A Hypothesis-Free Approach to Identifying Potential Effects of Relative Age in School Year: an Instrumental Variable Phenome-Wide Association Study in the UK Biobank.

A child's relative age within their school year ('relative age') is associated with educational attainment and mental health. However, hypothesis driven studies often re-examine the same outcomes and exposure, potentially leading to confirmation and reporting biases, and missing unknown effects. Hypothesis-free outcome-wide analyses can potentially overcome these limitations. We conducted a hypothesis-free investigation of the effects of relative age within school year. We used an instrumental variable (IV)-pheWAS in the UK Biobank (participants aged 40-69 years at baseline), using the PHESANT software package. We created two IVs for relative age: being born in September vs. August (n=64 075) and week of birth (n=383 309). Outcomes passing the Bonferroni-corrected P value threshold for either instrument were plotted to identify a discontinuity at the school year transition. 13 traits associated with at least one of the instruments showed a discontinuity. Previously identified effects included those with a younger relative age being less likely to have educational qualifications and more likely to have started smoking at a younger age. We detected a few associations not explored by previous studies. For example, those with younger relative age had better lung function as adults. Hypothesis-free approaches could help address confirmation and reporting biases in epidemiology.

Squid male alternative reproductive tactics are determined by birth date.

Alternative reproductive tactics (ARTs) are discontinuous phenotypes associated with reproduction, observed in males of many species. Typically, large males adopt a tactic of competing with rivals for mating, while small males adopt a tactic of stealing fertilization opportunities from the large males. The 'birth date hypothesis', proposing that the date of birth influences the determination of each male's reproductive tactic, has been tested only in teleost fish to date. Here, the birth date hypothesis was tested in ARTs of Japanese spear squid Heterololigo bleekeri (consort/sneaker) by analysing statolith growth increments. The birth date significantly differed between consorts (early-hatched) and sneakers (late-hatched). However, no differences were detected in growth history up to 100 days from hatching. Most immature males caught during the reproductive season were larger than sneakers, and their hatch date was similar to that of consorts, suggesting that these immature males had already been following a life-history pathway as a consort. These results indicate that ARTs of H. bleekeri are determined based on their hatch date in early life. This study firstly suggests that the birth date hypothesis applies to aquatic invertebrates, suggesting that the mechanism by which birth date determines the individual phenotype is a phenomenon more common than previously believed.

Temporal origin of mouse claustrum and development of its cortical projections.

The claustrum is known for its extensive connectivity with many other forebrain regions, but its elongated shape and deep location have made further study difficult. We have sought to understand when mouse claustrum neurons are born, where they are located in developing brains, and when they develop their widespread connections to the cortex. We established that a well-characterized parvalbumin plexus, which identifies the claustrum in adults, is only present from postnatal day (P) 21. A myeloarchitectonic outline of the claustrum can be derived from a triangular fiber arrangement from P15. A dense patch of Nurr1+ cells is present at its core and is already evident at birth. Bromodeoxyuridine birth dating of forebrain progenitors reveals that the majority of claustrum neurons are born during a narrow time window centered on embryonic day 12.5, which is later than the adjacent subplate and endopiriform nucleus. Retrograde tracing revealed that claustrum projections to anterior cingulate (ACA) and retrosplenial cortex (RSP) follow distinct developmental trajectories. Claustrum-ACA connectivity matures rapidly and reaches adult-like innervation density by P10, whereas claustrum-RSP innervation emerges later over a protracted time window. This work establishes the timeline of claustrum development and provides a framework for understanding how the claustrum is built and develops its unique connectivity.

An unexpected shift in constant year effects in female elite handball.

One of the most convincing studies about the importance of the cutoff date in relative age effects was when Helsen et al. (2000) showed that a shift in the date directly resulted in a change of birth month distributions in soccer. Over the past four decades, the role of the birth year has also been associated with relative age effects (as reflected in constant year effects). In this investigation, two studies attempted to replicate the shift of birth year distributions caused by a change in birth years in international female handball. In Study 1, the results from the female handball world championship 2017 showed a significant within-year effect overall and a constant year effect for players born 1988 and after. A second study was conducted with female players from world championships in 2009, 2011, 2013, and 2015. Results demonstrated small effect sizes for most tests. However, there was an unexpected trend toward a constant year effect shift at the age of 28 years. Several hypotheses are presented as an explanation for this trend.

