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Aim: The emergence of large‐scale patterns of animal body size is the central expectation of a wide range of (macro)ecological and evolutionary hypotheses. The drivers shaping these patterns include climate (e.g. Bergmann's rule), resource availability (e.g. 'resource rule'), biogeographic settings and niche partitioning (e.g. adaptive radiation). However, these hypotheses often make opposing predictions about the trajectories of body size evolution. Therefore, whether underlying drivers of body size evolution can be identified remains an open question. Here, we employ the most comprehensive global dataset of body size in amphibians, to address multiple hypotheses that predict patterns of body size evolution based on climatic factors, ecology and biogeographic settings to identify underlying drivers and their generality across lineages. Location: Global. Time Period: Present. Major Taxa Studied: Amphibians. Methods: Using a global dataset spanning 7270 (>87% of) species of Anura, Caudata and Gymnophiona, we employed phylogenetic Bayesian modelling to test the roles of climate, resource availability, insularity, elevation, habitat use and diel activity on body size. Results: Only climate and elevation drive body size patterns, and these processes are order‐specific. Seasonality in precipitation and in temperature predict body size clines in anurans, whereas caecilian body size increases with aridity. However, neither of these drivers explained variation in salamander body size. In both anurans and caecilians, size increases with elevational range and with midpoint elevation in caecilians only. No effects of mean temperature, resource abundance, insularity, time of activity or habitat use were found. Main Conclusions: Precipitation and temperature seasonality are the dominant climatic drivers of body size variation in amphibians overall. Bergmann's rule is consistently rejected, and so are other alternative hypotheses. We suggest that the rationale sustaining existing macroecological rules of body size is unrealistic in amphibians and discuss our findings in the context of the emerging hypothesis that climate change can drive body size shifts. [ABSTRACT FROM AUTHOR]

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: The diversity of brood size across animal species exceeds the diversity of most other life‐history traits. In some environments, reproductive success increases with brood size, whereas in others it increases with smaller broods. The dominant hypothesis explaining such diversity predicts that selection on brood size varies along climatic gradients, creating latitudinal fecundity patterns. Another hypothesis predicts that diversity in fecundity arises among species adapted to different microhabitats within assemblages. A more recent hypothesis concerned with the consequences of these evolutionary processes in the era of anthropogenic environmental change predicts that low‐fecundity species might fail to recover from demographic collapses caused by rapid environmental alterations, making them more susceptible to extinctions. These hypotheses have been addressed predominantly in endotherms and only rarely in other taxa. Here, we address all three hypotheses in amphibians globally. Location: Global. Time period: Present. Major taxa studied: Class Amphibia. Methods: Using a dataset spanning 2,045 species from all three amphibian orders, we adopt multiple phylogenetic approaches to investigate the association between brood size and climatic, ecological and phenotypic predictors, and according to species conservation status. Results: Brood size increases with latitude. This tendency is much stronger in frogs, where temperature seasonality is the dominant driver, whereas salamander fecundity increases towards regions with more constant rainfall. These relationships vary across continents but confirm seasonality as the key driver of fecundity. Ecologically, nesting sites predict brood size in frogs, but not in salamanders. Finally, we show that extinction risk increases consistently with decreasing fecundity across amphibians, whereas body size is a "by‐product" correlate of extinction, given its relationship with fecundity. Main conclusions: Climatic seasonality and microhabitats are primary drivers of fecundity evolution. Our finding that low fecundity increases extinction risk reinforces the need to refocus extinction hypotheses based on a suggested role for body size. [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]

Background: Adaptive radiation theory posits that ecological opportunity promotes rapid proliferation of phylogenetic and ecological diversity. Given that adaptive radiation proceeds via occupation of available niche space in newly accessed ecological zones, theory predicts that: (i) evolutionary diversification follows an 'early-burst' process, i.e., it accelerates early in the history of a clade (when available niche space facilitates speciation), and subsequently slows down as niche space becomes saturated by new species; and (ii) phylogenetic branching is accompanied by diversification of ecologically relevant phenotypic traits among newly evolving species. Here, we employ macroevolutionary phylogenetic model-selection analyses to address these two predictions about evolutionary diversification using one of the most exceptionally species-rich and ecologically diverse lineages of living vertebrates, the South American lizard genus Liolaemus. Results: Our phylogenetic analyses lend support to a density-dependent lineage diversification model. However, the lineage through-time diversification curve does not provide strong support for an early burst. In contrast, the evolution of phenotypic (body size) relative disparity is high, significantly different from a Brownian model during approximately the last 5 million years of Liolaemus evolution. Model-fitting analyses also reject the 'early-burst' model of phenotypic evolution, and instead favour stabilizing selection (Ornstein-Uhlenbeck, with three peaks identified) as the best model for body size diversification. Finally, diversification rates tend to increase with smaller body size. Conclusions: Liolaemus have diversified under a density-dependent process with slightly pronounced apparent episodic pulses of lineage accumulation, which are compatible with the expected episodic ecological opportunity created by gradual uplifts of the Andes over the last ~25My. We argue that ecological opportunity can be strong and a crucial driver of adaptive radiations in continents, but may emerge less frequently (compared to islands) when major events (e.g., climatic, geographic) significantly modify environments. In contrast, body size diversification conforms to an Ornstein-Uhlenbeck model with multiple trait optima. Despite this asymmetric diversification between both lineages and phenotype, links are expected to exist between the two processes, as shown by our trait-dependent analyses of diversification. We finally suggest that the definition of adaptive radiation should not be conditioned by the existence of early-bursts of diversification, and should instead be generalized to lineages in which species and ecological diversity have evolved from a single ancestor. [ABSTRACT FROM AUTHOR]