Dentinal Growth Research Articles

Silver diamine fluoride: A stem cell cytotoxicity and dentin growth factor release in-vitro study.

To investigate the effect of 38% SDF and its serial dilutions on the Stem cells from Human Exfoliated Deciduous teeth (SHED) and its ability to release growth factors from deciduous dentine. The viability of SHED post-exposure to 38%, 3.8%, 0.38%, 0.038%, and 0.0038% SDF were assessed at 2, 5, and 7 days using the CyQuant assay, and results were validated using the MTT assay. The osteogenic differentiation of the cells was also investigated post-exposure to 0.0038% SDF. The release of the growth factors; TGF-β1, FGF-b, BMP-2, and VEGF from deciduous dentin discs exposed to 38% SDF, 0.0038% SDF, Ca(OH)2, MTA, and 17% EDTA were examined using ELISA. Statistical analysis was performed using means and standard deviations (p < 0.05). Two-way ANOVA compared the means of more than two groups with Tukey's multiple comparison test. The unpaired t-test was also used to compare the differences between the two data sets. 38% SDF released dentinogenic growth factors from dentin discs, potentially explaining its role in reactionary dentinogenesis. Moreover, 0.0038% SDF resulted in a non-cytotoxic concentration that enhanced cellular proliferation and released bioactive molecules from dentin comparable to the 38% concentration. After further investigations, the 0.0038% dilution of SDF could present itself as a clinical concentration.

New methods for old challenges: A sampling protocol for sequential stable isotope analysis (δ13C and δ15N) of dentine collagen in high-crowned teeth

Intra-tooth or sequential stable isotope analyses are nowadays widely implemented in zooarchaeological research. Sequential isotopic analyses have been mainly restricted to the mineral fraction of the enamel, while a wider implementation in dentine collagen has been generally eluded, despite conforming an essential organic compound for paleodietary studies. In high-crowned teeth, dentine grows oblique to the vertical axis of growth and some challenges arise when trying to isolate dentine increments during a sequential sampling. Previous sampling strategies slice the whole dentine thickness and provide sequences where isotopic variation is largely attenuated. In this study, we show a new proposal for performing carbon and nitrogen isotope analyses of dentine collagen which better fits dentine's growth. We implemented it in mandibular second molars of an experimental modern sheep flock. Our sampling largely reduces the isotopic “damping” of previous approaches and provides short time-span samples. Sequential δ13C values obtained in dentine tissue yielded similar resolution to those obtained in enamel tissue of the same individuals. This proposal, especially suitable for caprine and other bovid species, broadens the implementation of dentine collagen signatures in the field of stable isotope analyses in zooarchaeology.

Patterns of trace element deposition in beluga whale teeth reflect early life history

Determination of trace element concentrations in continuously growing biological structures such as otoliths, whiskers, and teeth can provide important insight into physiological and ontogenetic processes. We examined concentrations of 11 trace elements (Li, Mg, Mn, Cu, Zn, Se, Rb, Sr, Cs, Ba, Pb) in the annual dentine growth layer groups (GLGs) of teeth of 66 Eastern Canadian Arctic belugas (Delphinapterus leucas). Several of these trace elements displayed clear and consistent patterns in early life, though few longer term trends or signals were present in trace element data for either females or males. Large changes in Sr and Ba concentrations in fetal dentine reflected in utero shifts in element deposition in the teeth of developing belugas. Marked changes in these elements during the first years after birth were likely associated with the onset of nursing and subsequent weaning. Mg, Mn, and Zn also displayed clear and consistent patterns in early life that correlated strongly with dentine stable nitrogen isotope (δ15N) data, suggesting these elements merit further study as potential tools for studying nursing and weaning. Depositional patterns of Zn and Pb, which have been linked to sexual maturation in female Pacific walruses (Odobenus rosmarus divergens), were inconsistent in beluga teeth. Some individuals (including males) displayed patterns strongly resembling those observed in female walruses, whereas many animals did not, perhaps because they had not yet reached sexual maturity. The lack of clear patterns in trace element deposition after the first few years of life may have resulted from pooling samples from multiple populations/regions collected across more than two decades, but may also indicate that elemental concentrations are primarily driven by other, extrinsic processes later in life, and might be useful as biomonitors of environmental element concentrations or tools for delineating population structure.

