δ 18 O of Fissurella maxima as a proxy for reconstructing Early Holocene sea surface temperatures in the coastal Atacama desert (25°S)
Flores, C., Gayo, E., Salazar, D., & Broitman, B.
Fissurella maxima is a keyhole limpet that is abundant and well preserved in archaeological shell midden sites along the coast of Chile, making it an appropriate species to use for reconstructions of past sea surface temperature (SST). In the present study we evaluate the potential of F. maxima shells as a proxy of SST by analysing δ18O of modern shells collected alive from the Atacama desert (area of Taltal, 25°S) and archaeological shells from two Early Holocene rockshelter sites: 224A and Paposo Norte 9. Reconstructed SST from modern F. maxima shells were related to SST obtained from in situ thermometers, supporting the use of this mollusc species as a paleotemperature archive. Mean SST reconstructed from Early Holocene archaeological shells (14.13 °C) was 2.86 °C cooler than mean temperature recorded in modern shells (16.99 °C). Mean SST reconstructed from modern shells was ~1.04 °C warmer than the mean temperature of in situ thermometers (15.95°C). Hence the paleo–SST data from archaeological sites 224A and Paposo Norte 9 enrich the Early Holocene nearshore paleoceanographic scenario of the Pacific coast of South America, with mean SST cooler than present-day SST. Our results validate the use of F. maxima shells as a SST proxy and contribute to a better understanding of the latitudinal distribution of the coastal upwelling regime during the Early Holocene, temporal changes in the structure of the Humboldt Current along the Holocene, and its influence on human adaptation through the prehistory of South America.
Palabras claves: Shell carbonate, Fissurella maxima, Oxygen stable isotope, South–east Pacific coast, Temperature reconstruction, Paleotemperature calibration
Respective roles of remote and local wind stress forcings in the development of warm SST errors in the South-Eastern Tropical Atlantic in a coupled high-resolution model
Goubanova, K., Sanchez-Gomez, E., Frauen, C., & Voldoire, A.
Processes involved in the development of the warm sea surface temperature (SST) bias in the Tropical South-Eastern Atlantic (SETA) in a high resolution (HR) version of the CNRM-CM model are evaluated based on full-field initialized seasonal hindcasts starting at 1 February of each year for 2000–2009. Whereas the initial SST growth is likely associated with local atmospheric forcing, its further development is due to remote oceanic processes. A mixed layer heat budget analysis in SETA indicates a spurious warm horizontal advection observed as far as south of 25°S that appears at the beginning of March. It is associated with an erroneous oceanic mean state at the equator resulting from the mean equatorial westerly wind bias. A sensitivity experiment with corrected wind stress over the equatorial region suggests that the remote forcing explains about 57% of the SETA SST bias in March–May. Comparison with a lower resolution (LR) version of the model reveals that in general similar processes are responsible for the SST bias in both models. A strong reduction of the bias in the HR model is observed only over the near-coastal Southern Benguela region due to a better representation of atmospheric and oceanic processes controlling the coastal upwelling. Overall, the results of the inter-comparison of the SETA SST bias evolution in different sensitivity experiments performed in this study can be interpreted in terms of the relative contributions of (erroneous) warm horizontal advection, associated with equatorial forcing, and cold horizontal advection, associated with local offshore Ekman transport.
Palabras claves: General circulation models, Model systematic biases, Atmosphere–Ocean coupling, Tropical Atlantic, Seasonal prediction, Benguela upwelling system
First Deployment and Validation of in Situ Silicate Electrochemical Sensor in Seawater
Barus, C., Chen Legrand, D., Striebig, N., Jugeau, B., David, A., & Valladares, M., Munoz Parra, P., Ramos, M.E., Dewitte, B., & Garçon, V.
