Mineral nutrition and heterotrophy in the water conservative holoparasite Hydnora Thunb. (Hydnoraceae)

There are large gaps in our understanding of parasite–host nutrient relationships. Our goal was to evaluate transdermal water loss, parasite–host mineral relationships, and heterotrophy in the holoparasitic genus Hydnora. We estimated in situ transdermal water loss in Hydnora and measured nutrient profiles and δ¹³C and δ¹⁵N signatures for Hydnora and hosts in southern Africa and Madagascar. For comparison we also measured δ¹³C and δ¹⁵N for aerial hemiparasites at the same sites. Transdermal water loss in Hydnora ranged from 0.14 ± 0.02 to 0.38 ± 0.04 mg cm⁻² h⁻¹ and was comparable to transpiration rates for water conservative xerophytes. Concentrations of P and K were higher in Hydnora relative to CAM hosts; other mineral concentrations were significantly lower in the parasite or were not different. δ¹³C signatures of holoparasites and hemiparasites relative to their hosts reflected host metabolism and differences in commitment to heterotrophic C gain. Holoparasite δ¹³C values were significantly enriched (by 0.55‰ ± 0.23) compared to host shoot and depleted compared to host root tissues (by −0.97‰ ± 0.12). Holoparasite δ¹³C values were not significantly different compared to the estimated whole host δ¹³C value. δ¹⁵N values for holoparasites and hemiparasites were significantly correlated with hosts. The water conservative nature of Hydnora spp. combined with parasite–host mineral nutrition profiles are suggestive of active processes of solute uptake. Stable isotope fractionation in host tissues dictated significant differences between parasite and host (shoot and root) δ¹³C signatures. The confirmation of complete heterotrophy and the lack of a confounding transpiration stream may make Hydnora a promising model organism for the examination of parasite solute uptake.     

N:P ratios, δN fractionation and nutrient resorption along a nitrogen to phosphorus limitation gradient in an oligotrophic wetland complex

The vegetation N:P ratio is thought to be a diagnostic indicator of the nature of nutrient limitation in wetland vegetation. It should therefore be closely linked to other indicators of nutrient acquisition and conservation, such as nitrogen stable isotope fractionation (δ¹⁵N), nutrient resorption efficiency (RE) and resorption proficiency (RP). However, the interrelationships among these traits and the N:P ratio remain unclear. We compared tissue nutrient concentrations, N:P ratios, δ¹⁵N fractionation, RE, and RP along an N to P limitation gradient in an oligotrophic wetland valley in the South Island of New Zealand. Within the valley, the soil TN:TP ratio increased from 1.3 to 18.0 in three discrete wetlands along the gradient. In pooled data from all vegetation communities within each site, the mass-based vegetation N:P ratio correlated significantly (r² = 0.35, P < 0.01) to soil TN:TP ratios and increased from 10.2 ± 2.7 to 13.5 ± 3.6 along the N to P limitation gradient. This was accompanied by an increase in tissue δ¹⁵N enrichment from 2.05 ± 1.12‰ to 6.27 ± 1.70‰, consistent with more open N cycling and lower N demand. These trends held within all vegetation types, but were particularly strong in a Typha orientalis (C-strategist) community (soil TN:TP vs vegetation N:P correlation r² = 0.78, P < 0.001; δ¹⁵N increase from 1.81 ± 0.44‰ to 7.73 ± 1.79‰). The individual N and P concentrations and retention patterns were more species-specific and less responsive to the nutrient limitation gradient. T. orientalis maximised N resorption as N limitation increased (increasing NRE from 50.8 ± 3.3% to 71.7 ± 7.4%; reducing NRP from 0.70 ± 0.12% to 0.36 ± 0.13%) but did not alter PRE or PRP, whereas the S-strategist Schoenus pauciflorus maximised P resorption as P limitation increased (increasing PRE from 48.0 ± 5.6% to 73.5 ± 10.1%; reducing PRP from 0.053 ± 0.008% to 0.015 ± 0.004%) but did not alter NRE or NRP. These results show that the tissue N:P ratio and its associated δ¹⁵N enrichment are highly responsive indicators of the relative availability of N and P at the site and community level. However, they are not indicators of species-specific physiological requirements for N and P, or of likely responses of individual species to N or P enrichment, which are better interpreted from indicators such as RE and RP that describe nutrient retention behaviour.     

