Sex differences in residency patterns of Risso's dolphins (Grampus griseus) in the Azores: Causes and management implications

Knowledge of the residency patterns of marine mammals is an important element for management and conservation strategies. Here we investigate a population of Grampus griseus off Pico Island, Azores. Our data set covers the period 2004–2007, based on at‐sea observations of 1,250 individually identified animals, 303 of known or assumed sex. Using photo identification and GPS locations we calculated mean monthly sighting rates and lagged identification rates to analyze temporal patterns, and estimated kernel density to study the home range. Our results show site fidelity and relatively restricted home ranges, which corroborate the existence of a resident population on the study site. We further document sex differences, including a higher number of males present in the area at any given time but females staying for longer consecutive periods, and male home ranges with significantly less overlap than those of females. These observations are consistent with a mating system based on multimale pods defending areas where females periodically return. We hypothesize that squid distribution is a major factor in structuring these patterns. These findings reinforce the need for a precautionary management approach that would include limiting pressure from commercial activities.     

Carbon (δ13C) and nitrogen (δ15N) stable isotope composition in plant and soil in Southern Patagonia's native forests

Stable isotope natural abundance measurements integrate across several biogeochemical processes in ecosystem N and C dynamics. Here, we report trends in natural isotope abundance (δ¹³C and δ¹⁵N in plant and soil) along a climosequence of 33 Nothofagus forest stands located within Patagonia, Southern Argentina. We measured 28 different abiotic variables (both climatic variables and soil properties) to characterize environmental conditions at each of the 33 sites. Foliar δ¹³C values ranged from ?35.4‰ to ?27.7‰, and correlated positively with foliar δ¹⁵N values, ranging from ?3.7‰ to 5.2‰. Soil δ¹³C and δ¹⁵N values reflected the isotopic trends of the foliar tissues and ranged from ?29.8‰ to ?25.3‰, and ?4.8‰ to 6.4‰, respectively, with no significant differences between Nothofagus species (Nothofagus pumilio, Nothofagus antarctica, Nothofagus betuloides). Principal component analysis and multiple regressions suggested that mainly water availability variables (mean annual precipitation), but not soil properties, explained between 42% and 79% of the variations in foliar and soil δ¹³C and δ¹⁵N natural abundance, which declined with increased moisture supply. We conclude that a decline in water use efficiency at wetter sites promotes both the depletion of heavy C and N isotopes in soil and plant biomass. Soil δ¹³C values were higher than those of the plant tissues and this difference increased as annual precipitation increased. No such differences were apparent when δ¹⁵N values in soil and plant were compared, which indicates that climatic differences contributed more to the overall C balance than to the overall N balance in these forest ecosystems.     

Effects of decomposition and storage conditions on the δ13C and δ15N isotope values of killer whale (Orcinus orca) skin and blubber tissues

Several different factors in the collection and preservation of whale skin and blubber samples were examined to determine their effect on the results obtained by stable nitrogen and carbon isotope (δ¹⁵N and δ¹³C) analysis. Samples of wet killer whale skin retained their original stable isotope values for up to 14 d at 4°C or lower. However, decomposition significantly changed the δ¹⁵N value within 3 d at 20°C. Storage at ?20°C was as effective as ?80°C for the preservation of skin and blubber samples for stable isotope analysis for at least a year. By contrast, once a skin sample had been freeze‐dried and lipid extracted, the stable isotope values did not change significantly when it was stored dry at room temperature for at least 12 mo. Preservation of whale skin samples for a month in DMSO‐salt solution, frozen or at room temperature, did not significantly change the δ¹⁵N and δ¹³C values of lipid extracted tissues, although the slight changes seen could influence results of a study if only small changes are expected.     

