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Adaptive plasticity at switch points in complex life cycles (e.g., hatching, metamorphosis) is well known, but the evolutionary history of such plasticity is not. Particularly unclear is how a single plastic response (e.g., shifts in hatching timing) evolves to respond to different threats and cues (e.g., abiotic and biotic). We conducted a comparative phylogenetic study of hatching plasticity in a group of frogs with arboreal embryos to determine when risk-accelerated hatching evolved in the clade, whether responses to two common egg-stage risks (snake predation and flooding) evolved independently, and whether the overall capacity for hatching plasticity was evolutionarily more conservative than responses to specific cues. Red-eyed treefrogs (Agalychnis callidryas) hatch early to escape from several egg-stage risks but otherwise hatch later, improving larval survival with predators. We reconstructed a phylogeny for Agalychnis and related genera based on three mitochondrial and four nuclear genes. We quantified onset of hatching competence, spontaneous hatching timing, responses to egg-stage risks, and costs of premature hatching in Agalychnis and Pachymedusa. We also assessed hatching plasticity in a basal phyllomedusine, Cruziohyla calcarifer. The capacity to hatch ~30% before the spontaneous hatching age appears ancestral for phyllomedusines, with little change over ~34-50 million years among the species examined. A strong hatching response to flooding, with no mortality of hatching-competent eggs, is similarly ancient and conserved. Premature hatchlings of Agalychnis and Pachymedusa are more vulnerable to fish predation than are full-term hatchlings, indicating a conserved risk trade-off across hatching that would make plasticity advantageous. In contrast, the hatching response to snake attack has undergone major changes at least twice in the Agalychnis--Pachymedusa clade, with two species showing substantially lower escape success than the others. Responses to different threats have thus evolved independently. The capacity for switch point plasticity may be evolutionarily more stable than the response to individual stage-specific threats. Key words: Agalychnis; amphibian; antipredator behavior; embryo behavior; hypoxic stress; inducible defense; life-history switch point; ontogenetic niche shift; Pachymedusa; phenotypic plasticity; phylogeny; predation.

How is organismal biology changing in the era of genomics? Here, I discuss one example, the changes and trends in the systematics of reptiles and amphibians. The polymerase chain reaction, [...]

Herbivory has evolved in many groups of vertebrates, but it is rare among both extinct and extant nonavian reptiles. Among squamate reptiles, (lizards, snakes, and their relatives), 7,800 species are considered to be herbivorous, and herbivory is restricted to lizards. Here, we show that within a group of South American lizards (Liolaemidae, [approximately equal to]170 species), herbivory has evolved more frequently than in all other squamates combined and at a rate estimated to be >65 times faster. Furthermore, in contrast to other herbivorous lizards and to existing theory, most herbivorous liolaemids are small bodied and live in cool climates. Herbivory is generally thought to evolve only in reptile species that are large bodied, live in warm climates, and maintain high body temperatures. These three well known 'rules' of herbivory are considered to form the bases of physiological constraints that explain the paucity of herbivorous reptile species. We suggest that the recurrent and paradoxical evolution of herbivory in liolaemids is explained by a combination of environmental conditions (promoting independent origins of herbivory in isolated cool-climate regions), ecophysiological constraints (requiring small body size in cool climates, yet high body temperatures for herbivores), and phylogenetic history. More generally, our study demonstrates how integrating information from ecophysiology and phylogeny can help to explain macroevolutionary trends. ecophysiology | macroevolution

Research has been conducted on the morphological transformations in vertebrate evolution. The body form evolution in the lizard family Anguidae has been investigated and the use of the molecular phylogeny, morphological data and phylogenetic comparative methods in testing the hypothesis for the snakelike body form evolution is discussed.

The yarrow's spiny lizard, Sceloporus jarrovii, has been studied relative to molecular phylogenetics and evolution of sexual dichromatism among populations. In the interest of understanding evolution of geographic variation in sexually dimorphic traits and understanding the role that sexual selection plays or doesn't play in speciation a phylogenetic analysis of geographic variation in sexual dichromatism in the lizard was carried out. The findings suggest that sexual selection may lead to striking phenotypic divergence in conspecific populations and striking convergence.

Systematics and comparative biology and polymorphism therein are discussed. Polymorphisms often ignored by those who study macroevolution, systematists and comparative evolutionary biologists. Integrating within-species variation and microevolutionary processes into studies of systematics and comparative evolutionary biology represents an example of benefits of exchanging ideas in the population genetics and systematics fields.

The developmental investigations of the Xiphophorus caudal fin are differentiated by the researcher's concept and phylogenetic evaluation of the sword-like feature of the fish. A study attributing this trait evolution to the prejudiced unproved theory of sexual selection, which foretells that the emergence of the male distinguishing characteristic is spurred by growing female favoritism, is defied by a recent phylogenetic study that employed DNA sequencing.

