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Variation in genome size spans multiple orders of magnitude among animals. Despite the longstanding debate regarding the adaptive value or costs of genomic complexity, genome size has been proposed to influence extinction risk under the rapidly changing environments of the Anthropocene.The main hypothesis suggests that genome enlargement increases the accumulation of deleterious mutations while reducing rates of organismal growth and development. These combined effects of larger genome size are predicted to trigger population declines that can lead to extinction, especially under rapidly changing environments that disrupt demographic resilience.Comparative evidence from terrestrial plants and across vertebrates has provided mixed support for this hypothesis. However, large‐scale comparative studies based on explicit phylogenetic approaches remain lacking. Using a global‐scale amphibian dataset and two recognised proxies of extinction risk (International Union for Conservation of Nature IUCN conservation categories and population trends), we test the prediction that genomes are larger (as estimated by C‐value) in species facing extinction risk. We combine these analyses with life‐history traits widely known to be implicated with extinctions (body size, fecundity), along with a range of environmental factors.Our phylogenetic analyses consistently failed to identify an effect of genome size on either of the two proxies for extinction risk. The only consistent predictor of extinction risk observed across models performed for amphibians combined and for orders separately was decreasing geographical range size. We also identified a role for larger body size, decreasing range of environmental temperature (for anurans) and increasing levels of UV‐B radiation (for salamanders) as drivers of increasing threat.Our study provides no support for the prediction that species with larger genomes suffer heightened risk of extinction. We discuss some fundamental limitations underlying the genome size‐extinction hypothesis, and suggest that it is not a promising avenue to elucidate the causes of biodiversity declines in the Anthropocene. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Aim: Body size explains most of the variation in fitness within animal populations and is therefore under constant selection from ecological and reproductive pressures, which often promote its evolution in sex‐specific directions, leading to sexual size dimorphism (SSD). Several hypotheses have been proposed to explain the vast diversity of SSD across species. These hypotheses emphasize: (a) the mate competition benefits to larger male size (sexual selection); (b) the benefits of larger female size for fecundity (fecundity selection); (c) the simultaneous benefits of niche divergence for males and females to reduce intersexual competition for ecological resources (natural selection); and (d) the underlying impact of geographical variation in climatic pressures expected to shape large‐scale patterns of SSD in synergy with the above selection pressures (e.g., intensification of fecundity selection as breeding seasons shorten). Based on a new, global‐scale amphibian dataset, we address the shortage of large‐scale, integrative tests of these four hypotheses. Location: Global. Time period: Extant. Major taxa studied: Class Amphibia. Methods: Using a > 3,500 species dataset spanning body size, ecological, life‐history, geographical and climatic data, we performed phylogenetic linear models to address the sexual, fecundity, ecological and climatic hypotheses of SSD. Results: Evolution of SSD is discordant between anurans and salamanders. Anuran SSD is shaped by climate (male‐biased SSD increases with temperature seasonality) and by nesting site. In salamanders, SSD converges across species that occupy the same types of microhabitats ("ecodimorphs"), whereas reproductive or climatic pressures have no effects on their SSD. These contrasts are associated with latitudinal gradients of SSD in anurans, but not in salamanders. Main conclusions: Amphibian SSD is driven by ecological and climatic pressures, whereas no roles for sexual or fecundity selection were detected. We show that macroevolutionary processes determined by different forms of selection lead to latitudinal patterns of trait diversity, and the lack of them. [ABSTRACT FROM AUTHOR]