VARIATION IN INTERNAL δ15N AND δ13C DISTRIBUTIONS AND THEIR BULK VALUES IN THE BROWN MACROALGA PADINA AUSTRALIS GROWING IN SUBTROPICAL OLIGOTROPHIC WATERS1

The utility of δ¹⁵N measurements in Padina australis Hauck as a probe for its external nitrogen (N) sources was tested by monitoring the bulk values of chemical components [δ¹⁵N, δ¹³C, and N and carbon (C) contents] and their internal distributions during a 12 d incubation in a controlled environment. Under the saturated conditions of isotopically heavier nitrate than that of original algal tissue, the bulk δ¹⁵N in P. australis was enriched, but less than what was predicted from a simple mixing model, signaling possible isotopic discrimination during N assimilation and subsequent N efflux from the cells. The enhanced N content (%), which occurred simultaneously with this δ¹⁵N shift, was a useful signal indicating this phenomenon. Bulk δ¹⁵N was enriched, especially around the meristem, in tissues growing under conditions of higher irradiance and temperature, probably due in part to dissolved organic nitrogen (DON) excretion. The δ¹³C enhancement in bulk algal tissues, also associated with high photosynthetic activity, may be an additional signal indicating this unbalanced internal δ¹⁵N distribution. However, in summer and winter environmental conditions with periodic nitrate supplies simulating typical fringing reef waters, the difference in measured algal bulk δ¹⁵N from theoretical predictions was within ±1.0‰. This difference is very small compared with the variation in δ¹⁵N in possible N sources in coastal areas. In the field, therefore, δ¹⁵N in Padina can be used effectively to trace N sources in both space and time after determining algal N content and δ¹³C to determine whether large alterations occur in algal δ¹⁵N.     

Use of a δ13C–δ15N relationship to determine animal trophic positions in a tropical Australian estuarine wetland

Stable isotope composition of organisms from different trophic groups collected from a semi‐isolated wetland pool in the Ross River estuary, northern Australia, was analysed to determine if there was a consistent relationship between δ¹³C, δ¹⁵N and trophic level that could be used to assign trophic positions. A strong linear negative relationship between δ¹³C and δ¹⁵N was detected for the three trophic levels considered (primary producers, primary consumers and secondary consumers). This relationship was consistent among trophic levels, differing only in height, that is, on δ¹⁵N values, which indicate trophic positions. A difference of 3.6–3.8‰ between trophic levels was present, suggesting a δ¹⁵N fractionation of approximately 3.7‰, a value slightly higher than the commonly assumed δ¹⁵N fractionation of approximately 3.4‰. The relationship between δ¹³C and δ¹⁵N was similar for invertebrate and fish primary consumers, indicating similar δ¹⁵N trophic fractionation for both groups, meaning trophic positions and trophic length could be reliably calculated based on either invertebrates or fish.     

Foliar δ13C response patterns along a moisture gradient arising from genetic variation and phenotypic plasticity in grassland species of Inner Mongolia

Plants depend upon both genetic differences and phenotypic plasticity to cope with environmental variation over different timescales. The spatial variation in foliar δ¹³C levels along a moisture gradient represents an overlay of genetic and plastic responses. We hypothesized that such a spatial variation would be more obvious than the variation arising purely from a plastic response to moisture change. Leymus chinensis and Stipa spp. were sampled from Inner Mongolia along a dry‐wet transect, and some of these species were transplanted to an area with a moisture gradient. For Stipa spp., the slope of foliar δ¹³C and mean annual precipitation along the transect was significantly steeper than that of foliar δ¹³C and mean annual precipitation after the watering treatment. For L. chinensis, there was a general decreasing trend in foliar δ¹³C under the different (increasing) watering levels; however, its populations showed an irregular relationship between foliar δ¹³C and moisture origin. Therefore, support for our hypothesis was obtained from Stipa spp., but not from L. chinensis.     