The latitudinal patterns in speciation in a related but more diverse group of amphibians, the anurans were assessed to evaluate the frequency of speciation via niche conservatism versus niche divergence in relation to latitude. In contrast to salamanders, the frogs showed no tendency for greater niche divergence in the tropics or for greater niche conservatism in temperate regions and hence it could be concluded that climatic pattern does not lead to straightforward relationships between speciation, latitude, and niche evolution.

Several theoretical, as well as practical studies are conducted to determine the role of evolutionary diversification and dispersal in the community assembly of the Middle American treefrogs. The patterns of community structure observed in a region are shown to be highly affected by the elevation mechanism.

The parallel evolution of similar body-size morphs in three sympatric clades of plethodontid salamanders (Desmognathus, Plethodon, Spelerpinae) in eastern North America is documented. A comprehensive, time-calibrated phylogeny of North American plethodontids from nuclear and mitochondrial DNA sequences is used for showing that the three clades have undergone replicated patterns of evolution in body size and that this parallel diversification has occurred in broad-scale sympatry.

Several parallel analyses are conducted to explain the evolutionary, as well as the biogeographic origins of the high tropical diversity found in the species-rich group of Old World frogs (Ranidae). The diversification rates of these frogs are shown to be similar in different environments.

A comparative phylogenetic approach is used in emydids to analyze the origins of sexual size dimorphisms (SSD) and to test several hypotheses for the evolution of SSD. Equivocal support is provided for the Bolnick-Doebeli hypothesis, which has related intersexual ecological divergence to interspecific ecological divergence.

A suite of analyses are designed and utilized to understand the role of competition and also study body-size diversification within the small, endemic radiation of Caribbean treefrogs, (Osteopilus). The results indicated that competition might have played a significant role in the rapid diversification observed for the body sizes in Caribbean treefrogs to the extremes seen in treefrog communities around the world.

A time-calibrated phylogeny and the morphometric data is employed to study the rates and patterns of the body-form evolution of the snake-like body form in the squamate reptiles. The discussed transition is shown to lead to the concerted evolution of limb reduction, digit loss and body elongation in the reptiles.

A case study on skull elements in Middle American treefrogs demonstrates statistically that the origins of different novel structures may be correlated and phylogenetically clustered into 'hot spots' of evolutionary novelty.

The article discusses the factors responsible for the scarcity of the species of treefrogs in low-lying tropical rainforests. The study experimented on 138 different species of treefrogs.

The ecological and evolutionary factors that promote speciation in Desmognathus and Plethodon salamanders from temperate eastern North America are explored. There is strong evidence of geographic isolation in speciation but no evidence for parapatric speciation along climatic gradients suggesting that niche conservatism plays the primary role in promoting allopatric speciation.

A comprehensive phylogeny for 45 extant species of eastern Plethodon based on DNA sequences of mitochondrial and nuclear genes is presented to examine rates and patterns of diversification and hybridization. Rapid diversification is seen within the glutinosus species group suggesting that the origin of species and the evolution of intrinsic reproductive isolating mechanisms may be decoupled in some cases and extensive hybridization may be a consequence rather than a cause of rapid diversification.

The evolution of body form in squamate reptiles is explored with an emphasis on how biogeography and community context may influence the number of times that snakelike body form evolves. The repeated origins of snakelike squamates appear to be associated with the in situ evolution of two ecomorphs that is short-tailed burrowers or long-tailed surface dwellers on different continental region with very little dispersal of most limb-reduced lineage between continental regions.

The combination of phylogenetics, ancestral area reconstruction, molecular dating methods, and ecological niche modeling is used to explore the evolutionary causes of the patterns of biogeography and species richness in the Northern Hemisphere treefrogs. The replicate patterns in Holarctic hylied reflect the importance of ecology and evolution to large-scale biogeography for better understanding and analysis of species richness patterns.

A study of how niche conservatism in climatic tolerances might limit geographic range expansion is studied. New tools from environmental bioinformatics might facilitate empirical tests of the role of niche conservatism across many different systems and questions, especially when coupled with phylogenetic analyses and with ecological and physiological studies at the local scale.

Several amphibians retain the primitive biphasic life cycle where eggs are laid in water that hatch into free-living aquatic larvae, but direct development of terrestrial eggs have evolved repeatedly and might have been crucial to the evolution of several amphibian groups. Conclusive evidence is presented for evolutionary reversal of direct development in vertebrates.

Sanger and Gibson-Brown (SGB) have published a critique of the Wiens and Slingluff (WS) paper that suggests that WS mischaracterized one part of the model of Cohn and Tickle. It was revealed that SGB have provided a valuable review and clarification of the development literature relating to the evolution of body from in squamates.

An argument that ecology can play an additional role in the origin of species that is different from the one described in literature on ecology and speciation is presented. The different ways in which phylogenetic niche conservatism, rather than ecological divergence, contributes to the formation of geographically isolated lineages, the necessary first step of the most common mode of speciation is described.

The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution. Sean B. Carroll. Norton, New York, 2006. 288 pp., illus. $25.95 (ISBN 0393061639 cloth). In his new [...]