Effects of body size and environment on diet-tissue δC fractionation in fishes

δ¹³C data are often used in trophodynamic research where diet-tissue fractionation (Δδ¹³C) is assumed to be 0-1‰ per trophic level and unaffected by the size of animals or their environment. Variation in Δδ¹³C will influence conclusions about food sources, energy pathways and trophic level. To assess the effects of body size, age and environmental conditions on Δδ¹³C, European sea bass (Dicentrarchus labrax) were reared on constant diets of dab (Limanda limanda) or (Ammodytes marinus) for 2years under natural environmental regimes. Bass were sampled approximately monthly to determine Δδ¹³C for muscle, heart and liver tissue and were 1.66‰, − 0.18‰, − 1.77‰ (sandeel diet) and 1.34‰, − 1.18‰, − 1.75‰ (dab diet) respectively. Arithmetic lipid correction increased Δδ¹³C to > 2‰ for muscle and liver. Δδ¹³C was dependent on body mass and experimental duration (age) and generally declined with weight or time even after correction for lipid content. For liver, increasing temperature increased Δδ¹³C. The Δδ¹³C estimates from this study were compared with all available published Δδ¹³C estimates for fish. Bass muscle Δδ¹³C was similar to previous estimates for fish white muscle Δδ¹³C (1.56 ± 1.10‰) and whole body Δδ¹³C (1.52 ± 1.13‰). Fractionations derived in this study, combined with those from the literature, support the use of diet-tissue fractionation values of between 1‰-2‰ for δ¹³C, rather than the commonly used 0‰ − 1‰. For muscle Δδ¹³C, 1.5‰ is appropriate.     

Effects of lipid removal and preservatives on carbon and nitrogen stable isotope ratios of squid tissues: Implications for ecological studies

Stable isotope analysis of carbon (C) and nitrogen (N) in animal tissues is an important approach to investigate the tropic status and habitat of marine species. Some biases due to lipid extractions and preservation can hinder the interpretation of results, yet their effects have not been investigated in squid. In this study, we evaluated the effects of lipid extraction and preservatives (dimethylsulfoxide (DMSO), 70% ethanol, and 10% buffered formaldehyde) on the δ¹³C, δ¹⁵N and C:N ratios in squid muscle. Beaks were placed under the same treatments with the exception of DMSO. Muscle and beak samples remained under treatment for 375 days and 416 days, respectively. Our results indicate that lipid extractions increased the mean values of unpreserved samples by 0.8‰ for δ¹³C and by 0.68‰ for δ¹⁵N. Preservatives also affected the isotopic composition in muscle at different magnitudes. DMSO remarkably reduced and increased the variability for δ¹³C and δ¹⁵N values among samples, formalin mainly reduced δ¹³C values by 1.5‰, whereas ethanol increased both δ¹³C and δ¹⁵N by ≤ 0.8‰. Lipid extractions eliminated the effect of DMSO and ethanol for δ¹³C and δ¹⁵N, and formalin only for δ¹⁵N. In beak, negligible shifts in δ¹³C, δ¹⁵N and C:N ratios were recorded after preservation in ethanol and formalin. Although lipid extractions can be recommended to reduce the effect of preservation, further research is needed to develop correction models for isotopic shifts associated with both lipid extractions in unpreserved and preserved muscle tissues. Lipid extractions per se could introduce a bias that may have important implications for ecological studies.     

Effect of lipid removal on carbon and nitrogen stable isotope ratios in crustacean tissues

