Life at the edge,cooperation in Antarctica

In a current article in the Journal of Vegetation Science, Molina‐Montenegro and colleagues extend the study of plant–plant interactions on stress gradients to extremes – the moss and lichen‐dominated communities of Antarctica. They found that the importance of facilitation at this extreme end of a ‘cold–harsh continuum’ was similar to that reported at the extreme ends of alpine gradients around the world. In other words, in contrast to recent theory and case studies in other systems, facilitative effects did not wane in extremely stressful conditions.     

Life at the edge

Extremophiles: Microbial Life in Extreme Environments (1998). Koki Horikoshi and William D. Grant (Eds). Wiley-Liss, 311 pp. hardback; ISBN 0 471 02618 2 ($134.50)     

Life at the leading edge

Cell migration requires sustained forward movement of the plasma membrane at the cell's front or "leading edge." To date, researchers have uncovered four distinct ways of extending the membrane at the leading edge. In lamellipodia and filopodia, actin polymerization directly pushes the plasma membrane forward, whereas in invadopodia, actin polymerization couples with the extracellular delivery of matrix-degrading metalloproteases to clear a path for cells through the extracellular matrix. Membrane blebs drive the plasma membrane forward using a combination of actomyosin-based contractility and reversible detachment of the membrane from the cortical actin cytoskeleton. Each protrusion type requires the coordination of a wide spectrum of signaling molecules and regulators of cytoskeletal dynamics. In addition, these different protrusion methods likely act in concert to move cells through complex environments in?vivo.     

Nature conservation at the edge

Currently, there is an increasing need for evidence-based strategies in nature conservation, for example when designing and establishing nature reserves. In this contribution, we critically assess the ecological relevance of recent nature conservation practices in Kenya (East Africa), a region of global biodiversity hotspots. More specifically, we overlay the distribution of species richness (here based on mammals, birds, amphibians and vascular plants) with the location of nature reserves, the Kenyan agro-ecological zones (areas representing diverging agricultural potentials), and with the spatial distribution of human population density. Our analyses indicate that the majority of protected areas are located in areas with comparatively low species richness, while areas with extraordinary high levels of species richness are not adequately covered by nature reserves. Areas of high agricultural productivity (and with high human demographic pressure) are mainly reserved for high-yield agriculture; however, these regions are also characterised by high species richness. The majority of nature reserves are restricted to the semi-arid regions of Kenya, marginal for agricultural usage, but also with low levels of species richness. Based on this analysis, we prioritize areas for future protection. This single-country case illustrates that agricultural production in high-yield areas outweighs nature conservation goals, even in global biodiversity hotspot regions, and that priority setting may conflict with effective nature conservation.     

Angiosperms at the edge: Extremity,diversity, and phylogeny

A hallmark of flowering plants is their ability to invade some of the most extreme and dynamic habitats, including cold and dry biomes, to a far greater extent than other land plants. Recent work has provided insight to the phylogenetic distribution and evolutionary mechanisms which have enabled this success, yet needed is a synthesis of evolutionary perspectives with plant physiological traits, morphology, and genomic diversity. Linking these disparate components will not only lead to better understand the evolutionary parallelism and diversification of plants with these two strategies, but also to provide the framework needed for directing future research. We summarize the primary physiological and structural traits involved in response to cold- and drought stress, outline the phylogenetic distribution of these adaptations, and describe the recurring association of these changes with rapid diversification events that occurred in multiple lineages over the past 15 million years. Across these threefold facets of dry-cold correlation (traits, phylogeny, and time) we stress the contrast between (a) the amazing diversity of solutions flowering plants have developed in the face of extreme environments and (b) a broad correlation between cold and dry adaptations that in some cases may hint at deep common origins.     

Actin crosslinking proteins at the leading edge

The lamellar membrane at the leading edge of motile cells participates in a series of complex movements that involve the assembly and reorganization of actin bundles and networks, both structures formed by actin crosslinking proteins. Immunofluorescence miscroscopy localizes within lamellipodia and filopodia several crosslinking proteins including fascin, fimbrin, α-actinin and filamin. While these proteins may organize actin into bundles and networks, fimbrin and α-actinin may play an additional role of linking the cytoskeleton to cell-substratum adhesion sites.     

