Differential effects of elevated ultraviolet-B radiation on the photochemical and reproductive performances of dicotyledonous and monocotyledonous arid-environment ephemerals

Four dicotyledonous Astcraceac and four monocotyledonous Iridaceac species were grown from seed under three different effective ultraviolet-B (UV-B, 280–320 nm) fluenccs, which approximated those received daily over the natural growing periods of these species at their southerly and northerly distribution limits under ambient stratospheric ozone, and at the northerly limit assuming a 20% ozone depletion. Diminished photochemical efficiencies, delayed flowering, decreased flower production, pollen germination and tube growth, and reduced numbers of seeds set, accompanied by corresponding increases in mass per seed, were observed mainly in dicotyledons under elevated UV-B radiation, despite their higher foliar and pollen polyphenolic contents, their possession of trinucleatc pollen and their natural occurrence at lower latitudes than monocotyledons with binucleate pollen. The results demonstrate the difficulties in determining plant sensitivity to UV-B radiation from polyphenolic content, pollen type and natural geographic distribution, and suggest that monocotyledons possess other attributes that confer greater resilience to UV-B radiation.     

Divergence in cuticular hydrocarbons between parapatric subspecies of the meadow grasshopper, Chorthippus parallelus (Orthoptera, Acrididae)

Two subspecies of the grasshopper Chorthippus parallelus (Orthoptera; Acrididae) meet and form a hybrid zone in the Pyrenees. Here we investigate whether the subspecies differ in the blend of cuticular hydrocarbons. Such differences may function as chemical signals, being detected via contact chemoreception and used during mate choice as in other insects. Gas chromatography shows that the subspecies have diverged in the composition of their cuticular hydrocarbons. This difference between subspecies exists over and above variation in cuticular hydrocarbons among individual populations. The majority of the difference can be attributed to the relative amounts of a small group of compounds present in the cuticle. The possible consequences of this chemical divergence for mating encounters between the subspecies are discussed.     

Oxidative stress and antioxidant content in Chlorella vulgaris after exposure to ultraviolet-B radiation

Growth of Chlorella vulgaris was measured in cultures irradiated with 0, 0.8, 2.0 and 4.4 kJ m² UV-B. Growth expressed as chlorophyll content, declined significantly with increased UV-B dose. Ultraviolet-B irradiated cultures in log phase of growth showed a 284% increase in oxygen radical generation and a 145% increase in lipid peroxidation compared with unirradiated cultures, whereas cultures in the stationary growth phase showed no significant changes in these parameters. The activities of superoxide dismutase and catalase increased by 40 and 500%, respectively, after exposure to a UV-B dose of 4.4 kJ m⁻². Contents of the lipophilic antioxidants α-tocopherol and β-carotene increased by 180 and 63 amol cell⁻¹ respectively, between log and stationary phases in unirradiated cultures; but in UV-B-irradiated cultures these increases were significantly depressed. Photoreducing capacities of chloroplasts were decreased following UV-B irradiation of both isolated chloroplasts and those isolated from irradiated algae. Cells exposed to UV-B exhibited increased size and starch accumulation. These results suggest that oxidative stress conditions related to UV-B exposure trigger an antioxidant response that includes an increase in the activity of the antioxidant enzymes (superoxide dismutase and catalase).     

Effects of UV-B radiation and nitrogen starvation on enzyme activities in isolated plasma membranes of Euglena gracilis

Circadian rhythms are characteristic of many physiological and biochemical processes in the freshwater flagellate Euglena gracilis. Earlier, we found that the rhythms of photosynthesis, phototaxis and cell shape followed the same pattern in control organisms, but were differently affected by stress such as UV-B irradiation and nitrogen deficiency. Here we extend our studies to use isolated plasma membranes to characterize the rhythms of some plasma membrane-bound enzymes. Also, we wanted to see whether stress-induced changes of these rhythms could be detected at the subcellular level and possibly be coupled to the changes seen in photosynthesis, phototaxis and cell shape. The isolation of plasma membranes using aqueous polymer two-phase partitioning was successful, as judged by the large enrichment of the plasma membrane-marker 5′-nucleotidase, and the difference in the polypeptide pattern compared with the microsomal fraction from which it was prepared. Two other enzymes were analyzed, K⁺, Mg²⁺-ATPase, and adenylyl cyclase. The specific activities of all three enzymes were decreased by UV-B radiation by ca 30–50%, compared with the control cultures. On the other hand, nitrogen deficiency not only reduced the activity of the K⁺.Mg²⁺-ATPase but also increased the activities of the 5′-nucleotidase and adenylyl cyclase. The different treatments also resulted in differences in polypeptide pattern, e.g., a polypeptide around 30 kDa seemed to be specific to plasma membranes of nitrogen-deficient cultures and one at 39 kDa for the UV-B radiated ones. All three enzymes showed diurnal rhythms that were affected by UV-B radiation. The peak in the rhythm of the ATPase was shifted by UV-B radiation, the rhythm of the 5′-nucleotidase nearly eliminated. The first peak of adenylyl cyclase activity was delayed, so that it looked more like a broad peak between 2 and 11 h after the onset of light. The rhythm of ATPase activity could be correlated with that of photosynthesis in both control and UV-B irradiated cultures. Also, the rhythms of adenylyl cyclase activity and cell shape changes showed some similarities.     