An electrochemical sensor is proposed to measure silicate concentration, in situ, in the ocean without any addition of liquid reagent. From the analytical principle to the laboratory prototype toward the first in situ, immersible sensor, the evolution of the mechanical design is presented and discussed. The developed in situ electronics were compared to the commercial potentiostat and gave promising results to detect low silicate signals with a limit of quantification of 1 μmol L−1.The flow rate of the pump appeared to be a crucial parameter in order to transfer the silicomolybdic complex formed from the “complexation cell” to the “detection cell” without dilution as well as to fill and rinse the whole circuit. The study of temperature effect revealed no influence on the electrochemical signal between ~7° and ~21°C. Finally the sensor was successfully deployed for the very first time on a mooring off Coquimbo, Chile and also integrated onto a PROVOR profiling float in the Mediterranean Sea off Villefranche-sur-Mer, France. The data collected and/or sent through satellite were in good agreement with the 2 reference samples and previously published values illustrating the great potential of this electrochemical sensor. A 7 days silicate time series from the mooring deployment off Chile is also presented.
Palabras claves: Autonomous sensor, Reagentless electrochemical detection, Silicate, Seawater, Mooring and float deployments
Rare long-distance dispersal of a marine angiosperm across the Pacific Ocean
Smith, T., York, P., Broitman, B., Thiel, M., Hays, G., van Sebille, E., Putman N.F., Macreadie P.I., & Sherman C.D.H
Long‐distance dispersal (LDD) events occur rarely but play a fundamental role in shaping species biogeography. Lying at the heart of island biogeography theory, LDD relies on unusual events to facilitate colonization of new habitats and range expansion. Despite the importance of LDD, it is inherently difficult to quantify due to the rarity of such events. We estimate the probability of LDD of the seagrass Heterozostera nigricaulis, a common Australian species, across the Pacific Ocean to colonize South America.
Palabras claves: Biogeography, Clonal organisms, Long distance dispersal, Oceanography, Seagrass
Species co-occurrence networks: Can they reveal trophic and non-trophic interactions in ecological communities?
Freilich, M., Wieters, E., Broitman, B., Marquet, P., & Navarrete, S.
Co‐occurrence methods are increasingly utilized in ecology to infer networks of species interactions where detailed knowledge based on empirical studies is difficult to obtain. Their use is particularly common, but not restricted to, microbial networks constructed from metagenomic analyses. In this study, we test the efficacy of this procedure by comparing an inferred network constructed using spatially intensive co‐occurrence data from the rocky intertidal zone in central Chile to a well‐resolved, empirically based, species interaction network from the same region. We evaluated the overlap in the information provided by each network and the extent to which there is a bias for co‐occurrence data to better detect known trophic or non‐trophic, positive or negative interactions. We found a poor correspondence between the co‐occurrence network and the known species interactions with overall sensitivity (probability of true link detection) equal to 0.469, and specificity (true non‐interaction) equal to 0.527. The ability to detect interactions varied with interaction type. Positive non‐trophic interactions such as commensalism and facilitation were detected at the highest rates. These results demonstrate that co‐occurrence networks do not represent classical ecological networks in which interactions are defined by direct observations or experimental manipulations. Co‐occurrence networks provide information about the joint spatial effects of environmental conditions, recruitment, and, to some extent, biotic interactions, and among the latter, they tend to better detect niche‐expanding positive non‐trophic interactions. Detection of links (sensitivity or specificity) was not higher for well‐known intertidal keystone species than for the rest of consumers in the community. Thus, as observed in previous empirical and theoretical studies, patterns of interactions in co‐occurrence networks must be interpreted with caution, especially when extending interaction‐based ecological theory to interpret network variability and stability. Co‐occurrence networks may be particularly valuable for analysis of community dynamics that blends interactions and environment, rather than pairwise interactions alone.
Palabras claves: Anthropogenic impacts, Co‐occurrence, Ecological networks, Food webs, Intertidal, Keystone species, Non‐trophic interactions, Species interactions
A nodule endophytic Bacillus megaterium strain isolated from Medicago polymorpha enhances growth, promotes nodulation by Ensifer medicae and alleviates salt stress in alfalfa plants
Chinnaswamy, A., Coba de la Peña, T., Stoll, A., de la Peña Rojo, D., Bravo, J., Rincón, A., Lucas M.M, & Pueyo J.J.
