Mean body sizes of amphibian species are poorly predicted by climate

Aim Climate is thought to exert a strong influence on animal body sizes. We examined the relationship between amphibian body size and several climatic variables to discern which climatic variables, if any, affect amphibian size evolution. Location Europe and North America. Methods We assembled a dataset of mean sizes of 356 (out of 360) amphibian species in Europe, the USA and Canada, and tested how they are related to temperature, precipitation, primary productivity and seasonality. First, we examined the body size distributions of all the species inhabiting equal‐area grid cells (of 96.3 km × 96.3 km) using randomizations to account for the effects of species richness. Second, we examined the relationship between mean species body size and the environmental predictors across their ranges accounting for phylogenetic effects. Results The observed amphibian body size distributions were mostly statistically indistinguishable from distributions generated by random assignment of species to cells. Median sizes in grid cells were negatively correlated with temperature in anurans and positively in urodeles. The phylogenetic analysis revealed opposite trends in relation to temperature. In both clades most climatic variables were not associated with size and the few significant relationships were very weak. Main conclusions Spatial patterns in amphibian body size probably reflect diversity gradients, and relationships with climate could result from spurious effects of richness patterns. The large explanatory power of richness in the grid‐cell analysis, and the small explanatory power of climate in the interspecific analysis, signify that climate per se has little effect on amphibian body sizes

Elevation is a stronger predictor of morphological trait divergence than competition in a radiation of tropical lizards

1. Adaptations for efficient performance are expected to shape animal morphology based on selection for microhabitat use and ecological forces. The presence of competitor species is predicted to cause niches to contract and enhance trait divergence. Therefore, increased species richness is expected to lead to greater trait divergence, and to result in reduced overlap and similarity between morphologies of sympatric species. 2. We examined patterns of morphospace occupancy and partitioning in the skink fauna of New Guinea, the world's largest tropical island. Because skink species richness is largely decoupled from elevation in New Guinea, we could examine the effects of both factors (as proxies for competition and abiotic conditions), on morphospace occupancy and partitioning. 3. We measured 1,860 specimens from 79 species of skinks throughout Papua New Guinea, and examined their morphospace occupancy in a spatial context. We calculated, for each assemblage within equal‐area cells, the volume of morphospace occupied by all skinks, the mean volume occupied per species, and the mean distance and overlap between all species pairs. We then examined whether these metrics are related to species richness and elevation. 4. Elevation is a stronger predictor of morphospace occupancy than species richness. As elevation increases, intraspecific variation decreases and morphologies become more similar to each other such that overall morphospace occupancy decreases. Highland skinks are, on average, smaller, thinner and shorter limbed than lowland species. 5. We hypothesise that harsh climates in the New Guinea highland habitats impose strong selection on skinks to occupy specific areas of morphospace that facilitate efficient thermoregulation in suboptimal thermal conditions. We conclude that the effect of competition on trait divergence on a community and assemblage scale is eclipsed by abiotic selection pressures in these harsh environments

Body mass and geographic distribution determined the evolution of the wing flight-feather molt strategy in the Neornithes lineage

The evolutionary history of many organisms is characterized by major changes in morphology and distribution. Specifically, alterations of body mass and geographic distribution may profoundly influence organismal life-history traits. Here, we reconstructed the evolutionary history of flight-feather molt strategy using data from 1,808 Neornithes species. Our analysis suggests that the ancestral molt strategy of first-year birds was partial or entirely absent, and that complete wing flight-feather molt in first-year birds first evolved in the late Eocene and Oligocene (25–40 Ma), at least 30 Myr after birds first evolved. Complete flight-feather molt occurred mainly at equatorial latitudes and in relatively low body mass species, following a diversification of body mass within the lineage. We conclude that both body mass and geographic distribution shaped the evolution of molt strategies and propose that the evolutionary transition towards complete juvenile molt in the Neornithes is a novel, relatively late adaptation

Gecko diversity : a history of global discovery

1935 gecko species (and 224 subspecies) were known in December 2019 in seven families and 124 genera. These nearly 2000 species were described by ~950 individuals of whom more than 100 described more than 10 gecko species each. Most gecko species were discovered during the past 40 years. The primary type specimens of all currently recognized geckos (including subspecies) are distributed over 161 collections worldwide, with 20 collections having about two thirds of all primary types. The primary type specimens of about 40 gecko taxa have been lost or unknown. The phylogeny of geckos is well studied, with DNA sequences being available for ~76% of all geckos (compared to ~63% in other reptiles) and morphological characters now being collected in databases. Geographically, geckos occur on five continents and many islands but are most species-rich in Australasia (which also houses the greatest diversity of family-level taxa), Southeast Asia, Africa, Madagascar, and the West Indies. Among countries, Australia has the highest number of geckos (241 species), with India, Madagascar, and Malaysia being the only other countries with more than 100 described species each. As expected, when correcting for land area, countries outside the tropics have fewer geckos

