Factors controlling upper Jurassic ammonite assemblages in north-central Mexico

Lower Kimmeridgian to Lower Tithonian (Upper Jurassic) sections studied at Sierra de Palotes (Durango) and Sierra de Catorce (San Luis Potosí), Mexico, show low-energy deposits in which the composition of fossil macroinvertebrate assemblages, including megabenthos, reflects biostratinomic control. Monotonous siltstones provide continuous records of ammonite assemblages and reflect dominant deposition of shells in living areas; meanwhile, discontinues records were forced by episodic post-mortem transportation of shells, which was especially accentuated under storm influence. Rhythmic marly-silty limestones and marls illustrate a fossil record probably determined by minor transgressive-regressive pulses. The major changes in lithofacies are reflected by condensed silty and phosphatic mudstones deposited during significant floodings affecting areas under dominant terrigenous sedimentation. These changes determined more or less significant variations in the composition of fossil assemblages according to their relation to changing ecological conditions. However, shifting ecospaces exhibit no direct relationship to changes in lithofacies. Post-mortem transportation, operating in relation to both marine floodings and changes in the pattern of upper-water currents, was the main biostratinomic factor affecting the areal distribution of ammonite populations. Shell transportation and sedimentation rate controlled preservation and ultimately influenced diversity in recorded ammonite assemblages. The post-mortem behaviour (interpreted from shell structure and preservation), and therefore distribution, of ammonite shells points to shallow-water environments during the Kimmeridgian - Early Tithonian in areas (such as SE Durango and San Luís Potosí) close to the changing boundary between dominant carbonate and terrigenous sedimentation. No reworking affecting ammonite biostratigraphy has been identified in the sections studied.     

Improved purification procedure and some serological and physica properties of cassava common mosaic virus from South America

Large quantities of cassava common mosaic virus (CCMV) were purified from systemically infected Nicotiana benthamiana plants. A polyclonal antiserum, with a titre of 1/128 in the tube precipitin test, was produced by immunising rabbits with purified virus. Viral antigens were detected in cassava, using both the double-antibody sandwich or plate-trapped antigen forms of enzyme-linked immunosorbent assay (ELISA). The virus reacted with antisera to the potexviruses potato virus X and tulip virus X in F(ab')₂ ELISA. As determined by ELISA, isolates of CCMV from cassava and chaya are closely serologically related to each other. Leaf extracts from infected N. benthamiana plants were infective to a dilution of 10^--⁴ but not 10^--⁵; after heating for 10 min at 65 °C but not 70 °C; and after storage at room temperature for 14 days. The virus has a sedimentation coefficient of 126 S_20,w, a single coat protein molecule of c . mol. wt 21 000, and a single-stranded RNA genome of c . mol. wt 2.0 ± 10⁶. Several dsRNA species, including the putative viral replicative form of c . mol. wt 4.1 ± 10⁶, were isolated from virus-infected cassava and N. benthamiana .     

High water roost selection by waders: maximizing feeding opportunities or avoiding predation?

During the highest spring tides the intertidal sediment flats of estuaries are fully inundated at high water, and waders have no choice but to move to supratidal roosts, e.g. on open farmland, saltpans or beaches. However, in many estuaries during the lowest neap or intermediate tides there are sectors of upper intertidal sediment flats that remain exposed even at the peak of high water, and so waders have the choice of roosting either there or in supratidal sites. In the Tagus Estuary, Portugal, as elsewhere, waders use both types of roosts during high water. Our main objective was to understand what makes waders opt for one of these two types of available roosts. We monitored wader use of saltpans and intertidal roosts from spring to neap tides, and measured foraging and alarm behaviour, prey availability and disturbance by predators. Most of the wader species studied chose intertidal (mudflat) roosts whenever these were available, and only roosted in saltpans during the peak of spring tides. We hypothesized that this preference was explained either by an attempt (i) to continue feeding into the high water period, or (ii) to minimize predation risk. Extending feeding time into the high water period did not seem to be very relevant for roost choice because both prey availability and foraging activity were low in both types of roosts. However, predator disturbance was several times higher in the saltpans than in the intertidal roosts, suggesting that this factor may be the determinant in the choice of roost type.     