A Gram‐positive, fast‐growing, endophytic bacterium was isolated from root nodules of Medicago polymorpha and identified as Bacillus megaterium. The isolate, named NMp082, co‐inhabited nodules with the symbiotic rhizobium Ensifer medicae. B. megaterium NMp082 contained nifH and nodD genes that were 100% identical to those of Ensifer meliloti, an unusual event that suggested previous lateral gene transfer from a different rhizobial species. Despite the presence of nodulation and nitrogen fixation genes, the endophyte was not able to form effective nodules; however, it induced nodule‐like unorganised structures in alfalfa roots. Axenic inoculation promoted plant growth in M. polymorpha, Medicago lupulina, Medicago truncatula and Medicago sativa, and co‐inoculation with E. medicae enhanced growth and nodulation of Medicago spp. plants compared with inoculation with either bacterium alone. B. megaterium NMp082 also induced tolerance to salt stress in alfalfa and Arabidopsis plants. The ability to produce indole acetic acid (IAA) and the 1‐aminocyclopropane‐1‐carboxylate (ACC) deaminase activity displayed by the endophyte in vitro might explain the observed plant growth promotion and salt stress alleviation. The isolate was also highly tolerant to salt stress, water deficit and to the presence of different heavy metals. The newly characterised endophytic bacterium possessed specific characteristics that point at potential applications to sustain plant growth and nodulation under abiotic stress.
Palabras claves: Bacillus megaterium, Endophyte, Medicago, Nodule, PGPB, Salt stress
The symbiosome: legume and rhizobia co-evolution towards a nitrogen-fixing organelle?
Coba de la Peña, T., Fedorova, E., Pueyo, J. J., & Lucas, M. M.
In legume nodules, symbiosomes containing endosymbiotic rhizobial bacteria act as temporary plant organelles that are responsible for nitrogen fixation, these bacteria develop mutual metabolic dependence with the host legume. In most legumes, the rhizobia infect post-mitotic cells that have lost their ability to divide, although in some nodules cells do maintain their mitotic capacity after infection. Here, we review what is currently known about legume symbiosomes from an evolutionary and developmental perspective, and in the context of the different interactions between diazotroph bacteria and eukaryotes. As a result, it can be concluded that the symbiosome possesses organelle-like characteristics due to its metabolic behavior, the composite origin and differentiation of its membrane, the retargeting of host cell proteins, the control of microsymbiont proliferation and differentiation by the host legume, and the cytoskeletal dynamics and symbiosome segregation during the division of rhizobia-infected cells. Different degrees of symbiosome evolution can be defined, specifically in relation to rhizobial infection and to the different types of nodule. Thus, our current understanding of the symbiosome suggests that it might be considered a nitrogen-fixing link in organelle evolution and that the distinct types of legume symbiosomes could represent different evolutionary stages toward the generation of a nitrogen-fixing organelle.
Palabras claves: Endosymbiosis, Legumes, Rhizobia, Nodule, Symbiosome, Lupin, Nitrogen fixation, Organelle evolution
Migratory interchange of humpback whales (Megaptera novaeangliae) among breeding grounds of Oceania and connections to Antarctic feeding areas based on genotype matching
Steel, D., Anderson, M., Garrigue, C., Olavarría, C., Caballero, S., Childerhouse, S., Clapham, P., Constantine, R., Dawson, S., Donoghue, M., Florez-González, L., Gibbs N., Hauser, N., Oremus, M., Paton, D., Poole, M.M., Robbins, J., Slooten, L., Thiele, D., Ward, J., & Baker, C.S.
