model II (adaptation to "seasonality"), suggesting that natural selection in high latitudes prefers individuals that grow faster even within a shorter growing season to individuals that have longer growing seasons by growing at lower temperatures. However, intrapopulation variation in reaction norms was also vertical: some full-sibling families grew faster than others across all temperatures examined. This tendency in intrapopulation genetic variation for thermal reaction norms may have restricted the evolution of latitudinal compensation, irrespective of the underlying selection pressure.

Variation in the ontogeny of sex steroid levels between latitudinal populations of the medaka.

INTRODUCTION: Sex steroids mediate the expression of sexual dimorphism during ontogeny, and populations that differ in the magnitudes of sexual dimorphism may accordingly differ in the ontogenetic patterns of their sex steroid levels. The medaka, Oryzias latipes species complex, shows geographic variation in the magnitude of sexual dimorphism with respect to the lengths of their anal and dorsal fins; dimorphism is greater in low-latitude populations than in high-latitude populations. However, sexual differences in the ontogenetic dynamics of sex steroids, and its interpopulation variation, have not been examined. RESULTS: We measured testosterone (T), estradiol-17ß (E2), and 11-ketotestosterone (11-KT) concentrations throughout ontogeny of laboratory-reared fish from two latitudinal populations: Aomori (northern) and Okinawa (southern). In both populations, the levels of all three steroids were high during early ontogenetic stages and decreased with growth. After reaching about 15 mm in standard length, when sexual dimorphisms in fin lengths became apparent, steroid levels increased and tended to plateau. Sexual differences in the steroid levels were observed only in the later ontogenetic stages; T and 11-KT levels were higher in males, while E2 levels were higher in females. Accordingly, interpopulation differences also became clearer; the southern fish tended to show higher T levels and lower E2 levels than the northern fish. CONCLUSIONS: The ontogenetic patterns of sex steroid levels paralleled the ontogeny of anal and dorsal fins in the two latitudinal populations, suggesting that interpopulation variation in the degree of sexual dimorphisms in fin lengths is mediated by sex steroid-dependent regulation of fin elongation.

Genetic Architecture of the Variation in Male-Specific Ossified Processes on the Anal Fins of Japanese Medaka.

Traits involved in reproduction evolve rapidly and show great diversity among closely related species. However, the genetic mechanisms that underlie the diversification of courtship traits are mostly unknown. Japanese medaka fishes (Oryzias latipes) use anal fins to attract females and to grasp females during courtship; the males have longer anal fins with male-specific ossified papillary processes on the fin rays. However, anal fin morphology varies between populations: the southern populations tend to have longer anal fins and more processes than the northern populations. In the present study, we conducted quantitative trait locus (QTL) mapping to investigate the genetic architecture underlying the variation in the number of papillary processes of Japanese medaka fish and compared the QTL with previously identified QTL controlling anal fin length. First, we found that only a few QTL were shared between anal fin length and papillary process number. Second, we found that the numbers of papillary processes on different fin rays often were controlled by different QTL. Finally, we produced another independent cross and found that some QTL were repeatable between the two crosses, whereas others were specific to only one cross. These results suggest that variation in the number of papillary processes is polygenic and controlled by QTL that are distinct from those controlling anal fin length. Thus, different courtship traits in Japanese medaka share a small number of QTL and have the potential for independent evolution.