ALBERT

Description: Due to the major role played by diatoms in the marine biological pump, opal/biogenic silica (bSi) has a strong potential as a proxy for paleoproduction reconstructions. Here, we present a detailed evaluation of the independent Fourier transform infrared spectroscopy (FTIRS) calibration introduced by Meyer-Jacob et al. (2014 a ), which is based on synthetic sediment mixtures with known concentrations of bSi and the application of partial least squares (PLS) regression, for the determination of bSi in marine sediments. To test the robustness of the FTIRS calibration for marine samples we selected 199 globally distributed samples, with available wet chemically inferred bSi concentrations and compared the results of both methods. We observe that the spectral characteristics in marine samples are comparable to those reported for a synthetic FTIR spectrum composed solely of spectral features in quartz, biogenic silica, and calcite. FTIRS-inferred and wet-chemically measured bSi concentrations for the set of 199 marine sediment samples are strongly correlated ( R 2  = 0.87; RMSE = 5.27%). Together with the high reproducibility of bSi values by the independent calibration our results corroborate the applicability of the independent FTIRS bSi calibration for quantification in marine samples. This together with the succinct sample preparation procedure, rapid analysis, reduced consumable and machine maintenance costs makes FTIRS a powerful and robust alternative for the quantitative analysis of bSi in marine sediments.

Description: Shortwave Infrared (SWIR) imaging spectroscopy enables accurate remote mapping of cloud thermodynamic phase at high spatial resolution. We describe a measurement strategy to exploit signatures of liquid and ice absorption in cloud top apparent reflectance spectra from 1.4-1.8  μ m. This signal is generally insensitive to confounding factors such as solar angles, view angles, and surface albedo. We first evaluate the approach in simulation, and then apply it to airborne data acquired in the Calwater-2 / ACAPEX campaign of Winter 2015. Here, NASA's “Classic” Airborne Visible Infrared Imaging Spectrometer (AVIRIS-C) remotely observed diverse cloud formations while the US Department of Energy ARM Aerial Facility (AAF) G-1 aircraft measured cloud integral and microphysical properties in situ . The coincident measurements demonstrate good separation of the thermodynamic phases for relatively homogeneous clouds.

Description: Lactobacillus plantarum produces a number of antimicrobial peptides (bacteriocins) that mostly target closely related bacteria. Although bacteriocins are important for the ecology of these bacteria, very little is known about how the peptides target sensitive cells. In this work, a putative membrane protein receptor of the two-peptide bacteriocin plantaricin JK was identified by comparing Illumina sequence reads from plantaricin JK-resistant mutants to a crude assembly of the sensitive wild-type Weissella viridescens genome using the polymorphism discovery tool VAAL. Ten resistant mutants harbored altogether seven independent mutations in a gene encoding an APC superfamily protein with 12 transmembrane helices. The APC superfamily transporter thus is likely to serve as a target for plantaricin JK on sensitive cells. Strains of Weissella viridescent with increased resistance to the two-peptide bacteriocin plantaricin JK carry mutations in a gene encoding a APC superfamily protein. The protein is likely to be an amino acid permease. The results indicate that the APC superfamily protein is involved in the action mechanism of plantaricin JK, possibly as a membrane receptor of the bacteriocin.

Description: The bi-spectral method retrieves cloud optical thickness ( τ ) and cloud droplet effective radius ( r e ) simultaneously from a pair of cloud reflectance observations, one in a visible or near infrared (VIS/NIR) band and the other in a shortwave-infrared (SWIR) band. A cloudy pixel is usually assumed to be horizontally homogeneous in the retrieval. Ignoring sub-pixel variations of cloud reflectances can lead to a significant bias in the retrieved τ and r e . In the literature, the retrievals of τ and r e are often assumed to be independent and considered separately when investigating the impact of sub-pixel cloud reflectance variations on the bi-spectral method. As a result, the impact on τ is contributed only by the sub-pixel variation of VIS/NIR band reflectance and the impact on r e only by the sub-pixel variation of SWIR band reflectance. In our new framework, we use the Taylor expansion of a two-variable function to understand and quantify the impacts of sub-pixel variances of VIS/NIR and SWIR cloud reflectances and their covariance on the τ and r e retrievals. This framework takes into account the fact that the retrievals are determined by both VIS/NIR and SWIR band observations in a mutually dependent way. In comparison with previous studies, it provides a more comprehensive understanding of how sub-pixel cloud reflectance variations impact the τ and r e retrievals based on the bi-spectral method. In particular, our framework provides a mathematical explanation of how the sub-pixel variation in VIS/NIR band influences the r e retrieval and why it can sometimes outweigh the influence of variations in the SWIR band and dominate the error in r e retrievals, leading to a potential contribution of positive bias to the r e retrieval. We test our framework using synthetic cloud fields from a large-eddy simulation and real observations from MODIS. The predicted results based on our framework agree very well with the numerical simulations. Our framework can be used to estimate the retrieval uncertainty from sub-pixel reflectance variations in operational satellite cloud products and to help understand the differences in τ and r e retrievals between two instruments.

