Animal evolution. The end of the intermediate taxa?

Contrary to general belief, there has not been a reliable, global phylogeny of animals at hand within the past few decades. Recent progress in molecular phylogeny is rapidly changing the situation and has provided trees that constitute a reference frame for discussing the still controversial evolution of body plans. These trees, once purged of their possible artefacts, have already yielded confirmation of traditional, anatomically based, phylogenies as well as several new and quite significant results. Of these, one of the most striking is the disappearance of two superphyla (acoelomates such as flatworms, pseudocoelomates such as nematodes) previously thought to represent grades of intermediate complexity between diploblasts (organisms with two germ layers) and triploblasts (organisms with three germ layers). The overall image now emerging is of a fairly simple global tree of metazoans, comprising only a small number of major branches. The topology nicely accounts for the striking conservation of developmental genes in all bilaterians and suggests a new interpretation of the 'Cambrian explosion' of animal diversity.     

The genius of E. E. metchnikoff— Discoveries over the centuries

On the 15 of May we celebrated the 150th anniversary of the outstanding Russian biologist Elias E. Metchnikoff (1845–1916)—Nobel Prize winner (1908), full and honorary member of many scientific academies of the world. His main works were applied to the zoology of invertebtates, evolution, embryology, immunology, microbiology, infectious pathology, gerontology, etc. Elias Metchnikoff published essays on anthropology, theory of orthobiosis, role of social and social-hygienic factors in solving the problems of old age and life elongation. On 30 May-2 June 1995 an International Symposium dedicated to Metchnikoff's 150th anniversary was held in Moscow. This is a text of the lecture given by us at the opening ceremony.     

The ‘Embryonic moults’ of the milkweed bug as seen by the S.E.M.

Deposition, detachment and removal of the three embryonic cuticles are studied. The menbrane-like cuticle 1 covers the embryo during katatrepsis and ‘disappears’ thereafter. Cuticle 2 deposition starts shortly before dorsal closure. Its apolysis is accompanied by contractions of the embryo. Ecdysis of cuticle 2 takes place during hatching. Only cuticle 3 (= first larval cuticle) shows differentiations like sensilla and cornea. Peaks of ecdysteroid (and probably JH) titre are observed during apolysis of cuticle 1 and cuticle 2 (Dorn, 1981). Transition from ectoderm to epidermis proper takes place shortly before and during onset of cuticle 2 synthesis.     

The formation of vesicles in the developmental cycle of the nodular endophyte of Hippophaë rhamnoides L.

Summary The mature vesicle of the Hippophaë rhamnoides root nodule endophyte is spherical, approximately 3–4 m in diameter and exhibits a high degree of apparently random septation. Electron micrographs are presented which show that this vesicular form in the endophytic development within the host cell originates as a swelling of the hyphal tip. The young vesicle is non-septate and in general attains a minimum diameter of 3 m before septation becomes evident. The number of septa then increases with vesicle maturity.     

Thoughts of a travelling ecologist 12.The plight of the monarch butterfly

<正>Nature conservation needs people who care about nature,and the efforts to convince people to care about the fate of nature has extensively relied on selected charismatic species,the"conservation icons".One famous example is the great panda,Ailuropoda melanoleuca,well known as the World Wide Fund for Nature(WWF)logo.When it comes to invertebrates,the     

The pharmacology of the isolated foregut of the locust schistocerca gregaria—I. the effect of a range of putative neurotransmitters

1. Isolated locust foreguts exhibited little or no spontaneous contractile activity.2. Proctolin (10⁻⁹m-10⁻⁶m) caused rapid and powerful contraction of the tissue while the response to similar doses of l-glutamate was much weaker.3. 5-HT (10⁻⁸M-5 × 10⁻⁶M), acting at ketanserin-sensitive receptors, was the most powerful tissue relaxant tested.4. Relaxation caused by octopamine (10⁻⁷M-10⁻⁵M), acting at ketanserin-insensitive receptors was less than 50% of that caused by similar concentrations of 5-HT.5. ACh (10⁻⁵M-10⁻³M) induced relaxation, mimicked by nicotine and antagonised by d-tubocurarine, was seen only in the presence of the anti-cholinesterase neostigmine.     

The primary DNA-binding subsite of the rat pol β. Energetics of interactions of the 8-kDa domain of the enzyme with the ssDNA

Interactions of the 8-kDa domain of the rat pol β and the intact enzyme with the ssDNA have been studied, using the quantitative fluorescence titration technique. The 8-kDa domain induces large topological changes in the bound DNA structure and engages much larger fragments of the DNA than when embedded in the intact enzyme. The DNA affinity of the domain is predominantly driven by entropy changes, dominated by the water release from the protein. The thermodynamic characteristics dramatically change when the domain is embedded in the intact polymerase, indicating the presence of significant communication between the 8-kDa domain and the catalytic 31-kDa domain. The diminished water release from the 31-kDa domain strongly contributes to its dramatically lower DNA affinity, as compared to the 8-kDa domain. Unlike the 8-kDa domain, the DNA binding of the intact pol β is driven by entropy changes, originating from the structural changes of the formed complexes.     

