DYNAMICS OF HYBRID INCOMPATIBILITY IN GENE NETWORKS IN A CONSTANT ENVIRONMENT

After an ancestral population splits into two allopatric populations, different mutations may fix in each. When pairs of mutations are brought together in a hybrid offspring, epistasis may cause reduced fitness. Such pairs are known as Bateson–Dobzhansky–Muller (BDM) incompatibilities. A well-known model of BDM incompatibility due to Orr suggests that the fitness load on hybrids should initially accelerate, and continue to increase as the number of potentially incompatible substitutions increases (the "snowball effect"). In the gene networks model, which violates a key assumption of Orr's model (independence of fixation probabilities), the snowball effect often does not occur. Instead, we describe three possible dynamics in a constant environment: (1) Stabilizing selection can constrain two allopatric populations to remain near-perfectly compatible. (2) Despite constancy of environment, punctuated evolution may obtain; populations may experience rare adaptations asynchronously, permitting incompatibility. (3) Despite stabilizing selection, developmental system drift may permit genetic change, allowing two populations to drift in and out of compatibility. We reinterpret Orr's model in terms of genetic distance. We extend Orr's model to the finite loci case, which can limit incompatibility. Finally, we suggest that neutral evolution of gene regulation in nature, to the point of speciation, is a distinct possibility.     

UBIQUINONE REDOX STATUS IN BRAIN IN VITRO

—The redox status of ubiquinone (Q) as an index of mitochondrial respiratory chain activity in chopped telencephalon from the rat was investigated. With 12mm -glucose under aerobic conditions Q was 73% oxidized. Three mm -amytal and 2 μm -rotenone, inhibitors of mitochondrial NADH oxidation, resulted in Q being further oxidized by 14 and 16%, respectively. Thus, amytal and rotenone result in shifts in Q redox status of rat telencephalon slices in accord with the known site of action of these compounds in isolated mitochondria. However, under anaerobic conditions Q redox status shifted to 25% oxidized while incubation with 1 mm -NaCN resulted in a shift to only 58% oxidized. This discrepancy may result from concomitant inhibition in the supply of reducing equivalents to Q from substrate by NaCN or it may reflect a differential sensitivity of neuronal and glial mitochondria to NaCN. Evaluation of Q oxidation-reduction can be used to measure the effects of drugs and physiological perturbations on the redox status of the mitochondrial compartment of intact brain preparations.     

FATIGUE FRACTURES IN TRACK ATHLETES

Pain in a foot or in the lower leg, not related to specific injury, in a track athlete who does a great deal of running, is the first symptom of fatigue fracture. X-ray films taken at the time pain begins may show no abnormality. Films taken a month or more later may show formation of callus, and perhaps a fracture line, at the point of pain.Usually no treatment beyond cessation of running for two months or more is needed.Since the incidence is highest in middle-distance runners who train intensively—quartermilers in particular—and may be related to the hardness of the running track, limiting running to alternate days and doing part of it on grass may help in prevention.     

WHY ARE CLUTCH SIZES MORE VARIABLE IN SOME SPECIES THAN IN OTHERS?

Animal species differ in the variability of their clutch sizes, as well as in mean clutch sizes. This phenomenon is particularly obvious in lizards, where virtually invariant clutch sizes have evolved independently in at least 23 lineages in seven families. Reduced variance in clutch size may arise either as an adaptation (because females with less variable clutch sizes have higher fitness) or as an indirect by-product of selection on other life-history characteristics. Comparative data on Australian scincid lizards indicate that variance in clutch sizes is lowest among species with low mean clutch sizes, small body sizes and a low variance in body sizes of adult females. Phylogenetic analysis shows that evolutionary decreases in the variance of clutch size have accompanied decreases in mean clutch sizes and decreases in the variance of adult female body sizes. Tropical lizards may also exhibit lower variance in clutch size. Most of these characteristics are correlated in occurrence, and may be allometrically tied to small body size. Hence, low variance in clutch size may be a consequence of allometric effects on a correlated suite of life-history characteristics. Exceptions to the general patterns noted above—especially, lizard species with invariant clutch sizes but large body sizes—may be due to loss of genetic variance for clutch sizes in lineages that have passed through a “bottleneck” of small body sizes and hence, low variance in clutch sizes.     

