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Micronutrients are fundamental for healthy brain development and deficiencies during early development can have a severe and lasting impact on cognitive outcomes. Evidence indicates that undernourished lactating individuals may produce breast milk containing lower concentrations of certain vitamins and minerals. Exclusively breastfed infants born to mothers deficient in micronutrients may therefore be at risk of micronutrient deficiencies, with potential implications for neurodevelopment. This systematic review aims to consider current knowledge on the effects of breast milk micronutrients on the developmental outcomes of infants. The databases Medline, Global Health, PsychInfo, Open Grey, and the Web of Science were searched for papers published before February 2021. Studies were included if they measured micronutrients in breast milk and their association with the neurodevelopmental outcomes of exclusively breastfed infants. Also, randomised control trials investigating neurocognitive outcomes following maternal supplementation during lactation were sought. From 5477 initial results, three observational studies were eligible for inclusion. These investigated associations between breast milk levels of vitamin B6, carotenoids, or selenium and infant development. Results presented suggest that pyroxidal, β-carotene, and lycopene are associated with infant neurodevelopmental outcomes. Limited eligible literature and heterogeneity between included papers prevented quantitative synthesis. Insufficient evidence was identified, precluding any conclusions on the relationship between breast milk micronutrients and infant developmental outcomes. Further, the evidence available was limited by a high risk of bias. This highlights the need for further research in this area to understand the long-term influence of micronutrients in breast milk, the role of other breast milk micronutrients in infant neurodevelopmental outcomes, and the impact of possible lactational interventions.

Highlights • First investigation of validity of longitudinal infant channel-space fNIRS analysis. • Novel image reconstruction analysis conducted. • Variability in array position is dominant factor driving different inferences. • Channel-space fNIRS analyses robust to implicit assumptions at group-level. • Hope to encourage more widespread use of image reconstruction in infant analyses., The first 1000 days from conception to two-years of age are a critical period in brain development, and there is an increasing drive for developing technologies to help advance our understanding of neurodevelopmental processes during this time. Functional near-infrared spectroscopy (fNIRS) has enabled longitudinal infant brain function to be studied in a multitude of settings. Conventional fNIRS analyses tend to occur in the channel-space, where data from equivalent channels across individuals are combined, which implicitly assumes that head size and source-detector positions (i.e. array position) on the scalp are constant across individuals. The validity of such assumptions in longitudinal infant fNIRS analyses, where head growth is most rapid, has not previously been investigated. We employed an image reconstruction approach to analyse fNIRS data collected from a longitudinal cohort of infants in The Gambia aged 5- to 12-months. This enabled us to investigate the effect of variability in both head size and array position on the anatomical and statistical inferences drawn from the data at both the group- and the individual-level. We also sought to investigate the impact of group size on inferences drawn from the data. We found that variability in array position was the driving factor between differing inferences drawn from the data at both the individual- and group-level, but its effect was weakened as group size increased towards the full cohort size (N = 53 at 5-months, N = 40 at 8-months and N = 45 at 12-months). We conclude that, at the group sizes in our dataset, group-level channel-space analysis of longitudinal infant fNIRS data is robust to assumptions about head size and array position given the variability in these parameters in our dataset. These findings support a more widespread use of image reconstruction techniques in longitudinal infant fNIRS studies.

As invasive cane toads (Rhinella marina) spread across Australia, we urgently need effective ways to reduce the impact of toads on native fauna. One potential approach is to target the chemical cues (pheromones) used by the pest species for communication. In particular, the ‘attraction cue’ relies on the strong cannibalistic response of toad tadpoles towards conspecific eggs and hatchlings. Chemicals released into the water by developing embryos can be mimicked using exudate from the parotoid (shoulder) glands of adult cane toads, and this toxin can be used to lure cane toad tadpoles into a trap without attracting native aquatic species. This method works well under controlled conditions in the laboratory, but we know very little about factors that influence the success of tadpole trapping in the field. Our extensive trapping trials showed strong responses to the attraction cue under a wide range of conditions, but with reduced trapping rates at low water temperature (particularly in Western Australian populations), for early-stage tadpoles, and if the bait is frozen prior to use. Efforts to control cane toads using toxin-baited traps should consider these factors when applying trapping protocols in the field.

One-third of children falter in cognitive development by pre-school age. Iron plays an important role in many neurodevelopmental processes, and animal studies suggest that iron sufficiency in pregnancy and infancy is particularly important for neurodevelopment. However, it is not clear whether iron deficiency directly impacts developmental outcomes, and, if so, whether impact differs by timing of exposure or developmental domain. We searched four databases for studies on iron deficiency or iron supplementation in pregnancy, or at 0–6 months, 6–24 months, or 2–4 years of age. All studies included neurodevelopmental assessments in infants or children up to 4 years old. We then qualitatively synthesized the literature. There was no clear relationship between iron status and developmental outcomes across any of the time windows or domains included. We identified a large quantity of low-quality studies, significant heterogeneity in study design and a lack of research focused on pregnancy and early infancy. In summary, despite good mechanistic evidence for the role of iron in brain development, evidence for the impact of iron deficiency or iron supplementation on early development is inconsistent. Further high-quality research is needed, particularly within pregnancy and early infancy, which has previously been neglected.

