Biochemical tracers reveal intra-specific differences in the food webs utilized by individual seabirds

Food web structure regulates the pathways and flow rates of energy, nutrients, and contaminants to top predators. Ecologically and physiologically meaningful biochemical tracers provide a means to characterize and quantify these transfers within food webs. In this study, changes in the ratios of stable N isotopes (e.g., δ¹⁵N), fatty acids (FA), and persistent contaminants were used to trace food web pathways utilized by herring gulls (Larus argentatus) breeding along the shores of the St Lawrence River, Canada. Egg δ¹⁵N values varied significantly among years and were used as an indicator of gull trophic position. Temporal trends in egg δ¹⁵N values were related to egg FA profiles. In years when egg δ¹⁵N values were greater, egg FA patterns reflected the consumption of more aquatic prey. Egg δ¹⁵N values were also correlated with annual estimates of prey fish abundance. These results indicated that temporal changes in aquatic prey availability were reflected in the gull diet (as inferred from ecological tracer profiles in gull eggs). Analysis of individual eggs within years confirmed that birds consuming more aquatic prey occupied higher trophic positions. Furthermore, increases in trophic position were associated with increased concentrations of most persistent organic contaminants in eggs. However, levels of highly brominated polybrominated diphenyl ether congeners, e.g, 2,2′,3,3′,4,4′,5,5′,6,6′-decabromoDE (BDE-209), showed a negative relationship with trophic position. These contrasting findings reflected differences among contaminant groups/homologs in terms of their predominant routes of transfer, i.e., aquatic versus terrestrial food webs. High trophic level omnivores, e.g., herring gulls, are common in food webs. By characterizing ecological tracer profiles in such species we can better understand spatial, temporal, and individual differences in pathways of contaminant, energy, and nutrient flow.     

Educational differences in smoking: international comparison

ObjectiveTo investigate international variations in smoking associated with educational level.DesignInternational comparison of national health, or similar, surveys.SubjectsMen and women aged 20 to 44 years and 45 to 74 years.Setting12 European countries, around 1990.ResultsIn the 45 to 74 year age group, higher rates of current and ever smoking among lower educated subjects were found in some countries only. Among women this was found in Great Britain, Norway, and Sweden, whereas an opposite pattern, with higher educated women smoking more, was found in southern Europe. Among men a similar north-south pattern was found but it was less noticeable than among women. In the 20 to 44 year age group, educational differences in smoking were generally greater than in the older age group, and smoking rates were higher among lower educated people in most countries. Among younger women, a similar north-south pattern was found as among older women. Among younger men, large educational differences in smoking were found for northern European as well as for southern European countries, except for Portugal.ConclusionsThese international variations in social gradients in smoking, which are likely to be related to differences between countries in their stage of the smoking epidemic, may have contributed to the socioeconomic differences in mortality from ischaemic heart disease being greater in northern European countries. The observed age patterns suggest that socioeconomic differences in diseases related to smoking will increase in the coming decades in many European countries.     

Note: individual differences in taste adaptation

Subjects who had previously participated in a taste adaptationstudy (DuBose, et al., 1977) were retested one year later usingthe same stimuli (.1 M and .36 M sucrose and NaCl) and experimentalconditions (3-minute continuous flow over anterior dorsal tonguesurface). Results indicated that individual differences in thereported degree of adaptation were maintained over the longintersession interval. Salivary sodium levels and salt recognitionthresholds could not account for the persisting individual differencesin adaptation to NaCl. Direct examination of subjects' tonguemovements is suggested.     

Competition avoidance drives individual differences in response to a changing food resource in sticklebacks

Within the same population, individuals often differ in how they respond to changes in their environment. A recent series of models predicts that competition in a heterogeneous environment might promote between‐individual variation in behavioural plasticity. We tested groups of sticklebacks in patchy foraging environments that differed in the level of competition. We also tested the same individuals across two different social groups and while alone to determine the social environment's influence on behavioural plasticity. In support of model predictions, individuals consistently differed in behavioural plasticity when the presence of conspecifics influenced the potential payoffs of a foraging opportunity. Whether individuals maintained their level of behavioural plasticity when placed in a new social group depended on the environmental heterogeneity. By explicitly testing predictions of recent theoretical models, we provide evidence for the types of ecological conditions under which we would expect, and not expect, variation in behavioural plasticity to be favoured.     

