Whence meiosis?

Sexual reproduction predominates among eukaryotic organisms on our planet. While debate continues over why this should be so, burgeoning genomic and functional information now allows us to begin to think reasonably about some of the events that may have occurred to make sex possible in the first place.     

Whence tit-for-tat?

Summary In theoretical and empirical studies of the evolution of cooperation, the tit-for-tat strategy (i.e. cooperate unless your partner did not cooperate in the previous interaction) is widely considered to be of central importance. Nevertheless, surprisingly little is known about the conditions in which tit-for-tat appears and disappears across generations in a population of interacting individuals. Here, we apply a newly developed classifier-system model (EvA) in addressing this issue when the key features of interactions are caricatured using the iterated prisoner's dilemma game. Our simple representation of behavioural strategies as algorithms composed of two interacting rules allowed us to determine conditions in which tit-for-tat can replace noncooperative strategies and vice versa. Using direct game-theoretic analysis and simulations with the EvA model, we determined that no strategy is evolutionarily stable, but larger population sizes and longer sequences of interactions between individuals can yield transient dominance by tit-for-tat. Genetic drift among behaviourally equivalent strategies is the key mechanism underlying this dominance. Our analysis suggests that tit-for-tat could be important in nature for cognitively simple organisms of limited memory capacity, in strongly kin-selected or group-selected populations, when interaction sequences between individuals are relatively short, in moderate-sized populations of widely interacting individuals and when defectors appear in the population with moderate frequency.     

Can the red palm mite threaten the Amazon vegetation?

The red palm mite Raoiella indica Hirst (Tenuipalpidae) was first reported in the New World in 2004, dispersing quickly and widely while adopting new plant species as hosts. Since then, it has caused severe damage in this region, especially to coconut (Cocos nucifera L.). It was first found in Brazil in 2009, in the northern Amazonian state of Roraima. In the present study, native and introduced plants were sampled between March 2010 and February 2011 in sites of the 15 Roraima municipalities, to estimate its distribution and the associated mite fauna. In addition, monthly samples were taken from a coconut plantation in Mucajaí throughout the same period, for an initial appraisal of the levels R. indica could reach. It was found in 10 municipalities, on 19 plant species of four families. Six species are reported for the first time as hosts. Among the associated predators, 89.1% were Phytoseiidae, most commonly Amblyseius largoensis (Muma), Iphiseiodes zuluagai Denmark & Muma and Euseius concordis (Chant). The highest densities of R. indica, 1.5 and 0.35 mites/cm² of leaflet (approx total of 331 and 77 mites/leaflet), were reached respectively in March 2010 and February 2011. The highest density of phytoseiids on coconut (0.009 mites/cm² or about 2 mites/leaflet) was reached in November 2010. The average densities of R. indica recorded for Roraima were comparable to those reported for countries in which the mite is reportedly economically damaging. The dispersal of R. indica through the Amazon forest may result in damage to cultivated and native palms, and plants of other families, if the projected increase in both the frequency and the severity of drought events occurs. Parts of the Amazon have undergone periods of low rainfall, a condition that appears to favour the biology of this mite. Its eventual arrival to northeastern Brazil may result in heavy economic and ecological losses.     

Why does the mammalian red blood cell have aquaporins?

Aquaporins are now known to mediate the rapid exchange of water across the plasma membranes of diverse cell types. This exchange has been studied and kinetically characterized in red blood cells (erythrocytes; RBC) from many animal species. In recent years, a favoured method has been one based on NMR spectroscopy. Despite knowledge of their molecular structure the physiological raison d' etre of aquaporins in RBCs is still only speculated upon. Here, we present two hypotheses that account for the fact that the exchange of water is so fast in RBCs. The first is denoted the "oscillating sieve" hypothesis and it posits that known membrane undulations at frequencies up to 30 Hz with displacements up to 0.3 microm are energetically favoured by the high water permeability of the membrane. The second denoted the "water displacement" hypothesis is based on the known rapid exchange across the RBC membrane of ions such as Cl- and HCO3- and solutes such as glucose, all of whose molecular volumes are significantly greater than that of water. The ideas are generalizable to other cell types and organelles.     