The analysis of tissue's naturally occurring stable carbon and nitrogen isotope ratios is a useful tool to delineate trophic relationships. However, the interpretation of δ¹³C and δ¹⁵N is complicated by the influence of multiple factors such as the tissue-specific lipid content. The aim of this work was to evaluate the effects of lipid extraction on δ¹³C and δ¹⁵N compositions in muscle, hepatopancreas and gonads of a marine decapod crustacean, the spider crab Maja brachydactyla. Samples were analyzed for stable isotopes before and after lipid removal, using a derived Soxhlet extraction method. Differences in δ¹³C and δ¹⁵N were measured among tissues before and after treatment. Lipid extraction of muscle did not have a significant effect on either δ¹³C or δ¹⁵N. By contrast, ecologically significant shifts for both carbon and nitrogen stable isotopes ratios (+ 2.9 ± 0.8‰ for δ¹³C, and + 1.2 ± 0.7‰ for δ¹⁵N) were noticed in the hepatopancreas. In regard to gonads, lipid extraction led to a shift only on δ¹³C (+ 1.3 ± 0.3‰). Finally, the derived Soxhlet extraction method removed the lipid influence for δ¹³C, and had an effect on δ¹⁵N composition for lipid-rich samples. We recommend this treatment for carbon stable isotope studies on decapod crustacean lipid-rich tissues.     

Cannibalism contributes significantly to the diet of cultured sand crabs, Portunus pelagicus (L.): A dual stable isotope study

The significance of cannibalism in the diet of juvenile pond-cultured blue swimmer crabs (Portunus pelagicus (L.)) was investigated using dual stable isotope analysis of carbon and nitrogen. In a laboratory feeding experiment, δ¹⁵N demonstrated a constant trophic shift (Δδ¹⁵N ≈+ 1.6‰), and therefore seemed to be a reliable indicator for assessing trophic position for P. pelagicus. This agrees with previously reported trends. Difference in growth rate did not seem to influence δ¹⁵N values. In contrast, δ¹³C did not display consistent shifts between trophic levels (range of Δδ¹³C: + 1 to + 1.7‰). The results from the pond experiment showed that larger individuals had a more enriched δ¹⁵N than smaller individuals, which, when compared to the results from the laboratory experiment, indicates that larger individuals were at a higher trophic level. This is most likely due to cannibalism prevailing in the pond rather than a direct result of faster growth rate. Cannibalistic behaviour might further increase growth, resulting in the observed positive correlation between size and δ¹⁵N.     

δN and δC analysis of a Posidonia sinuosa seagrass bed

Potential food sources and dominant invertebrates and fishes were collected for the examination of variability in ¹³C/¹²C and ¹⁵N/¹⁴N to determine the sources of carbon available to consumers within a Western Australian Posidonia sinuosa-dominated seagrass bed. Autotrophs showed a wide distribution of δ¹³C values, with P. sinuosa at −11.3 ± 0.8‰ and macroalgae ranging from −16.6 to −31.7‰. This variation allowed us to successfully identify macroalgae as the main contributor of carbon to the trophic structure, although no distinction could be made between epiphytic macroalgae on seagrass, or allochthonous macroalgal sources. The range in δ¹⁵N ratios among potential food items at the trophic base was too small to make it useful as tracer of nitrogen flow pathways, but it consistently increased from macrophytes and detritus (4.1–6.8‰), to invertebrates (5.7–7.4‰) located near the middle of the food web, to fishes (8.3–11.9‰), with piscivorous species such as Leviprora inops generally having a higher ¹⁵N. δ¹³C of seston (−12.8‰) and sedimentary organic matter (−8.7‰) indicate that seagrass material is the main contributor to these two carbon pools, and that very little of it contributes to animal biomass.     

Estimation of growth and food consumption in juvenile Japanese flounder Paralichthys olivaceus using carbon stable isotope ratio δC under laboratory conditions

To estimate the accumulated food consumption and growth of juvenile Japanese flounder Paralichthys olivaceus, we investigated the relationships between individual food consumption and growth, and the change in the stable carbon isotope ratio (δ¹³C). Japanese flounder juveniles were individually reared and their diet was switched from one formulated feed EP1 (δ¹³C = − 19.47‰) to another EP3 (δ¹³C = − 17.21‰) and fed at different feeding regimes. After the switch, the δ¹³C content of the dorsal muscle was exponentially shifted to a different level in proportion to the feeding and growth rates. Therefore, measuring the carbon stable isotope ratio is a useful tool for estimating the food consumption and growth rate of juveniles. In addition, since the velocity of change and the asymptotic value of the carbon stable isotope ratio varied in muscle, caudal fin and liver tissue, different tissues can be used for different time scale estimations.     

