What is parallelism?

Although parallel and convergent evolution are discussed extensively in technical articles and textbooks, their meaning can be overlapping, imprecise, and contradictory. The meaning of parallel evolution in much of the evolutionary literature grapples with two separate hypotheses in relation to phenotype and genotype, but often these two hypotheses have been inferred from only one hypothesis, and a number of subsidiary but problematic criteria, in relation to the phenotype. However, examples of parallel evolution of genetic traits that underpin or are at least associated with convergent phenotypes are now emerging. Four criteria for distinguishing parallelism from convergence are reviewed. All are found to be incompatible with any single proposition of homoplasy. Therefore, all homoplasy is equivalent to a broad view of convergence. Based on this concept, all phenotypic homoplasy can be described as convergence and all genotypic homoplasy as parallelism, which can be viewed as the equivalent concept of convergence for molecular data. Parallel changes of molecular traits may or may not be associated with convergent phenotypes but if so describe homoplasy at two biological levels-genotype and phenotype. Parallelism is not an alternative to convergence, but rather it entails homoplastic genetics that can be associated with and potentially explain, at the molecular level, how convergent phenotypes evolve.     

What is emotion?

There is no consensus in the literature on a definition of emotion. The term is taken for granted in itself and, most often, emotion is defined with reference to a list: anger, disgust, fear, joy, sadness, and surprise. This article expands on a thesis that motivational states can be compared to each other by means of a common currency (Philos. Trans. Roy. Soc. Lond. 270 (1975) 265-293). I have previously argued that this common currency is pleasure. Such a conclusion is based not on introspective intuition, as with early pre-scientific psychology (), but on experimental methods. As a follow-up to a definition of consciousness (Neurosci. Biobehav. Rev. 20 (1996) 33-40) as a four-dimensional experience (quality, intensity, hedonicity, and duration), I propose here that emotion is any mental experience with high intensity and high hedonic content (pleasure/displeasure).     

What is macroecology?

The symposium ‘What is Macroecology?’ was held in London on 20 June 2012. The event was the inaugural meeting of the Macroecology Special Interest Group of the British Ecological Society and was attended by nearly 100 scientists from 11 countries. The meeting reviewed the recent development of the macroecological agenda. The key themes that emerged were a shift towards more explicit modelling of ecological processes, a growing synthesis across systems and scales, and new opportunities to apply macroecological concepts in other research fields.     

What is Chondriolejeunea?

Chondriolejeunea, the former subgenus of Cololejeunea is raised to the generic rank on the base that the supposed large styli are in reality underleaves, inserted alternately to the two cell rows of ventral merophytes and having rhizoid initials at their base. Chondriolejeunea pseudostipulata (Schiffn.) Kis & Pócs, Chondriolejeunea shimizui (N. Kitag.) Kis & Pócs, Chondriolejeunea shimizui var. phangngana (N. Kitag.) Kis & Pócs, Chondriolejeunea chinii (Tixier) Kis & Pócs, comb. et stat. nov. Cololejeunea shimizui subsp. shihuishanensis M.L. So & R.L. Zhu, syn. nov. Speculation on the possible ways of evolution of tribe Cololejeuneae.     

What is metamorphosis?

Metamorphosis (Gr. meta- "change" + morphe "form") as a biologicalprocess is generally attributed to a subset of animals: mostfamously insects and amphibians, but some fish and many marineinvertebrates as well. We held a symposium at the 2006 Societyfor Integrative and Comparative Biology (SICB) annual meetingin Orlando, FL (USA) to discuss metamorphosis in a comparativecontext. Specifically, we considered the possibility that theterm "metamorphosis" could be rightly applied to non-animalsas well, including fungi, flowering plants, and some marinealgae. Clearly, the answer depends upon how metamorphosis isdefined. As we participants differed (sometimes quite substantially)in how we defined the term, we decided to present each of ourconceptions of metamorphosis in 1 place, rather than attemptingto agree on a single consensus definition. Herein we have gatheredtogether our various definitions of metamorphosis, and offeran analysis that highlights some of the main similarities anddifferences among them. We present this article not only asan introduction to this symposium volume, but also as a referencetool that can be used by others interested in metamorphosis.Ultimately, we hope that this article—and the volume asa whole—will represent a springboard for further investigationsinto the surprisingly deep mechanistic similarities among independentlyevolved life cycle transitions across kingdoms.     

What is life?

Background

Many traditional biological concepts continue to be debated by biologists, scientists and philosophers of science. The specific objective of this brief reflection is to offer an alternative vision to the definition of life taking as a starting point the traits common to all living beings.

Results and Conclusions

Thus, I define life as a process that takes place in highly organized organic structures and is characterized by being preprogrammed, interactive, adaptative and evolutionary. If life is the process, living beings are the system in which this process takes place. I also wonder whether viruses can be considered living things or not. Taking as a starting point my definition of life and, of course, on what others have thought about it, I am in favor of considering viruses as living beings. I base this conclusion on the fact that viruses satisfy all the vital characteristics common to all living things and on the role they have played in the evolution of species. Finally, I argue that if there were life elsewhere in the universe, it would be very similar to what we know on this planet because the laws of physics and the composition of matter are universal and because of the principle of the inexorability of life.

     

What is complexity?