Clutch size variability in an ostensibly fix-clutched lizard : effects of insularity on a Mediterranean gecko

The island syndrome describes the evolution of slow life history traits in insular environments. Animals are thought to evolve smaller clutches of larger offspring on islands in response to release from predation pressure and interspecific competition, and the resulting increases in population density and intraspecific competition. These forces become more pronounced with diminishing island size, and life histories are thus expected to become slowest on small, isolated islands. We measured clutch sizes in 12 insular populations of Mediodactylus kotschyi, a small gecko from the Cyclades Archipelago, a set of land-bridge islands in the Aegean Sea (Greece). We analyse variation in clutch size in relation to island area, island age, maternal body size, the presence of putative competitors and nesting seabirds (which increase resource abundance in the form of marine subsidies), and richness of predators. Clutch size of M. kotschyi decreases with increasing island area, in departure from classic island syndrome predictions, suggesting the evolution of faster life histories on smaller islands. There are no relationships between clutch size and island age, maternal size, the presence of competitors or predator richness. Instead, larger clutches on small islands could simply reflect the beneficial effect of marine subsidies derived from resident seabird colonies. Indeed, populations of M. kotschyi on islands with nesting seabirds have clutch sizes 30.9 % larger (1.82 vs. 1.39 eggs) than populations on islands without nesting seabirds. Thus, our data suggest that bottom-up effects of marine subsidies may supersede the expression of a simple island syndrome in the Aegean M. kotschyi

Inconsistent patterns of body size evolution in co-occurring island reptiles

Aim Animal body sizes are often remarkably variable across islands, but despite much research we still have a poor understanding of both the patterns and the drivers of body size evolution. Theory predicts that interspecific competition and predation pressures are relaxed on small, remote islands, and that these conditions promote body size evolution. We studied body size variation across multiple insular populations of 16 reptile species co‐occurring in the same archipelago and tested which island characteristics primarily drive body size evolution, the nature of the common patterns, and whether co‐occurring species respond in a similar manner to insular conditions. Location Aegean Sea islands. Time period 1984–2016. Major taxa studied Reptiles. Methods We combined fieldwork, museum measurements and a comprehensive literature survey to collect data on nearly 10,000 individuals, representing eight lizard and eight snake species across 273 islands. We also quantified a large array of predictors to assess directly the effects of island area, isolation (both spatial and temporal), predation and interspecific competition on body size evolution. We used linear models and meta‐analyses to determine which predictors are informative for all reptiles, for lizards and snakes separately, and for each species. Results Body size varies with different predictors across the species we studied, and patterns differ within families and between lizards and snakes. Each predictor influenced body size in at least one species, but no general trend was recovered. As a group, lizards are hardly affected by any of the predictors we tested, whereas snake size generally increases with area and with competitor and predator richness, and decreases with isolation. Main conclusions No factor emerges as a predominant driver of Aegean reptile sizes. This contradicts theories of general body size evolutionary trajectories on islands. We conclude that overarching generalizations oversimplify patterns and processes of reptile body size evolution on islands. Instead, species’ autecology and island particularities interact to drive the course of size evolution

Cryptic diversity and non-adaptive radiation of montane New Guinea skinks (Papuascincus; Scincidae)

New Guinea, the world’s largest and highest tropical island, has a rich but poorly known biota. Papuascincus is a genus of skinks endemic to New Guinea’s mountain regions, comprising two wide-ranging species and two species known only from their type series. The phylogeny of the genus has never been examined and the relationships among its species – as well as between it and closely related taxa – are hitherto unknown. We performed the first large-scale molecular-phylogenetic study of Papuascincus, including sampling across the genus' range in Papua New Guinea. We sequenced three mitochondrial and two nuclear markers from 65 specimens of Papuascincus and reconstructed their phylogenetic relationships. We also performed species-delimitation analyses, estimated divergence times and ancestral biogeography, and examined body-size evolution within the genus. Papuascincus was strongly supported as monophyletic. It began radiating during the mid-Miocene in the area now comprising the Central Cordillera of New Guinea, then dispersed eastward colonising the Papuan Peninsula. We found evidence of extensive cryptic diversity within the genus, with between nine and 20 supported genetic lineages. These were estimated using three methods of species delimitation and predominantly occur in allopatry. Distribution and body-size divergence patterns indicated that character displacement in size took place during the evolutionary history of Papuascincus. We conclude that the genus requires comprehensive taxonomic revision and likely represents a species-rich lineage of montane skinks