CONVERGENT EVOLUTION IN INVERTEBRATES

Resemblance between animal taxa may be due to convergence rather than to recent common ancestry. Constraints on biological materials and adaptation to particular habits or habitats will produce widespread convergence. How may we distinguish the two causes of resemblance? The relationship between convergence and taxonomy is discussed, demonstrating that the choice of taxonomic method will itself determine the extent to which convergence is perceived. In particular, cladistic analysis based on parsimony will tend to minimise and thus conceal convergence: neither the resulting cladogram nor a consistency index derived from it can be used to assess the prevalence of convergence. With any taxonomic system, there can be no substitute for evaluation of the morphological characters used. Complementary use of molecular characters shows promise: we wait further understanding of constraints in genetic evolution and of the possibilities of convergence at this level also. These general principles are illustrated with a range of examples from within and between invertebrate phyla: the phylogeny of Cnidaria and Platyhelminthes cannot be traced with certainty, but where the fossil record allows clear rooting, as for the echinoderms and in particular the echinoids, combination of morphological and molecular methods has made much progress. Sub-groups within a phylum, for example opisthobranch molluscs and the dipteran Phoridae, may show an uncontested phylogeny, and here studies have precisely identified convergence and shown that it may be the commoner cause of resemblance. Adaptation to exacting environments shown by terrestial and freshwater nemertines may also result in a predominance of convergent resemblance. Traditional grouping of phyla breaks down on re-examination of supposedly key characters, such as segmentation, body cavities, germ layers and symmetry, each of which must have had multiple origins: nor are developmental stages (especially not larvae) a reliable guide to relationships. Demarcation of phyla may be difficult, as with arthropods, and location of phyla is even more difficult, due to their early and rapid radiation. Over-simplified definition of characters has bedevilled invertebrate classification and the use of molecular data has not yet resolved the major controversies. The question ‘How common is convergence?’ remains unanswered and may be unanswerable. Our examples indicate that even the minimum detectable levels of convergence are often high, and we conclude that at all levels convergence has been greatly underestimated.     

COMMON EYE PROBLEMS IN CHILDREN

Most penetrating or lacerating injuries of the eye in children justify examination under anesthesia to avoid further harm to an uncooperative patient. The pediatrician in doubt should merely apply a sterile dressing and have an ophthalmologist examine the injury in hospital. Nonperforating injuries may result in severe bleeding 48 to 72 hours later; this may be averted by bandaging the eyes and maintaining rest for four or five days. Removal of foreign bodies should be followed by application of antibiotic ointment and patching to prevent contamination.Congenital stenosis of the lacrimal duct may clear spontaneously or through application of decongestants and sympathomimetic drops. More severe effects, especially infection, justify probing at six months or earlier. The operation should be done under general anesthesia, preferably in hospital.Acute conjunctivitis is best treated by local application of antibiotics or sulfonamides only. Chronic infections may be better managed with the addition of corticosteroids, which reduce local inflammation and control bacterial reaction. Bacterial study should be done only if empirical antibiotic therapy fails. Bacterial desensitization may be helpful. The same methods are effective in blepharitis, aided by hygienic measures. Corticosteroids are most useful in allergic inflammations.Refractive difference is difficult to test before a child can read, and apparent defects may be due to lack of cooperation. Marked inequality of the eyes may signify organic disorder. Strabismus, on the other hand, can be detected as early as 12 or 15 months and should be treated as early as possible by proper lenses, surgery, or both. Pediatricians and parents should be aware that many children appear to have strabismus because of wide epicanthi and deep-set eyes.     