Humpback whales (Megaptera novaeangliae) congregate to breed during the austral winter near tropical islands of the South Pacific (Oceania). It has long been assumed that humpback whales from Oceania migrate primarily to Antarctic feeding grounds directly south (International Whaling Commission Management Areas V and VI); however, there are few records of individual movement connecting these seasonal habitats. Based on genetic samples of living whales collected over nearly two decades, we demonstrate interchange between the breeding grounds of Oceania and Antarctic feeding Areas V, VI, and I (i.e., from 130°E to 60°W), as well as with the eastern Pacific (Colombia), and the migratory corridors of eastern Australia and New Zealand. We first compared genotype profiles (up to 16 microsatellite loci) of samples collected from Oceania breeding grounds to each other and to those from the eastern Pacific. The matching profiles documented 47 individuals that were present on more than one breeding ground, including the first record of movement between Oceania and Colombia. We then compared the 1179 genotypes from the breeding grounds to 777 from the migratory corridors of east Australia and New Zealand, confirming the connection of these corridors with New Caledonia. Finally, we compared genotypes from breeding grounds to 166 individuals from Antarctic feeding Areas I–VI. This comparison of genotypes revealed five matches: one between New Caledonia and Area V, one between Tonga and Area VI, two between Tonga and Area I (western edge), and one between Colombia and Area I (Antarctic Peninsula). Despite the relatively small number of samples from the Antarctic, our comparison has doubled the number of recorded connections with Oceania available from previous studies during the era of commercial whaling.
Palabras claves: Humpback, Megaptera novaeangliae, Migration, Genotyping
Miscanti-1: Human occupation during the arid Mid-Holocene event in the high-altitude lakes of the Atacama Desert, South America
Núñez, L., Loyola, R., Cartajena, I., López, P., Santander, B., Maldonado, A., De Souza, P., & Carrasco, C.
This paper presents an interdisciplinary study of the Miscanti-1 archaeological site, located in the Holocene terrace deposits accumulated on the eastern margin of Miscanti Lake (4120 m.a.s.l.), northern Chile (23.7° S, 67.7° W). The human response to environmental and climatic variability in the Mid-Holocene (9500-4500 cal yr BP) is discussed through the zooarchaeological, lithic and paleoenvironmental records. We propose that, due to the increased aridity of the period, Miscanti Lake became a brackish paleowetland that attracted discrete groups of hunter-gatherers from lower elevation Andean areas. In contrast with the high frequency of human occupations known for the humid Late Pleistocene and Early Holocene (12600-9500 yr cal BP), the Miscanti-1 site is one of the few occupations recorded in the Atacama Highlands during the Mid-Holocene period. Data analysis suggests logistic and short-term campsite use for hunting the wild camelids that were attracted by the wetlands and fresh water (8100–8300 yr cal BP). In contrast to previous proposals for this period, we propose that access to high altitude environments did not cease, but was made possible by a shift to highly scheduled mobility and a specialized bifacial technology. Finally, the temporal and spatial links of Miscanti-1 are discussed in a regional context.
Palabras claves: Atacama Desert, High-altitude environments, Mid-Holocene, South America, Data treatment, Data analysis
The potential beginning of a postwhaling recovery in New Zealand humpback whales (Megaptera novaeangliae)
Gibbs, N. J., Dunlop, R. A., Gibbs, E. J., Heberley, J. A., & Olavarría, C.
Between the 1940s and 1970s Southern Hemisphere populations of humpback whales (including eastern Australia and Oceania populations) were hunted to near extinction by extensive commercial whaling activities in Antarctica, with fewer whales taken in shore whaling operations in New Zealand, Australia (including Norfolk Island) and Tonga. Variable rates of recovery of these populations have been documented, ranging from recovery to prewhaling numbers in eastern Australian humpbacks to very little sign of recovery in many Oceania populations. Here we analyze recent sighting data collected over 12 yr, from annual surveys in Cook Strait, New Zealand. The data show an increase in sightings, at an estimated rate of 13% (95% CI of 4.9% and 21.7%) in 2015, of humpback whales migrating through Cook Strait. The wide confidence intervals preclude substantive conclusions about the rate of increase but suggest humpback whales are returning to this region in increasing numbers, indicating an influx of immigrants from neighboring areas, namely eastern Australia.
Palabras claves: Humpback whales, Trends, Recruitment, Recovery, Migration, New Zealand, Survey, Whaling, Megaptera novaeangliae