Dentinal growth layer counts of captive, known-age, mother and daughter belugas (Delphinapterus leucas): confirming two growth layer groups (GLG/2) per year; consequences for recovery and management

Captive mother and daughter belugas (Delphinapterus leucas) of Hudson Bay origin died at the Vancouver Aquarium, in November 2016, aged29.25 and 21.25 years. Aurora, captured at age three and captive since 1990, gave birth to Qila in 1995. Age and histories being known, the focusof this study was on total number of tooth growth layer groups (GLGs) present; one (GLG/1) or two (GLG/2) per year. Teeth from Aurora indicatedtwo growth layers per year (GLG/2) during pre-capture and captivity. Qila deposited GLG/2 throughout her captive life. Clearly an assumption ofGLG/1 over GLG/2 doubles the duration of all life stages, including lifespan and age at attainment of sexual maturity. Arguments for GLG/1 havebeen based on inferences (e.g. from fallout of bomb radio carbon) from adults of unknown age and history, while those for GLG/2 are based on theprojection of direct observations from newborn, known-age young to 21 and 29 year-old adults from captivity. Use of radiocarbon is ingenious butsuch analyses have not been rigorously tested on marine mammals and the sensitivity to necessary correction factors not addressed. The newinformation from this study contradicts the GLG/1 hypothesis in that such an assumption would place Aurora’s birth at the 1958 peak fallout ofbomb radiocarbon (14C) yet she was born 29 years later in 1987, while the birth of her daughter Qila would pre-date the birth of her mother by 13years. This paper re-assesses three studies that assigned GLG/1 based ages to older adults using GLG/2 and concludes that their supposed birthswould also pre-date the realistic births of their own mothers plus as many as two previous generations. Proponents of GLG/1 have overestimatedthe ages of previous calves-at-capture by 200–800%. Given the growth pattern in teeth of these 21 year and 29 year old female belugas, withincreasingly finer dentine GLGs deposited as the pulp tissue diminishes, it is difficult to envisage the GLG/1 tooth structures of those assumed tobe 60–80 years; none are as yet available. An holistic analysis using direct observations and cross-referenced parameters does not substantiateGLG/1which implies a 40% reduction of the intrinsic rate of natural increase; as a consequence, overestimating historical population size as wellas recovery target population and the predicted date of recovery in Cumberland Sound.

Intra‐tooth isotopic analysis (δ13C and δ15N) of dentine collagen in high‐crowned teeth: A new experimental study with modern sheep specimens

AbstractHypsodont teeth molars develop in a short lapse of time. Both dentine and enamel dental tissues do not regenerate once formed. This fact allows the reconstruction of isotopic sequences covering short moments of the individual's life span, a useful approach in current zooarchaeological and paleontological studies. Sampling design usually follows a serial or sequential extraction of dental bands perpendicular to the tooth growth axis, from the apex to the root. However, dentine develops following a secretion of layers oblique to the tooth vertical axis, and this pattern makes hard to isolate isotopic signals. A new experimental study with modern sheep breeds was conducted, covering a whole year and where carbon and nitrogen isotopic signatures of consumed plants were known. Three diet periods with different isotopic compositions were alternated during sheep's life. In this contribution, we test the resolution of a dentine sampling procedure to obtain intra‐tooth isotopic variability of δ13Ccollagen and δ15Ncollagen values tied to diet shifts in sheep. Dentine was sequentially sampled in previously demineralized second and third mandibular molars. Samples were treated with standard protocols of collagen purification and then subjected to stable carbon and nitrogen isotope analysis. In M2 and M3 isotopic sequences obtained, diet shifts are recorded along two progressive trends of increasing–decreasing values, but some affections of the sampling procedure are also present. We conclude that the dentine sequential sampling here implemented allows for obtaining reliable intra‐tooth isotopic data tied to dietary conditions in high‐crowned teeth, although dentine growth patterns should be considered in detail in final interpretations. The integration of this high‐resolution analysis in archaeological studies offers a new scope of possibilities for studying dietary patterns, seasonal dietary changes, and animal husbandry practices in past populations.

Synchrotron radiation-based phase-contrast microtomography of human dental calculus allows nondestructive analysis of inclusions: implications for archeological samples.