IMPACT OF TAXONOMY,GEOGRAPHY, AND DEPTH ON δ13C AND δ15N VARIATION IN A LARGE COLLECTION OF MACROALGAE1

The natural abundance of carbon stable isotopes (δ¹³C) of marine macrophytes has been measured in previous studies and used to analyze differences in C_i assimilation among the three macroalgal phyla, Chlorophyta, Ochrophyta, and Rhodophyta, and seagrasses, distinguishing diffusive CO₂ entry from the operation of a CO₂‐concentrating mechanisms (CCM). The work reported here further resolves the patterns of δ¹³C variation in aquatic macrophytes related to their taxonomy, geographic location (and consequently climatic conditions), and vertical zonation. Analyses of δ¹³C for 87 species are reported, including eight that have not been previously examined, belonging to taxa in the three macroalgal phyla, plus two species of seagrasses, collected at different latitudes. For one species of each phylum, analyses were also conducted through a vertical depth gradient. Representative species were used in a pH drift experiment, in order to compare the mechanism of C_i acquisition for photosynthesis with the δ¹³C subsequently determined on the same specimen. Our results suggest that the δ¹³C values were mostly determined by taxonomy. Depth effects on C stable isotope composition differed among taxa. The parallel measurements of δ¹⁵N are more difficult to interpret mechanistically; there are no robust phylogenetic and large‐scale biogeographic correlations; local factors of natural (e.g., upwellings) and anthropogenic (e.g., sewage outfall) inputs predominate in determining the macrophyte δ¹⁵N.     

Moss δ13C: an accurate proxy for past water environments in polar regions

Increased aridity is of global concern. Polar regions provide an opportunity to monitor changes in bioavailable water free of local anthropogenic influences. However, sophisticated proxy measures are needed. We explored the possibility of using stable carbon isotopes in segments of moss as a fine‐scale proxy for past bioavailable water. Variation in δ¹³C with water availability was measured in three species across three peninsulas in the Windmill Islands, East Antarctica and verified using controlled chamber experiments. The δ¹³C from Antarctic mosses accurately recorded long‐term variations in water availability in the field, regardless of location, but significant disparities in δ¹³C between species indicated some make more sensitive proxies. δ¹³C_SUGAR derived from living tissues can change significantly within the span of an Antarctic season (5 weeks) in chambers, but under field conditions, slow growth means that this technique likely represents multiple seasons. δ¹³C_CELLULOSE provides a precise and direct proxy for bioavailable water, allowing reconstructions for coastal Antarctica and potentially other cold regions over past centuries.     

Thawing permafrost increases old soil and autotrophic respiration in tundra: Partitioning ecosystem respiration using δ13C and ∆14C

Ecosystem respiration (R_eco) is one of the largest terrestrial carbon (C) fluxes. The effect of climate change on R_eco depends on the responses of its autotrophic and heterotrophic components. How autotrophic and heterotrophic respiration sources respond to climate change is especially important in ecosystems underlain by permafrost. Permafrost ecosystems contain vast stores of soil C (1672 Pg) and are located in northern latitudes where climate change is accelerated. Warming will cause a positive feedback to climate change if heterotrophic respiration increases without corresponding increases in primary production. We quantified the response of autotrophic and heterotrophic respiration to permafrost thaw across the 2008 and 2009 growing seasons. We partitioned R_eco using Δ¹⁴C and δ¹³C into four sources–two autotrophic (above – and belowground plant structures) and two heterotrophic (young and old soil). We sampled the Δ¹⁴C and δ¹³C of sources using incubations and the Δ¹⁴C and δ¹³C of R_eco using field measurements. We then used a Bayesian mixing model to solve for the most likely contributions of each source to R_eco. Autotrophic respiration ranged from 40 to 70% of R_eco and was greatest at the height of the growing season. Old soil heterotrophic respiration ranged from 6 to 18% of R_eco and was greatest where permafrost thaw was deepest. Overall, growing season fluxes of autotrophic and old soil heterotrophic respiration increased as permafrost thaw deepened. Areas with greater thaw also had the greatest primary production. Warming in permafrost ecosystems therefore leads to increased plant and old soil respiration that is initially compensated by increased net primary productivity. However, barring large shifts in plant community composition, future increases in old soil respiration will likely outpace productivity, resulting in a positive feedback to climate change.     