Temperature record in the oxygen stable isotopes of Pacific sardine otoliths: Experimental vs. wild stocks from the Southern California Bight

Pacific sardines (Sardinops sagax) are commercially fished in Canada, USA, and Mexico along approximately 5000 km of coastal waters that experience a wide range of temperatures. Trinational management of the species can be problematic because the connectivity between spawning, recruitment, stock residency, and migration in some years may not be well predicted. Oxygen isotopic value of otoliths (δ¹⁸O_otolith) has been used to infer stock residency and movement of fish populations within regions, but few studies have used laboratory data to establish a predictive temperature model to validate δ¹⁸O_otolith values of wild fish. We conducted a growth experiment with juveniles at different temperatures using Southern California Bight (SCB) seawater to test the assumption that Pacific sardine otoliths accurately record environmental water temperature in the presence of constant salinity. Sardine δ¹⁸O_otolith values were significantly and negatively correlated with temperature according to the linear model:

δ¹⁸Ootolith(‰)−δ¹⁸Owater(‰)=−0.132(±0.003 SE)×Temperature(°C)+2.455(±0.043 SE)     

Variation in bulk tissue, fatty acid and monosaccharide δ13C values between autotrophic and heterotrophic plant organs

The flowers of 23 species of grass and herb plants were collected from a mesotrophic grassland to assess natural variability in bulk, monosaccharide and fatty acid δ¹³C values from one plant community and were compared with previous analyses of leaves from the same species. The total mean bulk δ¹³C value of flower tissues was −28.1‰, and there was no significant difference between the mean δ¹³C_flower values for grass (−27.8‰) and herb (−28.2‰) species. On average bulk δ¹³C_flower values were 1.1‰ higher than bulk δ¹³C_leaf values, however, the δ¹³C_flower and δ¹³C_leaf values of grasses did not differ between organs suggesting that carbon isotope discrimination is different in grass and herb species. The abundance of different monosaccharides abundance varied between plant types, i.e. xylose concentrations in the grass flowers were as high as 40%, compared with up to 15% in the herb species, but the general relationship δ¹³C_arabinose > δ¹³C_xylose > δ¹³C_glucose > δ¹³C_galactose which had been observed in leaves was similar in flowers (total mean δ¹³C values = −25.9‰, −27.2‰, −28.8‰ and −28.1‰, respectively). However, the average 5.4‰ depletion in the δ¹³C values of the C_16:0, C_18:2 and C_18:3 fatty acids in flowers compared to bulk tissue was significantly greater than observed for leaves. The trend C_16:0 < C_18:2 < C_18:3 previously observed in leaves was also observed in grass flowers (δ¹³C_C16:0 = −33.8‰; δ¹³C_C18:2 = −33.1‰; δ¹³C_C18:3 = −34.2‰) but not herb flowers (δ¹³C_C16:0 = −34.1‰; δ¹³C_C18:2 = −32.4‰; δ¹³C_C18:3 = −34.5‰). We conclude: (i) that the biological processes influencing carbon isotope discrimination in grass flowers are different from herbs flowers; and, (ii) that a range of post-photosynthetic fractionation effects caused the observed differences between flower and leaf δ¹³C values, especially the significant ¹³C-depletion in flower fatty acid δ¹³C values.     

Oxygen and carbon isotope compositions of middle Cretaceous vertebrates from North Africa and Brazil: Ecological and environmental significance

In order to investigate mid-Cretaceous terrestrial climates of low paleolatitudes, Moroccan, Tunisian and Brazilian vertebrate apatites have been analyzed for their oxygen and carbon isotope compositions of phosphates (δ¹⁸O_p) and carbonates (δ¹⁸O_c, δ¹³C_c). At each site, coexisting theropod dinosaurs, titanosaurid sauropods, pterosaurs, crocodilians, turtles and fish have distinct δ¹⁸O_p and δ¹³C_c values reflecting their ecologies, diets and foraging environments. Oxygen isotope compositions of surface waters (δ¹⁸O_w) estimated from turtle and crocodile δ¹⁸O_p values range from − 5.0 ± 1.0‰ to − 2.4 ± 1.0‰, which do not differ from mean annual rainwater values occurring today under inter-tropical sub-arid to arid climates. High water temperatures ranging from 21 ± 6 °C to 34 ± 2 °C deduced from fish δ¹⁸O_p values are in agreement with those published for mid-Cretaceous low latitudes. Temporary or seasonal droughts are inferred from high δ¹⁸O_p values of lungfish teeth, even though lower reptile δ¹⁸O_p values suggest the use of distinct and most likely larger or regularly renewed bodies of water. Environmental conditions of the studied low latitude regions during the Aptian-Cenomanian interval were somewhat similar to those experienced today under semi-arid to arid tropical or equatorial climates, but with higher mean surface temperatures than present-day ones.     

