Anatomy and evolution in the Macaronesian Sonchus subgenus Dendrosonchus (Compositae: Lactuceae)

The members of the genus Sonchus subgenus Dendrosonchus are woody perennials possessing the pachycaul construction which has been proposed as ancestral to that of modern trees and herbs. The endemic flora of Macaronesia, particularly the Canary Islands, is generally considered to be a Tertiary relict, although an opposing view concerning woody plants of island floras has recently been expressed. The anatomy of Dendrosonchus is examined and trends of evolution can be interpreted from the vessel elements of the secondary xylem. With the use of the length to breadth ratios of vessel elements a gradual trend from primitive to derived is illustrated for the members of each of the two sections of Dendrosonchus , which are considered to have evolved in parallel. The wood rays, features of the cypsela and stem anatomy are also shown to be useful in elucidating the evolution of a small, closely related group of plants. Sonchus arboreus in the section Atalanthus and S. brachylobus in the section Dendrosonchus are similar to the two ancestral types proposed for the subgenus. The most derived species are considered to be S. pinnatus subsp. palmensis in the section Atalanthus and S. acaulis in the section Dendrosonchus. The ancestral type for the genus is considered to have been woody and probably of the Dendrosonchus type.     

The Effect of Temperature and Light on Gas Exchange and Acid Accumulation in the C3-CAM Plant Clusia minor L

Gas exchange and organic acid accumulation of the C₃-CAM intermediateClusia minor L. were investigated in response to various day/nighttemperatures and two light regimes (low and high PAR). For bothlight levels equal day/night temperatures between 20°C and30°C caused a typical C₃ gas exchange pattern with all CO₂uptake occurring during daylight hours. A day/ night temperatureof 15°C caused a negative CO₂ balance over a 24 h periodfor low-PAR-grown plants while high-PAR-grown plants showeda CAM gas exchange pattern with most CO₂ uptake taking placeduring the dark period. However, there was always a considerablenight-time accumulation of malic acid which increased when thenight-time temperature was lowered and had its maximum (54 mmolm^–2) at day/night temperature of 30/15°C. A significantamount of malic acid accumulation (23 mmol m^–2) in low-PAR-grownplants was observed only at 30/15°C. Recycling of respiratoryCO₂ in terms of malic acid accumulation reached between 2·0and 21·5 mmol m_–2 for high-PAR-grown plants whilethere was no significant recycling for low-PAR-grown plants.Both low and high-PAR-grown plants showed considerable night-timeaccumulation of citric acid. Indeed under several temperatureregimes low-PAR-grown plants showed day/night changes in citricacid levels whereas malic acid levels remained approximatelyconstant or slightly decreased. It is hypothesized that lowand high-PAR-grown plants have different requirements for citrate.In high-PAR-grown plants, the breakdown of citrate preventsphotoinhibition by increasing internal CO₂ levels, whereas inlow-PAR-grown plants the night-time accumulation of citric acidmay function as an energy and carbon saving mechanism. Key words: C. minor, C₃, CAM, citric acid, light intensity     

Seed size and survival in the soil in arid Australia

Abstract We investigated the relationship between seed size and seed survival in the soil in 67 species from arid Australia. There was a very weak, marginally significant positive relationship between the viability of fresh seeds and diaspore mass. However, by the time seeds had been buried in the soil for 1 year in nylon mesh bags, there was a highly significant positive relationship between diaspore mass and diaspore viability. Over the range of seed masses observed, a tenfold increase in diaspore mass was associated with a threefold increase in the odds of surviving 1 year of burial in the soil. Thus, large‐seeded species were favoured over small‐seeded species during this important selective process. However, the magnitude of this advantage was small compared with the advantage experienced by small‐seeded species during seed production. We also investigated aspects of diaspore morphology in relation to viability retention during burial. We found no relationship between seed survival and the amount of protective tissue per unit diaspore surface area. Diaspore mass was a better predictor of survival than was diaspore surface area.     

