Effects of Trophic Level and Metamorphosis on Discrimination of Hydrogen Isotopes in a Plant-Herbivore System

The use of stable isotopes in ecological studies requires that we know the magnitude of discrimination factors between consumer and element sources. The causes of variation in discrimination factors for carbon and nitrogen have been relatively well studied. In contrast, the discrimination factors for hydrogen have rarely been measured. We grew cabbage looper caterpillars (Trichoplusia ni) on cabbage (Brassica oleracea) plants irrigated with four treatments of deuterium-enriched water (δD = −131, −88, −48, and −2‰, respectively), allowing some of them to reach adulthood as moths. Tissue δD values of plants, caterpillars, and moths were linearly correlated with the isotopic composition of irrigation water. However, the slope of these relationships was less than 1, and hence, discrimination factors depended on the δD value of irrigation water. We hypothesize that this dependence is an artifact of growing plants in an environment with a common atmospheric δD value. Both caterpillars and moths were significantly enriched in deuterium relative to plants by ∼45‰ and 23‰ respectively, but the moths had lower tissue to plant discrimination factors than did the caterpillars. If the trophic enrichment documented here is universal, δD values must be accounted for in geographic assignment studies. The isotopic value of carbon was transferred more or less faithfully across trophic levels, but δ15N values increased from plants to insects and we observed significant non-trophic 15N enrichment in the metamorphosis from larvae to adult

Geographic distribution of feather δ34S in Europe

Geographic distribution models of environmentally stable isotopes (the so-called “isoscapes”) are widely employed in animal ecology, and wildlife forensics and conservation. However, the application of isoscapes is limited to elements and regions for which the spatial patterns have been estimated. Here, we focused on the ubiquitous yet less commonly used stable sulfur isotopes (δ34S). To predict the European δ34S isoscape, we used 242 feather samples from Eurasian Reed Warbler (Acrocephalus scirpaceus) formed at 69 European wetland sites. We quantified the relationships between sample δ34S and environmental covariates using a random forest regression model and applied the model to predict the geographic distribution of δ34S. We also quantified within-site variation in δ34S and complementarity with other isotopes on both individual and isoscape levels. The predicted feather δ34S isoscape shows only slight differences between the central and southern parts of Europe while the coastal regions were most enriched in 34S. The most important covariates of δ34S were distance to coastline, surface elevation, and atmospheric concentrations of SO2 gases. The absence of a systematic spatial pattern impedes the application of the δ34S isoscape, but high complementarity with other isoscapes advocates the combination of multiple isoscapes to increase the precision of animal tracing. Feather δ34S compositions showed considerable within-site variation with highest values in inland parts of Europe, likely attributed to wetland anaerobic conditions and redox sensitivity of sulfur. The complex European geography and topography as well as using δ34S samples from wetlands may contribute to the absence of a systematic spatial gradient of δ34S values in Europe. We thus encourage future studies to focus on the geographic distribution of δ34S using tissues from diverse taxa collected in various habitats over large land masses in the world (i.e., Africa, South America, or East Asia

The Lantern Vol. 52, No. 2, Spring 1986

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Periprandial changes of the sympathetic–parasympathetic balance related to perceived satiety in humans

Food intake regulation involves various central and peripheral mechanisms. In this study the relevance of physiological responses reflecting the autonomic nervous system were evaluated in relation to perceived satiety. Subjects were exposed to a lunch-induced hunger-satiety shift, while profiling diverse sensory, physiological, and biochemical characteristics at 15 min intervals. Sensory ratings comprised questionnaires with visual analogues scales about their feeling of satiety, desire to eat, fullness, and hunger. Physiological characteristics included heart rate, heart rate variability, and blood pressure, while biochemical markers such as cortisol levels and α-amylase activity were monitored in saliva. The four sensory ratings correlated with heart rate and salivary α-amylase suggesting a higher sympathetic tone during satiety. Furthermore, heart rate variability was associated with age and waist-to-hip ratio and cortisol levels negatively correlated with body mass index. Finally, neither chewing nor swallowing contributed to a heart rate increase at food consumption, but orosensory stimulation, as tested with modified sham feeding, caused a partial increase of heart rate. In conclusion, after meal ingestion critical physiological alterations reveal a elevated sympathetic tone, which is a potential measure of satiety