Determinants of helminth aggregation in natural host populations: individual differences or spatial heterogeneity?

We assessed the importance of spatial heterogeneity for the aggregation of helminth populations in the bank vole Clethrionomys glareolus (Arvicolinae) using a previously published method which allows to analyse parasite aggregation at two host population levels, i.e., within and between spatial samples of the host population.
In the main empirical material from Finnish Lapland (Pallasjärvi), all five helminth species were significantly aggregated within study sites, but only three rare species showed significant aggregation among sites. In all helminth species, the total aggregation was primarily (79-98%) determined by aggregation within sites, i.e., between host individuals. Despite the larger spatial scale and more heterogeneous landscape, the comparative material from South Finland (Luhanka) supported the generally high proportion of the total aggregation due to within-site heterogeneity.
Despite the clear interspecific differences in patchiness of helminth populations, the proportion of the total aggregation due to among-site heterogeneity did not vary significantly among helminth species. The results indicate a link between aggregation at two population levels; species that showed strong within-site aggregation were also characterised by pronounced spatial heterogeneity and significant among-site aggregation.     

Etiology of individual differences in birth weight of twins as a function of maternal smoking during pregnancy.

Birth weight is in large extent influenced by gestational age. In addition genetic and environmental factors determine intrauterine growth and birth weight. The contributions of these factors may be influenced by maternal smoking during pregnancy. We examined birth weight and maternal smoking in a sample of 2930 twin pairs from the Netherlands Twin Register using structural equation modelling. Gestational age accounted for 27-44% of the variance in birth weight. A lower variability of birth weight and a lower association of birth weight with gestational age was found in twins whose mothers smoked during pregnancy. The variance not associated with gestational age was independent of maternal smoking during pregnancy. A systematic smaller part of the variability in birth weight was associated with variability in gestational age in second born twins compared to first born twins. The heritability of interindividual differences in birth weight was modest (10% for twins with non-smoking mothers and 11% for twins with smoking mothers). Common environmental influences other than gestational age accounted for a slightly larger part of the variance not associated with gestational age (17-20%).     

Preventing thromboembolism after myocardial infarction: effect of low-dose heparin or smoking.

A trial of low-dose subcutaneous heparin to prevent thromboembolic complications after myocardial infarction was carried out in 78 patients. Of the 37 heparin-treated patients only two (5%) developed evidence of leg vein thrombosis, while 14 (34%) of the 41 controls did so, and five controls developed pulmonary emboli. Leg vein thrombosis developed in 12 (50%) of the 24 controls who did not smoke cigarettes but in only two (13%) of the 17 controls who were cigarette smokers. Non-smokers who have a myocardial infarction should be given low-dose heparin subcutaneously to prevent leg vein thrombosis and pulmonary embolism.     

Functional-anatomic correlates of individual differences in memory

Memory abilities differ greatly across individuals. To explore a source of these differences, we characterized the varied strategies people adopt during unconstrained encoding. Participants intentionally encoded object pairs during functional MRI. Principal components analysis applied to a strategy questionnaire revealed that participants variably used four main strategies to aid learning. Individuals' use of verbal elaboration and visual inspection strategies independently correlated with their memory performance. Verbal elaboration correlated with activity in a network of regions that included prefrontal regions associated with controlled verbal processing, while visual inspection correlated with activity in a network of regions that included an extrastriate region associated with object processing. Activity in regions associated with use of these strategies was also correlated with memory performance. This study reveals functional-anatomic correlates of verbal and perceptual strategies that are variably used by individuals during encoding. These strategies engage distinct brain regions and may separately influence memory performance.     

The bold and the shy: individual differences in rainbow trout

Boldness and shyness were investigated as 'personality' traits in hatchery-reared rainbow trout Oncorhynchus mykiss . Bold fish spent more time in an open area and were more active than shy fish and these behaviours could be used as indicators of boldness and shyness. These differences were related to learning ability in a simple conditioning task. Bold fish learned the task more quickly than shy fish.     