Tracking C and N dynamics and stabilization in soil amended with wheat residue and its corresponding bioethanol by‐product: a 13C/15N study

Removing agricultural cellulosic residues from fields for the production of ‘second generation biofuels'has the potential to profoundly alter C and N cycling in soil, increasing the risk of soil organic matter depletion and favoring soil–atmosphere gaseous exchanges. However, these negative impacts could potentially be offset by amending the soil with the solid by‐product which is generated during bioethanol production. In a 100 days laboratory study, we investigated the fate of C and N after soil amendment with doubly labeled (¹³C, ¹⁵N) wheat residue (WR) and the corresponding bioethanol by‐product (i.e. nonfermentable wheat residue NFWR) with and without extra N addition. Substituting WR with the corresponding amount of recovered bioethanol by‐product partially compensated the C losses of full crop residue removal. When the equivalent amount of C was added as WR and NFWR, NFWR‐derived C was found in significantly higher proportion in macroaggregates in soil (17.0 vs. 8.9%) after 100 days. Addition of both WR and NFWR reduced soil organic C (SOC) mineralization, i.e. it caused a negative priming effect in soil. However, this pattern was reversed when extra N was added. Both WR and NFWR increased the proportion of soil water‐stable macroaggregates from 16% (in control) to 20–24% (in the different treatments). The results suggest that the more recalcitrant compounds derived from bioethanol production may stabilize more strongly and persist within the protected fractions of SOM pools. Our study demonstrates that NFWR, compared with WR application, neither increased N₂O emissions nor had a negative impact on aggregate formation in the midterm. This demonstrates that NFWR has potential for replenishing SOC stocks.     

Fast response of Scots pine to improved water availability reflected in tree‐ring width and δ13C

Drought‐induced forest decline, like the Scots pine mortality in inner‐Alpine valleys, will gain in importance as the frequency and severity of drought events are expected to increase. To understand how chronic drought affects tree growth and tree‐ring δ¹³C values, we studied mature Scots pine in an irrigation experiment in an inner‐Alpine valley. Tree growth and isotope analyses were carried out at the annual and seasonal scale. At the seasonal scale, maximum δ¹³C values were measured after the hottest and driest period of the year, and were associated with decreasing growth rates. Inter‐annual δ¹³C values in early‐ and latewood showed a strong correlation with annual climatic conditions and an immediate decrease as a response to irrigation. This indicates a tight coupling between wood formation and the freshly produced assimilates for trees exposed to chronic drought. This rapid appearance of the isotopic signal is a strong indication for an immediate and direct transfer of newly synthesized assimilates for biomass production. The fast appearance and the distinct isotopic signal suggest a low availability of old stored carbohydrates. If this was a sign for C‐storage depletion, an increasing mortality could be expected when stressors increase the need for carbohydrate for defence, repair or regeneration.     

Nitrogen and carbon isotope variability in the green‐algal lichen Xanthoria parietina and their implications on mycobiont–photobiont interactions

Stable isotope patterns in lichens are known to vary largely, but effects of substrate on carbon and nitrogen stable isotope signatures of lichens were previously not investigated systematically. N and C contents and stable isotope (δ¹⁵N, δ¹³C) patterns have been measured in 92 lichen specimens of Xanthoria parietina from southern Bavaria growing on different substrates (bark and stone). Photobiont and mycobiont were isolated from selected populations and isotopically analyzed. Molecular investigations of the internal transcribed spacer of the nuclear ribosomal DNA (ITS nrDNA) region have been conducted on a subset of the specimens of X. parietina. Phylogenetic analysis showed no correlation between the symbionts X. parietina and Trebouxia decolorans and the substrate, isotope composition, or geographic origin. Instead specimens grown on organic substrate significantly differ in isotope values from those on minerogenic substrate. This study documents that the lichens growing on bark use additional or different N sources than the lichens growing on stone. δ¹⁵N variation of X. parietina apparently is controlled predominantly by the mass fraction of the mycobiont and its nitrogen isotope composition. In contrast with mycobionts, photobionts of X. parietina are much more ¹⁵N‐depleted and show less isotopic variability than mycobionts, probably indicating a mycobiont‐independent nitrogen acquisition by uptake of atmospheric ammonia.     

