Baring it all: undressing Cambrian ‘Orsten’ phosphatocopine crustaceans using synchrotron radiation X‐ray tomographic microscopy

Synchrotron radiation X‐ray tomographic microscopy (SRXTM) was used to virtually dissect and peel the shields off of the microscopic, bivalved phosphatocopine crustaceans in the Cambrian ‘Orsten’ type of preservation of Sweden. Doing so opened up for an array of concealed internal structures to be observed in a fully enclosed specimen of Hesslandona ventrospinata and a semi‐enclosed specimen of Hesslandona angustata. For comparison, also a head‐larva stage specimen of H. angustata, with shields in ‘butterfly position’, was analysed. The X‐ray tomographic data sets revealed excellently preserved structures, such as labrum, sternum, antennae, mandibular and post‐mandibular limbs with their minute setae, all of which were more or less disguised by the enclosing shields. This, moreover, allowed assignment to growth stages of the specimens, which is impossible based solely on external morphology and size. Micro‐spherules observed inside the shields of the semi‐enclosed H. angustata specimen may represent remains of food particles, and the feeding biology of phosphatocopines is discussed in detail. Our analyses suggest that phosphatocopines were particle feeders. The SRXTM technique offers the ability to three‐dimensionally reconstruct the morphology in high resolution, construct virtual serial sections and study concealed structures. The resulting data allow for new structures to be revealed for previously known taxa and for new taxa to be identified, with the added benefit of not destroying the specimens in the process. Hence, we do not longer have to rely on serendipitous finds of broken and/or open phosphatocopine specimens to elucidate their diagnostic ventral morphology.     

P53 and the defenses against genome instability caused by transposons and repetitive elements

The recent publication by Wylie et al. is reviewed, demonstrating that the p53 protein regulates the movement of transposons. While this work presents genetic evidence for a piRNA‐mediated p53 interaction with transposons in Drosophila and zebrafish, it is herein placed in the context of a decade or so of additional work that demonstrated a role for p53 in regulating transposons and other repetitive elements. The line of thought in those studies began with the observation that transposons damage DNA and p53 regulates DNA damage. The presence of transposon movement can increase the rate of evolution in the germ line and alter genes involved in signal transduction pathways. Transposition can also play an important role in cancers where the p53 gene function is often mutated. This is particularly interesting as recent work has shown that de‐repression of repetitive elements in cancer has important consequences for the immune system and tumor microenvironment.     

The light‐driven sodium ion pump: A new player in rhodopsin research

Rhodopsins are one of the most studied photoreceptor protein families, and ion‐translocating rhodopsins, both pumps and channels, have recently attracted broad attention because of the development of optogenetics. Recently, a new functional class of ion‐pumping rhodopsins, an outward Na⁺ pump, was discovered, and following structural and functional studies enable us to compare three functionally different ion‐pumping rhodopsins: outward proton pump, inward Cl^? pump, and outward Na⁺ pump. Here, we review the current knowledge on structure‐function relationships in these three light‐driven pumps, mainly focusing on Na⁺ pumps. A structural and functional comparison reveals both unique and conserved features of these ion pumps, and enhances our understanding about how the structurally similar microbial rhodopsins acquired such diverse functions. We also discuss some unresolved questions and future perspectives in research of ion‐pumping rhodopsins, including optogenetics application and engineering of novel rhodopsins.

     