Divergence in parturition timing and vegetation onset in a large herbivore-differences along a latitudinal gradient.

In northern environments, the period of access to high-quality forage is limited, exerting strong selective pressure to optimize the timing of parturition. We analysed timing and variation in moose (Alces alces) parturition dates of 555 females at 18 study sites across 12° of latitude (56-68° N, 1350 km) in Sweden. We found evidence for a spatial match of parturition timing to vegetation onset, but no evidence that moose adjust parturition to vegetation onset in a given year. We found a breakpoint at 64° N. Despite adaptation across latitudes, temporal divergences occurred. Females below 64° N calved after vegetation onset and females above 64° N calved before. Here, parturition before vegetation onset might be a strategy to optimize forage utilization time with the very short growing season. Highly seasonal environments such as at higher latitudes may make it advantageous to adapt parturition towards long-term climatic patterns by matching the most favourable period. Given the direction of temporal divergence, our study suggests that climate change may have less of an impact on moose parturition at northern latitudes than southern latitudes.

Birth date promotes a tortoise or hare tactic for body mass development of a long-lived male ungulate.

Maternal and early-life influences may affect life-long individual phenotype, potentially influencing reproductive success. However, some individuals may compensate for a poor start to life, which may improve longevity and reproductive success later in life. We developed four models to assess whether maternal characteristics (age, body mass and previous year cumulative lactation demand) and/or birth date influenced a long-lived mammal's phenotype to maturity. We used a directional separation analysis to assess the relative influence of each maternal characteristic and birth date on captive male white-tailed deer (Odocoileus virginianus) body mass and antler size. We found that birth date was the only characteristic that persistently influenced male body mass. Depending on when offspring were born, they used alternative tactics to increase their body mass. Birth date positively influenced body mass at 1, 2 and 3 years of age-indicating males displayed faster growth and compensated for late birth (hare tactic). However, early-, heavy-born males were heavy juveniles, and juvenile body mass positively influenced mature body mass (slow but steady growth; tortoise tactic). Our findings provide a first evidence that a long-lived ungulate can display alternative tactics to achieve heavy body mass; individuals are either born early and heavy and are heavy throughout life (tortoise), or light, late-born individuals compensate for a poor start in life by growing at a faster rate to equal or surpass the body mass of early-born individuals (hare). Either tactic may be viable if it influences reproductive success as body mass positively influences access to mates in ungulates.

The Relative Age Effect on Anthropometry, Body Composition, Biological Maturation and Motor Performance in Young Brazilian Soccer Players.

The present study aimed to investigate the influence of months of birth on anthropometry, body composition, biological maturation, and motor performance in young Brazilian soccer players. Young Brazilian soccer players from the Under-13 (n = 50; 13.6 ± 0.3 years), Under-15 (n = 50; 15.5 ± 0.4 years), and Under-17 categories (n = 46; 17.7 ± 0.3 years) took part in this study. Athletes were divided according to chronological age, 1st tertile (January to April); 2nd tertile (May to August); and 3rd tertile (September to December). Anthropometry, body composition, biological maturation, and motor performance variables were evaluated for all participants. There were no differences between the U-13, U-15, and U-17 categories regarding birth tertiles (p > 0.05). Differences between the ages and birth tertiles were observed for the stature, body mass, and lean body mass (p < 0.05). Moreover, differences were found in maturational status between the ages and birth tertiles (p < 0.05). In general, U-13 players showed lower values compared to U-15 and U-17 players in tests of motor performance. In addition, there was a difference in motor performance between the birth tertiles only for RSA variables. The months of birth influenced the stature, body mass, lean body mass, and repeated sprint ability in the U-13 and U-15 categories. Thus, care should be taken during the process of talent selection, as many young players could be underestimated due to their date of birth.

Leveling the Playing Field: A New Proposed Method to Address Relative Age- and Maturity-Related Bias in Soccer.