ELBOW AND WRIST INJURIES IN SPORTS

Any disabling injury of the elbow or wrist should be studied roentgenographically for evidence of fracture which may not be otherwise evident but which may cause permanent disability unless the joint is immobilized for healing.“Tennis elbow” may be treated with physical therapy and analgesic injection but may require splinting or tendon stripping. Elbow sprain can occur in the growing epiphysis but is rare in adults. A jarring fall on the hand may cause fracture or dislocation at the elbow.Full extension of the joint should be restored gradually by active exercise rather than passive or forcible stretching.Fracture at the head of the radius may cause joint hemorrhage with severe pain which can be relieved by aspiration. A displacing fracture at the head of the radius requires removal of the head to prevent arthritic changes. Myositis ossificans contraindicates operation until after it has cleared.Healing of wrist fractures may be facilitated by exercise of the shoulder and elbow while the wrist is still in a cast. Fractures of the navicular bone are difficult to detect even roentgenographically and splinting may have to be done on clinical evidence alone.     

SPLENECTOMY IN BLOOD DYSCRASIA

The decision for splenectomy must be based on a knowledge of the three functions of the spleen: Hematopoiesis (usually ceasing during fetal life but sometimes resuming when bone marrow function fails); filtration of abnormal and senescent cells and control of bone marrow activity, most probably humoral.When bone marrow function fails, splenectomy is contraindicated since splenic hematopoiesis becomes a vital function. On the other hand, when a large proportion of erythrocytes are abnormally shaped (spherocytes), although otherwise adequate, the spleen may trap these cells in its filter and destroy large numbers. Splenectomy is beneficial in almost every case of congenital spherocytosis, but in only half the cases of the acquired defect.In panhematocytopenia, thrombocytopenia and neutropenia, all apparently due to depression of hematopoiesis by endocrine or other action of the spleen, splenectomy may be beneficial if medical therapy fails.A surgeon undertaking splenectomy should recognize two special problems: (1) The presence of accessory spleens, which if not removed may negate the effects of the operation, and (2) the apparently high rate of infection in infants and children who have undergone splenectomy.     

蛇莓克隆构型对光照强度的可塑性反应

克隆植物构型的可塑性反应可能是它在资源斑块性状分布的环境中获取资源对策的重要方面,因而可能具有重要的生态学意义。在一田间实验中,匍匐茎草本蛇毒（Duchesnea indica Focke）经历了不同相对光照强度的处理,以研究光照强度对蛇莓克隆构型的影响。结果表明：随着相对光照强度的增加,间隔子的长度逐渐降低,分枝角度、分枝强度和分株密度呈二次曲线变化。结合植物对环境异质性的利用对策,对的揭示的蛇莓克隆构型可塑性进行了讨论。     

THE NUCLEOLI IN MITOTIC DIVISIONS OF MAMMALIAN CELLS IN VITRO

In a number of mammalian cell strains nucleoli persisted through mitosis. This phenomenon was especially pronounced in several cell lines derived from Chinese hamster tissues. All the methods employed, including radioautography with tritiated uridine, cytochemical stains (methyl green-pyronin and azure B), fluorescent microscopy (coriphosphine O), ribonuclease digestion, and electron microscopy, demonstrated that the bodies identified as persistent nucleoli in the mitotic stages had the same characteristics as did the nucleoli in the interphase. Persistent nucleoli may attach to the chromosomes or may be free in the cytoplasm. In cells where no persistent nucleoli as such were noted, nucleolar material was observed to attach to the chromosomes in shapeless masses which moved with the chromosomes during anaphase. At least a portion of the nucleolar material was included in the daughter nuclei, presumably for immediate use for protein synthesis after cell division.     

ELECTROMYOGRAPHY IN STRABISMUS

Electromyography of the human extraocular muscles is a new research tool designed to elucidate many problems in ocular physiology. Although at present it affords little clinical help in the diagnosis and treatment of strabismus, it may in time be of value in neuro-ophthalmologic disease.     

