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Egg size and structure reflect important constraints on the reproductive and life-history characteristics of vertebrates.sup.1. More than two-thirds of all extant amniotes lay eggs.sup.2. During the Mesozoic era (around 250 million to 65 million years ago), body sizes reached extremes; nevertheless, the largest known egg belongs to the only recently extinct elephant bird.sup.3, which was roughly 66 million years younger than the last nonavian dinosaurs and giant marine reptiles. Here we report a new type of egg discovered in nearshore marine deposits from the Late Cretaceous period (roughly 68 million years ago) of Antarctica. It exceeds all nonavian dinosaur eggs in volume and differs from them in structure. Although the elephant bird egg is slightly larger, its eggshell is roughly five times thicker and shows a substantial prismatic layer and complex pore structure.sup.4. By contrast, the new fossil, visibly collapsed and folded, presents a thin eggshell with a layered structure that lacks a prismatic layer and distinct pores, and is similar to that of most extant lizards and snakes (Lepidosauria).sup.5. The identity of the animal that laid the egg is unknown, but these preserved morphologies are consistent with the skeletal remains of mosasaurs (large marine lepidosaurs) found nearby. They are not consistent with described morphologies of dinosaur eggs of a similar size class. Phylogenetic analyses of traits for 259 lepidosaur species plus outgroups suggest that the egg belonged to an individual that was at least 7 metres long, hypothesized to be a giant marine reptile, all clades of which have previously been proposed to show live birth.sup.6. Such a large egg with a relatively thin eggshell may reflect derived constraints associated with body shape, reproductive investment linked with gigantism, and lepidosaurian viviparity, in which a 'vestigial' egg is laid and hatches immediately.sup.7. A fossil egg unearthed from Cretaceous deposits in Antarctica is more than 20 cm long, exceeds all known nonavian eggs in volume, is soft-shelled, and was perhaps laid by a giant marine lizard such as a mosasaur., Author(s): Lucas J. Legendre [sup.1] , David Rubilar-Rogers [sup.2] , Grace M. Musser [sup.1] , Sarah N. Davis [sup.1] , Rodrigo A. Otero [sup.3] , Alexander O. Vargas [sup.3] , [...]

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Living beings are autopoietic systems with highly context‐dependent structural dynamics and interactions, that determine whether a disturbance in the genotype or environment will lead or not to phenotypic change. The concept of epigenesis entails how a change in the phenotype may not correspond to a change in the structure of an earlier developmental stage, including the genome. Disturbances of embryonic structure may fail to change the phenotype, as in regulated development, or when different genotypes are associated to a single phenotype. Likewise, the same genotype or early embryonic structure may develop different phenotypes, as in phenotypic plasticity. Disturbances that fail to trigger phenotypic change are considered neutral, but even so, they can alter unexpressed developmental potential. Here, we present conceptual diagrams of the "epigenic field": similar to Waddington's epigenetic landscapes, but including the ontogenic niche (organism/environment interactional dynamics during ontogeny) as a factor in defining epigenic fields, rather than just selecting among possible pathways. Our diagrams illustrate transgenerational changes of genotype, ontogenic niche, and their correspondence (or lack thereof) with changes of phenotype. Epigenic fields provide a simple way to understand developmental constraints on evolution, for instance: how constraints evolve as a result of developmental system drift; how neutral changes can be involved in genetic assimilation and de‐assimilation; and how constraints can evolve as a result of neutral changes in the ontogenic niche (not only the genotype). We argue that evolutionary thinking can benefit from a framework for evolution with conceptual foundations at the organismal level. Research Highlights: The niche of the organism during ontogeny (ontogenic niche) helps define potential developmental pathways, rather than just selecting among them.Neutral environmental changes and neutral epimutations can influence the path taken by evolution. [ABSTRACT FROM AUTHOR]

Resonant interactions with electromagnetic whistler-mode waves are a primary driver of energetic electron dynamics in the Earth's radiation belts. The most intense waves can resonate with electrons nonlinearly, and effects of such nonlinear resonant interactions significantly differ from the classical quasi-linear diffusion. There have been continuous efforts on the theoretical investigation and implementation of these effects into radiation belt models, but not all nonlinear effects have been revealed yet. The two most investigated effects are phase trapping and phase bunching, which are responsible for electron acceleration and precipitation into the Earth's atmosphere, respectively, i.e., for the first cyclotron resonance with waves generated at the equator and propagating to higher latitudes, phase trapping increases electrons' energy, whereas phase bunching decreases the electron pitch-angle (and magnetic moment). However, recent studies reported a new effect called positive phase bunching, which may increase the electron pitch-angle and move them away from the loss-cone. This paper aims to characterize possible contributions of this effect to long-term electron dynamics, including multiple resonant interactions. Using an iterated mapping technique, we show that although the positive phase bunching effect can modify electron trajectories, it does not change the average rate of electron mixing in phase space. Thus, this effect may be safely neglected in long-term simulations of radiation belt dynamics. We also discuss possible verification of the positive phase bunching effect using short (single resonance), bursty electron precipitation events. [ABSTRACT FROM AUTHOR]

In a recent commentary, Nespolo (2003) makes reference to his personal experience as exattendant to the course of evolution imparted by Dr. Humberto Maturana and Dr. Jorge Mpodozis at the Facultad de Ciencias of the Universidad de Chile to construct a negative criticism of Chilean undergraduate teaching of evolution. As ex-attendants of the mentioned course of evolution we have had an experience that is directly comparable to that of Dr. Nespolo. Here we wish to point out our opinion regarding this course, which is markedly different. First, it is a caricature to state that in this course natural selection is taught as being wrong. A serious and critical revision of natural selection, the synthetic theory, and evolutionary ecology is a fundamental part of the course. These and other topics are presented by researchers from those fields, such as Drs. Germán Manríquez and Rodrigo Medel. The scientific contributions of both researchers receive positive comments in Nespolo (2003).