Description: Granivorous rodent populations in deserts are primarily regulated through precipitation-driven resource pulses rather than pulses associated with mast-seeding, a pattern more common in mesic habitats. We studied heteromyid responses to mast-seeding in the desert shrub blackbrush ( Coleogyne ramosissima ), a regionally dominant species in the Mojave–Great Basin Desert transition zone. In a 5-year study at Arches National Park, Utah, USA, we quantified spatiotemporal variation in seed resources in mast and intermast years in blackbrush-dominated and mixed desert vegetation and measured responses of Dipodomys ordii (Ord's kangaroo rat) and Perognathus flavescens (plains pocket mouse). In blackbrush-dominated vegetation, blackbrush seeds comprised 〉79% of seed production in a mast year, but 0% in the first postmast year. Kangaroo rat abundance in blackbrush-dominated vegetation was highest in the mast year, declined sharply at the end of the first postmast summer, and then remained at low levels for 3 years. Pocket mouse abundance was not as strongly associated with blackbrush seed production. In mixed desert vegetation, kangaroo rat abundance was higher and more uniform through time. Kangaroo rats excluded the smaller pocket mice from resource-rich patches including a pipeline disturbance and also moved their home range centers closer to this disturbance in a year of low blackbrush seed production. Home range size for kangaroo rats was unrelated to seed resource density in the mast year, but resource-poor home ranges were larger ( P  〈   0.001) in the first postmast year, when resources were limiting. Blackbrush seeds are higher in protein and fat but lower in carbohydrates than the more highly preferred seeds of Indian ricegrass ( Achnatherum hymenoides ) and have similar energy value per unit of handling time. Kangaroo rats cached seeds of these two species in similar spatial configurations, implying that they were equally valued as stored food resources. Blackbrush mast is a key resource regulating populations of kangaroo rats in this ecosystem. Blackbrush is a dominant masting desert shrub with seeds that are dispersed by heteromyid seed predators. Ord's kangaroo rat density, spatial distribution, and interactions with the plains pocket mouse were dramatically affected by seed resource availability associated with the occurrence of mast and intermast years. Blackbrush seeds are a key resource regulating heteromyid population dynamics and behavior in this ecosystem.

Description: Alloparental care – care for unrelated young – is rare in animals, and its ecological or evolutionary advantages or, alternative maladaptive nature, remain unclear. We investigate alloparental care in the socially monogamous cichlid fish Perissodus microlepis from Lake Tanganyika that exhibits bi-parental care. In a genetic parentage analysis, we discovered a surprisingly high percentage of alloparental care represented by brood mixing, extra-pair paternity and extra-pair maternity in all broods that we investigated. The percentage of nondescendant juveniles of other parents, i.e., brood mixing, ranged from 5% to 57% (mean = 28%). The distribution of genetic parentage also suggests that this socially monogamous species has, in fact, polygamous mating system. The prevalence of genetically mixed broods can be best explained by two, not mutually exclusive hypotheses on farming-out and fostering behaviors. In the majority of broods, the sizes of the parents’ own (descendant) offspring were significantly larger than those of the adopted (nondescendant) juveniles, supporting the ‘selfish shepherd effect’ hypothesis, i.e., that foster parents preferentially accept unrelated “smaller or not larger” young since this would tend to lower the predation risks for their own larger offspring. There was also a tendency for larger parents particularly mothers, more so than smaller parents, to care predominantly for their own offspring. Larger parents might be better at defending against cuckoldry and having foreign young dumped into their broods through farming-out behavior. This result might argue for maladaptive effects of allopatric care for the foster parents that only larger and possibly more experienced pairs can guard against. It needs to be determined why, apparently, the ability to recognize one's own young has not evolved in this species. We investigate alloparental care in the socially monogamous cichlid fish Perissodus microlepis from Lake Tanganyika that exhibits biparental care. In a genetic parentage analysis, we discovered a surprisingly high percentage of alloparental care represented by brood mixing, extra-pair paternity and extra-pair maternity in all broods that we investigated. The prevalence of genetically mixed broods can be best explained by two, not mutually exclusive hypotheses on farming-out and fostering behaviours. We also find evidence supporting the ‘selfish shepherd effect’ hypothesis that foster parents preferentially accept unrelated “smaller or not larger” young since this would tend to lower the predation risks for their own larger offspring.

Description: Understanding how speciation can occur without geographic isolation remains a central objective in evolutionary biology. Generally, some form of disruptive selection and assortative mating are necessary for sympatric speciation to occur. Disruptive selection can arise from intraspecific competition for resources. If this competition leads to the differential use of habitats and variation in relevant traits is genetically determined, then assortative mating can be an automatic consequence (i.e., habitat isolation). In this study, we caught Midas cichlid fish from the limnetic (middle of the lake) and benthic (shore) habitats of Crater Lake Asososca Managua to test whether some of the necessary conditions for sympatric speciation due to intraspecific competition and habitat isolation are given. Lake As. Managua is very small (〈900 m in diameter), extremely young (maximally 1245 years of age), and completely isolated. It is inhabited by, probably, only a single endemic species of Midas cichlids, Amphilophus tolteca . We found that fish from the limnetic habitat were more elongated than fish collected from the benthic habitat, as would be predicted from ecomorphological considerations. Stable isotope analyses confirmed that the former also exhibit a more limnetic lifestyle than the latter. Furthermore, split-brood design experiments in the laboratory suggest that phenotypic plasticity is unlikely to explain much of the observed differences in body elongation that we observed in the field. Yet, neutral markers (microsatellites) did not reveal any genetic clustering in the population. Interestingly, demographic inferences based on RAD-seq data suggest that the apparent lack of genetic differentiation at neutral markers could simply be due to a lack of time, as intraspecific competition may only have begun a few hundred generations ago. This study shows that Midas cichlid fish in the extremely young and small crater lake Asososca Managua differentially use the limnetic and benthic habitats. Some of the conditions for sympatric speciation are given, and demographic analyses suggest that the young age of the population has precluded the build-up of genetic differentiation at neutral markers yet.