Parasites of three commercially exploited bivalve mollusc species of the estuarine region of the Cachoeira river (Ilhéus, Bahia, Brazil)

This paper reports the parasites found in three commercially exploited bivalve molluscs (Mytella guyanensis, Anomalocardia brasiliana and Iphigenia brasiliana) of an estuarine region of Ilhéus, south of Bahia, Brazil (14°48′23′′S; 39°02′47′′W). Samples of 20 individuals of each species were collected fortnightly from August 2005 to August 2006. A total of 1480 individuals was collected and processed by standard histologic techniques; the histologic sections were stained with Harris haematoxylin and eosin and examined with light microscope. The water temperature in the study area varied from 24 to 30.5 °C and the salinity from 0 to 23 ppt. Remarkable differences were found in the parasitic community between the three mollusc species involved in the study, which occupied different habitats in the estuarine region of the Cachoeira river. The following parasites were found: intracellular rickettsia-like colonies in digestive epithelia; intracellular gregarine Nematopsis sp. in gills, mantle, gonad, digestive gland and foot muscle; sporocysts of a Bucephalidae trematode in gonads, mantle, gills, digestive gland and foot; unidentified digenetic metacercariae in digestive gland and gonad; metacestodes of Tylocephalum sp. in connective tissue in the digestive gland and in gonad; and an unidentified metazoan in mantle and intestinal lumen. No significant temporal variation in the prevalence of any parasite was detected, which could be due to the narrow temperature range of the region and the absence of patterns of salinity and rainfall variation through the year. The infestation by sporocyst was the only pathological threat detected for the studied populations because of its potential for host castration. The low infection intensity and/or prevalence of the other parasites and the lack of obvious lesions suggest that there is no other serious pathological risk for the studied mollusc populations.     

Seasonal variations in bulk tissue, fatty acid and monosaccharide δC values of leaves from mesotrophic grassland plant communities under different grazing managements

Leaves of 26 grass, herb, shrub and tree species were collected from mesotrophic grasslands to assess natural variability in bulk, fatty acid and monosaccharide δ¹³C values under different grazing management (cattle- or deer-grazed) on three sample dates (May, July and October) such that interspecific and spatiotemporal variations in whole leaf tissues and compound-specific δ¹³C values could be determined. The total mean leaf bulk δ¹³C value for plants was −28.9‰ with a range of values spanning 7.5‰. Significant interspecific variation between bulk leaf δ¹³C values was only determined in October (P = <0.001) when δ¹³C values of the leaf tissues from both sites was on average 1.5‰ depleted compared to during July and May. Samples from May were significantly different between fields (P = 0.03) indicating an effect from deer- or cattle-grazing in young leaves. The average individual monosaccharide δ¹³C value was 0.8‰ higher compared with whole leaf tissues. Monosaccharides were the most abundant components of leaf biomass, i.e. arabinose, xylose, mannose, galactose and glucose, and therefore, fluctuations in their individual δ¹³C values had a major influence on bulk δ¹³C values. An average depletion of ca. 1‰ in the bulk δ¹³C values of leaves from the deer-grazed field compared to the cattle-grazed field could be explained by a general depletion of 1.1‰ in glucose δ¹³C values, as glucose constituted >50% total leaf monosaccharides. In October, δ¹³C values of all monosaccharides varied between species, with significant variation in δ¹³C values of mannose and glucose in July, and mannose in May. This provided an explanation for the noted variability in the tissue bulk δ¹³C values observed in October 1999. The fatty acids C_16:0, C_18:2 and C_18:3 were highly abundant in all plant species. Fatty acid δ¹³C values were lower than those of bulk leaf tissues; average values of −37.4‰ (C_16:0), −37.0‰ (C_18:2) and −36.5‰ (C_18:3) were determined. There was significant interspecific variation in the δ¹³C values of all individual fatty acids during October and July, but only for C_18:2 in May (P = <0.05). This indicated that seasonal trends observed in the δ¹³C values of individual fatty acids were inherited from the isotopic composition of primary photosynthate. However, although wide diversity in δ¹³C values of grassland plants ascribed to grazing management, interspecific and spatiotemporal influences was revealed, significant trends (P = <0.0001) for fatty acid and monosaccharide δ¹³C values: δ¹³C_16:0 < δ¹³C_18:2 < δ¹³C_18:3 and δ¹³C_arabinose > δ¹³C_xylose > δ¹³C_glucose > δ¹³C_galactose, respectively, previously described, appear consistent across a wide range of species at different times of the year in fields under different grazing regimes.     