Mercury bioaccumulation and biomagnification in Ozark stream ecosystems

Crayfish (Orconectes spp.), Asian clam (Corbicula fluminea), northern hog sucker (hog sucker; Hypentelium nigricans), and smallmouth bass (smallmouth; Micropterus dolomieu) from streams in southeastern Missouri (USA) were analyzed for total mercury (HgT) and for stable isotopes of carbon (δ13C), nitrogen (δ15N),and sulfur (δ34S) to discern Hg transfer pathways. HgT concentrations were generally lowest in crayfish (0.005–0.112µg/g dw) and highest in smallmouth (0.093–4.041 mg/gdw), as was δ15N. HgT was also lower and δ15N was higher in all biota from a stream draining a more heavily populated historical lead–zinc mining area than from similar sites with mostly undeveloped forested watersheds. δ13C in biota was lowest at spring-influenced sites, reflecting CO2 inputs and temperature influences, and δ34S increased from south to north in all taxa. However, HgT was not strongly correlated with either δ13C or δ34S in biota. Trophic position (TP) computed from crayfish δ15N was lower in hog suckers (mean = 2.8) than in smallmouth (mean=3.2), but not at all sites. HgT, δ13C, δ34S, and TP in hog suckers increased with total length (length) at some sites, indicating site-specific onto genetic diet shifts. Changes with length were less evident in smallmouth. Length-adjusted HgT site means in both species were strongly correlated with HgT in crayfish (r2=0.97, P \u3e 0.01), but not with HgT in Corbicula (r2= 0.02, P \u3e 0.05).ANCOVA and regression models incorporating only TP and, for hog suckers, length, accurately and precisely predicted HgT concentrations in both fish species from allocations. Although low compared to many areas of the USA, HgT (and therefore methyl mercury) concentrations in small mouth and hog suckers are sufficiently high to represent a threat to human health and wildlife. Our data indicate that in Ozark streams, Hg concentrations in crayfish are at least partly determined by their diet, with concentrations in hog suckers, smallmouth, and possibly other higher-level consumers largely determined by concentrations in crayfish and other primary and secondary consumers, fish growth rates, and TP

Appendix B. Maps showing densities of occurrence locations of eastern red bats (Lasiurus borealis) and hoary bats (Lasiurus cinereus) in eastern North America, grouped by sex.

Maps showing densities of occurrence locations of eastern red bats (Lasiurus borealis) and hoary bats (Lasiurus cinereus) in eastern North America, grouped by sex

Appendix F. Video sequence of probability density surfaces showing areas where stable hydrogen isotope analysis indicated that 19 individual hoary bats (Lasiurus cinereus) found dead beneath wind turbines at a wind energy facility in New York from 20 July to 9 September 2007 probably molted into new hair the previous summer.

Video sequence of probability density surfaces showing areas where stable hydrogen isotope analysis indicated that 19 individual hoary bats (Lasiurus cinereus) found dead beneath wind turbines at a wind energy facility in New York from 20 July to 9 September 2007 probably molted into new hair the previous summer

Appendix A. Discussion of caveats associated with the analysis and an assessment of the origin-estimation model.

Discussion of caveats associated with the analysis and an assessment of the origin-estimation model

Appendix E. Video sequence of probability density surfaces showing areas where stable hydrogen isotope analysis indicated that 18 individual hoary bats (Lasiurus cinereus) found dead beneath wind turbines at a wind energy facility in Texas between 14 August and 12 September 2008 probably molted into new hair the previous summer.

Video sequence of probability density surfaces showing areas where stable hydrogen isotope analysis indicated that 18 individual hoary bats (Lasiurus cinereus) found dead beneath wind turbines at a wind energy facility in Texas between 14 August and 12 September 2008 probably molted into new hair the previous summer