Introduction Infants and children in low- and middle-income countries are frequently exposed to a range of poverty-related risk factors, increasing their likelihood of poor neurodevelopmental outcomes. There is a need for culturally objective markers, which can be used to study infants from birth, thereby enabling early identification and ultimately intervention during a critical time of neurodevelopment. Method In this paper, we investigate developmental changes in auditory event related potentials (ERP) associated with habituation and novelty detection in infants between 1 and 5 months living in the United Kingdom and The Gambia, West Africa. Previous research reports that whereas newborns’ ERP responses are increased when presented with stimuli of higher intensity, this sensory driven response decreases over the first few months of life, giving rise to a cognitively driven, novelty-based response. Anthropometric measures were obtained concurrently with the ERP measures at 1 and 5 months of age. Neurodevelopmental outcome was measured using the Mullen Scales of Early Learning (MSEL) at 5 months of age. Results The described developmental change was observed in the UK cohort, who exhibited an intensity-based response at 1 month and a novelty-based response at 5 months of age. This change was accompanied by greater habituation to stimulus intensity at 5 compared to 1 month. In the Gambian cohort we did not see a change from an intensity-to a novelty-based response, and no change in habituation to stimulus intensity across the two age points. The degree of change from an intensity towards a novelty-based response was further found to be associated with MSEL scores at 5 months of infant age, whereas infants’ growth between 1 and 5 months was not. Discussion Our study highlights the utility of ERP-based markers to study young infants in rural Africa. By implementing a well-established paradigm in a previously understudied population we have demonstrated its use as a culturally objective tool to better understand early learning in diverse settings world-wide. Results offer insight into the neurodevelopmental processes underpinning early neurocognitive development, which may in the future contribute to early identification of infants at heightened risk of adverse neurodevelopmental outcome., Highlights • Infants in low- and middle-income countries are at risk of poor cognitive outcomes. • There is a need for objective markers of infant brain development across settings. • We measured infants' event related potentials at 1–5 month in the UK and The Gambia. • Results show attenuated habituation and novelty responses in the Gambian cohort. • ERP P3, but not growth measures, were associated with neurodevelopment at 5 months.

Attempts to cull an invasive species often create a paradoxical situation, whereby the consequent reduction in invader densities frees the survivors from intraspecific competition—and hence, increases the viability of those survivors. Our laboratory experiments with invasive cane toads (Rhinella marina) show that this backfire effect can occur with pheromone‐baited trapping. Eliminating most of the tadpoles from a tank accelerates metamorphosis of the survivors and increases the size (and thus quality) of those metamorphs. Thus, trapping is likely to reduce recruitment only if the program catches all, or almost all, of the tadpoles in a waterbody. In contrast, toad control using the suppression pheromone, either alone or alongside trapping, causes similar rates of mortality as via trapping alone, but the survivors exhibit smaller mass at metamorphosis and a longer, not shorter, larval period. Thus, the combination of pheromone‐based suppression and trapping can reduce effective recruitment of cane toads more successfully than can either method when used alone.

Understanding how invasive species flourish under climatic conditions outside those found within their native range can inform management. In southeastern Australia, cane toads (Rhinella marina) are spreading into montane areas cooler than have been predicted to be suitable. We monitored the presence of active toads in two high-elevation sites (750–1010 m above sea level [asl]) and two adjacent low-elevation sites (150–210 m asl) in northeastern New South Wales over spring and summer. We radio-tracked 28 field-collected adult toads (n = 5–9 toads per site) and quantified their thermoregulatory opportunities and body temperatures. Toads were active at low-elevation sites in spring, but were not seen in high-elevation sites until late summer. At low elevations, toads had access to a wide range of temperatures and selected cool diurnal refugia. In montane sites, toads had less control over their temperatures, because thermal differentials between exposed and sheltered microhabitats were smaller. Overall though, body temperatures of toads at high-elevation sites in summer were not different to those of conspecifics at lower elevations in spring. As a result, toads at high elevations moved as far (mean daily displacement around 50 m) as did low-elevation conspecifics. Toads in high elevations spent the day in superficial shelter, often partly exposed. Thus, although toads only appear in high-elevation sites seasonally, their behaviour at those sites (spending the day exposed; moving extensively at night) likely exacerbates their ecological impact by bringing them to the attention of vulnerable native predators.