MISCONDUCT IN MEDICAL STUDENTS

Medical students, subject to unique challenges and stressors, frequently engage in misconduct. In this observational study, carried out in a medical school in Colombia, we developed a survey to explore the association between misconduct and stress, potential stressors and other possible contributing factors, such as sex, age and academic year. Of the 433 students that responded to our survey, 97.9% did not fully disagree with at least one of the mentioned misconducts and 99.8% admitted to at least one transgression. Based on a scale we developed, 61.4% of the students consistently agreed with misconduct and 44.9% frequently engaged in misconduct. A logistic regression model suggests that being male (OR 1.90, CI 95% 1.27–2.84) and stress (OR 1.04, CI 95% 1.01–1.06) may increase the likelihood of misconduct. In a subgroup of students, excluding those in their last year of studies, higher academic semester (OR 1.25, CI 95%: 1.10–1.42) may also be a risk factor for misconduct. Most of the observed variation in the data, however, is not explained by these factors. Other modifiers, such as student personality and sub‐culture, may play a greater role in determining misconduct. The proportion of medical students that engage in misconduct is very high and warrants the attention of the medical education community.     

PHOTOTROPISM IN YOUNG RATS

Before the eyelids have opened young rats are negatively heliotropic. They behave very much as does the larva of the blow-fly. The angle of orientation by lights opposed at 180° may be calculated by an equation based upon the elementary requirement of phototropism, namely that orientation is attained when the illumination of bilaterally disposed photoreceptors is equal. The precision of orientation decreases very nearly in proportion to the sum of the logarithms of the acting light intensities, due to photokinetic head movements. When the eyelids are opened, the rats move toward a darkened place in the field of vision, usually toward the shaded region immediately to one side of the lamp house. Therefore, when heliotropic, the rat is not "seeking the dark". The phototropism of these animals may be brought into conflict with their pronounced stereotropism, and the resolution of such conflicts may perhaps be utilized for the investigation of central nervous states.     

PACEMAKERS IN NITELLA : III. ELECTRICAL ALTERNANS

An electrical impulse traveling along a Nitella cell may produce a complete or a partial response. The two kinds of response may occur in regular alternation. The partial response varies greatly and may be so far reduced as to appear as a local thickening in the upstroke of the action curve, usually accompanied by a more or less pronounced hump. In consequence a considerable variety of action curves is produced. The observations show that different regions of the cell may react differently.     

CAROTENOPROTEINS IN INVERTEBRATES

True carotenoproteins are defined as complexes in which a carotenoid and a protein are in stoichiometric combination. Very few carotenoproteins have been purified, but their presence in extracts may often be presumed from spectroscopic evidence. Carotenoids have been found in stoichiometric association with simple proteins, lipoproteins and glycoproteins. Many lipoproteins also occur in which carotenoids form part of the lipid prosthetic group. Although the relationship between the carotenoid and the remainder of the complex may in these cases not appear to be stoichiometric, it often shows some evidence of selectivity. Carotenoproteins are widely distributed among the invertebrate phyla. They are found mainly in exoskeleton or ectoderm and in eggs and ovaries. Their isolation by standard techniques of protein chemistry is facilitated by their characteristic spectral properties. The ease with which carotenoid prosthetic groups are removed from apoproteins suggests that covalent linkages are not involved in the complex formation. The union of carotenoid with apoprotein has been shown, in at least two cases, to stabilize the carotenoid against photo-oxidation and the protein against denaturative changes of tertiary structure. In crustacyanin, the carapace pigment of the lobster, there is clear evidence that the carotenoid is responsible for establishing the very complex quaternary structure. Only astaxanthin, astaxanthin esters and canthaxanthin have been unequivocally identified as carotenoid prosthetic groups of true carotenoproteins. Experiments in the specificity of interaction of a series of carotenoids with the apoprotein of crustacyanin have indicated the requirement of one or both of the 4- and 4′-keto groups of the carotenoid for interaction with the protein. It is suggested that, at least in this case, the carotenoid-protein interaction might occur between carotenoid keto groups and basic residues of the protein in such a way as to provide a lock on the tertiary configuration. Carotenoproteins may participate in a variety of functions including protective coloration, photosensitivity, electron transport and enzymic activity. They appear, furthermore, to play some part in development.     