Darwin at the edge of the visible universe

Simon Conway Morris marvels at the perfection of sensory organs: shaped by eons of evolution, they can detect a single photon or an individual molecule. Only scientific instruments are able to reach beyond the limits of nature''s detectors.“Sans teeth, sans eyes, sans taste, sans everything”, observes Shakespeare''s Jaques bitterly in As You Like It. Today, we might bristle with prosthetics that keep our senses ticking along, but unless your job as a fighter pilot or tea specialist depends on 20/20 vision or subtle taste, then for the most part lack of acuity in our senses passes largely unremarked. It was not always so. For much of human history, defects in seeing, hearing or smelling the sabre-tooth tiger had irreversible consequences. One does not have to subscribe to the Rousseauean notion of the ‘noble savage'' to appreciate the example of the native Tierra del Fuegians Jemmy Button and York Minster—returning to their homeland on the Beagle—delighting in pointing out distant ships that none of the English crew could see until a telescope was hoisted to their less acute eyes.Charles Darwin, of course, opened the door to understanding the evolution of sensory systems, but perhaps there is one aspect of this particular Darwinian mantra that deserves a re-examination. By definition, sensory systems are functional: photons demand eyes, wafting molecules olfactory surfaces, and pressure waves ears. Equally fascinating are those sensory modalities that are entirely alien to human perception: echolocation, electro-communication, infrared sensation and even ultraviolet vision. Unsurprisingly, they have all independently evolved many times, reinforcing the Darwinian concept of adaptation. Yet each also represents a customized, jury-rigged contraption, using whatever happens to be at hand. Think of the multiple co-option of crystallins in eyes; infrared detectors in insects are probably derived from cuticular mechanoreceptors and, more confidently, we can trace the lineage of the electric organs of fish from their musculature.These sensory devices may be contraptions, but they have nevertheless evolved repeatedly to interpret the limits of the physical universe. As an example, consider the epitome of Darwinian analysis: the cameraeye. Much has been made, rightly so, of the ease with which it has evolved; whether by co-opting proteins such as opsins and the crystallins, or the unremarkable transition from the simple spot eye in a flatworm to the cryptic intelligence with which the blue-whale views its world. Might there be a less-considered perspective? The shift in refractive indices across the lens corrects almost perfectly for its spherical aberration (Jagger & Sands, 1999), but the retina can also detect single photons. In comparison to the camera eye, the compound version is unavoidably deficient, but this does not prevent some insects flying by starlight. In the re-tellings of the story of how eyes evolve, perhaps we have lost sight of Darwin''s somewhat mischievous rumination on the perfection of the eye. His straw-man conceals the fact that not only do eyes evolve, but they might be as near to perfect as they ever will be.And what about the other senses? The olfactory systems of insects and mammals are startlingly similar, and the former can detect a single molecule. In audition, the sensitivity of the male mosquito antenna is such that it is triggered by an infinitesimal deflection, equivalent to the top of the Eiffel Tower moving less than 1 mm (Göpfert & Robert, 1999). For vertebrates, the sensitivity of the transduction process in the inner ear is close to that of thermal noise (Denk & Webb, 1989). This represents an absolute barrier not only for biology, but also for the eye and nose; a photon or a molecule are the irreducible limits of detection.This is not to say that all sensory systems are equally acute; the echolocation skills of bats or the sensitivity of snakes to infrared radiation clearly show the extent of sensory capacities and sensitivities. However, in horseshoe bats, the exceptional tuning of the ear to specific frequencies—notably with an acoustic fovea in the cochlea and specific neural organization in the auditory cortex (Neuweiler 1990)—suggests that the limits of perception are close, or have perhaps been reached in existing lifeforms. Such extraordinarily fine-tuned sensitivities are also found in the infrared apparatus of crotalid snakes, which have facial pits that behave similarly to pinhole camera-eyes, and can detect minute temperature differences (Bakken & Krochmal, 2007).There is a further insight. Whilst infrared detectors have evolved in many snakes, insects and mammals, the system in the crotalids—and also that found independently in the beetle Acanthocnemus (Kreis et al, 2005)—is a bolometer: a thin sheet of highly vascularized tissue, suspended in an insulated cavity. Astronomers, as well as others, use analogous systems. Such convergence between evolution and technology is not surprising, and is further exemplified by the similarities between the fibre-optic systems of some siliceous sponge spicules and telecommunications technologies (Aizenberg et al, 2004). Biology has reached the edges of the physical universe, but scientific instruments allow us to see deeper, not least into the mysterious world of quantum physics. Without such instruments we would be blind, but we should remember that the way that cognitive processes allow us to understand a universe that is largely beyond our Darwinian senses, remains deeply enigmatic.     

Compartment boundaries: at the edge of development.

Compartment boundaries have fascinated biologists for more than 25 years. We now know that these boundaries play important roles in pattern formation, yet how these boundaries are established during development remained a mystery. Here, we describe the exciting progress that has been made recently towards elucidating the mechanisms of boundary formation.     

MutLalpha: at the cutting edge of mismatch repair

The mismatch repair process corrects errors in newly synthesized DNA. In this issue, Modrich and colleagues (Kadyrov et al., 2006) show that a component of the human mismatch repair machinery, MutLalpha, has endonuclease activity. MutLalpha introduces single-strand breaks near the mismatch and thus generates new entry points for the exonuclease EXOI to degrade the strand containing the mismatch.     

Molecular imprinting: at the edge of the third millennium

Molecularly imprinted polymers (MIPs) represent a new class of materials that have artificially created receptor structures (1-3). Since their discovery in 1972, MIPs have attracted considerable interest from scientists and engineers involved with the development of chromatographic adsorbents, membranes, sensors and enzyme and receptor mimics.     

Life at the edge: Roe deer occurrence at the opposite ends of their geographical distribution,Norway and Portugal

In the face of climate change and habitat fragmentation there is an increasingly urgent need to learn more about factors that influence species distribution patterns and levels of environmental tolerance. Particular insights can be obtained by looking at the edges of a species range, especially from species with wide distributions. The European roe deer was chosen as a model species due to its widespread distribution. By using pellet group counts, we studied summer and winter habitat use of this herbivore at two of the extreme edges of its distribution – southwest of Portugal, and northeast of Norway – in relation to a range of fine-scale environmental factors including forest structure, vegetation characteristics and human disturbance. Our first prediction that roe deer would respond differently to human activity in both counties was supported. While in Norway roe deer are always close to houses, in Portugal they are either far (in summer) or indifferent (winter). However, everywhere and in every season, roe deer are far from roads. Our second prediction that roe deer better tolerate anthropogenic disturbances in the area where the importance of limiting factors is higher (Norway) was validated. However, our third prediction that anthropogenic disturbance would be less tolerated by roe deer outside the limiting seasons in each country was not supported. Our results suggest that roe deer perceive human activities differently in the two countries and that roe deer better tolerate anthropogenic disturbances in Norway.