Purification and properties of cassava green mottle, a previously undescribed virus from the Solomon Islands

A sap-transmissible virus obtained from cassava with a green mottle disease occurring at Choiseul, Solomon Islands, was transmitted to 30 species in 12 plant families and was readily seed-borne in Nicotiana clevelandii. In cassava plants infected by inoculation with sap, the first leaves to be infected systemically developed a mottle with some necrosis whereas leaves produced subsequently were symptomless but contained the virus. Most other species developed chlorotic or necrotic local lesions and systemic mottle or necrosis. This was followed, in several species, by production of small symptomless virus-containing leaves. The virus was cultured in N. clevelandii; Chenopodium quinoa was used for local-lesion assays. Leaf extracts from infected N. clevelandii were infective after dilution to 10–⁵ but usually not at 10–⁶, after heating for 10 min at 60°C but not at 65°C, and after storage at 20°C for at least 12 days. The virus has isometric particles of 26 nm diameter which sediment as three components, all containing a protein of mol. wt c. 53000. The two fastest sedimenting components respectively contain single-stranded RNA of mol. wt, estimated after glyoxylation, c. 2.9 × 10⁶ and 2.3 × 10⁶. Both RNA species are needed for infection of plants. In tests with antiserum prepared to purified virus particles, the virus was detected in cassava and N. clevelandii by gel-diffusion precipitin tests, by immunosorbent electron microscopy and by ELISA. Despite its similarity to nepoviruses, the virus did not react with antisera to 18 members of the group. It was named cassava green mottle virus and is considered to be a previously undescribed nepovirus.     

SENSORY PROPERTIES AFFECTING ACCEPTABILITY OF "BRESAOLA" FROM PODOLIAN YOUNG BULLS

Three muscles ( Semimembranosus, Quadriceps femoris, Adductor ) from Podolian young bulls (aged 18 months) were processed into bresaolas, which were compared with commercial products, in terms of sensory profile and preference expressed by consumers. Slope analysis was conducted to study the preference drivers. The preference of homogeneous groups of consumers and the relationships with sensory properties of bresaola were investigated using partial least squares (PLS) regression analysis. The products differed for several sensory properties, such as sweetness, flavor intensity ( P <  0.001), saltiness ( P <  0.01), peppered, seasoned and tenderness ( P <  0.05). The slope analysis showed that taste/flavor ( k =  0.86) and appearance ( k =  0.76) play an important role in orienting consumer preference, while texture ( k =  0.54) is less important. No general trend was found for product liking. Conversely, PLS regression clustered the consumers in homogeneous groups: one preferred the commercial products characterized by sensory properties such as peppered, saltiness, seasoned and marbling, another one was more oriented toward properties such as sweetness, odor and chewiness, which characterized Podolian bresaolas.

PRACTICAL APPLICATION

Partial least squares regression analysis clustered the consumers in homogeneous groups according to their liking: those preferring peppered, salty, seasoned and marbling bresaolas versus those oriented toward sweet and odorous products. In addition, the relationship between overall liking and attribute liking (appearance, taste/flavor and texture) was analyzed by linear regression analysis. This may be helpful in order to establish meaningful criteria for grading bresaolas and identify the particular attributes that move its acceptance (i.e., taste/flavor and appearance rather than texture).     

Iron limits primary productivity during spring bloom development in the central North Atlantic

We present in situ biophysical measurements and bioassay experiments that demonstrate iron limitation of primary productivity during the spring bloom in the central North Atlantic. Mass balance calculations indicate that nitrate drawdown is iron (Fe)-limited and that aeolian Fe supply to this region cannot support maximal phytoplankton growth during the bloom. Using a simple simulation model, we show that relief of Fe limitation during the spring bloom can increase nitrate drawdown and, hence, new primary production, by 70%. We conclude that the episodic nature of iron supplied by dust deposition is an important factor controlling the dynamics of the spring bloom. From this, we hypothesize that variability in the timing and magnitude of the spring bloom in response to aeolian Fe supply will affect carbon drawdown and food web dynamics in the central North Atlantic.     