Laboratory experiments have shown that the viability of embryos of the invasive cane toad (Rhinella marina) can be reduced by exposure to chemical cues from older conspecific larvae. These effects (very strong in laboratory trials) may offer an exciting new approach to controlling this problematic invasive species in Australia. However, the degree to which the method works in natural environments has yet to be assessed.Our experiments in the laboratory and in seminatural outdoor waterbodies show that chemical cues from tadpoles do indeed suppress the growth, development, and survival of conspecific larvae that are exposed as embryos and do so in a dose‐dependent manner; higher tadpole densities cause greater suppression of embryos.In seminatural outdoor waterbodies, suppressor‐exposed tadpoles were less than half as likely to survive to metamorphosis as were controls, and were much smaller when they did so and hence, less likely to survive the metamorph stage. Additionally, female cane toads were less likely to oviposit in a waterbody containing free‐ranging (but not cage‐enclosed) tadpoles, suggesting that the presence of tadpoles (rather than the chemical cues they produce) may discourage oviposition.Broadly, our results suggest that the suppression effect documented in laboratory studies does indeed occur in the field also, and hence that we may be able to translate that approach to develop new and more effective ways to reduce rates of recruitment of peri‐urban populations of cane toads in their invasive range., When cane toad eggs are exposed to cane toad tadpoles during development, the eggs often experience stunted development and do not produce viable tadpoles. While adult toads will avoid laying their eggs in ponds containing toad tadpoles, this behavior does not occur if the tadpoles are contained within a small net. This is encouraging for the control of cane toads in Australia as it suggests that adult toads can be manipulated into laying their eggs into ponds where their clutch will not develop into successful tadpoles.

Attempts to control invasive species using species-specific pheromones need to incorporate an understanding of interactive effects among those pathways. The larvae of invasive cane toads (Rhinella marina) utilise chemical cues to repulse, attract or suppress conspecific larvae. We can exploit these effects to reduce toad abundance, but the effects of each cue may not be additive. That is, exposure to one type of cue may lessen the impact of exposure to another cue. To assess this possibility, we exposed toad larvae to combinations of cues. Tadpoles that had been exposed to the suppression cue during larval development exhibited no response to the attraction cue, resulting in lower capture rates in attractant-baited traps. Suppression, however, did not affect a tadpole's response to the alarm cue, and exposure to the alarm cue during tadpole development did not affect response to the attraction cue. Tadpoles exposed to the suppression cue were smaller than control tadpoles at 10 days post-exposure, and consequently were more vulnerable to gape-limited invertebrate predators. Our results demonstrate that the responses by toad tadpoles to chemical cues interact in important ways, and are not simply additive when combined. Control efforts need to incorporate an understanding of such interactions if we are to most effectively use chemical-communication pathways to control invasive amphibians.

Physiological plasticity may facilitate invasion of novel habitats; but is such plasticity present in all populations of the invader or is it elicited only by specific climatic challenges? In cold-climate areas of Australia, invasive cane toads (Rhinella marina) can rapidly acclimate to cool conditions. To investigate whether this physiological plasticity is found in all invasive cane toads or is only seen in cool climates, we measured the acclimation ability of toads from across Australia and the island of Hawai'i. We collected toads from the field and placed them at either 12 or 24°C for 12 h before measuring their righting response as a proxy for critical thermal minimum (CTmin). Toads from the coolest Australian region (New South Wales) demonstrated plasticity (as previously reported), with exposure to 12°C (vs. 24°C) decreasing CTmin by 2°C. In toads from other Australian populations, CTmins were unaffected by our thermal treatments. Hawai'ian toads from a cool, wet site also rapidly acclimated to cool conditions, whereas those from warmer and drier Hawai'ian sites did not. Thermal plasticity has diverged among populations of invasive cane toads, with rapid acclimation manifested only in two cool-climate populations from widely separated sites. Predictions about the potential range of invasive species thus must consider the possibility of geographic (intraspecific) heterogeneity in thermal plasticity; data from other parts of the species' range may fail to predict levels of plasticity elicited by thermal challenges.

Summary The cane toad (Rhinella marina) invasion of Australia has now reached areas much colder than most of its native range in tropical America. Understanding the toad's ability to function in such conditions can clarify its potential for further spread. In northeastern New South Wales (NSW), cane toads have been recorded up to 1100 m above sea level (asl). Our monitoring over summer 2012–2013 confirmed that ground temperatures were lower at three high-elevation (750–1010 m asl) sites than at two nearby lower (100–210 m asl) sites (by day, 18°C vs. 25°C; at night, 17–18°C vs. 20–25°C, respectively). Critical thermal minima (CTmins) of field-collected toads (loss of the righting reflex) were lower for high-elevation than low-elevation toads (5·5°C vs. 7·5°C), but laboratory acclimation abolished this difference. A toad's CTmin was not affected by site of collection, nor by 1 month's exposure to warm (24°C) or cool (12°C) conditions; instead, a toad's CTmin was determined by its thermal exposure over the previous 12 h. Locomotor ability was affected by test temperature, by elevation and by acclimation. Toads from high elevations exhibited equal endurance at cold and warm test temperatures after month-long acclimation to cold conditions, whereas toads from low elevations performed better at high temperatures regardless of previous temperature treatments. Cane toads at the southern edge of their expanding Australian range can function under cool conditions by adjusting their thermal tolerance within a few hours of encountering low temperatures. The toads' ability for rapid thermal acclimation suggests that current models underestimate the potential range of abiotic conditions accessible to this invading species.