APOGEE Chemical Abundance Patterns of the Massive Milky Way Satellites

The SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey has obtained high-resolution spectra for thousands of red giant stars distributed among the massive satellite galaxies of the Milky Way (MW): the Large and Small Magellanic Clouds (LMC/SMC), the Sagittarius Dwarf Galaxy (Sgr), Fornax (Fnx), and the now fully disrupted Gaia Sausage/Enceladus (GSE) system. We present and analyze the APOGEE chemical abundance patterns of each galaxy to draw robust conclusions about their star formation histories, by quantifying the relative abundance trends of multiple elements (C, N, O, Mg, Al, Si, Ca, Fe, Ni, and Ce), as well as by fitting chemical evolution models to the [α/Fe]–[Fe/H] abundance plane for each galaxy. Results show that the chemical signatures of the starburst in the Magellanic Clouds (MCs) observed by Nidever et al. in the α-element abundances extend to C+N, Al, and Ni, with the major burst in the SMC occurring some 3–4 Gyr before the burst in the LMC. We find that Sgr and Fnx also exhibit chemical abundance patterns suggestive of secondary star formation epochs, but these events were weaker and earlier (∼5–7 Gyr ago) than those observed in the MCs. There is no chemical evidence of a second starburst in GSE, but this galaxy shows the strongest initial star formation as compared to the other four galaxies. All dwarf galaxies had greater relative contributions of AGB stars to their enrichment than the MW. Comparing and contrasting these chemical patterns highlight the importance of galaxy environment on its chemical evolution.

Impact of the local environmental variability on the patterns of coral recruitment on Indo-Pacific reefs

<p>Coral reefs are threatened by a range of human activities at both local and global scales. The result of these impacts has resulted in a worldwide decline in the coral reef ecosystems. Corals are the principle reef builders and the maintenance of their populations is fundamental for healthy reef ecosystems. Local environmental factors are critically important in shaping coral populations, particularly at the post-settlement phase, when young coral colonies are most vulnerable to disturbances. In this context, understanding the environmental factors that drive coral recruitment and affect coral survivorship in the early life history stages is vital to effectively manage coral reefs. In this thesis I began by investigating the effect of abiotic and biological factors on coral recruitment and juvenile coral life history stages using settlement panels deployed in the Wakatobi Marine National Park (SE Sulawesi, Indonesia). My objectives were to assess the spatio-temporal variability in coral recruitment rates and juvenile abundance. I used a modelling approach to identify the environmental factors that affected the distribution and abundance patterns of corals. Then, I focused on the main environmental factors, identified from previously published research, affecting coral recruitment. I conducted a caging experiment to assess the impact of fish predation on coral juveniles. Finally, I analysed the development of the benthic community and the interactions between corals and benthic organisms in the first two years of colonisation of artificial bare surfaces. I found high spatial and temporal variability in recruitment rates over seven years of data, values were lower than on other Indo-Pacific reefs and ranged from 9.6 (±8.21 SE) to 317.19 (±12.76 SE) rec. m⁻²; while juvenile abundance ranged from 4.2 (±1.49 SE) to 33 (±6.36 SE) juv. m⁻². The local characteristics of the sites, such as coral cover, influenced the distribution of coral colonies in early life history stages; furthermore differences in coral density between the two life history stages (juvenile and recruits) were consistent over time. However, no single or combination of factors adequately explained abundance patterns for either recruits or juveniles. Fish predation did not appear to be the main cause of coral post-settlement mortality in the Wakatobi and it affected only 10.8% of the coral juveniles in the experiment. In contrast, 58.51% of the coral juveniles were found to be overgrown by algae and other invertebrates, however only turf and green encrusting algae affected coral survivorship. Coral colony abundance and the number of interactions with other benthic organisms, especially crustose coralline algae (CCA) and sponges, increased over time on panels and they were different between the front and back side of the panels, which was attributed to differences in light and predation regimes. Coral recruitment was higher on older benthic communities, although none of the known coral recruitment promoters, such as CCA, or competitors, such as turf algae, were correlated with coral abundance. My results show that changes in coral populations between the recruit and juvenile stages are likely driven by small-scale processes. The site characteristics determine the final patterns, which vary over time following temporal fluctuations in environmental factors. The effect of the interactions between algae and sponges with coral recruits and their influence on juvenile survivorship suggests these organisms having a role in coral recruitment success and highlight their importance as a focus for reef management. Furthermore, the use of long term studies allowed a better understanding of the high variability present in coral recruitment and the trends of the recruitment process, which are useful information for conservative purposes.</p>

Impact of the local environmental variability on the patterns of coral recruitment on Indo-Pacific reefs

