Multiple testing for SNP-SNP interactions

Most genetic diseases are complex, i.e. associated to combinations of SNPs rather than individual SNPs. In the last few years, this topic has often been addressed in terms of SNP-SNP interaction patterns given as expressions linked by logical operators. Methods for multiple testing in high-dimensional settings can be applied when many SNPs are considered simultaneously. However, another less well-known multiple testing problem arises within a fixed subset of SNPs when the logic expression is chosen optimally. In this article, we propose a general asymptotic approach for deriving the distribution of the maximally selected chi-square statistic in various situations. We show how this result can be used for testing logic expressions - in particular SNP-SNP interaction patterns - while controlling for multiple comparisons. Simulations show that our method provides multiple testing adjustment when the logic expression is chosen such as to maximize the statistic. Its benefit is demonstrated through an application to a real dataset from a large population-based study considering allergy and asthma in KORA. An implementation of our method is available from the Comprehensive R Archive Network (CRAN) as R package 'SNPmaxsel'

Visual adaptation to thin and fat bodies transfers across identity

Visual perception is highly variable and can be influenced by the surrounding world. Previous research has revealed that body perception can be biased due to adaptation to thin or fat body shapes. The aim of the present study was to show that adaptation to certain body shapes and the resulting perceptual biases transfer across different identities of adaptation and test stimuli. We designed two similar adaptation experiments in which healthy female participants adapted to pictures of either thin or fat bodies and subsequently compared more or less distorted pictures of their own body to their actual body shape. In the first experiment (n = 16) the same identity was used as adaptation and test stimuli (i.e. pictures of the participant’s own body) while in the second experiment (n = 16) we used pictures of unfamiliar thin or fat bodies as adaptation stimuli. We found comparable adaptation effects in both experiments: After adaptation to a thin body, participants rated a thinner than actual body picture to be the most realistic and vice versa. We therefore assume that adaptation to certain body shapes transfers across different identities. These results raise the questions of whether some type of natural adaptation occurs in everyday life. Natural and predominant exposure to certain bodily features like body shape – especially the thin ideal in Western societies – could bias perception for these features. In this regard, further research might shed light on aspects of body dissatisfaction and the development of body image disturbances in terms of eating disorders

Begging, food provisioning, and nestling competition in great tit broods infested with ectoparasites

Ectoparasites are a ubiquitous environmental component of breeding birds, and it has repeatedly been shown that hematoph-agous ectoparasites such as fleas and mites reduce the quality and number of offspring of bird hosts, thereby lowering the value of a current brood. Selection acting on the hosts will favor physiological and behavioral responses that will reduce the parasites' impact. However, the results of the few bird studies that addressed the question of whether parasitism leads to a higher rate of food provisioning are equivocal, and the begging response to infestation has rarely been quantified. A change in begging activity and parental rate of food provisioning could be predicted in either direction: parents could reduce their investment in the brood in order to invest more in future broods, or they could increase their investment in order to compensate for the parasites' effect on the current brood. Since the nestlings are weakened by the ectoparasites they may beg less, but on the other hand they may beg more in order to obtain more food. In this study we show experimentally that (1) hen fleas (Ceratophyllus gallinae) reduce the body mass and size of great tit (Parus major) nestlings, (2) nestlings of parasitized broods more than double their begging rate, (3) the male parents increase the frequency of feeding trips by over 50%, (4) the females do not adjust feeding rate to the lowered nutritional state of nestlings, and (5) food competition among siblings of parasitized broods is increased. Ultimately the difference in the parental feeding response may be understood as the result of a sex-related difference in the trade-off of i0vesting in current versus future brood

Effect of an ectoparasite on lay date, nest-site choice, desertion, and hatching success in the great tit (Pants major)