To boldly go: individual differences in boldness influence migratory tendency

Partial migration, whereby only a fraction of the population migrates, is thought to be the most common type of migration in the animal kingdom, and can have important ecological and evolutionary consequences. Despite this, the factors that influence which individuals migrate and which remain resident are poorly understood. Recent work has shown that consistent individual differences in personality traits in animals can be ecologically important, but field studies integrating personality traits with migratory behaviour are extremely rare. In this study, we investigate the influence of individual boldness, an important personality trait, upon the migratory propensity of roach, a freshwater fish, over two consecutive migration seasons. We assay and individually tag 460 roach and show that boldness influences migratory propensity, with bold individuals being more likely to migrate than shy fish. Our data suggest that an extremely widespread personality trait in animals can have significant ecological consequences via influencing individual-level migratory behaviour.     

Foraging costs in bumblebees: field conditions cause large individual differences

Summary: Here, we present results from two foraging studies with the bumblebee Bombus terrestris L. We used the doubly labelled water technique which makes it possible to estimate energetic costs of free flight in a natural environment. One study was carried out in windy weather in the open, the second in a large greenhouse under controlled conditions. Individual mass-specific metabolic rates from the open-air study varied widely (159.5 to 750.2 W kg^-1; n = 7) and differed significantly from expected values predicted from laboratory data. Results from the greenhouse study were closer to expectations and the range of individual metabolic rates was much narrower (405.0 to 485.5 W kg^-1; n = 8). The range of field metabolic rates was three to four times larger than that of laboratory studies (Heinrich, 1975; Ellington et al., 1990; Cooper, 1993), which might reflect the fact that only a relatively small percentage (25 - 30 %) of bees are 'co-operative' in laboratory flight cost measurements (Hanauer-Thieser and Nachtigall, 1995; C.P. Ellington and T.J. Wolf, pers. observations). However, all bees flew in the field studies, even in strong winds. We conclude that estimates of energetic costs of free flight using laboratory data (time/activity/laboratory = TAL), an approach regularly used in tests of foraging models, might not be appropriate under many natural conditions. Whereas the TAL method provided a good estimate of mean metabolic rate it is a poor method for studies in which individual variations are of interest.     

Investigating individual differences in brain abnormalities in autism

Autism is a psychiatric syndrome characterized by impairments in three domains: social interaction, communication, and restricted and repetitive behaviours and interests. Recent findings implicate the amygdala in the neurobiology of autism. In this paper, we report the results of a series of novel experimental investigations focusing on the structure and function of the amygdala in a group of children with autism. The first section attempts to determine if abnormality of the amygdala can be identified in an individual using magnetic resonance imaging in vivo. Using single-case voxel-based morphometric analyses, abnormality in the amygdala was detected in half the children with autism. Abnormalities in other regions were also found. In the second section, emotional modulation of the startle response was investigated in the group of autistic children. Surprisingly, there were no significant differences between the patterns of emotional modulation of the startle response in the autistic group compared with the controls.     

Psychoactive pollution suppresses individual differences in fish behaviour

Environmental contamination by pharmaceuticals is global, substantially altering crucial behaviours in animals and impacting on their reproduction and survival. A key question is whether the consequences of these pollutants extend beyond mean behavioural changes, restraining differences in behaviour between individuals. In a controlled, two-year, multigenerational experiment with independent mesocosm populations, we exposed guppies (Poecilia reticulata) to environmentally realistic levels of the ubiquitous pollutant fluoxetine (Prozac). Fish (unexposed: n = 59, low fluoxetine: n = 57, high fluoxetine: n = 58) were repeatedly assayed on four separate occasions for activity and risk-taking behaviour. Fluoxetine homogenized individuals'' activity, with individual variation in populations exposed to even low concentrations falling to less than half that in unexposed populations. To understand the proximate mechanism underlying these changes, we tested the relative contribution of variation within and between individuals to the overall decline in individual variation. We found strong evidence that fluoxetine erodes variation in activity between but not within individuals, revealing the hidden consequences of a ubiquitous contaminant on phenotypic variation in fish—likely to impair adaptive potential to environmental change.     

The importance of individual differences in grapheme-color synesthesia

In this issue of Neuron, Hubbard et al. show individual differences in how grapheme-color synesthetes perform on cognitive tasks. Importantly, these behavioral differences were correlated with fMRI measures. Such individual differences have important ramifications for synesthesia research. If individual differences are ignored, then synesthesia research will be characterized by erroneous conclusions and failures to replicate.