<p>Coral reefs are threatened by a range of human activities at both local and global scales. The result of these impacts has resulted in a worldwide decline in the coral reef ecosystems. Corals are the principle reef builders and the maintenance of their populations is fundamental for healthy reef ecosystems. Local environmental factors are critically important in shaping coral populations, particularly at the post-settlement phase, when young coral colonies are most vulnerable to disturbances. In this context, understanding the environmental factors that drive coral recruitment and affect coral survivorship in the early life history stages is vital to effectively manage coral reefs. In this thesis I began by investigating the effect of abiotic and biological factors on coral recruitment and juvenile coral life history stages using settlement panels deployed in the Wakatobi Marine National Park (SE Sulawesi, Indonesia). My objectives were to assess the spatio-temporal variability in coral recruitment rates and juvenile abundance. I used a modelling approach to identify the environmental factors that affected the distribution and abundance patterns of corals. Then, I focused on the main environmental factors, identified from previously published research, affecting coral recruitment. I conducted a caging experiment to assess the impact of fish predation on coral juveniles. Finally, I analysed the development of the benthic community and the interactions between corals and benthic organisms in the first two years of colonisation of artificial bare surfaces. I found high spatial and temporal variability in recruitment rates over seven years of data, values were lower than on other Indo-Pacific reefs and ranged from 9.6 (±8.21 SE) to 317.19 (±12.76 SE) rec. m⁻²; while juvenile abundance ranged from 4.2 (±1.49 SE) to 33 (±6.36 SE) juv. m⁻². The local characteristics of the sites, such as coral cover, influenced the distribution of coral colonies in early life history stages; furthermore differences in coral density between the two life history stages (juvenile and recruits) were consistent over time. However, no single or combination of factors adequately explained abundance patterns for either recruits or juveniles. Fish predation did not appear to be the main cause of coral post-settlement mortality in the Wakatobi and it affected only 10.8% of the coral juveniles in the experiment. In contrast, 58.51% of the coral juveniles were found to be overgrown by algae and other invertebrates, however only turf and green encrusting algae affected coral survivorship. Coral colony abundance and the number of interactions with other benthic organisms, especially crustose coralline algae (CCA) and sponges, increased over time on panels and they were different between the front and back side of the panels, which was attributed to differences in light and predation regimes. Coral recruitment was higher on older benthic communities, although none of the known coral recruitment promoters, such as CCA, or competitors, such as turf algae, were correlated with coral abundance. My results show that changes in coral populations between the recruit and juvenile stages are likely driven by small-scale processes. The site characteristics determine the final patterns, which vary over time following temporal fluctuations in environmental factors. The effect of the interactions between algae and sponges with coral recruits and their influence on juvenile survivorship suggests these organisms having a role in coral recruitment success and highlight their importance as a focus for reef management. Furthermore, the use of long term studies allowed a better understanding of the high variability present in coral recruitment and the trends of the recruitment process, which are useful information for conservative purposes.</p>

Evaluation of RNA later as a Field-Compatible Preservation Method for Metaproteomic Analyses of Bacterium-Animal Symbioses

Metaproteomics, the large-scale identification and quantification of proteins from microbial communities, provide direct insights into the phenotypes of microorganisms on the molecular level. To ensure the integrity of the metaproteomic data, samples need to be preserved immediately after sampling to avoid changes in protein abundance patterns.

A novel random forest approach to revealing interactions and controls on chlorophyll concentration and bacterial communities during coastal phytoplankton blooms

Increasing occurrence of harmful algal blooms across the land–water interface poses significant risks to coastal ecosystem structure and human health. Defining significant drivers and their interactive impacts on blooms allows for more effective analysis and identification of specific conditions supporting phytoplankton growth. A novel iterative Random Forests (iRF) machine-learning model was developed and applied to two example cases along the California coast to identify key stable interactions: (1) phytoplankton abundance in response to various drivers due to coastal conditions and land-sea nutrient fluxes, (2) microbial community structure during algal blooms. In Example 1, watershed derived nutrients were identified as the least significant interacting variable associated with Monterey Bay phytoplankton abundance. In Example 2, through iRF analysis of field-based 16S OTU bacterial community and algae datasets, we independently found stable interactions of prokaryote abundance patterns associated with phytoplankton abundance that have been previously identified in laboratory-based studies. Our study represents the first iRF application to marine algal blooms that helps to identify ocean, microbial, and terrestrial conditions that are considered dominant causal factors on bloom dynamics.