PERSPECTIVE: DARWIN,PROGRESS, AND ECONOMIC PRINCIPLES

Darwin's concept of progress was an economic one, with the accumulation of adaptations having a strong analogy to technological innovations. This interpretation makes it easier to understand his differences with Lamarck and others whose views he considered metaphysically objectionable. It also clarifies his relationship to Malthus and such features of his theory as the episodic nature of evolutionary change. His position is consistent with modern theories of biotic invasions and long-term evolutionary trends. It also accords well with current efforts to produce a synthesis between biology and economics.     

Phylogeny and adaptive radiation within the Anomopoda: a preliminary exploration

The distinctness of the Anomopoda and the polyphyletic nature of the so-called Cladocera are emphasized.An attempt is made to reconstruct the ancestral anomopod, which probably lived in Palaeozoic times. This task is facilitated by the availability of detailed information on extant forms, which includes functional as well as purely morphological considerations and enables us to understand the means whereby complex mechanisms were transformed during evolution. Comparative studies on the ecology and habits of extant forms also throw light on the probable way of life of the ancestral anomopod.Adaptive radiation within the Anomopoda is briefly surveyed and an outline of the suggested phylogeny of the order is indicated.Institute of Environmental and Biological Sciences, University of Lancaster     

A VIP hybrid antagonist: From developmental neurobiology to clinical applications

Summary 1. The 28 amino acid vasoactive intestinal peptide, VIP, was originally isolated from the intestine, following a bioassay measuring vasodilating properties. Immunocytochemistry, receptor binding assays and in situ hybridizations have demonstrated VIP abundance in the nervous system, suggesting multiple bioactivities.2. A pharmacological approach was chosen to dissect VIP activities and a prototype VIP antagonist (Met-Hybrid) consisting of a carboxyl fragment of VIP_7–28 and a six amino acid fragment of neurotensin, neurotensin_6–11-VIP_7–28 was synthesized.3. This hybrid peptide was designed to maintain the binding capacity of one parent molecule (VIP), while loosing the agonistic properties, representing a classical competitive receptor antagonist. Furthermore, the new molecule exhibited increased specificity to central nervous system VIP receptors.4. The Met-Hybrid was originally discovered as a potent inhibitor of VIP functionin vivo. In the adult rodent, acute administration of the antagonist resulted in blockade of VIP-mediated potentiation of sexual behavior and chronic intracerebroventricular application impaired VIP-associated learning abilities. During ontogeny, chronic injections of the molecule resulted in neuronal damage, disruption of the diurnal rhythmicity of motor behavior, and retardation in the acquisition of neonatal reflexes in the rat.5. During gestation, severe microcephaly was induced by acute administration of the Met-Hybrid to pregnant mice. The hybrid antagonist inhibited VIP-stimulated mitosis in whole embryo cultures and in a variety of cancer cell linesin vitro andin vivo, suggesting therapeutical potential.     

Islands: stability, diversity, conservation

Islands present both a diversity and a stability paradox. They are often highly species-poor but have considerable biological interest in terms of extraordinary endemic genera and taxonomically isolated groups. They appear to be stable, as in some cases these organisms have persisted for many millions of years, and having an oceanic climate, extreme climatic events may be comparatively rare. However, when subject to extrinsic (anthropogenic) disturbance they do not appear to be stable, but often suffer catastrophic ecological change. These apparent paradoxes are resolved when it is realized that all these features are consequences of the same island characteristics: biotic isolation and oceanicity. As a result of these two characteristics, far oceanic islands are quantitatively different from continental systems in the nature of their ecological processes, which appear to give rise to an extreme punctuated equilibrium model of evolutionary change. Endemics may be ancient relict endemics displaying prolonged stasis and persistence, or products of adaptive radiation representing rapid punctuational events. A process-based definition of a relict endemic (palaeoendemic) is one whose founding lineage (i.e. the original continental source taxon) has not left any descendents. A corollary of this definition is that the time of divergence between an endemic and its continental sister-group should predate the colonization of the island by the now endemic lineage. An example is Dicksonia arborescens which has been on St Helena for at least 9 Myrs and no longer occurs in the likely source area of Africa. These relict endemics, frequent on islands, are important as the last remnants of tranches of biodiversity that have vanished elsewhere. Island conservation strategies require an integrated understanding of both sides of the diversity and stability paradox so that both island processes and island organisms can be conserved.     

Species-independent, geographical structuring of chloroplast DNA haplotypes in a montane herb Ipomopsis (Polemoniaceae)

Two hypotheses have been proposed to explain the occurrence of hybrid zones between red-flowered Ipomopsis aggregata and white-flowered I. tenuituba . Either local adaptation to hummingbird and hawkmoth pollinators has given rise to sympatric (or parapatric) divergence of flower colour and morphology (primary intergradation at hybrid zones), or alternatively two previously allopatric species are coming into contact at several geographical areas of secondary intergradation. We examined restriction site patterns in nuclear DNA (nrDNA), chloroplast DNA (cpDNA) and mitochondrial DNA (mtDNA) from populations of I. aggregata and I. tenuituba representing seven zones of sympatry. No variation was detected in a 350-bp fragment of mtDNA and uninformative levels of variation were observed for nrDNA. We detected 22 potentially informative restriction site polymorphisms in cpDNA, all of which united geographical areas containing populations of both species. We detected no informative species-specific markers. Studies of other species (e.g. oaks) have detected similar species-independent geographical structure of cpDNA. However, in these cases secondary interegradation could be inferred from species-specific nuclear alleles. The pattern in Ipomopsis is consistent with both primary intergradation (independent speciation in each area of sympatry) or secondary intergradation involving complete cytoplasmic replacement. Thus, additional data are needed to explain the origin of hybrid zones in Ipomopsis .