Purpose: Dental calculus forms on teeth during the life of an individual and its investigation can yield information about diet, health status, and environmental pollution. Currently, the analytical techniques used to visualize the internal structure of human dental calculus and entrapped inclusions are limited and require destructive sampling, which cannot always be justified. Approach: We used propagation phase-contrast synchrotron radiation micro-computed tomography (PPC-SR- ) to non-destructively examine the internal organization of dental calculus, including its microstructure and entrapped inclusions, on both modern and archeological samples. Results: The virtual histological exploration of the samples shows that PPC-SR- is a powerful approach to visualize the internal organization of dental calculus. We identified several important features, including previously undetected negative imprints of enamel and dentine growth markers (perikymata and periradicular bands, respectively), the non-contiguous structure of calculus layers with multiple voids, and entrapped plant remains. Conclusions: PPC-SR- is an effective technique to explore dental calculus structural organization, and is especially powerful for enabling the identification of inclusions. The non-destructive nature of synchrotron tomography helps protect samples for future research. However, the irregular layers and frequent voids reveal a high heterogeneity and variability within calculus, with implications for research focusing on inclusions.

Genome-wide screening for deubiquitinase subfamily identifies ubiquitin-specific protease 49 as a novel regulator of odontogenesis

Proteins expressed by the paired box gene 9 (PAX9) and Msh Homeobox 1 (MSX1) are intimately involved in tooth development (odontogenesis). The regulation of PAX9 and MSX1 protein turnover by deubiquitinating enzymes (DUBs) plausibly maintain the required levels of PAX9 and MSX1 during odontogenesis. Herein, we used a loss-of-function CRISPR-Cas9-mediated DUB KO library kit to screen for DUBs that regulate PAX9 and MSX1 protein levels. We identify and demonstrate that USP49 interacts with and deubiquitinates PAX9 and MSX1, thereby extending their protein half-lives. On the other hand, the loss of USP49 reduces the levels of PAX9 and MSX1 proteins, which causes transient retardation of odontogenic differentiation in human dental pulp stem cells and delays the differentiation of human pluripotent stem cells into the neural crest cell lineage. USP49 depletion produced several morphological defects during tooth development, such as reduced dentin growth with shrunken enamel space, and abnormal enamel formation including irregular mineralization. In sum, our results suggest that deubiquitination of PAX9 and MSX1 by USP49 stabilizes their protein levels to facilitate successful odontogenesis.

Structure and Deformation Behavior of Human Dentin

The relationship between structure and stress accommodation mechanisms (deformation and fracture) of human dentin on macro-, micro- and nano- scales is discussed. Dentin is the hard basis of human teeth with complicated hierarchically organized structure, which is attested as a natural composite consisted of a bioorganic matrix armed by collagen fibers and apatite crystallites. Dentin exhibits the unique strength properties. On the macroscopic level, under tensile load, it behaves like a brittle solid, and like a viscoelastic one in the case of compression. At the same time, on the microscopic scale cracks in dentin grow in a viscoelastic manner under tensile loading. Structure, mechanical properties and crack growth of human dentin on macro-, micro- and nano- scales, including TEM study, are considered in detail. It was shown that a brittle response under tension is the macroscopic feature of dentin caused by dentin channels, while viscoelasticity is its intrinsic property.

Ecosystem shifts inferred from long-term stable isotope analysis of male Antarctic fur seal Arctocephalus gazella teeth

The Atlantic sector of the Southern Ocean has been rapidly changing over the last century. Many of those changes are driven by climate anomalies such as the El Niño-Southern Oscillation and the Southern Annular Mode, which affect biological processes that scale up the food web. We used δ13C and δ15N time series of dentine growth layer groups (as a proxy of individual foraging history from multiple years, n = 41 teeth) to assess temporal shifts in foraging habits of subadult/adult male Antarctic fur seals Arctocephalus gazella (AFSs) in 2 areas of high concentration of Antarctic krill Euphausia superba: the South Shetland Islands and the South Orkney Islands. Our analyses, which represent the first long-term isotopic assessment of male AFS sampled in Antarctic waters, revealed a significant decrease of δ13C (0.04‰ yr-1) from 1974 to 2015 and a decrease of δ15N after the late 1990s. The observed changes are likely driven by shifts in latitudinal and longitudinal distribution of krill and increased incorporation of 15N-enriched sources (higher trophic level prey and/or feeding in different areas) in the most recent period for reasons that are not yet clear. We were able to trace ecosystem changes through isotopic bio-archives of Antarctic fur seals, highlighting the role of this species as an ecosystem indicator of the trophic cascade effects caused by climate change in the Southern Ocean.