Avian brain evolution: new data from Palaeogene birds (Lower Eocene) from England

Investigation of how the avian brain evolved to its present state is informative for studies of the theropod–bird transition, and as a parallel to mammalian brain evolution. Neurological anatomy in fossil bird species can be inferred from endocranial casts, but such endocasts are rare. Here, we use computed tomographic analysis to determine the state of brain anatomy in two marine birds from the Lower Eocene London Clay Formation of England. The brains of Odontopteryx (Odontopterygiformes) and Prophaethon (Pelecaniformes) are remarkably similar to those of extant seabirds, and probably possessed similar somatosensory and motor capabilities. Each virtual endocast exhibits a degree of telencephalic expansion comparable to living avian species. However, the eminentia sagittalis (wulst), a feature characteristic of all living birds, is poorly developed. Our findings support the conclusion that much of the telencephalic expansion of modern birds was complete by the end of the Mesozoic, but that overall telencephalic volume has increased throughout the Cenozoic through dorsal expansion of the eminentia sagittalis. We suggest that improvements in cognition relating to telencephalic expansion may have provided neornithine avian clades with an advantage over archaic lineages at the Cretaceous–Tertiary boundary, explaining their survival and rapid diversification in the Cenozoic. © 2009 The Natural History Museum. Journal compilation © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155 , 198–219.     

Role of ethylene in the regulation of cell death and leaf loss in ozone-exposed European beech

To test the involvement of ethylene in mediating ozone-induced cell death and leaf loss in European beech ( Fagus sylvatica L.), tree seedlings were exposed to proportionally increased or decreased field ozone levels for up to 6 months. Ozone treatment caused cell death and accelerated leaf loss at higher than ambient levels, but had only minor effects at ambient and no effects at subambient ozone levels. The emission of ethylene, the levels of its precursor, 1-aminocyclopropane-1-carboxylate (ACC), and mRNA levels of specific ACC synthase ( FS-ACS2 ) and ACC oxidase ( FS-ACO1 ) isoforms showed a persistent increase and preceded cell death by approximately 2 weeks. Inhibition of ethylene biosynthesis led to reduced lesion formation whereas application of ACC accelerated ozone-induced cell death and leaf loss. Similar results were obtained when adult beech trees were exposed to 2 × ozone by a whole tree free-air canopy exposure system. The results suggest a role of ethylene in amplifying ozone effects under field conditions in this major European broad-leaved tree species.     

Extreme habitats are not refuges: poeciliids suffer from increased aerial predation risk in sulphidic southern Mexican habitats

Extreme environments are often considered a predation refuge for organisms living in them. In southern Mexico several species of poeciliid fishes are undergoing incipient speciation in a variety of extreme (i.e. permanently dark and/or sulphidic) freshwater systems, and previous research has demonstrated reproductive isolation between populations from sulphidic and adjacent benign habitats. In the present study, we investigated bird predation rates (measured as successful captures per minute) in two sulphidic surface and several benign surface habitats, to test the hypothesis that extreme habitats are predation refuges. We found capture rates to be approximately 20 times higher in sulphidic environments: probably facilitated by extremophile poeciliids spending most of their time at the water surface, where they engage in aquatic surface respiration as a direct response to hypoxia. Even birds that are usually not considered major fish predators regularly engage in fish predation in the toxic habitats of southern Mexico. Our results demonstrate that extreme environments do not necessarily represent a refuge from predation, and we discuss the general importance of predation in driving incipient speciation in these systems. Finally, we hypothesize that natural selection via avian predation may play an important role in maintaining reproductive isolation between divergent poeciliid populations. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 417–426.