Evolution of diel activity patterns in skinks (Squamata: Scincidae), the world's second‐largest family of terrestrial vertebrates

Many animals have strict diel activity patterns, with unique adaptations for either diurnal or nocturnal activity. Diel activity is phylogenetically conserved, yet evolutionary shifts in diel activity occur and lead to important changes in an organism's morphology, physiology, and behavior. We use phylogenetic comparative methods to examine the evolutionary history of diel activity in skinks, one of the largest families of terrestrial vertebrates. We examine how diel patterns are associated with microhabitat, ambient temperatures, and morphology. We found support for a nondiurnal ancestral skink. Strict diurnality in crown group skinks only evolved during the Paleogene. Nocturnal habits are associated with fossorial activity, limb reduction and loss, and warm temperatures. Our results shed light on the evolution of diel activity patterns in a large radiation of terrestrial ectotherms and reveal how both intrinsic biotic and extrinsic abiotic factors can shape the evolution of animal activity patterns

A database of the morphology, ecology and literature of the world's limb‐reduced skinks

Aim Limb-reduced squamates are a convenient model system to investigate macroevolutionary trends in morphology. Here, we provide morphological, ecological and literature data on all known species of limb-reduced skinks (Scincidae) and their relatives, representing one of the most diverse and widely distributed groups of limb-reduced squamates. Location Global. Taxon Skinks (Reptilia, Squamata: Scincidae). Limb-reduced forms. Methods Morphological data were sourced from the primary literature, spanning a period of over 150 years. Linear body measurements were averaged across all values in the literature, preserving proportionality to body length. For digits and presacral vertebrae, we used maximum recorded counts. Ecological and biogeographical data were sourced from habitat assessments in the primary literature, online databases and field guides. Literature data were sorted according to type of study. To exemplify the applicability of the database, we used Markov-chain ordered models to estimate the evolutionary frequency of limb reduction and loss in skinks. Results We find evidence of limb reduction and loss in a total of 394 species worldwide, representing ~23% of all skink species, and ~30% of genera. The distribution of limb-reduced and limbless forms differs from that of fully limbed forms, as they are present in all biogeographic realms with the almost complete exclusion of the Americas. We estimate that limb reduction evolved more than 50 times in skinks, and that loss of at least one limb pair evolved at least 24 times. Main conclusions The dataset captures a broad spectrum of morphological and ecological variation in a large, globally distributed taxonomic group. It establishes a widely applicable definition of limb reduction based on limb proportions as a reference for future studies. Such an extensive collection of morphological and ecological data can pave the way for investigations of dramatic morphological transitions and their ecological drivers at a global and local scale

Macroecological and biogeographical patterns of limb reduction in the world's skinks

First published: 08 December 2022Aim: Limb reduction is a dramatic evolutionary transition, yet whether it is achieved in similar trajectories across clades, and its environmental drivers, remain unclear. We investigate the macroevolutionary and biogeographical patterns of limb reduction in skinks, where limb reduction occurred more often than in any other tetrapod clade, and test their associations with substrate categories using a global database. We test for habitat associations of body shapes in a group of Australian skinks using quantitative habitat data. Location: Global (Scincidae), Australia (Sphenomorphinae). Taxon: Skinks, Australian Sphenomorphinae. Materials and Methods: We use morphological data to explore the patterns of limb reduction in the world's skinks, investigating how body proportions differ across skink clades and subfamilies. We examine the relationships between body shape and substrate (coarsely classified). Further, we investigate the relationships between body shape and high-resolution soil and climate properties extracted from each species' distribution for Australian sphenomorphines. Results: Relationships between limb lengths and trunk elongation show idiosyncratic patterns across skink clades. Presacral vertebrae numbers positively correlate with trunk elongation in all taxa, except Glaphyromorphus. Skinks from sandy habitats show greater disparity between forelimb and hindlimb lengths than all other substrate categories. In sphenomorphines, shorter limbs and elongated trunks correlate with colder, more humid microhabitats and richer soils; high limb disparity correlates with hot, arid microhabitats and sandy, poor substrates. Main Conclusions: The evolutionary trajectories of limb reduction in skinks are cladespecific and sometimes unique. Selection for specific limb proportions and body sizes in limb-reduced forms changes across substrates. On poor, sandy substrates of arid environments, body shapes with longer hindlimbs may be more efficient for locomotion in a granular fluid (i.e. sand) and exploit the air–substrate interface than complete limblessness. On richer, more humid substrates, such morphology is rare, indicating that navigating cluttered substrates selects for more equal and shorter limb lengths.Marco Camaiti, Alistair R. Evans, Christy A. Hipsley, Mark N. Hutchinson, Shai Meiri, Rodolfo de Oliveira Anderson, Alex Slavenko, David G. Chappl