Inequalities in children's mental health before and during the COVID-19 pandemic: findings from the UK Household Longitudinal Study.

BACKGROUND: There are concerns that child mental health inequalities may have widened during the COVID-19 pandemic. We investigated whether child mental health inequalities changed in 2020/2021 compared with prepandemic. METHODS: We analysed 16 361 observations from 9272 children in the population representative UK Household Longitudinal Study. Child mental health was measured using the Strengths and Difficulties Questionnaire (SDQ) at ages 5 and 8 years in annual surveys 2011-2019, and at ages 5-11 years in July 2020, September 2020 and March 2021. Inequalities in cross-sectional SDQ scores among 5 and 8 year olds, before and during the pandemic, were modelled using linear regression. Additionally, interactions between time (before/during pandemic) and: sex, ethnicity, family structure, parental education, employment, household income and area deprivation on mental health were explored. RESULTS: A trend towards poorer mental health between 2011 and 2019 continued during the pandemic (b=0.12, 95% CI 0.08 to 0.17). Children with coupled, highly educated, employed parents and higher household income experienced greater mental health declines during the pandemic than less advantaged groups, leading to narrowed inequalities. For example, the mean difference in child SDQ scores for unemployed compared with employed parents was 2.35 prepandemic (1.72 to 2.98) and 0.02 during the pandemic (-1.10 to 1.13). Worse scores related to male sex and area deprivation were maintained. White children experienced worse mental health than other ethnicities, and greater declines during the pandemic. CONCLUSION: Mental health among UK 5 and 8 year olds deteriorated during the pandemic, although several inequalities narrowed. Interventions are needed to improve child mental health while ensuring inequalities do not widen.

The mechanism of sex ratio adjustment in a pollinating fig wasp.

Sex ratio strategies in species subject to local mate competition (LMC), and in particular their fit to quantitative theoretical predictions, provide insight into constraints upon adaptation. Pollinating fig wasps are widely used in such studies because their ecology resembles theory assumptions, but the cues used by foundresses to assess potential LMC have not previously been determined. We show that Liporrhopalum tentacularis females (foundresses) use their clutch size as a cue. First, we make use of species ecology (foundresses lay multiple clutches, with second clutches smaller than first) to show that increases in sex ratio in multi-foundress figs occur only when foundresses are oviposition site limited, i.e. that there is no direct response to foundress density. Second, we introduce a novel technique to quantify foundress oviposition sequences and show, consistent with the theoretical predictions concerning clutch size-only strategies, that they produce mainly male offspring at the start of bouts, followed by mostly females interspersed by a few males. We then discuss the implications of our findings for our understanding of the limits of the ability of natural selection to produce 'perfect' organisms, and for our understanding of when different cue use patterns evolve.

Kin competition promotes dispersal in a male pollinating fig wasp.

Despite theoretical predictions, there is little empirical evidence that kin competition avoidance promotes dispersal. We show that dispersal by male Platyscapa awekei pollinating fig wasps is promoted by both low returns in the natal fig and kin competition avoidance, with strategies depending on the interaction between phenotype (body size) and local conditions. We discuss the paucity of similar work, how males might assess conditions, and then contrast male dispersal and fighting behaviour. This indicates that differences in the scale at which behaviours affect competition can mean that they are the product of dissimilar selective forces even when they have the same recipients. More generally, this could explain why other social interactions are often mixtures of cooperation and conflict.

Sex ratio strategies and the evolution of cue use.

Quantitative tests of sex allocation theory have often indicated that organism strategies deviate from model predictions. In pollinating fig wasps, Lipporrhopalum tentacularis, whole fig (brood) sex ratios are generally more female-biased than predicted by local mate competition (LMC) theory where females (foundresses) use density as a cue to assess potential LMC. We use microsatellite markers to investigate foundress sex ratios in L. tentacularis and show that they actually use their clutch size as a cue, with strategies closely approximating the predictions of a new model we develop of these conditions. We then provide evidence that the use of clutch size as a cue is common among species experiencing LMC, and given the other predictions of our model argue that this is because their ecologies mean it provides sufficiently accurate information about potential LMC that the use of other more costly cues has not evolved. We further argue that the use of these more costly cues by other species is due to the effect that ecological differences have on cue accuracy. This implies that deviations from earlier theoretical predictions often indicate that the cues used to assess environmental conditions differ from those assumed by models, rather than limits on the ability of natural selection to produce "perfect" organisms.

Clutch size: a major sex ratio determinant in fig pollinating wasps?

Under local mate competition, sex ratio theory predicts that increasing numbers of ovipositing females (foundresses) on a site should lead to higher proportions of males in their broods. Fig pollinators have confirmed this prediction. It is also predicted that with decreasing clutch size, solitary foundresses should produce increasing proportions of sons. We show this to be true. Further, when several females compete, brood size decreases. As a result, the proportion of males increases, and this could provide a mechanistic explanation of sex ratio response to numbers of colonizing females. Therefore, sex ratio data on fig wasps need to be reassessed to determine whether females 'count' other foundresses, as is generally accepted, or whether they simply 'count' the number of eggs that they lay.

Oviposition strategies, host coercion and the stable exploitation of figs by wasps.

A classic example of a mutualism is the one between fig plants (Ficus) and their specialized and obligate pollinating wasps. The wasps deposit eggs in fig ovules, which the larvae then consume. Because the wasps derive their fitness only from consumed seeds, this mutualism can persist only if the wasps are prevented from laying eggs in all ovules. The search for mechanisms that can limit oviposition and stabilize the wasp-seed conflict has spanned more than three decades. We use a simple foraging model, parameterized with data from two Ficus species, to show how fig morphology reduces oviposition rates and helps to resolve the wasp-seed conflict. We also propose additional mechanisms, based on known aspects of fig biology, which can prevent even large numbers of wasps from ovipositing in all ovules. It has been suggested that in mutualistic symbioses, the partner that controls the physical resources, in this case Ficus, ultimately controls the rate at which hosts are converted to visitors, regardless of relative evolutionary rates. Our approach provides a mechanistic implementation of this idea, with potential applications to other mutualisms and to theories of virulence.