Effects of habitat isolation on pollinator communities and seed set

Destruction and fragmentation of natural habitats is the major reason for the decreasing biodiversity in the agricultural landscape. Loss of populations may negatively affect biotic interactions and ecosystem stability. Here we tested the hypothesis that habitat fragmentation affects bee populations and thereby disrupts plant-pollinator interactions. We experimentally established small ”habitat islands” of two self-incompatible, annual crucifers on eight calcareous grasslands and in the intensively managed agricultural landscape at increasing distances (up to 1000 m) from these species-rich grasslands to measure effects of isolation on both pollinator guilds and seed set, independently from patch size and density, resource availability and genetic erosion of plant populations. Each habitat island consisted of four pots each with one plant of mustard (Sinapis arvensis) and radish (Raphanus sativus). Increasing isolation of the small habitat islands resulted in both decreased abundance and species richness of flower-visiting bees (Hymenoptera: Apoidea). Mean body size of flower-visiting wild bees was larger on isolated than on nonisolated habitat islands emphasizing the positive correlation of body size and foraging distance. Abundance of flower-visiting honeybees depended on the distance from the nearest apiary. Abundance of other flower visitors such as hover flies did not change with increasing isolation. Number of seeds per fruit and per plant decreased significantly with increasing distance from the nearest grassland for both mustard and radish. Mean seed set per plant was halved at a distance of approximately 1000 m for mustard and at 250 m for radish. In accordance with expectations, seed set per plant was positively correlated with the number of flower-visiting bees. We found no evidence for resource limitation in the case of mustard and only marginal effects for radish. We conclude that habitat connectivity is essential to maintain not only abundant and diverse bee communities, but also plant-pollinator interactions in economically important crops and endangered wild plants. Received: 7 May 1999 / Accepted: 19 July 1999     

Programme of senescence in petals and carpels of Pisum sativum L. flowers and its control by ethylene

The role of ethylene in the control of senescence of both petals and unpollinated carpels of pea was investigated. An increase in ethylene production accompanied senescence, and the inhibitors of ethylene action were effective in delaying senescence symptoms in different flower verticils. Pollination did not seem to trigger the senescence syndrome in the corolla as deduced from the observation that petals from pollinated and unpollinated flowers and from flowers whose carpels had been removed senesced at the same time. A cDNA clone encoding a putative ethylene-response sensor (psERS) was isolated from pea flowers, and the pattern of expression of its mRNA was studied during development and senescence of different flower tissues. The levels of psERS mRNA paralleled ethylene production (and also levels of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) mRNA) in both petals and styles. Silver thiosulfate treatments were efficient at preventing ACO and psERS mRNA induction in petals. However, the same inhibitor showed no ability to modify expression patterns in pea carpels around the anthesis stage, suggesting different controls for ethylene synthesis and sensitivity in different flower organs. Received: 18 June 1998 / Accepted: 22 December 1998     

The presence of heterospecific pollen on stigmas of nectariferous and nectarless orchids and its consequences for their reproductive success

Summary The widespread occurrence of nonorchid, heterospecific pollen grains on the stigmatic surfaces of a range of nectariferous and nectarless European orchids (Dactylorhiza. Orchis, Goodyera, andGymnadenia species) is reported for the first time, and the impact of heterospecific pollination on orchid reproductive success is experimentally investigated. There are three main components of stigmatic contamination by heterospecific pollen: the frequency of contamination, the diversity of foreign species present on the stigma, and the amount of pollen deposited. Six out of seven of the species examined have greater than 85% of stigmas contaminated with wind and insect-dispersed pollen. From one to nine insect-dispersed foreign pollen species are present per stigma, including pollen of members of the families Apiaceae, Asteraceae, Caryohpyllaceae, Ericaceae, and Primulaceae. Average loads per stigma vary from 13 to 176 grains, with individual stigma loads ranging from one to 909. Whether or not the orchid provides nectar has a major impact on these three components. Nectarless orchids have the greatest frequencies of contamination, diversity of species, and average load per stigma. Insect-dispersed pollen is deposited both by pollinators and visitors but, in spite of low levels of pollination, nectarless orchids still exhibit higher frequencies of heterospecific pollen contamination. The effect of the presence of heterospecific pollen on the reproductive success of orchids is tested in this study for the first time. Average-to-high, naturally occurring loads of heterospecific pollen derived from a mixture ofArmeria maritima,Caltha palustris,Cochlearia officinalis,Cytisus scoparius, andPrimula vulgaris and consisting of 50–250 grains per load are placed onto stigmas ofDactylorhiza purpurella which are subsequently self-pollinated with half of a pollinium. All pollinations produce capsules indicating that heterospecific pollen does not affect fruit set. Although experimental and control fruits are similar in size, they differ in total seed weight and composition. Total seed weight is reduced and the proportion of seeds with normal embryos decreased while the proportion of unfertilised ovules increased following pollination with heterospecific pollen, indicating a detrimental effect on fertilisation. Lower reproductive success caused by fertilisation failure is likely to be most severe in nectarless species because of their generally higher levels of contaminated stigmas. As nectarless orchids are known to have lower fruit set compared with nectariferous ones, this finding suggests that the reproductive success of nectarless orchids may be even lower than previously realised.Abbreviations RS reproductive success     