VARIATIONS IN THE NATURAL HISTORY OF PSORIASIS

Latent psoriasis is a state which exists before the development of clinical psoriasis and wherein probably some as yet undiscovered defect exists. Investigation concerning a group of persons with latent psoriasis might disclose basic aberrations.The natural course of psoriasis may be altered by therapy. Folic acid antagonists and intradermal corticosteroids may at times eclipse psoriatic lesions. Oral adrenal corticosteroids may prove morbidistatic but on discontinuance a rebound flare may occur which is both protracted and recalcitrant. Antimalarial agents when employed as therapy for coexistent arthridites may cause psoriasis to become more severe.The Goeckerman regimen which employs topical tar and ultraviolet light therapy produces in some 75 per cent of patients a prolonged remission. As it is safe and repeatable it is favored for the usual severe case of psoriasis.Psoriasis therapy is better assessed by considering its effect on the natural evolution of the disease.     

真菌和氮素在食物链中与胃癌病因关系的探讨

作者等根据假设,即真菌与氮素通过食物链过程进入人体,由于真菌毒素或其代谢产物与胃内亚硝酸盐、胍类、胺类等合成致癌性亚硝基化合物,并在慢性胃炎的基础上逐渐发展为胃癌,在我国胃癌高,低发区进行了综合考察。本文报告考察结果,发现胃液内杂色曲霉(Aspergillus versicolor)检出率最高,高低发区对比差异显著(p<0.001)。此菌与胃液的pH值、酸度、NO_2~-含量、胃粘膜活检结果关系密切。已知杂色曲霉产的杂色曲霉素(sterigmatocystin)可诱发大鼠的腺胃癌,因此考虑此菌与人胃癌的发生可能有关,但是否为因果关系,尚需进一步实验研究。     

COMPARATIVE MEGASPOROGENESIS IN PAPILIONACEAE

Megasporogenesis in 16 species of Papilionaceae has been investigated. Archesporial development in Papilionaceae is usually hypodermal, but subhypodermal origin has been observed. The archesporial cell develops directly into the megasporocyte, or divides to produce a parietal cell and a primary sporogenous cell. The parietal cell is always oriented toward the micropylar end of the developing ovule. It may or may not divide to contribute to the nucellar mass as the primary sporogenous cell enlarges to form the megasporocyte. A single megasporocyte is produced in most species investigated. Of those species that form more than one megasporocyte, few develop more than one tetrad of megaspores, and in no case is more than one megagametophyte produced. Meiosis occurs in the megasporocyte to form a tetrad of megaspores. Several variations in tetrad patterns are explored here. Monosporic development is the prevalent condition in Papilionaceae; however, bisporic development does occur.     

MEIOSIS IN VITRO: SPOROGENESIS IN CULTURED FERN PLANTS

Sporangia containing mature, functional spores can be induced to form on pinnae of Todea barbara sporophytes maintained in nutrient culture. Meiosis is initiated in the sporogenous cells and proceeds to completion in vitro with the formation of viable spores. Sporangial development, meiosis and the production of spores occur in plants which exhibit signs of senescence. Fertile leaves are characterized by a reduction in chlorophyll concentration and total cellular nitrogen when compared to sterile leaves. The data suggest that the process of sporogenesis may be correlated with a reduction in metabolic activity of the leaf.     