Despite various solutions proposed to solve the relative age effect (RAE), it is still a major problem confounding talent identification and selection processes. In the first phase, we sampled 302 under 7-21 academy soccer players from two Belgian professional soccer clubs to explore the potential of a new approach to solve the inequalities resulting from relative age- and maturity-related bias. This approach allocates players into four discrete quartile groups based on the midway point of their chronological and estimated developmental (ED) birth dates (calculated using the growth curves for stature of Belgian youth). With the use of chi square analyses, a RAE was found (p < 0.01) for the overall sample (Q1 = 41.4% vs. Q4 = 14.9%) that completely disappeared after reallocation (Q1 = 26.5%; Q2 = 21.9%; Q3 = 27.5%; Q4 = 24.2%). According to the new allocation method, the stature difference was reduced, on average, by 11.6 cm (from 24.0 ± 9.9 to 12.4 ± 3.4 cm, d = 1.57). Body mass difference between the two methods was 1.9 kg (20.1 ± 11.3-18.2 ± 13.1 kg, respectively, d = 0.15). The new method created a maximum chronological age difference of 1.9 vs. 0.8 years for the current method. With the use of this method, 47% of the players would be reallocated. Twenty-three percent would be moved up one age category, and 21% would be moved down. In the second phase, we also examined 80 UK academy soccer players to explore if reallocating players reduces the within-playing group variation of somatic and physical fitness characteristics. The percentage coefficient of variation (%CV) was reduced (0.2-10.1%) in 15 out of 20 metrics across U11-U16 age categories, with the U13 age category demonstrating the largest reductions (0.9-10.1%) in CV. The U12 and U13 age categories and associated reallocation groupings showed trivial to small (ES = 0.0-0.5) between-method differences and trivial to moderate (ES = 0.0-1.1) differences within the U14-U16 age categories. A reduction in RAE may lead to fewer dropouts and thus a larger player pool, which benefits, in turn, talent identification, selection, and development.

Research in Another un-Examined (RAE) context. A chronology of 35 years of relative age effect research in soccer: is it time to move on?

It is approximately 35 years since the publication of the first relative age effect paper in sport and despite the volume of empirical studies, book chapters, conference presentations, and column inches dedicated to this topic we appear to be no further on in eliminating or attenuating this discriminatory practice. This commentary argues that the ongoing use of univariate methods, focusing on primary or secondary analyses of birth-date data, unearthed from previously un-examined contexts is not conducive to stimulating discussion or providing empirical solutions to relative age effects. This paper concludes by suggesting a departure from the traditionally narrow view of relative age inquiry and instead consider the role of transdisciplinary research.

Relative Age Effect in 14- to 18-Year-Old Athletes and Their Initial Approach to This Effect-Has Anything Changed Over the Past 10 Years?

One of the environmental variables associated with early talent development and the achievement of a high level of proficiency in sport is the relative age effect (RAE). The purpose of our study was threefold: (a) to calculate the RAE in young Israeli athletes (ages 14-18 years); (b) to examine how the athletes perceived this effect, if the effect indeed exists; and (c) to compare the RAE findings of this study with those of two previous studies on elite male (Lidor et al., 2010) and female (Lidor et al., 2014) Israeli ballplayers. Participants in the current study were 1,397 athletes (390 females and 1,007 males) who competed in five individual (gymnastics, judo, swimming, tennis, and track and field) and five team (basketball, soccer, team handball, volleyball, and water polo) sports. Data on the RAE, as well as on a number of aspects associated with this effect as perceived by the athletes, were collected via two closed questions. Data analyses showed that the RAE was found to be significant among the male athletes in four sports-swimming, basketball, soccer, and team handball; those who were born early in the year had a higher representation in these sport programs. However, this effect was not found to be significant in the female athletes. Most of the female and male athletes did not think that their birth date influenced their athletic success. However, a large portion of those who were born in the first quarter of the year (Q1) and the second quarter of the year (Q2) among the male athletes felt that they exhibited stronger abilities in the sports program compared to their peers who were born in the third and fourth quarters of the year (Q3 and Q4, respectively). The data of the current study provide additional support for the use of an "open door" approach to accepting children to sport programs by policymakers and coaches in Israel.