Chemical constituents in otoliths have become a valuable tool for fish ecologists seeking to reconstruct migratory patterns and life‐history diversity in a wide range of species worldwide. This ...approach has proved particularly effective with fishes that move across substantial salinity gradients over the course of their life, including many diadromous species. Freshwater endmembers of several elemental and isotope ratios (e.g. Sr:Ca, Ba:Ca and 87Sr:86Sr) are typically identifiably distinct from marine values, and often differ among freshwater tributaries at fine spatial scales. Because these chemical tags are generally incorporated in proportion to their ambient dissolved concentrations, they can be effective proxies for quantifying the presence, duration and frequency of movements between freshwater and marine habitats. The development of high precision probe‐based analytical techniques, such as laser ablation inductively coupled plasma mass spectrometry (ICP‐MS) and microbeam methods, has allowed researchers to glean increasingly detailed life‐history profiles of these proxies across otoliths. Researchers are also combining multiple chemical proxies in an attempt to refine interpretations of habitat residence patterns. A thorough understanding of the spatial and temporal variation in water chemistry as well as environmental and physiological controls on incorporation of specific elements into otoliths is required for confident estimation of lifetime salinity experience. First some assumptions, methodological considerations and data processing options that are particularly relevant to diadromous otolith chemistry studies are discussed. Insights into diadromous migrations obtained from decades of otolith chemistry research, highlighting the increasingly recognized importance of contingent behaviour and partial migration are then discussed. Finally, areas for future research and the need to integrate otolith chemistry studies into comprehensive assessments of the effects of global environmental change are identified.
Otolith chemistry is often useful for tracking provenance of fishes, as well as examining migration histories. Whereas elements such as strontium and barium correlate well with salinity and ...temperature, experiments that examine manganese uptake as a function of these parameters have found no such correlation. Instead, dissolved manganese is available as a redox product, and as such, is indicative of low-oxygen conditions. Here we present evidence for that mechanism in a range of habitats from marine to freshwater, across species, and also present ancillary proxies that support the mechanism as well. For example, iodine is redox-sensitive and varies inversely with Mn; and sulfur stable isotope ratios provide evidence of anoxic sulfate reduction in some circumstances. Further, S may be incorporated trophically whereas other elements appear to be taken up directly from water. This research suggests a potential means to identify individual fish exposure to hypoxia, over entire lifetimes. With further testing and understanding, in the future fish may be able to be used as “mobile monitors” of hypoxic conditions.
•Otolith Mn is more abundant in otoliths from fish living in hypoxia than in normoxia.•This suggests that reduced Mn is the major form taken up.•Other redox-sensitive elements are documented in otoliths and are additional proxies.•δ34S supports Mn as a hypoxia proxy but suggests a dietary pathway for S uptake.•Otoliths may be useful to track fish lifetime exposure to hypoxia.
We present high-resolution images of NGC 2071-IR in the J, H, and K bands and in the emission at 2.12 m of the v = 1-0 S(1) line of molecular hydrogen. We also present moderate-resolution K-band ...spectra of two young stellar objects, IRS 1 and IRS 3, within NGC 2071-IR, that are candidate sources of one or more of the outflows observed in the region. Two of the eight originally identified infrared point sources in NGC 2071-IR are binaries, and we identify two new sources, one coincident with the radio source Very Large Array-1 and highly reddened. The H2 Q(3)/S(1) line intensity ratios at IRS 1 and IRS 3 yield high and very high extinctions, respectively, to them, as is implied by their near-infrared colors and K-band continuum slopes. The spectra also reveal the presence of hot, dense circumstellar molecular gas in each, suggesting that both are strong candidates for having energetic molecular outflows. We agree with a previous suggestion that IRS 1 is the likely source of an east-west-oriented outflow and conclude that this outflow is probably largely out of the plane of the sky. We also conclude that if IRS 3 is the source of the large-scale northeast-southwest outflow, as has been previously suggested, its jet/wind must precess in order to explain the angular width of that outflow. We discuss the nature of the point sources and their possible contributions, if any, to the complex morphology of the H2 line emission.