Antibiofilm potential over time of a tricalcium silicate material and its association with sodium diclofenac.

The objectives of this study are to investigate, over time, the antimicrobial activity against polymicrobial biofilms and ability to inhibit biofilm formation, of Biodentine (BD) alone and with 5% and 10% sodium diclofenac (DC). The antimicrobial activity of BD alone and modified with 5% and 10% DC against polymicrobial biofilm growth in dentin was determined by a modified direct contact test. The study groups were (1) BD; (2) BD + 5% DC; and (3) BD + 10% DC. The viability of microorganisms after 1 and 4weeks was quantified by means of an ATP assay and flow cytometry. The antibiofilm efficacy of the materials, preventing polymicrobial biofilm formation over time, was assessed by confocal laser scanning microscopy (CLSM). The results obtained with both the ATP test and flow cytometry showed that BD alone and with 5% and 10% DC exerted antibiofilm activity with respect to the control, in the two evaluated times (p < 0.001). Comparison between groups showed a tendency of increased antimicrobial effect, both over time and depending on the DC concentration. These results coincide with those obtained in CLSM analysis, where efficacy increased with time and DC concentration. Biodentine, over time, showed antimicrobial and antibiofilm efficacy on polymicrobial biofilms. The addition of 5% and 10% DC to BD enhanced this effect, in a concentration- and time-dependent manner.

Dentin Growth after Direct Pulp Capping with the Different Fractions of Plasma Rich in Growth Factors (PRGF) vs. MTA: Experimental Study in Animal Model

Background: This study aimed to evaluate the area of dentin growth in rabbit incisors after pulp capping with plasma rich in growth factors (PRGF) compared with mineral trioxide aggregate (MTA) by fluorescence. Methods: twenty-seven upper and lower incisors of rabbits were divided into 4 groups: poor PRGF (F1) (n = 9 teeth), rich PRGF (F2) (n = 8 teeth), ProRoot MTA (positive control, n = 5 teeth), and untreated (NC) (negative control, n = 5). Fluorochrome markers were injected 24 h before surgery and the day before euthanasia, 28 days after the vital pulp therapy (VPT). Two transverse cuts were performed to every tooth: the first cut (A), 1 mm incisal to the gingival margin, and the second cut (B), 5 mm apical to the first cut. The sections were assessed with histomorphometric evaluation by fluorescence microscopy, comparing the dentin area between fluorescence marks and the total mineralized area. Results: The higher percentage of dentin growth was observed in the F2 group (B = 63.25%, A = 36.52%), followed by F1 (B = 57.63%, A = 30,12%) and MTA (B = 38.64%, A = 15.74%). The group with lowest percentage of dentin growth was the NC group (B = 29.22%, A = 7.82%). Significant difference (p < 0.05) was found between F2 group and MTA, also statistically significant difference has been observed comparing dentin growth areas of NC group with F1 and F2 groups. Conclusions: The application of PRGF rich and poor fraction as a pulp capping material stimulated dentin formation more intensively than MTA and NC.

Ontogenetic profiles of dentine isotopes (δ15N and δ13C) reveal variable narwhal Monodon monoceros nursing duration

Stable isotope analysis (SIA) of sequential dentine growth layer groups can be used to estimate the lifetime diet of individuals and infer major ontogenetic shifts such as the completion of nursing. We used SIA of dentine from narwhalMonodon monocerosembedded canine teeth to investigate ontogenetic dietary patterns, with a focus on nursing duration. We also determined whether nursing duration differed between sexes and between 2 periods during which narwhals may have undergone dietary shifts due to warming. Embedded teeth from both sexes were collected near Pond Inlet, Nunavut, Canada, in 1982 and 1983 (n = 17) and 2015 and 2017 (n = 14). Nursing duration ranged from ~2 to ~6 yr, with 60% of narwhals being nursed beyond the previously published estimate of &lt;2 yr. The proportion of individuals nursed &lt;2 yr versus &gt;2 yr did not differ between sexes or periods. This study not only revealed that narwhals vary extensively in their nursing duration, but also indicated that extended nursing (&gt;2 yr) with gradual introduction of solid food over this period was common. These findings provide insights into narwhal life-history strategies, as extended nursing may be another feature of a long-lived, slow-reproducing mammal adapted to unique polar conditions that are threatened by global warming.

