This report associates NoV with NEC. NoV appeared to precipitate NEC in predisposed infants. Spatial clustering and epidemiologic links between cases and a health care worker with gastroenteritis suggests that NoV should be investigated among the etiologies of NEC outbreaks and that interventions targeted to interruption of NoV transmission should be considered.

Background Differences in postembryonic developmental trajectories can profoundly alter adult phenotypes and life histories. Thyroid hormone (TH) regulates metamorphosis in many vertebrate taxa with multiphasic ecologies, and alterations to TH metabolism underlie notable cases of paedomorphosis in amphibians. We tested the requirement for TH in multiple postembryonic developmental processes in zebrafish, which has a monophasic ecology, and asked if TH production was compromised in paedomorphic Danionella. Results We showed that TH regulates allometric growth in juvenile zebrafish, and inhibits relative head growth. The lateral line system showed differential requirements for TH: the hormone promotes canal neuromast formation and inhibits neuromast proliferation in the head, but causes expansion of the neuromast population in the trunk. While Danionella morphology resembled that of larval zebrafish, the two Danionella species analyzed were not similar to hypothyroid zebrafish in their shape or neuromast distribution, and both possessed functional thyroid follicles. Conclusions Although zebrafish do not undergo a discrete ecological transformation, we found that multiple tissues undergo transitions in developmental trajectories that are dependent on TH, suggesting the TH axis and its downstream pathways as likely targets for adaptation. Nonetheless, we found no evidence that evolutionary paedomorphosis in Danionella is the result of compromised TH production.

BackgroundChanges in post-embryonic developmental trajectories can profoundly alter adult phenotypes and life history transitions. In vertebrate clades with complex, biphasic life cycles, thyroid hormone (TH) regulates metamorphosis, and alterations to TH metabolism underlie famous cases of paedomorphosis. We tested the requirement for TH in multiple post-embryonic developmental processes in the zebrafish, and asked if TH loss was associated with paedomorphosis in miniaturized Danionellas.ResultsWe found that TH regulates the relative growth of different body parts in zebrafish, inhibiting head growth at juvenile stages. The lateral line also showed sensitivity to the hormone: head neuromasts were inhibited by TH, while trunk neuromasts required TH for their proliferation. While several aspects of Danionella morphology resembled that of larval zebrafish, these species did not resemble hypothyroid zebrafish in their shape or lateral line, and these fish showed functional thyroid follicles.ConclusionsAlthough zebrafish do not undergo a discrete ecological transformation, we found that multiple tissues go through a protracted metamorphosis, and that TH ushers in growth patterns and processes typical of juveniles. We found no evidence that compromised TH metabolism is responsible for paedomorphosis in Danionellas. Nonetheless, modulations to TH-sensitive pathways affect evolutionarily-relevant traits, and are likely important targets for adaptation.Bullet PointsThyroid hormone regulates shifts in relative growth trajectories in different zebrafish tissuesThyroid hormone inhibits head growth in juvenile zebrafish, and regulates juvenile growth patternsThyroid hormone stimulates formation of neuromast canals in the head and ‘stitches’ on the trunk of zebrafishDanionella, the miniaturized sister group to Danio morphologically resemble larval zebrafish and do not form neuromast canalsHypothyroidism is not the cause of paedomorphosis in DanionellaGrant SponsorsNIH R00GM105874NIH R03HD091634Burroughs Wellcome Collaborative Research Travel Grant 1017439

Across the ~30,000 species of ray-finned fish, fins show incredible diversity in overall shape and in the patterning of the supportive bony rays. Fin length mutant zebrafish have provided critical insights into the developmental pathways that regulate relative fin size. However, the processes that govern skeletal patterning along the proximodistal axis of the fin have remained less well understood. Here, we show that thyroid hormone (TH) regulates proximodistal identity of fin rays in terms of pattering, gene expression profiles, and morphogenetic processes during outgrowth. This role for TH in specifying proximodistal identity appears conserved between development and regeneration, in all the fins, and between species. We demonstrate that proximodistal identity is regulated independently from pathways that determine size, and we show that modulating proximodistal patterning relative to growth can recapitulate components of the vast fin ray diversity found in nature.

The static stability of a fish in the water is determined by the relative locations of its center of mass and center of buoyancy. These locations may not be constant, but may depend on the volume of the swim bladder. Changes in swim bladder volume affect both the distribution of mass and the overall volume of the fish, thus affecting the location of the center of mass and center of buoyancy, respectively. To determine the static stability and to examine the influence of the swim bladder on static stability, we used micro-computed tomography to estimate the locations of the center of mass and center of buoyancy in bluegill sunfish (Lepomis macrochrius). In fish oriented head up in the scanner, we found that the center of buoyancy is located 0.441 body lengths from the snout and 0.19 body lengths above the ventral surface of the pelvic girdle, and that the center of mass is 0.0012 BL posterior to and 0.00045 BL ventral to the center of buoyancy. Swim bladders from our specimens ranged in size from 1.9% to 7.6% total body volume, and we found no correlation between swim bladder volume and the distance between the center of mass and center of buoyancy. However, in fish scanned in a head-down orientation, the center of mass is anterior and dorsal to the center of buoyancy—the opposite configuration of that found in fish oriented head up. This change in center of mass and center of buoyancy seems to be caused by changes in the location of the swim bladder in the body: the centroid of the swim bladder is located more posteriorly in fish oriented head-down. The air in the bladder “rises” while heavier tissues “sink,” driving a change in tissue distribution and changing the location of the center of mass relative to the center of buoyancy. We conclude that while static stability does not change with swim bladder volume, pitch angle could have a marked effect on static stability.