Fatty acids and stable isotopes (δ13C and δ15N) reveal temporal changes in narwhal (Monodon monoceros) diet linked to migration patterns

Narwhals (Monodon monoceros) are sentinel species in the Arctic and to investigate marine food web changes from 1982–2011 we examined diet using fatty acids, δ¹⁵N, and δ¹³C, in narwhals from Baffin Bay (BB) and northern Hudson Bay (NHB). We predicted temporal changes would be greater in NHB due to a significant reduction in summer ice cover. In NHB, δ¹⁵N significantly increased, δ¹³C displayed a parabolic trend, and fatty acids gradually shifted, albeit not significantly, over time. δ¹⁵N was stable, δ¹³C decreased, and fatty acids significantly changed over time in BB. Stable isotope mixing models indicated a dietary reduction in capelin and increase in Greenland halibut from 1994–2000 to 2006–2011 in BB, while capelin was an important dietary component for narwhals in NHB in recent years (2006–2011). These dietary changes may be attributed to changes in sea ice and narwhal migration. Seasonal dietary changes, as evidenced by changes in blubber fatty acids and skin and muscle stable isotopes, were not as apparent in the NHB population, which may be indicative of a reduced migratory distance. Long‐term monitoring of narwhal diet and migratory patterns associated with reduced sea ice provides invaluable information about how the marine ecosystem will redistribute with global warming.     

Nitrogen and carbon contents and δ15N and δ13C signatures in six bryophyte species: assessment of long‐term deposition changes (1980–2010) in Spanish beech forests

In this study we used recent (2010) and herbarium material (1980) of six bryophyte species to assess long‐term atmospheric deposition in natural forested areas in northern Spain. For this purpose, tissue nitrogen and carbon content, as well as δ¹³C and δ¹⁵N signatures of samples of Hypnum cupressiforme, Polytrichastrum formosum, Leucobryum juniperoideum, Rhytidiadelphus loreus, Homalothecium lutescens and Diplophyllum albicans were analysed and comparisons made between years and species. In addition, the usefulness of each of the six species was evaluated. The range of values observed was similar to that in other studies carried out in rural areas. Significantly lower values were found in 2010 for N (H. cupressiforme), δ¹⁵N (R. loreus and D. albicans), C (R. loreus) and δ¹³C (all except L. juniperoideum). Our natural areas are thus now less influenced by atmospheric pollutants than they were, most probably due to changes in some traditional local activities. Differences were observed between species for all the four parameters studied, so different species must not be analysed together. Finally, R. loreus and H. lutescens seem to be good bioindicators, sensitive even with a few samples, although further studies are needed to corroborate their usefulness.     

Exposure to predator odor and resulting anxiety enhances the expression of the α2δ subunit of voltage‐sensitive calcium channels in the amygdala

The α₂δ subunit of voltage‐sensitive calcium channels (VSCCs) is the molecular target of pregabalin and gabapentin, two drugs marked for the treatment of focal epilepsy, neuropathic pain, and anxiety disorders. Expression of the α₂δ subunit is up‐regulated in the dorsal horns of the spinal cord in models of neuropathic pain, suggesting that plastic changes in the α₂δ subunit are associated with pathological states. Here, we examined the expression of the α₂δ‐1 subunit in the amygdala, hippocampus, and frontal cortex in the trimethyltiazoline (TMT) mouse model of innate anxiety. TMT is a volatile molecule present in the feces of the rodent predator, red fox. Mice that show a high defensive behavior during TMT exposure developed anxiety‐like behavior in the following 72 h, as shown by the light–dark test. Anxiety was associated with an increased expression of the α₂δ‐1 subunit of VSCCs in the amygdaloid complex at all times following TMT exposure (4, 24, and 72 h). No changes in the α₂δ‐1 protein levels were seen in the hippocampus and frontal cortex of mice exposed to TMT. Pregabalin (30 mg/kg, i.p.) reduced anxiety‐like behavior in TMT‐exposed mice, but not in control mice. These data offer the first demonstration that the α₂δ‐1 subunit of VSCCs undergoes plastic changes in a model of innate anxiety, and supports the use of pregabalin as a disease‐dependent drug in the treatment of anxiety disorders.     