Evidence for stabilising selection acting on flowering time in Arum maculatum (Araceae): the influence of phylogeny on adaptation

The relationship between flowering time and reproductive success was investigated in the fly-pollinated, monoecious perennial herb Arum maculatum L. (Araceae). This species temporarily traps its principle pollinator, a psychodid midge. Probability of fruit set was analysed in relation to early, peak and late periods of the flowering phenology of four British populations between 1992 and 1997. In three out of five cases, plants which flowered during early and late periods were significantly less likely to set fruit. In addition, one population showed a similar relationship for percentage fruit set of individual inflorescences, and seeds from peak-flowering plants were significantly heavier. There was no variation in number of female flowers per inflorescence over the flowering season. Probability of fruit set appears to be mediated by the likelihood of trapping psychodid midges that have previously been trapped and picked up pollen, an unlikely event during early and late flowering periods when few inflorescences are open. The majority of plants in all populations produce only one inflorescence which means that timing of flowering may be crucial to reproductive success. We interpret our findings as evidence that stabilising selection may be acting on some populations and/or during some years. The ultimate cause, however, can be related to the very short (12–18 h) female phase of each inflorescence, a phylogenetically conservative trait within the Araceae. Received: 19 August 1998 / 15 February 1999     

Mud-puddling behavior in tropical butterflies: in search of proteins or minerals?

We experimentally investigated the attraction of adult butterflies to moist soil and dirt places (a behavior termed `mud-puddling') in two species-rich tropical communities on the island of Borneo. At a rain forest site, 227 individuals (46 species) were attracted to the baits, compared to 534 individuals (54 species) at a farmland site. With one single exception, all attracted butterflies were males. Of various salt and amino acid solutions, only sodium was accepted, but overall, albumin solutions turned out to be the most attractive puddling resource. Butterfly families differed consistently in their resource preferences. Representatives of the families Papilionidae and Pieridae more often visited NaCl solutions, but still accepted albumin, whereas representatives of the Nymphalidae, Hesperiidae and, in particular, Lycaenidae preferred the protein resource. In experiments using decoys prepared from pinned butterfly specimens, representatives of the Papilionidae and Pieridae were more strongly attracted to baits provided with decoys made from conspicuous, medium-sized yellow Eurema species (Pieridae), whereas dummies made from small, cryptically colored lycaenids (Prosotas and Caleta species) were ineffective. Decoys did not influence the attraction of lycaenid butterflies towards baits. Hence, visual cues play an important role in locating puddling resources for papilionids and pierids, while for lycaenid butterflies searching for nitrogen sources, olfactory cues emitted by decaying organic matter are more likely to be important. The strong attraction of male butterflies to nitrogen-rich resources suggests that, as in the case of sodium, these nutrients may increase reproductive success. Received: 5 October 1998 / Accepted: 7 December 1998     

Floral color change and the attraction of insect pollinators in lungwort (Pulmonaria collina)

We studied the effect of floral color change on long- and short-distance attraction of insect pollinators to the herb lungwort, Pulmonaria collina. Lungwort flowers change color with age from red to blue. Young red flowers had a significantly greater pollen and nectar reward and were significantly more often unpollinated than old blue ones. Red and blue flowers both influenced long-distance attractiveness of plants, defined as the number of insect approaches towards an individual plant. After reaching a plant, flower visitors preferred to visit young red flowers. Therefore, short-distance attractiveness, defined as the number of flowers visited successively on an individual plant, was influenced mainly by the number of young red flowers. The co-occurrence of the change in reproductive ability, in amount of reward, and in flower color enabled lungwort plants to direct pollinators to reproductive, highly rewarding red flowers. The data suggest that by maintaining changed flowers lungwort plants can increase their long-distance attraction and simultaneously enhance the probability of flower visits to pre-changed flowers. Thus, we propose floral color change as a mechanism that can increase the efficiency of pollen transfer to enhance plant fitness. Received: 2 November 1998 / Accepted: 14 July 1999