The 125th anniversary of the first postulation of the soil origin of endophytic bacteria – a tribute to M.L.V. Galippe

Aims

In spite of the important role played by herbivory in plant community structure and the fact that it constitutes one of the most important ecological disturbance processes in the dynamics of both natural and anthropic systems, few studies have concentrated on the consequences of browsing on vegetation spatial patterns. The main objective of this study was to examine the role of domestic livestock pressure in the spatial distribution pattern and interspecific competition of two sand dune shrubs: Retama monosperma and the endangered species Thymus carnosus.

Methods

We compared three areas featuring different intensities of livestock pressure. Two 25 × 25 m plots were established in each study area, and the crown heights, diameters and x, y coordinates of every individual in each plot were recorded.

Results

Livestock activity produced a considerable effect, not only on plant cover and size (larger and higher crowns of both species in non herbivory plots) but also on spatial pattern. Whereas light herbivory lead to a random spatial pattern for both species, high herbivory resulted in a repulsion one.

Conclusions

Under high and no livestock pressure, T. carnosus is displaced by R. monosperma, creating a repulsion point pattern distribution between the two species. However, when livestock disturbance was low, our data reveal relatively higher T. carnosus cover values than in the other livestock pressure scenarios, along with a random distribution pattern.     

Contributions to the mathematical theory of epidemics—II. The problem of endemicity

(1) A mathematical investigation has been made of the prevalence of a disease in a population from which certain individuals are being removed as the result of the disease, whilst fresh individuals are being introduced as the result of birth or immigration. Allowance is made for the effects of the immunity produced as the result of an attack of the disease, but the effect of deaths from other causes is not taken into account, and the action of the disease is supposed to be independent of the age of the individual. (2) As a special case of the above, results have been obtained for a closed population in which no deaths occur and to which no fresh individuals are added, but in which the individuals after being infected acquire immunity, and then may be again infected. A threshold density of population exists analogous to that described in the previous paper, which is such that no disease can exist in a population, the density of which is below the threshold. (3) In other special cases investigated when either immigration or birth is operative in the supply of fresh individuals, as well as in the general case, only one steady state of disease is possible. To reach this state the population must be of a certain density which will be determined by the functions characterizing the infectivity, morbidity, etc., of the disease. (4) Increase of the immigration rate or of the birth-rate results in an increase in the rate of infection of the healthy individuals and also in the percentage rate of infection, the percentage of sick, and in the percentage of mortality from the disease. This result is, of course, a necessary consequence of our assumption that the disease is the only cause of death. (5) More particular results have been obtained by substituting constants in the place of the undetermined functions assumed in the general theory. Further, under these conditions the nature of the steady states has been more fully investigated and it has been shown that in all cases, except one, the steady states are stable ones. In the exception, a disturbance would result in purely periodic oscillations about the steady state.     

The Functional Role of the Hollow Region of the Butterfly Pyrameis atalanta （L.） Scale

Questions concerning the functional role of the hollow region of the butterfly Pyrameis atalanta （L.） scale are experimentally investigated. Attention was initially directed to this problem by observation of the complex microstrucmre of the butterfly scale as well as other studies indicating higher lift on butterfly wings covered with scale. The aerodynamic forces were measured for two oscillating scale models. Results indicated that the air cavity of an oscillating model of the Pyrameis atalanta （L.） scale increased the lift by a factor of 1.15 and reduced the damping coefficients by a factor of 1.38. The modification of the aerodynamic effects on the model of butterfly scale was due to an increase of the virtual air mass, which influenced the body. The hollow region of the scale increased the virtual air mass by a factor of 1.2. The virtual mass of the butterfly scale with the hollow region was represented as the sum of air mass of two imaginary geometrical figures： a circular cylinder around the scale and a right-angled parallelepiped within the hollow region. The interaction mechanism of the butterfly Pyrameis atalanta （L.） scale with a flow was described. This novel interaction mechanism explained most geometrical features of the airpermeable butterfly scale （inverted V-profile of the ridges, nozzle of the tip edge, hollow region, and openings of the upper lamina） and their arrangement.     

The British Species of the Plagiothecium denticulatum–P. silvaticum Group

Abstract

Anomodon viticulosus was subjected to several different patterns of alternating wet and dry periods, and assimilation was measured at intervals over 49 days. Short periods of desiccation intercalated between 6-day moist periods had little effect on subsequent performance. Short moist periods breaking otherwise continuous desiccation had a very pronounced effect in mitigating desiccation damage. The results provide some evidence for a fairly slight, but probably cumulative, specific deleterious effect of drying and remoistening.     

The foraging behavior of honeybees on hairy vetch. III. — Differences in the vetch

Summary The time required for each of 50 honeybees to forage from a hairy vetch blossom, and the time required for each bee that tripped blossoms to trip a different blossom was measured three times each in two fields. There were highly significant differences in the speed with which bees tripped and foraged from blossoms in the two fields. It appeared that the blossoms in one field were easier to trip than the blossoms in the other. The bees spent less time foraging from the blossoms in the field in which tripping was most rapid, probably because there was less nectar in the blossoms in that field than in the other field. The bees that did not trip blossoms foraged from blossoms more rapidly than the bees that did trip the blossoms. After all known sources of variation had been removed there was a highly significant correlation between the times required for bees to trip and to forage from blossoms; this is interpreted as indicating differences in the efficiency of individual bees. In one of the fields many of the bees foraged through punctures in the blossoms made by carpenter bees. An attempt was made to measure the relationship of the amount of sugar collected by bees per unit time to the attractiveness of competing plants.Published as Technical Contribution No. 4636 from theTexas Agricultural Experiment Station.