Fractionation of stable isotopes in the Arctic marine copepod Calanus glacialis: Effects on the isotopic composition of marine particulate organic matter

Fractionation of δ¹³C and δ¹⁵N between food, consumer, and faecal pellets was studied in the Arctic marine copepod Calanus glacialis Jaschnov, fed with isotopically distinct algal monocultures. Temporal variations in δ¹³C and δ¹⁵N of copepods that were fed ice algae and phytoplankton followed those of a control group consisting of starved animals. There were no significant trends in the δ¹³C and δ¹⁵N values of copepods that were starved for 42 days, suggesting that the isotopic composition of non-lipid body tissues is unaffected by the metabolic processes during prolonged periods of starvation. The stable isotopic composition of starved copepods therefore seems to reflect food consumed during the previous period of feeding and growth. Faecal pellets produced by feeding copepods were depleted in ¹³C and ¹⁵N by 6.3-11.2‰ and 0.7-9.1‰, respectively, relative to the food ingested. These results indicate that faecal pellet production is an important pathway for the trophic fractionation of δ¹³C, whereas other fractionation pathways, such as excretion of ammonia, may be relatively more important for δ¹⁵N. The strong depletion of ¹³C in faecal pellets compared to the food suggests that grazing by herbivorous copepods on primary production adds to the variability of δ¹³C in marine particulate organic matter.     

Effects of body size and environment on diet-tissue δN fractionation in fishes

Nitrogen stable isotope natural abundance data are often used in trophodynamic research. The assumed nitrogen diet-tissue fractionation (Δδ¹⁵N) determines conclusions about trophic level, potential food sources and ontogenetic diet shifts. Δδ¹⁵N is usually assumed to be 3.0-3.4‰ per trophic level and unaffected by the size or age of animals or their environment. To assess the effects of body size, experimental duration and environmental conditions on fish tissue Δδ¹⁵N, two populations of European sea bass (Dicentrarchus labrax) were reared on constant diets of dab (Limanda limanda) muscle or sandeel (Ammodytes marinus) for 2 years under natural light and temperature regimes. Bass were sampled at approximately monthly intervals to determine Δδ¹⁵N for muscle, heart and liver tissue. Mean values of Δδ¹⁵N were 3.83‰, 3.54‰, 2.05‰ (sandeel diet) and 3.98‰, 3.32‰, 1.95‰ (dab diet) for muscle, heart and liver tissue respectively. The assumption that fractionation was independent of body mass was upheld for muscle and heart tissue, but not for liver. Time effects on muscle Δδ¹⁵N were explainable by a sinusoidal function with a period of 1 year and wave height ∼ 0.3‰. Time resulted in increases in heart δ¹⁵N and decreases in liver δ¹⁵N which were small compared to background variation, equating to 1/6 of a trophic level over 2 years, and unlikely to have great significance in ecological studies. Heart and liver δ¹⁵N were also affected by temperature probably reflecting the metabolic functions of these tissues and their associated rates of turnover. However in heart the explanatory power of temperature appeared tied to that of time. Although the Δδ¹⁵N for bass muscle on both diets approached 4‰, the Δδ¹⁵N values from this study, when combined with those from the literature, suggest that where fish species specific data are not available, a mean Δδ¹⁵N for fish muscle of 3.2‰ should be applied (mean white muscle Δδ¹⁵N = 3.15). The literature based mean Δδ¹⁵N for whole fish was lower than that of white muscle suggesting that a separate Δδ¹⁵N (2.9‰) should be applied when sampling whole fish.     

