Lack of Equivalence in the Elemental and Stable Isotope Chemistry Within the Sagittal Otolith Pair of the Summer Flounder, Paralichthys dentatus

In fish that are not bilaterally symmetrical, the left and right sagittae are often not symmetrical, exhibiting divergent growth patterns and mass, and may have differences in chemical composition. We investigated this in the asymmetrical summer flounder Paralichthys dentatus, collected from different nursery habitats along the US east coast. Significant differences were detected in otolith mass, δ13C, δ18O, Li:Ca, Mg:Ca, and Sr:Ca, and overall chemical signatures. These results refute the hypothesis of left-right equivalence that is prevalent for bilaterally symmetrical fishes. We tested whether a specific side was better suited for classification. The best models differed between sagittae and resulted in different classification accuracies. The left otolith produced better classification accuracies. Simulated samples of randomized sets of left or right otoliths produced mean accuracies intermediate to classification and were often highly variable. We recommend that future otolith chemistry studies involving bilaterally asymmetrical species test the hypothesis of equivalence within the sagittae before randomly choosing an otolith for chemical analyses

Spatial Variation in Otolith Chemistry of Atlantic Croaker Larvae in the Mid-Atlantic Bight

Larval Atlantic croaker Micropogonias undulatus (1 to 7 mm in standard length) were collected on the east coast of the United States from North Carolina to Delaware during 2000. We defined 3 water-mass boundaries for potential groups of spawning Atlantic croaker using temperature and salinity measured at each sampling station. We tested the hypothesis that distinct otolith chemistries existed among 3 groups of larval Atlantic croaker collected from these water masses using solution-based inductively coupled plasma-mass spectrometry. Multivariate analysis of variance indicated that otolith chemistry differed significantly among water masses. Using a quadratic discriminant function, we were able to correctly classify fish from the Mid-Atlantic Bight (MAB) 73 % of the time, South Atlantic Bight (SAB) 53 % of the time, and Chesapeake Bay plume 36 % of the time. The correct reclassification rates observed were significantly better than random. Results from this study indicate that it is possible to obtain measurable elemental concentrations from otoliths much smaller than previously analyzed (weight 0.015 to 1.976 μg). Moreover, contrary to previous studies, our results indicate that it is possible to distinguish natal signatures among larvae on different spawning grounds in the MAB and SAB. Further, this new information could benefit investigations of dispersal from offshore spawning grounds to estuaries or other nursery habitats

Patterns of Larval Atlantic Croaker Ingress into Chesapeake Bay, USA

We compared ingress patterns of Atlantic croaker Micropogonias undulatus larvae into Chesapeake Bay, USA, with published ingress patterns through barrier island inlets, the accepted model for larval fish ingress. This model asserts that larvae ingress on night flood tides at the flooddominated side of the inlet and at all depths. At the Chesapeake Bay mouth and in the adjacent coastal waters, we compared the distribution of abundance, size, age, and growth rates of croaker prior to ingress, In contrast to the barrier island inlet model, croaker larvae were more abundant at depth than closer to the surface regardless of location. However, the response to light was variable, where croaker larvae farther offshore showed no response to light, but croaker larvae in the bay mouth were more abundant at night. Croaker larvae followed an expected pattern of increasing age and length from offshore stations to the bay mouth station. Further, among nearshore coastal stations there was evidence of larger and older croaker larvae at the northern portion of the bay mouth than at middle or southern stations. Patterns in growth were similar at all locations, indicating the likelihood of a single source location or similar environments among transport pathways for croaker larvae. Ingress can occur across the entire mouth of Chesapeake Bay; however, net tidal inflow may result in age and size structuring, which allows more rapid movement into the northern flood-dominated portions of the bay mouth

Germline Chd8 haploinsufficiency alters brain development in mouse.

The chromatin remodeling gene CHD8 represents a central node in neurodevelopmental gene networks implicated in autism. We examined the impact of germline heterozygous frameshift Chd8 mutation on neurodevelopment in mice. Chd8+/del5 mice displayed normal social interactions with no repetitive behaviors but exhibited cognitive impairment correlated with increased regional brain volume, validating that phenotypes of Chd8+/del5 mice overlap pathology reported in humans with CHD8 mutations. We applied network analysis to characterize neurodevelopmental gene expression, revealing widespread transcriptional changes in Chd8+/del5 mice across pathways disrupted in neurodevelopmental disorders, including neurogenesis, synaptic processes and neuroimmune signaling. We identified a co-expression module with peak expression in early brain development featuring dysregulation of RNA processing, chromatin remodeling and cell-cycle genes enriched for promoter binding by Chd8, and we validated increased neuronal proliferation and developmental splicing perturbation in Chd8+/del5 mice. This integrative analysis offers an initial picture of the consequences of Chd8 haploinsufficiency for brain development

Germline Chd8 haploinsufficiency alters brain development in mouse

The chromatin remodeling gene CHD8 represents a central node in neurodevelopmental gene networks implicated in autism. We examined the impact of germline heterozygous frameshift Chd8 mutation on neurodevelopment in mice. Chd8+/del5 mice displayed normal social interactions with no repetitive behaviors but exhibited cognitive impairment correlated with increased regional brain volume, validating that phenotypes of Chd8+/del5 mice overlap pathology reported in humans with CHD8 mutations. We applied network analysis to characterize neurodevelopmental gene expression, revealing widespread transcriptional changes in Chd8+/del5 mice across pathways disrupted in neurodevelopmental disorders, including neurogenesis, synaptic processes and neuroimmune signaling. We identified a co-expression module with peak expression in early brain development featuring dysregulation of RNA processing, chromatin remodeling and cell-cycle genes enriched for promoter binding by Chd8, and we validated increased neuronal proliferation and developmental splicing perturbation in Chd8+/del5 mice. This integrative analysis offers an initial picture of the consequences of Chd8 haploinsufficiency for brain development