Broods of attractive three-spined stickleback males require greater paternal care

The relationship between egg number and survival in nests of three-spined sticklebacks Gasterosteus aculeatus was tested in the field. Nests were deprived of paternal care during a variable period by removal of the father while preventing egg predation by protection of the nest by a net. Upon male removal, a number of male traits were quantified. Nest-content variables and embryo survival were assessed at the end of the deprivation period. Proportional egg mortality was significantly positively correlated with the length of the deprivation period, the number of eggs present in the nest and egg size, thus suggesting that nests with more and larger eggs need more paternal care. Males with the most symmetrical ventral spines achieved the highest reproductive success as measured by the number of eggs in the nest. In addition, their nests contained relatively larger eggs. Spine length symmetry correlated with the blue intensity of the eye thus giving females several cues to assess male quality.     

Helicobacter pylori infection and colorectal cancer risk: a meta-analysis

BACKGROUND: Several studies suggested an association between Helicobacter pylori infection and colorectal carcinoma or adenoma risk. However, different authors reported quite varying estimates. We carried out a systematic review and meta-analysis of published studies investigating this association and paid special attention to the possibility of publication bias and sources of heterogeneity between studies. Materials and METHODS: An extensive literature search and cross-referencing were performed to identify all published studies. Summary estimates were obtained using random-effects models. The presence of possible publication bias was assessed using different statistical approaches. RESULTS: In a meta-analysis of the 11 identified human studies, published between 1991 and 2002, a summary odds ratio of 1.4 (95% CI, 1.1-1.8) was estimated for the association between H. pylori infection and colorectal cancer risk. The graphical funnel plot appeared asymmetrical, but the formal statistical evaluations did not provide strong evidence of publication bias. The proportion of variation of study results because of heterogeneity was small (36.5%). CONCLUSIONS: The results of our meta-analysis are consistent with a possible small increase in risk of colorectal cancer because of H. pylori infection. However, the possibility of some publication bias cannot be ruled out, although it could not be statistically confirmed. Larger, better designed and better controlled studies are needed to clarify the situation.     

The relative importance of size and asymmetry in sexual selection

Developmental stability reflects the ability of individualsto cope with their environment during ontogeny given their geneticbackground. An inability to cope with environmental and geneticperturbations is reflected in elevated levels of fluctuatingasymmetry and other measures of developmental instability. Bothtrait size and symmetry have been implicated as playing an importantrole in sexual selection, although their relative importancehas never been assessed. We collected information on the relationshipbetween success in sexual competition and size and asymmetry,respectively, to assess the relative importance of these twofactors in sexual selection. Studies that allowed comparisonof the relationships for the same traits' size and symmetryand success in sexual competition constituted the data, whichtotaled 73 samples from 33 studies of 29 species. The averagesample-size weighted correlation coefficients between matingsuccess or attractiveness and size and asymmetry, respectively,were used as measures of effect size in a meta-anatysis. Analysiswas conducted on samples, studies, and species separately. Wefound evidence of an overall larger effect of symmetry at thespecies level of analysis, but similar effects at the sampleor study levels. The difference in effect size for charactersize and character symmetry was larger for secondary sexualcharacters than for ordinary morphological characters at thelevel of analysis of samples. The results lend support to theconclusion that symmetry plays an important general role insexual selection, especially symmetry of secondary sexual characters.     

Asymmetry as a predictor of growth, fecundity and survival

Measures of developmental stability such as fluctuating asymmetry have been assumed to predict individual performance because asymmetry reflects an inability to cope with stressful situations, and because asymmetry hampers locomotion. However, the magnitude of this relationship between important fitness components (growth, fecundity, survival) and asymmetry has never been assessed. Based on a literature survey, estimates of the correlation between asymmetry and the three fitness components are presented. Pearson's correlation coefficients weighted for sample size between asymmetry and growth, fecundity, and survival, respectively, were –0.15, –0.35, and –0.25, respectively, with all three coefficients being highly significant. All three relationships were extremely robust given very large fail-safe numbers. The results were independent of whether studies or species were used as units of analysis. Hence asymmetry is a robust predictor of performance in fitness domains such as growth, fecundity, and survival, although only accounting for 2.1%, 12.3%, and 6.0% of the variance. This may be of importance for studies of sexual selection, but also for ecological and conservation biological studies, where the performance of individuals or groups of individuals are assessed.     

Size and asymmetry: are there costs to winning the royalty race?

Body size and morphology are key fitness-determining traits that can vary genotypically. They are likely to be important in social insect queens, which mate in swarms and found colonies independently, but genetic influences on queen morphology have been little investigated. Here, we show that the body size and morphology of queens are influenced by their genotype in the leaf-cutting ant Acromyrmex echinatior, a species in which certain lineages (patrilines) bias their development towards reproductive queens rather than sterile workers. We found no relationship between the queen-worker skew of patrilines and the size or morphology of queens, but there was a significant relationship with fluctuating asymmetry, which was greater in more queen-biased patrilines. Our results suggest that queen-biased patrilines do not incur a fitness cost in terms of body size, but may face more subtle costs in developmental stability. Such costs may constrain the evolution of royal cheating in social insects.     

Unbiased estimation of individual asymmetry

The importance of measurement error (ME) for the estimation of population level fluctuating asymmetry (FA) has long been recognized. At the individual level, however, this aspect has been studied in less detail. Recently, it has been shown that the random slopes of a mixed regression model can estimate individual asymmetry levels that are unbiased with respect to ME. Yet, recent studies have shown that such estimates may fail to reflect heterogeneity in these effects. In this note I show that this is not the case for the estimation of individual asymmetry. The random slopes adequately reflect between‐individual heterogeneity in the underlying developmental instability. Increased levels of ME resulted in, on average, lower estimates of individual asymmetry relative to the traditional unsigned asymmetry. This well‐known shrinkage effect in Bayesian analysis adequately corrected for ME and heterogeneity in ME resulting in unbiased estimates of individual asymmetry that were more closely correlated with the true underlying asymmetry.