Arguments for or against a trend in the evolution of complexity are weakened by the lack of an unambiguous definition of complexity. Such definitions abound for both dynamical systems and biological organisms, but have drawbacks of either a conceptual or a practical nature. Physical complexity, a measure based on automata theory and information theory, is a simple and intuitive measure of the amount of information that an organism stores, in its genome, about the environment in which it evolves. It is argued that physical complexity must increase in molecular evolution of asexual organisms in a single niche if the environment does not change, due to natural selection. It is possible that complexity decreases in co-evolving systems as well as at high mutation rates, in sexual populations, and in time-dependent landscapes. However, it is reasoned that these factors usually help, rather than hinder, the evolution of complexity, and that a theory of physical complexity for co-evolving species will reveal an overall trend towards higher complexity in biological evolution.     

What is altruism?

Altruism is generally understood to be behavior that benefits others at a personal cost to the behaving individual. However, within evolutionary biology, different authors have interpreted the concept of altruism differently, leading to dissimilar predictions about the evolution of altruistic behavior. Generally, different interpretations diverge on which party receives the benefit from altruism and on how the cost of altruism is assessed. Using a simple trait-group framework, we delineate the assumptions underlying different interpretations and show how they relate to one another. We feel that a thorough examination of the connections between interpretations not only reveals why different authors have arrived at disparate conclusions about altruism, but also illuminates the conditions that are likely to favor the evolution of altruism.     

What is infrasound?

Definitions of infrasound and low-frequency noise are discussed and the fuzzy boundary between them described. Infrasound, in its popular definition as sound below a frequency of 20 Hz, is clearly audible, the hearing threshold having been measured down to 1.5 Hz. The popular concept that sound below 20 Hz is inaudible is not correct.

Sources of infrasound are in the range from very low-frequency atmospheric fluctuations up into the lower audio frequencies. These sources include natural occurrences, industrial installations, low-speed machinery, etc.

Investigations of complaints of low-frequency noise often fail to measure any significant noise. This has led some complainants to conjecture that their perception arises from non-acoustic sources, such as electromagnetic radiation.

Over the past 40 years, infrasound and low-frequency noise have attracted a great deal of adverse publicity on their effects on health, based mainly on media exaggerations and misunderstandings. A result of this has been that the public takes a one-dimensional view of infrasound, concerned only by its presence, whilst ignoring its low levels.     

What is hierarchical selection?

It has been proposed that natural selection occurs on a hierarchy of levels, of which the organismic level is neither the top nor the bottom. This hypothesis leads to the following practical problem: in general, how does one tell if a given phenomenon is a result of selection on level X or level Y. How does one tell what the units of selection actually are? It is convenient to assume that a unit of selection may be defined as a type of entity for which there exists, among all entities on the same “level” as that entity, an additive component of variance for some specific component F of fitness which does not appear as an additive component of variance in any decomposition of this F among entities at any lower level. But such a definition implicitly assumes that if f(x, y) depends nonadditively on its arguments, there must be interaction between the quantities which x and y represent. This assumption is incorrect. And one cannot avoid this error by speaking of “transformability to additivity” instead of merely “additivity”. A general mathematical formulation of the concepts of interaction and non-interaction is proposed, followed by a correspondingly modified approach to the definition of a unit of selection. The practical difficulty of verifying the presence of hierarchical selection is discussed.     

What is resource partitioning?

The concept of resource partitioning, as originally developed, relates to evolutionary change in species in response to selection pressures generated by interspecific competition. More recently it has taken on another meaning, one that is not defined in terms of evolutionary function, and which refers simply to differences in resource use between species regardless of the origins of the differences. Such a shift in usage has several drawbacks for ecological theory, which are discussed. Of most practical significance to ecologists is the inappropriate justification conferred on the continued use of a category that contains characters that are not equivalents. Ecologists are therefore frequently in the position of explaining the presence of species in an area by reference to the by-products of their adaptive evolution.     

How Neutral is Ecology?

Neutral ecological theory comes in two flavors—a two-stage model with space implicit and a spatially explicit version. Reconciliation of the two flavors has proven problematic. Panmixis, an implicit assumption of the two-stage model, is neither realistic for nor supported by tropical forest trees. However, in spatially explicit versions, stochastic species input in local communities is still necessary to retain high species richness. A unified theory of biodiversity must include both stochasticity and relevant ecological mechanisms.     

How hydrophobic is alanine?

By a number of measures, alanine is poised at the threshold between those amino acids that promote the membrane integration of transmembrane alpha-helices and those that do not. We have measured the preference of alanine to partition into the lipid-water interface region over the central acyl chain region of the endoplasmic reticulum (ER) membrane both by its ability to promote the formation of so-called helical hairpins, i.e. a pair of transmembrane helices separated by a tight turn, and by mapping the position relative to the membrane of the lumenal end of a transmembrane alpha-helix that ends with a block of 10 alanines. Both measures show that Ala has a weak but distinct preference for the interface region, which is in agreement with recent biophysical measurements on pentaeptide partitioning in simple water-lipid or water-octanol systems (Jayasinghe, S., Hristova, K., and White, S. H. (2001) J. Mol. Biol. 312, 927-934). Considering the complexity of the translocon-mediated insertion of membrane proteins into the ER, the agreement between the biochemical and biophysical measurements is striking and suggests that protein-lipid interactions are already important during the very early steps of membrane protein assembly in the ER.     

All signaling is local?

The mechanism of signal transmission following ligand stimulation of receptor tyrosine kinases in living cells is poorly understood. Recent studies have visualized the spatio-temporal pattern of EGF signaling, indicating that receptor density is an important factor in the mechanism of lateral propagation of local EGF signaling.