Foraging-induced craniofacial plasticity is associated with an early, robust and dynamic transcriptional response.

Phenotypic plasticity is the ability of a single genotype to vary its phenotype in response to the environment. Plasticity of the skeletal system in response to mechanical input is widely studied, but the timing of its transcriptional regulation is not well understood. Here, we used the cichlid feeding apparatus to examine the transcriptional dynamics of skeletal plasticity over time. Using three closely related species that vary in their ability to remodel bone and a panel of 11 genes, including well-studied skeletal differentiation markers and newly characterized environmentally sensitive genes, we examined plasticity at one, two, four and eight weeks following the onset of alternate foraging challenges. We found that the plastic species exhibited environment-specific bursts in gene expression beginning at one week, followed by a sharp decline in levels, while the species with more limited plasticity exhibited consistently low levels of gene expression. This trend held across nearly all genes, suggesting that it is a hallmark of the larger plasticity regulatory network. We conclude that plasticity of the cichlid feeding apparatus is not the result of slowly accumulating gene expression difference over time, but rather is stimulated by early bursts of environment-specific gene expression followed by a return to homeostatic levels.

Ontogeny and social context regulate the circadian activity patterns of Lake Malawi cichlids.

Activity patterns tend to be highly stereotyped and critical for executing many different behaviors including foraging, social interactions, and predator avoidance. Differences in the circadian timing of locomotor activity and rest periods can facilitate habitat partitioning and the exploitation of novel niches. As a consequence, closely related species often display highly divergent activity patterns, suggesting that shifts from diurnal to nocturnal behavior, or vice versa, are critical for survival. In Africa's Lake Malawi alone, there are over 500 species of cichlids, which inhabit diverse environments and exhibit extensive phenotypic variation. We have previously identified a substantial range in activity patterns across adult Lake Malawi cichlid species, from strongly diurnal to strongly nocturnal. In many species, including fishes, ecological pressures differ dramatically across life-history stages, raising the possibility that activity patterns may change over ontogeny. To determine if rest-activity patterns change across life stages, we compared the locomotor patterns of six Lake Malawi cichlid species. While total rest and activity did not change between early juvenile and adult stages, rest-activity patterns did, with juveniles displaying distinct activity rhythms that are more robust than adults. One distinct difference between juveniles and adults is the emergence of complex social behavior. To determine whether social context is required for activity rhythms, we next measured locomotor behavior in group-housed adult fish. We found that when normal social interactions were allowed, locomotor activity patterns were restored, supporting the notion that social interactions promote circadian regulation of activity in adult fish. These findings reveal a previously unidentified link between developmental stage and social interactions in the circadian timing of cichlid activity.

The transcriptional state and chromatin landscape of cichlid jaw shape variation across species and environments.

Adaptive phenotypes are shaped by a combination of genetic and environmental forces, but how they interact remains poorly understood. Here, we utilize the cichlid oral jaw apparatus to better understand these gene-by-environment effects. First, we employed RNA-seq in bony and ligamentous tissues important for jaw opening to identify differentially expressed genes between species and across foraging environments. We used two Lake Malawi species adapted to different foraging habitats along the pelagic-benthic ecomorphological axis. Our foraging treatments were designed to force animals to employ either suction or biting/scraping, which broadly mimic pelagic or benthic modes of feeding. We found a large number of differentially expressed genes between species, and while we identified relatively few differences between environments, species differences were far more pronounced when they were challenged with a pelagic versus benthic foraging mode. Expression data carried the signature of genetic assimilation, and implicated cell cycle regulation in shaping the jaw across species and environments. Next, we repeated the foraging experiment and performed ATAC-seq procedures on nuclei harvested from the same tissues. Cross-referencing results from both analyses revealed subsets of genes that were both differentially expressed and differentially accessible. This reduced dataset implicated notable candidate genes including the Hedgehog effector, KIAA0586 and the ETS transcription factor, etv4, which connects environmental stress and craniofacial morphogenesis. Taken together, these data provide novel insights into the epigenetic, genetic and cellular bases of species- and environment-specific bone shapes.

Study protocol of a randomised trial of Summer STRIPES: a peer-delivered high school preparatory intervention for students with ADHD.

INTRODUCTION: High schoolers with attention-deficit/hyperactivity disorder (ADHD) experience substantial impairments, particularly in the school setting. However, very few high school students with ADHD receive evidence-based interventions for their difficulties. We aim to improve access to care by adapting evidence-based psychosocial intervention components to a low-resource and novel school-based intervention model, Summer STRIPES (Students Taking Responsibility and Initiative through Peer Enhanced Support). Summer STRIPES is a brief peer-delivered summer orientation to high school with continued peer-delivered sessions during ninth grade. METHODS AND ANALYSIS: Participants will be 72 rising ninth grade students with ADHD who are randomised to receive either Summer STRIPES or school services as usual. Summer STRIPES will be delivered by 12 peer interventionists in a school setting. Outcomes will be measured at baseline, start of ninth grade, mid-ninth grade and end-of-ninth grade. At each assessment, self, parent and teacher measures will be obtained. We will test the effect of Summer STRIPES (compared with school services as usual) on ADHD symptoms and key mechanisms (intrinsic motivation, extrinsic motivation, executive functions) as well as key academic outcomes during the ninth-grade year (Grade Point Average (GPA), class attendance). ETHICS AND DISSEMINATION: Findings will contribute to our understanding of how to improve access and utilisation of care for adolescents with ADHD. The protocol is approved by the institutional review board at Seattle Children's Research Institute. The study results will be disseminated through publications in peer-reviewed journals and presentations at scientific conferences. TRIALS REGISTRATION NUMBER: NCT04571320; pre-results.