FUNGISTASIS IN SOILS

1. Fungistasis in soil is a widespread phenomenon affecting most fungal propagules, though some are insensitive. In most instances, it is coexistent with the presence of living microorganisms, and is annulled by energy-yielding nutrients. Fungistasis with characteristics similar to that in soil may also occur on leaves of plants. 2. Germination and growth of bacteria and actinomycetes is also restricted in soils. The characteristics of their inhibition appear to be the same as those for fungi. Therefore, the concept of a widespread microbial inhibition in soil can be applied to all three groups of microorganisms. 3. Fungistasis can be detected by various direct methods, or indirectly by methods involving the use of porous or permeable carriers. It may be expressed as a restriction on the final amount of germination (the usual parameter), germination rate (with time), and rate of germ-tube or hyphal growth. Since the expression of fungistasis is often complete in soil, titration with nutrients may be required to distinguish between the sensitivities of different fungi. 4. Fungistasis generally is expressed most strongly at soil moisture contents somewhat less than saturation. Its expression usually is maximal in neutral or slightly alkaline soils. In acidic conditions fungistasis may be lessened because of suppression of bacterial and actinomycete activity. Increased sensitivity of some fungi in soils of pH > 7.0 may be caused by a directly unfavourable effect of pH on the fungus. 5. Fungal species with small spores tend to be highly sensitive to fungistasis. These spores tend to germinate slowly and to require exogenous nutrients for germination. By contrast, species with larger spores and sclerotia often do not require exogenous nutrients for germination. The larger spores tend to germinate rapidly and to exhibit low sensitivity, as compared with small spores. A few nutrient-independent spores are insensitive to fungistasis. At least a part of the difference in sensitivity is related to germination time; spores which germinate slowly compete poorly with the soil micro-flora for their nutrients. 6. Fungistasis is often temporarily annulled by enriching the soil with energy-yielding nutrients. Usually, complex materials such as plant residues are most effective. A few weeks after such treatment, the level of fungistasis may, however, be increased. Annulment of fungistasis by compounds not utilized as energy sources has not yet been demonstrated. 7. Several soils naturally suppressive to Fusarium wilt diseases were more fungistatic to Fusarium than soils conducive to wilt. Potential means by which fungistasis may be manipulated to control root-infecting fungi are (a) through stimulation of germination with nutrients, thus exposing the germ tube to lysis, and (b) by increasing the fungistatic level of soil through appropriate amendments. 8. Volatile substances identified in soils, some of which are potentially inhibitory to fungi include (a) ammonia, which apparently is evolved from ammonium salts in some arid soils of high pH, (b) ethylene, which has been identified in some soils of pH < 7.0 (though high levels of this gas seem to be tolerated by most fungi), (c) allyl alcohol, and (d) other unidentified substances. Non-volatile inhibitors include high molecular weight substances revealed by molecular sieve chromatography of soil extracts. Microbial metabolites such as those present in staled fungal cultures also have been proposed to account for fungistasis. In a few soils fungistasis persists after sterilization because of the presence of inhibitory concentrations of calcium carbonate, iron or aluminium. Inherent in the proposition that inhibitory substances provide the primary mechanism of fungistasis is the concept of a highly complex phenomenon, involving various highly specific inhibitory and counteracting stimulatory substances, with the outcome for the fungus depending on the kinds and relative amounts of each present. 9. By the nutrient-deficiency hypothesis, the level of available nutrients in soil is insufficient to support germination of nutrient-dependent propagules, except in nutrient-rich microsites. Inhibition of nutrient-independent propagules is explained by loss of endogenous nutrients required for germination, through microbial nutrient competition. Evidence for this hypothesis is (a) the imposition of fungistasis on numerous nutrient-independent propagules during incubation on leaching model systems designed to simulate microbial nutrient competition in soil, (b) similar losses of endogenous nutrients occurring on soil and the leaching system, and (c) the fact that soils are chronically deficient in energy in relation to the microbial populations present, with the consequence that enforced inactivity is imposed upon most of the population at any given time for this reason alone, regardless of the presence or absence of fungistatic substances. Journal series article no. 7747 from the Michigan Agricultural Experiment Station.