We quantified the relative contributions of water and food to strontium (Sr) and barium (Ba) deposited in otoliths of juvenile mummichogsFundulus heteroclitus. Fish were reared in seawater spiked ...with86Sr and137Ba significantly beyond natural values to obtain distinct isotopic signatures for water and food. Element abundances (Sr:Ca and Ba:Ca) and isotope ratios (88Sr:86Sr and138Ba:137Ba) were quantified in water samples using solution-based inductively coupled plasma-mass spectrometry (ICP-MS), and88Sr:86Sr and138Ba:137Ba ratios in otoliths were quantified using laser ablation ICP-MS. The relative contributions of water and food sources to otolith aragonite were assessed using a simple linear isotope mixing model. Water sources contributed 83% of Sr and 98% of Ba in otoliths formed in spiked seawater. Our results indicate that water chemistry is the dominant factor controlling the uptake of Sr and Ba in the otoliths of marine fishes. Thus, chemical signatures recorded in the otoliths of marine fishes should reflect the ambient water composition of these elements at the time of deposition.
Within the framework of a German mosquito monitoring programme, the ‘Mueckenatlas’ (mosquito atlas) has been established as an instrument of citizen participation in mosquito mapping. In 2015, a ...strikingly large number of Aedes albopictus, which had not been considered established in Germany, was submitted. Three of six collection sites showed local reproduction, with demonstration of developmental stages over three months at two sites. The third populated site was checked only once in October. Developmental stages of Ae. albopictus were found again at these three sites in spring 2016, including one site in southeastern Germany where reproduction had already been documented in 2014. Although population genetic analyses performed on specimens collected at the latter locality in 2014 and 2015 did not provide proof for hibernation, the finding of developmental stages at this and two other very same sites as in the year before and at very early times in the season strongly suggest accomplished overwintering of Ae. albopictus in Germany.
Obviously, the second extremely mild winter in Germany in a row and ongoing adaptation of Ae. albopictus to the temperate European climate allow the species to push northwards from endemic regions in the south. Due to the vector competence of Ae. albopictus for numerous pathogens, including dengue, chikungunya and Zika viruses, action should be taken immediately after the detection of local reproduction to eliminate the populations.
Understanding spatial and temporal variation in chemical constituents across salinity gradients is essential for using proxies to track riverine inflow, mixing processes, and migration of mobile ...fauna. We analyzed the freshwater endmembers and mixing curves of a suite of trace element concentrations (Mg, Ca, Mn, Sr, and Ba) and stable isotope ratios (δ¹⁸O and⁸⁷Sr/⁸⁶Sr) in tributaries and estuaries of the south Texas coastal bend region. While Sr/Ca and⁸⁷Sr/⁸⁶Sr were consistent across tributaries due to the dominance of carbonate bedrock underlying the region, Ba/Ca showed some river-specific variation perhaps due to upstream urbanization. In contrast, both Mn/Ca and δ¹⁸O showed a high degree of variability between 2 years due to their sensitivity to redox conditions and net evaporation, respectively. Mixing curves for Ca and Sr were moderately curvilinear, suggesting the potential importance of alternative processes altering mixing relationships, such as submarine groundwater discharge (SGD). Mixing of Mg was linear and consistent with conservative behavior, while Ba showed a low salinity peak and there was no apparent mixing relationship for Mn. Mixing of⁸⁷Sr/⁸⁶Sr was curvilinear as expected, although the steepness of the mixing curve was lower than expected under linear mixing assumptions, further indicating the possible influence of SGD. Unexpectedly, δ¹⁸O values were elevated above marine values across the entire salinity gradient, perhaps due to drought conditions during the sampling period. Together, these results point to the individualistic spatiotemporal dynamics of chemical constituents and illustrate the care that must be taken when choosing an appropriate proxy for salinity.
The biogenic structures of stationary organisms can be effective recorders of environmental fluctuations. These proxy records of environmental change are preserved as geochemical signals in the ...carbonate skeletons of scleractinian corals and are useful for reconstructions of temporal and spatial fluctuations in the physical and chemical environments of coral reef ecosystems, including The Great Barrier Reef (GBR). We compared multi-year monitoring of water temperature and dissolved elements with analyses of chemical proxies recorded in Porites coral skeletons to identify the divergent mechanisms driving environmental variation at inshore versus offshore reefs. At inshore reefs, water Ba/Ca increased with the onset of monsoonal rains each year, indicating a dominant control of flooding on inshore ambient chemistry. Inshore multi-decadal records of coral Ba/Ca were also highly periodic in response to flood-driven pulses of terrigenous material. In contrast, an offshore reef at the edge of the continental shelf was subject to annual upwelling of waters that were presumed to be richer in Ba during summer months. Regular pulses of deep cold water were delivered to the reef as indicated by in situ temperature loggers and coral Ba/Ca. Our results indicate that although much of the GBR is subject to periodic environmental fluctuations, the mechanisms driving variation depend on proximity to the coast. Inshore reefs are primarily influenced by variable freshwater delivery and terrigenous erosion of catchments, while offshore reefs are dominated by seasonal and inter-annual variations in oceanographic conditions that influence the propensity for upwelling. The careful choice of sites can help distinguish between the various factors that promote Ba uptake in corals and therefore increase the utility of corals as monitors of spatial and temporal variation in environmental conditions.