Green or red: what stops the traffic in the tetrapyrrole pathway?

Regulation of tetrapyrrole biosynthesis is crucial to plant metabolism. The two pivotal control points are formation of the initial precursor, 5-aminolaevulinic acid (ALA), and the metal-ion insertion step: chelation of Fe(2+) into protoporphyrin IX leads to haem and phytochromobilin, whereas insertion of Mg(2+) is the first step to chlorophyll. Recent studies with mutants and transgenic plants have demonstrated that perturbation of the branch point affects ALA formation. Moreover, one of the signals that controls the expression of genes for nuclear-encoded chloroplast proteins has been shown to be Mg-protoporphyrin-IX. Here, we discuss the regulation of branch-point flux and the relative contributions of the haem and chlorophyll branches to the regulation of ALA synthesis and thus to flow through the tetrapyrrole pathway.     

Is the surface area of the red cell membrane skeleton locally conserved?

The incompressibility of the lipid bilayer keeps the total surface area of the red cell membrane constant. Local conservation of membrane surface area requires that each surface element of the membrane skeleton keeps its area when its aspect ratio is changed. A change in area would require a flow of lipids past the intrinsic proteins to which the skeleton is anchored. in fast red cell deformations, there is no time for such a flow. Consequently, the bilayer provides for local area conservation. In quasistatic deformations, the extent of local change in surface area is the smaller the larger the isotropic modulus of the skeleton in relation to the shear modulus. Estimates indicate: (a) the velocity of relative flow between lipid and intrinsic proteins is proportional to the gradient in normal tension within the skeleton and inversely proportional to the viscosity of the bilayer; (b) lateral diffusion of lipids is much slower than this flow; (c) membrane tanktreading at frequencies prevailing in vivo as well as the release of a membrane tongue from a micropipette are fast deformations; and (d) the slow phase in micropipette aspiration may be dominated by a local change in skeleton surface.     

Whence comes Trypanosoma lewisi antigen which induces ablastic antibody: Studies in the occult?

I propose that trypanosomes have three antigen compartments: the intracellular, plasma membrane, and extracellular compartments. The intracellular antigens are released when trypanosomes lyse; the plasma membrane antigens are the structural or transport components of the plasma membrane and the adhering surface coat; the extracellular antigens are secreted by the trypanosomes. I further suggest that ablastinogen, the Trypanosoma lewisi antigen which induces ablastic antibody, is a plasma membrane antigen, and that the T. lewisi trypanocidal antigens are in the surface coat. The T. lewisi exoantigens described by D'Alesandro (1972) are, as he stated, different from ablastinogen and trypanocidal antigens. I suggest that the exoantigens are secreted extracellular antigens. Data from the literature are presented to support the hypothesis, and an experimental protocol to test the hypothesis is outlined.     

Can the red mangrove provide food,feed and fertilizer?

The red mangrove is one of the principal features of the coastal vegetation throughout tropical America, Mexico, the West Indies, the Bahamas, Bermuda and southern Florida. It is of primary importance as a land retainer and builder. Secondarily, its bark is a source of tannin and yields resins suitable for plywood adhesive. Mangrove wood is heavy and durable. The bark, leaves and shoots furnish various dyes and the bark is an excellent fuel and is much used locally for medicinal purposes. In southern Florida there has been active interest in the value of mangrove leaf meal as cattle feed, the dried and ground leaves have been sold as “Maritime Tea” and prepared in tablet form as a dietary supplement. The leaf meal and the sawdust have been tested as soil conditioners. Despite their high tannin content, red mangrove leaves may warrant investigation as an abundant source of protein.     

Are red algae plants?