Analysis of narwhal tusks reveals lifelong feeding ecology and mercury exposure

The ability of animals to respond to changes in their environment is critical to their persistence. In the Arctic, climate change and mercury exposure are two of the most important environmental threats for top predators.1-3 Rapid warming is causing precipitous sea-ice loss, with consequences on the distribution, composition, and dietary ecology of species4-7 and, thus, exposure to food-borne mercury.8 Current understanding of global change and pollution impacts on Arctic wildlife relies on single-time-point individual data representing a snapshot in time. These data often lack comprehensive temporal resolution and overlook the cumulative lifelong nature of stressors as well as individual variation. To overcome these challenges, we explore the unique capacity of narwhal tusks to characterize chronological lifetime biogeochemical profiles, allowing for investigations of climate-induced dietary changes and contaminant trends. Using temporal patterns of stable isotopes (δ13C and δ15N) and mercury concentrations in annually deposited dentine growth layer groups in 10 tusks from Northwest Greenland (1962-2010), we show surprising plasticity in narwhal feeding ecology likely resulting from climate-induced changes in sea-ice cover, biological communities, and narwhal migration. Dietary changes consequently impacted mercury exposure primarily through trophic magnification effects. Mercury increased log-linearly over the study period, albeit with an unexpected rise in recent years, likely caused by increased emissions and/or greater bioavailability in a warmer, ice-free Arctic. Our findings are consistent with an emerging pattern in the Arctic of reduced sea-ice leading to changes in the migration, habitat use, food web, and contaminant exposure in Arctic top predators.

Antibacterial effect of a brominated self-etch adhesive on carious dentin - An in vivo study

ObjectivesThis in vivo study compared the antibacterial effect of a self-etch adhesive with and without the brominated monomer 12-methacryloyloxydodecyl-pyridinium bromide (MDPB) on carious dentin after selective caries removal. Methods10 patients showing deep primary carious lesions at two posterior teeth without pulpal symptoms were included. At visit I, carious tissue was selectively removed and carious dentin was sampled with a sterile roundbur (Komet No. 18). One cavity was restored with composite (SDR, Ceram X; DENTSPLY DeTrey) using an MDPB-containing self-etch adhesive (Clearfil Protect Bond, Kuraray Noritake; PB). The other restoration served as a control (Clearfil SE Bond II, Kuraray Noritake; SE). At visit II after 8 weeks, carious dentin was sampled again. Bacterial growth in carious dentin was differentiated using microbial cultivation. Bacterial DNA from intact cells and cell-free DNA were quantified using 16S rRNA gene-based real-time PCR and the microbial community composition was analyzed by amplicon deep-sequencing. Wilcoxon test was applied for statistical analysis. ResultsBoth treatments showed a decrease of intact bacterial cells in carious dentin at visit II compared to visit I (PB: visit I: 1.1*106, visit II: 1.7*105 (p = 0.03); SE: visit I: 1.1*107, visit II = 2.4*105 (p = 0.002)). No statistically significant reduction of cell-free bacterial DNA was detected (PB: visit I: 6.1*105, visit II: 1.6*105 (p = 0.08); SE: visit I: 5.3*105, visit II: 2.9*105 (p = 0.10)). The decrease of intact cell-derived (p = 0.371) and cell-free DNA (p = 0.455) did not differ significantly between PB and SE. Lactobacillus was most abundant within the microbial community at both visits. Alpha-diversity was not affected by treatment and samples showed high intra- and interindividual diversity. Conclusion and clinical significanceBoth self-etch adhesives have an antibacterial effect due to a decrease of bacterial DNA after selective caries removal. However, the results do not reveal any additional antibacterial effect by MDPB.The study is registered with the German Clinical Trials Register (DRKS00011532).

The Development of Dentin Microstructure Is Controlled by the Type of Adjacent Epithelium.