Reconstructing fish movements is critical to understand the diversity of habitats required to sustain mobile species. Chemical constituents in otoliths have been invaluable for the field of fish ...migration ecology to track natal origins and reconstruct lifetime movement patterns. However, alternative non-lethal structures, such as scales, are preferred for imperiled species to avoid mortality. We analyzed 29 individual scales from highly migratory and vulnerable Atlantic tarpon Megalops atlanticus (hereafter referred to as tarpon) in the Gulf of Mexico to identify migrations across salinity gradients and associated trophic shifts using paired measurements of elemental (Sr/Ca) and isotopic (δ13C and δ15N) proxies. Although tarpon can inhabit freshwater, the specific patterns of facultative oligohaline habitat use are unknown. Individual scale-based salinity and diet histories were highly variable, with 4 contingents identified depending on the presence and sequence of movements. Scale salinity proxies (Sr/Ca and δ13C) indicated that tarpon spent on average 42 ± 34% of their scale-based life histories within oligohaline habitats. Transhaline movements were accompanied by shifts in δ15N that indicated putative trophic shifts between marine or estuarine and oligohaline food webs. Oligohaline habitat use is common yet individually facultative for tarpon. This information is critical to devise sustainable fisheries management plans that account for the full range of diverse habitats used by this species throughout its life. Chemical analyses of scales have the potential to be broadly informative about migrations and trophic interactions in species where lethal methods must be avoided.
Epigenetic consequences of exposure to psychostimulants are substantial but the relationship of these changes to compulsive drug taking and abstinence is not clear. Here, we used a paradigm that ...helped to segregate rats that reduce or stop their methamphetamine (METH) intake (nonaddicted) from those that continue to take the drug compulsively (addicted) in the presence of footshocks. We used that model to investigate potential alterations in global DNA hydroxymethylation in the nucleus accumbens (NAc) because neuroplastic changes in the NAc may participate in the development and maintenance of drug-taking behaviors. We found that METH-addicted rats did indeed show differential DNA hydroxymethylation in comparison with both control and nonaddicted rats. Nonaddicted rats also showed differences from control rats. Differential DNA hydroxymethylation observed in addicted rats occurred mostly at intergenic sites located on long and short interspersed elements. Interestingly, differentially hydroxymethylated regions in genes encoding voltage (Kv1.1, Kv1.2, Kvb1 and Kv2.2)- and calcium (Kcnma1, Kcnn1 and Kcnn2)-gated potassium channels observed in the NAc of nonaddicted rats were accompanied by increased mRNA levels of these potassium channels when compared with mRNA expression in METH-addicted rats. These observations indicate that changes in differentially hydroxymethylated regions and increased expression of specific potassium channels in the NAc may promote abstinence from drug-taking behaviors. Thus, activation of specific subclasses of voltage- and/or calcium-gated potassium channels may provide an important approach to the beneficial treatment for METH addiction.
Patterns of migration and habitat use in diadromous fishes can be highly variable among individuals. Most investigations into diadromous movement patterns have been restricted to populations in ...regulated rivers, and little information exists for those in unregulated catchments. We quantified movements of migratory barramundi Lates calcarifer (Bloch) in two large unregulated rivers in northern Australia using both elemental (Sr/Ba) and isotope ((87)Sr/(86)Sr) ratios in aragonitic ear stones, or otoliths. Chemical life history profiles indicated significant individual variation in habitat use, particularly among chemically distinct freshwater habitats within a catchment. A global zoning algorithm was used to quantify distinct changes in chemical signatures across profiles. This algorithm identified between 2 and 6 distinct chemical habitats in individual profiles, indicating variable movement among habitats. Profiles of (87)Sr/(86)Sr ratios were notably distinct among individuals, with highly radiogenic values recorded in some otoliths. This variation suggested that fish made full use of habitats across the entire catchment basin. Our results show that unrestricted movement among freshwater habitats is an important component of diadromous life histories for populations in unregulated systems.
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