Although a small set of external factors account for much of the spatial variation in plant and animal diversity, the search continues for general drivers of variation in parasite species richness among host species. Qualitative reviews of existing evidence suggest idiosyncrasies and inconsistent predictive power for all proposed determinants of parasite richness. Here, we provide the first quantitative synthesis of the evidence using a meta-analysis of 62 original studies testing the relationship between parasite richness across animal, plant and fungal hosts, and each of its four most widely used presumed predictors: host body size, host geographical range size, host population density, and latitude. We uncover three universal predictors of parasite richness across host species, namely host body size, geographical range size and population density, applicable regardless of the taxa considered and independently of most aspects of study design. A proper match in the primary studies between the focal predictor and both the spatial scale of study and the level at which parasite species richness was quantified (i.e. within host populations or tallied across a host species' entire range) also affected the magnitude of effect sizes. By contrast, except for a couple of indicative trends in subsets of the full dataset, there was no strong evidence for an effect of latitude on parasite species richness; where found, this effect ran counter to the general latitude gradient in diversity, with parasite species richness tending to be higher further from the equator. Finally, the meta-analysis also revealed a negative relationship between the magnitude of effect sizes and the year of publication of original studies (i.e. a time-lag bias). This temporal bias may be due to the increasing use of phylogenetic correction in comparative analyses of parasite richness over time, as this correction yields more conservative effect sizes. Overall, these findings point to common underlying processes of parasite diversification fundamentally different from those controlling the diversity of free-living organisms.

Meta-analysis is the gold standard for synthesis in ecology and evolution. Together with estimating overall effect magnitudes, meta-analyses estimate differences between effect sizes via heterogeneity statistics. It is widely hypothesized that heterogeneity will be present in ecological/evolutionary meta-analyses due to the system-specific nature of biological phenomena. Despite driving recommended best practices, the generality of heterogeneity in ecological data has never been systematically reviewed. We reviewed 700 studies, finding 325 that used formal meta-analysis, of which total heterogeneity was reported in fewer than 40%. We used second-order meta-analysis to collate heterogeneity statistics from 86 studies. Our analysis revealed that the median and mean heterogeneity, expressed as I , are 84.67% and 91.69%, respectively. These estimates are well above "high" heterogeneity (i.e., 75%), based on widely adopted benchmarks. We encourage reporting heterogeneity in the forms of I and the estimated variance components (e.g., τ ) as standard practice. These statistics provide vital insights in to the degree to which effect sizes vary, and provide the statistical support for the exploration of predictors of effect-size magnitude. Along with standard meta-regression techniques that fit moderator variables, multi-level models now allow partitioning of heterogeneity among correlated (e.g., phylogenetic) structures that exist within data.

Sexual selection hypotheses stipulate that the major histocompatibility complex genes (MHC) constitute a key molecular underpinning for mate choice in vertebrates. The last four decades saw growing empirical literature on the role of MHC diversity and dissimilarity in mate choice for a wide range of vertebrate animals, but with mixed support for its significance in natural populations. Using formal phylogenetic metaanalysis and meta-regression techniques, we quantitatively review the existing literature on MHC-dependent mating preferences in nonhuman vertebrates with a focus on the role of MHC diversity and dissimilarity. Overall, we found small, statistically nonsignificant, average effect sizes for both diversity-and dissimilarity-based mate choice (r = 0.113 and 0.064, respectively). Importantly, however, meta-regression models revealed statistically significant support regarding female choice for diversity, and choice for dissimilarity (regardless of choosy sex) only when dissimilarity is characterized across multiple loci. Little difference was found among vertebrate taxa; however, the lack of statistical power meant statistically significant effects were limited to some taxa. We found little sign of publication bias; thus, our results are likely to be robust. In light of our quantitative assessment, methodological improvements and fruitful future avenues of research are highlighted.

Statistical correlations of biodiversity patterns across multiple trophic levels have received considerable attention in various types of interacting assemblages, forging a universal understanding of patterns and processes in free-living communities. Host-parasite interactions present an ideal model system for studying congruence of species richness among taxa as obligate parasites are strongly dependent upon the availability of their hosts for survival and reproduction while also having a tight coevolutionary relationship with their hosts. The present meta-analysis examined 38 case studies on the relationship between species richness of hosts and parasites, and is the first attempt to provide insights into the patterns and causal mechanisms of parasite biodiversity at the community level using meta-regression models. We tested the distinct role of resource (i.e. host) availability and evolutionary co-variation on the association between biodiversity of hosts and parasites, while spatial scale of studies was expected to influence the extent of this association. Our results demonstrate that species richness of parasites is tightly correlated with that of their hosts with a strong average effect size (r  0.55) through both host availability and evolutionary co-variation. However, we found no effect of the spatial scale of studies, nor of any of the other predictor variables considered, on the correlation. Our findings highlight the tight ecological and evolutionary association between host and parasite species richness and reinforce the fact that host-parasite interactions provide an ideal system to explore congruence of biodiversity patterns across multiple trophic levels.

It is suggested that a wide variety of oxidation reactions at platinum anodes in aqueous media involve mediation of the interfacial reaction by charged hydrous oxide species formed as surface-bonded species at adatom sites on the metal surface. Such species are formed on Pt at potentials as low as 0.2V (RHE) in acid media and, with precautions taken to minimize deactivation problems, many reactive organic compounds commence oxidation in this region. This cyclic redox mechanism of reaction is complicated in the case of metals, though not with thermal oxides (RuO2), by significant variation in the total number of active species at the interface. Recent spectroscopic data support the view that Pt(IV) species are present on Pt/Ru alloys at low potentials. The species formed on pure Pt in acid above 0.2V is assumed to be Pt(OH)62--9 based species; the OH ligands not only accelerate many oxidation processes but inhibit certain reduction processes at the