Ectoparasites are common in most bird species, but experimental evidence of their effects on life-history traits is scarce. We investigated experimentally the effects of the hematophagous hen flea (Ceratophyllus gallinae) on timing of reproduction, nest-site choice, nest desertion, clutch size, and hatching success in the great tit (Parus major). When great tits were offered a choice on their territory between an infested and a parasite-free nest-box, they chose the one without parasites. When there was no choice, the great tits in a territory containing an infested nest-box delayed laying the clutch by 11 days as compared with the birds that were offered a parasite-free nesting opportunity. The finding that there was no difference in phenotypic traits related to dominance between the birds nesting in infested boxes and birds nesting in parasite-free boxes suggests that the delay is not imposed by social dominance. Nest desertion between laying and shortly after hatching was significandy higher in infested nests. There was no difference between infested and parasite-free nests in clutch size, but hatching success and hence brood size at hatching were significantly smaller in infested nests. Nest-box studies of great tits have been seminal in the development of evolutionary, ecological, and behavioral theory, but recently a polemic has arisen in the literature about the validity of the conclusions drawn from nest-box studies where the naturally occurring, detrimental ectoparasites are eliminated by the routine removal of old nests between breeding seasons. Our study suggests that this criticism is valid and that the evaluation of the effects of ectoparasites may improve our understanding of behavioral traits, life-history traits, or population dynamic

Clutch size and malarial parasites in female great tits

life-history models predict an evolutionary trade-off in the allocation of resources to current versus future reproduction. This corresponds, at the physiological level, to a trade-off in the allocation of resources to current reproduction or to the immune system, which will enhance survival and therefore future reproduction. For clutch size, life-history models predict a positive correlation between current investment in eggs and the subsequent parasite load. In a population of great tits, we analyzed the correlation between natural clutch size of females and the subsequent prevalence of Plasmodium spp., a potentially harmful blood parasite. Females that showed, 14 days after hatching of the nestlings, an infection with Plasmodium had a significantly larger clutch (9.3 eggs ± 0.5 SE, n = 18) than uninfected females (8.0 eggs ± 0.2 SE, n = 80), as predicted by the allocation trade-off. Clutch size was positively correlated with the prevalence of Plasmodium, but brood size 14 days after hatching was not. This suggests that females incur higher costs during laying the clutch than during rearing nestlings. Infection status of some females changed between years, and these changes were significantly correlated with a change in clutch size as predicted by the trade-off. The link between reproductive effort and parasitism may represent a possible mechanism by which the cost of egg production is mediated into future survival and may thereby be an important selective force in the shaping of clutch siz

Nestling begging intensity and parental effort in relation to prelaying carotenoid availability

Carotenoids are antioxidants playing major roles in physiological functions at various stages of an animal's life. Female birds deposit large amounts of carotenoids into their eggs. Carotenoids are, however, a limiting resource, and females are expected to balance carotenoid deposition into the eggs with their utilization for themselves. Carotenoid availability is thus likely to determine both the levels of yolk carotenoids and maternal care during rearing. Carotenoids have been shown to benefit the embryo and the growing nestling, and it can be hypothesized that an increase in carotenoid availability during laying leads to higher nestling condition and competitive ability. We manipulated carotenoid availability to great tit pairs prior to and during egg laying and later partially cross-fostered chicks at hatching. During the rearing period, we measured how carotenoid availability affected nestlings begging behavior and male and female feeding effort. We also manipulated the ectoparasite load, predicting that carotenoid supplementation would help adults and nestling to cope with parasites. Nestlings hatched from eggs laid by carotenoid-supplemented females and raised in small broods begged more intensely. Nestlings in small deparasitized broods also begged more actively. The feeding effort of control females increased with brood size, whereas the feeding effort of carotenoid-supplemented females was high whatever the brood size. Male feeding effort was unaffected by our treatment. Our results support the hypothesis that maternally derived carotenoids increase nestling begging behavior and hence competitive ability. They further suggest that carotenoid availability determines the level of parental investment and can mediate trade-offs between life-history trait