Stable nitrogen and carbon isotope discrimination between juveniles and adults in an income-breeding small mammal (Peromyscus maniculatus)

We investigated the stable nitrogen- and carbon-isotope compositions of blood, liver, muscle and hair of income breeding deer mice (Peromyscus maniculatus) to determine the extent to which stable isotope compositions of mothers and offspring differed. We found small differences between the δ¹⁵N and δ¹³C values of dependent offspring and adult tissues (by a magnitude of −0.8‰ to 1.1‰ for ¹⁵N and 0.3–0.9‰ for ¹³C), and limited ¹⁵N discrimination between juvenile tissues and milk, which explains the small mother-offspring trophic effects in isotopic composition. Discrimination of ¹⁵N between offspring and adults was greater than expected but smaller than known for capital breeding mammals, suggesting that different biochemical pathways for milk production and processing may affect the discrimination of ¹⁵N in these systems.     

Metallothioneins and trace elements in digestive gland,gills, kidney and gonads of Octopus vulgaris

Metallothionein-like proteins (MT) and V, Cr, Co, Ni, Zn, Cu, As and Cd were determined in digestive gland, gills, kidney and gonads of Octopus vulgaris, from the Portuguese coast. To our knowledge these are the first data on MT in octopus. High concentrations (µg g^− 1, dry mass) of Zn (48050) and Cd (555) were found in digestive gland, and MT reached levels one order of magnitude above the ones registered in wild bivalves. Significantly higher levels of MT in digestive gland and gills of specimens from A and B were in line with elevated Cd concentrations. Principal component analyses (PCA) point to MT-Cd and MT-Cr associations in digestive gland and gills. Despite the high levels of Zn in specimens from B, association with Zn was not obtained. Due to the affinity of MT to various elements, it should not be excluded the possibility of Cd replacing Zn in Zn-MT. Kidney presented higher levels of Cd, Co, Ni and As than gills and gonads, and in the case of As surpassing the levels in digestive gland, but PCA showed no relation with MT. Likewise the MT levels in gonads had no correspondence to the metal concentration variation.     

Hominid environments at Hadar from paleosol studies in a framework of Ethiopian climate change

The amount and seasonal distribution of paleo-rainfall is a major concern of paleoanthropology because they determine the nature of the vegetation and the structure of the ecosystem, particularly in eastern Africa. The δ¹⁸O and δ¹³C of paleosol carbonates are quantitative proxies of these critical features of the paleoenvironment. The Afar region of Ethiopia lies between the African and Indian summer monsoons, and is prone to profound climate change. In the western Afar, the dominant paleoenvironment of the Hadar Formation during the late Pliocene was a major meandering river's distal low, flat floodplain, on which muds accreted that were continuously transformed into vegetated soils with Bk horizons rich in CaCO₃. The mean δ¹³C of paleosols throughout the Hadar Formation translates to an average vegetative cover across the extensive floodplain of about 30% of the C₄ grasses and 70% of unspecified C₃ plants. The character of the paleosols, such as the one at Locality 333, and their δ¹⁸O_Carbonate argue for a highly seasonal rainfall of about twice today's amount, implying that the C₃ plants were mostly sizeable trees and that the biome for Australopithecus afarensis was a grassy woodland. The amount of grasses abruptly increased in the lower Busidima Formation with its early Homo and artifacts to a more open grassy woodland of ca. 50% grasses. However, this transition in δ¹³C is not mirrored in the δ¹⁸O, which persists at a quite negative average value of −6.4‰ over the entire >2-Myr duration of both formations. This value for the carbonate means that the paleosoil water was a quite negative −4.1‰, a significant 5‰ more negative than our estimate of modern rain at Hadar. We put the negative δ¹⁸O of paleo-Hadar's rainfall into an isotopic framework of the dynamic history of climate change in sub-Saharan northern Africa. There have been two end-member climate regimes: (1) an earlier persistently pluvial Pliocene regime, with its strong summer monsoon, as registered in the Hadar Formation; and (2) the modern cyclical, mostly arid regime that began ca. 1 Myr ago, which has been punctuated by about ten cyclically predictable brief millennia-long pluvial episodes. The best known pluvial of the latter regime is the latest one, the African Humid Period (AHP), just 9.0-6.5 kyr ago, whose δ¹⁸O_Rainfall matches that for paleo-Hadar. The known climatological factors that brought on the AHP are probably the same ones that were persistently present for the Afar of the Pliocene. This dynamic rainfall history undoubtedly has influenced hominid occupation of the keystone Afar area at the gateway out of, and into, Africa.     