ABSTRACTConsiderable amount of research has been focused on dentin mineralization, odontoblast differentiation, and their application in dental tissue engineering. However, very little is known about the differential role of functionally and spatially distinct types of dental epithelium during odontoblast development. Here we show morphological and functional differences in dentin located in the crown and roots of mouse molar and analogous parts of continuously growing incisors. Using a reporter (DSPP‐cerulean/DMP1‐cherry) mouse strain and mice with ectopic enamel (Spry2+/−;Spry4−/−), we show that the different microstructure of dentin is initiated in the very beginning of dentin matrix production and is maintained throughout the whole duration of dentin growth. This phenomenon is regulated by the different inductive role of the adjacent epithelium. Thus, based on the type of interacting epithelium, we introduce more generalized terms for two distinct types of dentins: cementum versus enamel‐facing dentin. In the odontoblasts, which produce enamel‐facing dentin, we identified uniquely expressed genes (Dkk1, Wisp1, and Sall1) that were either absent or downregulated in odontoblasts, which form cementum‐facing dentin. This suggests the potential role of Wnt signalling on the dentin structure patterning. Finally, we show the distribution of calcium and magnesium composition in the two developmentally different types of dentins by utilizing spatial element composition analysis (LIBS). Therefore, variations in dentin inner structure and element composition are the outcome of different developmental history initiated from the very beginning of tooth development. Taken together, our results elucidate the different effects of dental epithelium, during crown and root formation on adjacent odontoblasts and the possible role of Wnt signalling which together results in formation of dentin of different quality. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Age relationships with telomere length, body weight and body length in wild dugong (Dugong dugon).

The ability to estimate age and determine the growth status of free-ranging dugongs (Dugong dugon) is vital to providing insight into the basic biology of this endangered species. Currently, age estimation in dugong carcasses relies on counting dentin growth layer groups (GLGs) in tusks, but a disadvantage is they need to be intact. We explored whether measures of telomere length could be used as an alternative approach to age estimation in dugongs given that in other species, telomere length and age are inversely related. In this study, relative telomere length (rTL) was measured by qPCR in skin samples from 24 dugongs of varying ages determined by counts of GLGs. In addition, relationships between age by GLG counts and body weight and length and were examined. Our findings indicate that age estimated by GLGs was negatively correlated with telomere length using the logistic formula with a rate of telomere attrition of approximately 0.036 rTL/year between the ages of 5–20 years. By comparison, both body weight and length were positively correlated with GLG-based age, with growth rates of ~8.8 kg/year for weight and ~3.58 cm/year for length, respectively. After that, growth rates slowed substantially and then plateaued. The results suggest that physical maturity in dugongs occurs at 20 years of age and that measures of rTL might serve as a tool for age estimation in dugongs, living and deceased.

Blurred time resolution of tooth dentin serial sections.

The growth of tooth dentin is incremental, so its formation represents a dietary record in early life. With archeological skeletons, applying sequential stable isotope analysis to the horizontal sections of tooth dentin has revealed weaning patterns and dietary changes that took place during childhood. However, the assignment of ages to dentin serial sections (DSSs) is problematic due to the changing extension rate and oblique growth layers of dentin, and these effects have not been quantified. This study presents a mathematical model for investigating the corresponding age range of the horizontal DSSs of human permanent incisors, canines, and molars. Parameters describing the tooth dentin microstructure were taken from previous studies, and dentin growth patterns were modeled. The model was implemented as the R package MDSS. The developed model shows that the true corresponding age of the sections differed by a few years on average from the estimated age with equal temporal divisions, that the model gave values extending across a wide range, and that these differences become large for sections formed at older ages. The stable isotope ratio of the sections presented an aggregate representation of possibly complex dietary changes across a few years, and dietary changes over short times, such as several months, could not be accurately reconstructed even when using a finer horizontal sectioning method. These results demonstrate that DSSs correspond to an unexpectedly wider (i.e., three to four times) and different (i.e., -2 to 0.5 years on average) age range than previously assumed and that complicated patterns of dietary change blur in the isotopic trajectory of the sections. Alternative experimental methods, such as imaging-assisted oblique sampling, should be used to retrieve an accurate and precise sequential dietary record from tooth dentin.