Losses of soil carbon by converting tropical forest to plantations: erosion and decomposition estimated by δ13C

Indonesia lost more tropical forest than all of Brazil in 2012, mainly driven by the rubber, oil palm, and timber industries. Nonetheless, the effects of converting forest to oil palm and rubber plantations on soil organic carbon (SOC) stocks remain unclear. We analyzed SOC losses after lowland rainforest conversion to oil palm, intensive rubber, and extensive rubber plantations in Jambi Province on Sumatra Island. The focus was on two processes: (1) erosion and (2) decomposition of soil organic matter. Carbon contents in the Ah horizon under oil palm and rubber plantations were strongly reduced up to 70% and 62%, respectively. The decrease was lower under extensive rubber plantations (41%). On average, converting forest to plantations led to a loss of 10 Mg C ha^?1 after about 15 years of conversion. The C content in the subsoil was similar under the forest and the plantations. We therefore assumed that a shift to higher δ¹³C values in plantation subsoil corresponds to the losses from the upper soil layer by erosion. Erosion was estimated by comparing the δ¹³C profiles in the soils under forest and under plantations. The estimated erosion was the strongest in oil palm (35 ± 8 cm) and rubber (33 ± 10 cm) plantations. The ¹³C enrichment of SOC used as a proxy of its turnover indicates a decrease of SOC decomposition rate in the Ah horizon under oil palm plantations after forest conversion. Nonetheless, based on the lack of C input from litter, we expect further losses of SOC in oil palm plantations, which are a less sustainable land use compared to rubber plantations. We conclude that δ¹³C depth profiles may be a powerful tool to disentangle soil erosion and SOC mineralization after the conversion of natural ecosystems conversion to intensive plantations when soils show gradual increase of δ¹³C values with depth.     

The legacy of enhanced N and S deposition as revealed by the combined analysis of δ13C, δ18O and δ15N in tree rings

This study aimed to evaluate the effects of long‐term repeated aerial nitrogen (N) and sulphur (S) misting over tree canopies of a Sitka spruce plantation in Scotland. We combined δ¹³C and δ¹⁸O in tree rings to evaluate the changes in CO₂ assimilation (A) and stomatal conductance (g_s) and to assess their contribution to variations in the intrinsic water‐use efficiency (WUE_i, i.e., the A/g_s ratio). Measurements of δ¹⁵N enabled shifts in the ecosystem N cycling following misting to be assessed. We found that: (i) N applications, with or without S, increased the ratio between A and g_s in favour of A, thus supporting a fertilizer effect of added N. (ii) After the treatments ceased, the trees quickly adjusted to the reductions of N deposition, but not to the reduction in S deposition, which had a negative effect on WUE_i by reducing A. This indicates that the beneficial role of N deposition may be negated in forests that previously received a high load of acid rain. (iii) δ¹⁵N in tree rings reflected the N dynamics caused by canopy retention, with the fingerprint also present in the litter, after the experiment stopped. (iv) Both our results (obtained using canopy applications) and a collection of published data (obtained using soil applications) showed that generally WUE_i increased in response to an increase of N applications, with the magnitude of the changes related to soil conditions and the availability of other nutrients. The shifts observed in δ¹⁵N in tree rings also suggest that both the quantity of the applied N and its quality, mediated by processes occurring during canopy N retention, are important determinants of the interactions between N and C cycles. Stable isotopes are useful probes to understand these processes and to put the results of short‐term experiments into context.