Quantifying phenotypic evolutionary rates and their variation across phylogenetic trees is a major issue in evolutionary biology. A number of phylogenetic comparative methods (PCMs) currently perform such task. However, available PCMs can locate rate shifts pertaining to entire portions of the phylogeny, but not those expected to occur at the level of individual species and lineages, such as with the idea that body size changes more rapidly in insular vertebrates. Still, most PCMs cannot deal with fossil phylogenies, albeit fossils provide highly desirable information when it comes to understand trait variation and evolution. We developed a PCM based on phylogenetic ridge regression, which we named RRphylo, which assigns an evolutionary rate to each branch of the phylogeny, and is designed to locate rate shifts relating to entire clades, as well as to unrelated tree tips. We tested RRphylo on simulated trees and data to assess its performance under different conditions. Then, we repeated its application with two real case scenarios, the evolution of flight in ornithodirans and mammals and body size evolution in insular mammals, which are usually subsumed to evolve under different range regimes than terrestrial and continental species respectively. RRphylo performs well across all different conditions. The simulation experiments demonstrated it has low Type I and Type II error rate. We found significant evidence that flight accelerates the rate of body size evolution in vertebrates, and that the acquisition of very large body size slows down the rate. Still, insular mammals body size evolution is not faster than in continental species. RRphylo is a new PCM ideal to estimate variation and shift in the rate of phenotypic evolution with fossil data. In addition to testing evolutionary rate variation, it is open to a variety of further questions, such as the evolution of rates in time, the estimation of ancestral states and the estimation of phenotypic trends over time.

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BackgroundMany small vertebrates on islands grow larger, mature later, lay smaller clutches/litters, and are less sexually dimorphic and aggressive than their mainland relatives. This set of observations is referred to as the 'Island Syndrome'. The syndrome is linked to high population density on islands. We predicted that when population density is low and/or fluctuating insular vertebrates may evolve correlated trait shifts running opposite to the Island Syndrome, which we collectively refer to as the 'reversed island syndrome' (RIS) hypothesis. On the proximate level, we hypothesized that RIS is caused by increased activity levels in melanocortin receptors. Melanocortins are postranslational products of the proopiomelanocortin gene, which controls pleiotropically pigmentation, aggressiveness, sexual activity, and food intake in vertebrates.ResultsWe tested the RIS hypothesis performing a number of behavioral, genetic, and ontogenetic tests on a blue colored insular variant of the Italian Wall lizard Podarcis sicula, living on a small island off the Southern Italian coast. The population density of this blue-colored variant was generally low and highly fluctuating from one year to the next.In keeping with our predictions, insular lizards were more aggressive and sexually dimorphic than their mainland relatives. Insular males had wide, peramorphic heads. The growth rate of insular females was slower than growth rates of mainland individuals of both sexes, and of insular males. Consequently, size and shape dimorphism are higher on the Island. As predicted, melanocortin receptors were much more active in individuals of the insular population. Insular lizards have a higher food intake rate than mainland individuals, which is consistent with the increased activity of melanocortin receptors. This may be adaptive in an unpredictable environment such as Licosa Island. Insular lizards of both sexes spent less time basking than their mainland relatives. We suspect this is a by-product (spandrel) of the positive selection for increased activity of melanocortins receptors.ConclusionsWe contend that when population density is either low or fluctuating annually as a result of environmental unpredictability, it may be advantageous to individuals to behave more aggressively, to raise their rate of food intake, and allocate more energy into reproduction.

Aim Islands are thought to promote correlated ecological and life‐history shifts in species, including increased population density, and an infrequent production of few, large, offspring. These patterns are collectively termed ‘the island syndrome’. We present here the first, phylogenetically informed, global test of the ‘island syndrome’ hypothesis, using lizards as our model organisms. Location World‐wide. Methods We assembled a database containing 641 lizard species, their phylogenetic relationships, geographic ranges and the following life‐history traits: female mass, clutch size, brood frequency, hatchling body mass and population density. We tested for life‐history differences between insular and mainland forms in light of the island syndrome, controlling for mass and latitude, and for phylogenetic non‐independence. We also examined the effects of population density and, in insular endemics, of island area, on lizard reproductive traits. Results We found that insular endemic lizards lay smaller clutches of larger hatchlings than closely related mainland lizards of similar size, as was expected by the island syndrome. In general, however, insular endemics lay more frequently than mainland ones. Species endemic to small islands lay as frequently as mainland species. Continental and insular lizards have similar productivity rates overall. Island area had little effect on lizard reproductive traits. No trait showed association with population density. Main conclusions Island endemic lizards mainly follow the island syndrome. We hypothesize that large offspring are favoured on islands because of increased intra‐specific aggression and cannibalism by adults. Stable populations on islands lacking predators may likewise lead to increased intra‐specific competition, and hence select for larger hatchlings that will quickly grow to adult size. This view is supported by the fact that lizard populations are denser on islands – although population density per se was uncorrelated with any of the traits we examined.

Aim A major Late Quaternary vertebrate extinction event affected mostly large‐bodied ‘megafauna’. This is well documented in both mammals and birds, but evidence of a similar trend in reptiles is scant. We assess the relationship between body size and Late Quaternary extinction in reptiles at the global level. Location Global. Methods We compile a body size database for all 82 reptile species that are known to have gone extinct during the last 50,000 years and compare them with the sizes of 10,090 extant reptile species (97% of known extant diversity). We assess the body size distributions in the major reptile groups: crocodiles, lizards, snakes and turtles, while testing and correcting for a size bias in the fossil record. We examine geographical biases in extinction by contrasting mainland and insular reptile assemblages, and testing for biases within regions and then globally by using geographically weighted models. Results Extinct reptiles were larger than extant ones, but there was considerable variation in extinction size biases among groups. Extinct lizards and turtles were large, extinct crocodiles were small and there was no trend in snakes. Lizard lineages vary in the way their extinction is related to size. Extinctions were particularly prevalent on islands, with 73 of the 82 extinct species being island endemics. Four others occurred in Australia. The fossil record is biased towards large‐bodied reptiles, but extinct lizards were larger than extant ones even after we account for this. Main conclusions Body size played a complex role in the extinction of Late Quaternary reptiles. Larger lizard and turtle species were clearly more affected by extinction mechanisms such as over exploitation and invasive species, resulting in a prevalence of large‐bodied species among extinct taxa. Insularity was by far the strongest correlate of recent reptile extinctions, suggesting that size‐biased extinction mechanisms are amplified in insular environments.