Fetal and early postnatal lead exposure measured in teeth associates with infant gut microbiota

BackgroundLead (Pb) is an environmentally ubiquitous heavy metal associated with a wide range of adverse health effects in children. Both lead exposure and the early life microbiome— which plays a critical role in human development—have been linked to similar health outcomes, but it is unclear if the adverse effects of lead are partially driven by early life gut microbiota dysbiosis. The objective of this study was to examine the association between in utero and postnatal lead levels (measured in deciduous baby teeth) and early life bacterial and fungal gut microbiota in the first year of life. MethodsData from the Wayne County Health, Environment, Allergy and Asthma Longitudinal Study (WHEALS) birth cohort were analyzed. Tooth lead levels during the 2nd and 3rd trimesters and postnatally (<1 year of age) were quantified using high-resolution microspatial mapping of dentin growth rings. Early life microbiota were measured in stool samples collected at approximately 1 and 6 months of age, using both 16S rRNA (bacterial) and ITS2 (fungal) sequencing. Of the 1,258 maternal-child pairs in WHEALS, 146 had data on both tooth metals and early life microbiome. ResultsIn utero tooth lead levels were significantly associated with gut fungal community composition at 1-month of age, where higher levels of 2nd trimester tooth lead was associated with lower abundances of Candida and Aspergillus and higher abundances of Malassezia and Saccharomyces; 3rd trimester lead was also associated with lower abundances of Candida. Though lead did not significantly associate with the overall structure of the infant gut bacterial community, it associated with the abundance of some specific bacterial taxa, including the increased abundance of Collinsella and Bilophila and a decreased abundance of Bacteroides taxa. ConclusionsThe observed associations between lead exposure and infant gut microbiota could play a role in the impact of lead on childhood development. Given the paucity of research examining these associations in humans—particularly for fungal microbiota—further investigation is needed.

Feeding ecology of two subspecies of bottlenose dolphin: a tooth tale

Two subspecies of bottlenose dolphins are observed, not simultaneously, in a narrow coastal area of the western South Atlantic Ocean. However, their trophic interaction is unknown. Such information can be explored using stable isotope composition in teeth, warranting time series data. We analyzed carbon and nitrogen isotopic values (δ13C and δ15N) of dentin growth layer groups in teeth of Tursiops truncatus truncatus and Tursiops truncatus gephyreus stranded along this area of potential co-occurrence in order to investigate the trophic, spatial and temporal dimensions of their isotopic niches. For each subspecies, we calculated isotopic niche width and the possible overlap in resource use between them. We modeled δ13C and δ15N according to age to verify ontogenetic variations in resources use. We also measured the ratio of individual variation by that of the population to estimate the degree of individual specialization within each subspecies. Mean isotopic values differed only for carbon values (δ13CTtg = − 12.7‰; δ13CTtt = − 14.3‰), and a small overlap in resource use between subspecies was observed. Individual specialization was evident in both subspecies suggesting temporal consistency in resource use and indicating they forage upon various preys. Although weaning age and feeding habit seem similar, subspecies diverge especially in habitat use, indicating they adapted for feeding in different environments. These results show a clear habitat partitioning between subspecies and only a small overlap on resource use within the area, reinforcing the hypothesis of a parapatric distribution with very occasional contacts in this region of the western South Atlantic Ocean.

Prolonged maternal investment in northern bottlenose whales alters our understanding of beaked whale reproductive life history.

Nursing and weaning periods are poorly understood in cetaceans due to the difficulty of assessing underwater behaviour in the wild. However, the onset and completion of weaning are critical turning points for individual development and survival, with implications for a species' life history including reproductive potential. δ15N and δ13C deposited in odontocete teeth annuli provide a lifetime record of diet, offering an opportunity to investigate variation and trends in fundamental biology. While available reproductive parameters for beaked whales have largely been inferred from single records of stranded or hunted animals and extrapolated across species, here we examine the weaning strategy and nursing duration in northern bottlenose whales (Hyperoodon ampullatus) by measuring stable isotopes deposited in dentine growth layer groups (GLGs). Using a collection of H. ampullatus teeth taken from whales killed during the whaling era (N = 48) and from two stranded specimens, we compared ontogenetic variation of δ15N and δ13C found in annual GLGs across all individuals, by sex and by region. We detected age-based trends in both δ15N and δ13C that are consistent across regions and males and females, and indicate that nursing is prolonged and weaning does not conclude until whales are 3-4 years old, substantially later than previous estimates of 1 year. Incorporating a prolonged period of maternal care into H. ampullatus life history significantly reduces their reproductive potential, with broad implications for models of beaked whale life history, energetics and the species' recovery from whaling.