For 200 years prior to the 1938 publication of H. F. Copeland, all authorities (with one exception) classified red algae (Rhodophyta) within Kingdom Plantae or its equivalent. Copeland's reclassification of red algae within Kingdom Protista or Protoctista drew from an alternative tradition, dating to Cohn in 1867, in which red algae were viewed as the earliest or simplest eukaryotes. Analyses of ribosomal RNA (rRNA) sequence data initially favoured Copeland's reclassification. Many more rRNA gene (rDNA) sequences are now available from the eukaryote lineages most closely related to red algae, and based on these data, the hypothesis that red algae and green plants are sister groups cannot be rejected. An increasing body of sequence, intron-location and functional data from nuclear- and mitochondrially encoded proteins likewise supports a sister-group relationship between red algae and green plants. Submerging Kingdoms Plantae, Animalia and Fungi into Eukarya would provide a more natural framework for the eventual resolution of whether red algae are plants or prorists.     

How many pathways for invasion of the red blood cell by the malaria parasite?

Merozoites of the malaria parasite Plasmodium falciparum use several receptors for cellular engagement when they invade human red blood cells. Recently, a merozoite erythrocyte-binding protein, EBA-140, has been identified that specifically binds to glycophorin C on red blood cells. Up to 50% of Melanesians have a deletion in this gene, and the resultant Gerbich-negative red blood cells are relatively resistant to invasion. While discovery of multiple pathways for invasion could confound the search for suitable vaccine targets, they could also be considered in the design of therapeutic interventions that prevent malaria parasites entering red blood cells.     

Are red leaves photosynthetically active?

At irradiances close to those representing a sunny day, red and green leaves of poinsettia (Euphorbia pulcherrima) showed only minor differences in their photosynthetic capacities despite the strong differences in their pigment composition. However, contrarily to green leaves, red leaves did not show inhibition of photosynthesis at high irradiances, because anthocyanins protected chloroplasts from photoinhibition.     

Genetic assessment of the red squirrel in Illinois: Immigrants or Exotics?

Novel populations pose unusual challenges for wildlife managers because knowledge regarding the source of these populations is essential to develop sound management approaches. One example that illustrates the complexity of this issue is the small population of red squirrels (Tamiasciurus hudsonicus) identified in northeastern Illinois in the 1970s. To elucidate the source of the red squirrel population in Illinois, we examined both contemporary and less recent patterns of genetic structure using nuclear microsatellite loci and mitochondrial DNA. Analyses revealed the Illinois subpopulation was primarily comprised of descendents of immigrants from Indiana, but there was also evidence of a translocation of squirrels from Minnesota. We recommend continued protection for the red squirrel in Illinois due to its restricted geographic range, small population size, and status as a native population. © 2011 The Wildlife Society.     

Does tent caterpillar attack reduce the food quality of red alder foliage?

Summary We assayed the quality of red alder trees for western tent caterpillar growth and survival to test the hypothesis that caterpillar feeding stimulates plant defenses in both attacked and adjacent trees. Three years of high tent caterpillar density were necessary before deterioration in foliage quality occurred, and even then only foliage from trees which were almost completely defoliated in the current year reduced the growth of caterpillars. Both tent size and mean egg mass size increased after the second year of high density which indicates that good conditions still existed for tent caterpillars after 2 to 3 years of heavy feeding.Egg masses which were moved to areas where trees had not recently supported a high caterpillar population produced significantly smaller tents than endemic controls in 1982. Therefore the small tent and egg mass size of the high density population in 1982 was inherent to the insects rather than modified by food source. In 1983 the tents from introduced egg masses were as large as naturally occurring tents.If lightly attacked trees within areas of high caterpillar density are better defended against insect attack, this does not show up in their ability to support caterpillar growth and survival. We found no evidence to support the hypothesis that trees communicate insect attack and stimulate chemical defenses in adjacent trees. Reduced foliage quality seems to be a result of extensive insect damage rather than a defense against insect damage.