Nitrogen evolution in the halo, thick disc, thin disc, and bulge of the Galaxy

ABSTRACT We study the evolution of nitrogen (N) in the Galactic halo, thick disc, thin disc, and bulge by comparing detailed chemical evolution models with recent observations. The models used in this work have already been constrained to explain the abundance patterns of α-elements and the metallicity distribution functions of halo, disc, and bulge stars; here, we adopt them to investigate the origin and evolution of N in the different Galactic components. First, we consider different sets of yields and study the importance of the various channels proposed for N production. Secondly, we apply the reference models to study the evolution of both the Galactic discs and bulge. We conclude that: i) primary N produced by rotating massive stars is required to reproduce the plateau in log(N/O) and [N/Fe] ratios at low metallicity, as well as the secondary and primary production from low- and intermediate-mass stars to reproduce the data of the thin disc; ii) the parallel model can provide a good explanation of the evolution of N abundance in the thick and thin discs, and we confirm that the thick disc has evolved much faster than the thin disc, in agreement with the results from the abundance patterns of other chemical elements; and iii) finally, we present new model predictions for N evolution in the Galactic bulge, and we show that the observations in bulge stars can be explained if massive stars rotate fast during the earliest phases of Galactic evolution, in agreement with findings from the abundance pattern of carbon.

Detailed elemental abundances of binary stars: Searching for signatures of planet formation and atomic diffusion

Binary star systems are assumed to be co-natal and coeval, thus to have identical chemical composition. In this work we aim to test the hypothesis that there is a connection between observed element abundance patterns and the formation of planets using binary stars. Moreover, we also want to test how atomic diffusion might influence the observed abundance patterns. We conduct a strictly line-by-line differential chemical abundance analysis of 7 binary systems. Stellar atmospheric parameters and elemental abundances are obtained with extremely high precision (&lt; 3.5%) using the high quality spectra from VLT/UVES and Keck/HIRES. We find that 4 of 7 binary systems show subtle abundance differences (0.01 - 0.03 dex) without clear correlations with the condensation temperature, including two planet-hosting pairs. The other 3 binary systems exhibit similar degree of abundance differences correlating with the condensation temperature. We do not find any clear relation between the abundance differences and the occurrence of known planets in our systems. Instead, the overall abundance offsets observed in the binary systems (4 of 7) could be due to the effects of atomic diffusion. Although giant planet formation does not necessarily imprint chemical signatures onto the host star, the differences in the observed abundance trends with condensation temperature, on the other hand, are likely associated with diverse histories of planet formation (e.g., formation location). Furthermore, we find a weak correlation between abundance differences and binary separation, which may provide a new constraint on the formation of binary systems.

The effect of microbial selection on the occurrence-abundance patterns of microbiomes

Theoretical models are useful to investigate the drivers of community dynamics. Notable are models that consider the events of death, birth, and immigration of individuals assuming they only depend on their abundance — thus, all types share the same parameters. The community level expectations arising from these simple models and their agreement to empirical data have been discussed extensively, often suggesting that in nature, rates might indeed be neutral or their differences not important. But, how robust are these model predictions to type-specific rates? And, what are the consequences at the level of types? Here, we address these questions moving from simple to diverse communities. For this, we build a model where types are differently adapted to the environment. We adapt a computational method from the literature to compute equilibrium distributions of the abundance. Then, we look into the occurrence-abundance pattern often reported in microbial communities. We observe that large immigration and biodiversity — common in microbial systems — lead to such patterns, regardless of whether the rates are neutral or non-neutral. We conclude by discussing the implications to interpret and test empirical data.

Microhabitats Utilization by Solitary Parasitoids and Predatory Insects as Indicators of Oil Palm Agroecosystem’s Capacity to Support Insect Species Diversity

Microhabitats capacity to support insect species diversity and persistence were evaluated implementing solitary parasitoids and predatory insects according to different phases of herbicide and chemical fertilizer applications. Two species of the genus Xanthopimpla (Ichneumonidae) and one species of the genus Pompilus (Pompilidae) showed relationships on vegetation-type microhabitats, notably natural weeds, leguminous cover crops, and the beneficial plant Turnera subulata, while two species of the genus Evania (Evaniidae) showed relationships with chipped oil palm trunks. One species from the genus Odontomachus (Formicidae) as an exclusive predatory ant was related to both chipped oil palm trunks and the beneficial plant T. subulata. Xanthopimpla parasitoids exhibited abundance fluctuations difference around natural weeds during herbicide application phases between three- and six-years old oil palm stands, with decreased and increased abundance patterns of the former and the latter, respectively. 18 years old oil palm stand showed increased abundance patterns only along with the different phases of chemical fertilizer applications. The importance of natural weeds diversity, restrictions of leguminous cover crops, frequency of herbicide applications, and the arrangements between beneficial plants and wood-based microhabitats that benefited insect parasitoids and predators were discussed.