Differentiation of benthic marine primary producers using stable isotopes and fatty acids: Implications to food web studies

A two-dimensional biomarker approach, using stable isotopes (δ¹³C, δ¹⁵N) and fatty acids, was used to evaluate differences both amongst and within benthic primary producer types (seagrass, fleshy red algae, calcareous red algae, brown algae, and seagrass periphyton) that are typical of the nearshore, temperate Australian region. The primary source of variance (as examined by permutational ANOVA) for all biomarkers examined was amongst primary producer types, as opposed to amongst species within type. δ¹³C showed a clear separation (Monte Carlo p < 0.05) between seagrass (range of means = −10.1 to −14.0‰) and macroalgae (−14.6 to −25.2‰), but could not differentiate amongst the algal types examined. Similarly, distinct δ¹⁵N signatures (p < 0.05) were found only for seagrass (range of means = 3.6-4.1‰) versus calcareous red algae (4.6-5.5‰), with all other types overlapping in their mean δ¹⁵N values. In contrast, multivariate analysis of fatty acid data (using Canonical Analysis of Principal coordinates; CAP) distinguished not only between seagrass and macroalgae, but also between red and brown algae (and to a limited extent between the calcareous and fleshy red algal types). The principal unsaturated fatty acids in the samples were C₂₀ polyunsaturates (found primarily in the macroalgae and periphyton), and C₁₈ mono- and polyunsaturates, with high proportions of 18:2n-6 and 18:3n-3 typical of the seagrasses. The C₁₈ monounsaturate 18:1n-7 was one of the most diagnostic compounds for the red algae examined, being present in very low amounts in seagrass and virtually absent in the brown algae. Conversely, brown algae were high in 18:4n-3, with 20:4n-3 particularly diagnostic of the kelp Ecklonia radiata. In contrast to stable isotopes, fatty acids helped distinguish different algal groups, thereby providing support that a two-dimensional approach using stable isotopes and fatty acids is likely to provide the most useful tool to distinguish primary producers in food web structure.     

Stable isotope fractionation between maternal and embryo tissues in the Bonnethead shark (<Emphasis Type="Italic">Sphyrna tiburo</Emphasis>)

Evaluating tissue fractionation between mothers and their offspring is fundamental for informing our interpretation of stable isotope values in young individuals and can provide insight into the dynamics of maternal provisioning. The objectives of this study were to investigate the isotopic relationships between maternal reproductive (i.e., yolk, yolk-sac placenta) and somatic tissues (i.e., muscle and liver) relative to embryos in the Bonnethead Shark Sphyrna tiburo, to evaluate the fractionation of stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes between these tissues. Additionally, we examined intra-uterine variability in the isotopic relationships to ascertain whether this species may exhibit variable nutrient allocation. Embryos showed similar magnitudes of enrichment in ¹³C (i.e., Δδ¹³C, difference between adult and embryo) relative to adult tissues (Δδ¹³C?=?~1.0‰). However, embryos were depleted in ¹⁵N relative to adult muscle tissues (Δδ¹⁵N?=??1.0‰), a finding that contrasts Δδ¹⁵N values reported for other placentotrophic sharks. Embryo-muscle Δδ¹⁵N was correlated with length, supporting the contention that the magnitude of enrichment between embryonic and maternal tissues results from the shift from yolk to placental feeding. Embryo δ¹⁵N and Δδ¹⁵N values showed significant intra-uterine variability; a result not observed for δ¹³C and Δδ¹³C values. The contrasting patterns in fractionation among placentotrophic sharks highlight the importance of evaluating these relationships across elasmobranch taxa with consideration for different tissues, reproductive strategies and stages of gestation. The divergent findings support future evaluation of stable isotope relationships between mothers and offspring for purposes of estimating inherent isotopic variability and how this variability may inform physiological and dietary mechanisms.