Floral biology of a primary rain forest palm, Astrocaryum mexicanum Liebm.

A detailed account of the changes in visitor numbers and behaviour, inflorescence phenology, and breeding systems is presented. Inflorescences open early in the morning (05.00 hours). Stigmas remain receptive for 15 h, while anther dehiscence occurs 20 h after inflorescence opening. Maximum pollen viability occurs the next day at 05.00 hours. This combination of features largely precludes self-pollination. Controlled pollinations show that apomixis and auto-pollination are absent, and indicate strong incompatibility. In contrast, cross-pollinations do not differ in fruit set from open-pollinated controls. The fruit set in inflorescences exposed to pollinators for different periods after opening (and later stopping pollinator activity by fumigation), indicates that pollination occurs soon after inflorescence opening.
The visitors comprise a numerous and diverse fauna (15 families; 34 species). Features such as pollen loads, abundance, behaviour, and diet patterns, segregate them into: herbivores and predators (Aves, Orthoplera), pollen thieves (Apidae), and true pollinators (most Coleoptera and Diptera). The elevation in inflorescence temperature during opening, and 24 h later, is discussed in relation to cantharophily.
Astrocaryum mexicanum is an example of a highly diverse pollination system in which many animals can coexist. It represents an important resource during the dry season, and provides food and space for refuge and mating. The genetic consequences of having a host of pollinators with different dispersal capabilities are explored.     

Salt Glands in Pappophorum (Poaceae)

Salt glands were observed in two species of Pappophorum, belongingto the tribe Pappophoreae (Chloridoideae, Poaceae). Glands resemblethose described in other genera of the Gramineae; they comprisetwo cells, a large basal one and smaller upper one. Gland densityper unit surface was much higher in P. philippianum, a facultativehalophyte, than in P. pappiferum, a glycophyte. The relevanceof the recretion process for the elimination of accumulatedNa in these two species is considered. The evolutionary significanceof the presence of glands in Pappophoreae and other membersof the Chloridoideae is discussed. Salt glands, Pappophorum philippianum, P. pappiferum, Poaceae     

Direct and indirect effects of climate on decomposition in native ecosystems from central Argentina

Abstract Climate affects litter decomposition directly through temperature and moisture, determining the ecosystem potential decomposition, and indirectly through its effect on plant community composition and litter quality, determining litter potential decomposition. It would be expected that both the direct and indirect effects of climate on decomposition act in the same direction along gradients of actual evapotranspiration (AET). However, studies from semiarid ecosystems challenge this idea, suggesting that the climatic conditions that favour decomposition activity, and the consequent ecosystem potential decomposition, do not necessarily lead to litter being easier to decompose. We explored the decomposition patterns of four arid to subhumid native ecosystems with different AET in central‐western Argentina and we analysed if ecosystem potential decomposition (climatic direct effect), nutrient availability and leaf litter potential decomposition (climatic indirect effect) all increased with AET. In general, the direct effect of climate (AET) on decomposition (i.e. ecosystem potential decomposition), showed a similar pattern to nutrient availability in soils (higher for xerophytic and mountain woodlands and lower for the other ecosystems), but different from the pattern of leaf litter potential decomposition. However, the range of variation in the ecosystem potential decomposition was much higher than the range of variation in litter potential decomposition, indicating that the direct effect of climate on decomposition was far stronger than the indirect effect through litter quality. Our results provide additional experimental evidence supporting the direct control of climate over decomposition, and therefore nutrient cycling. For the ecosystems considered, those with the highest AET are the ecosystems with the highest potential decomposition. But what is more interesting is that our results suggest that the indirect control of climate over decomposition through vegetation characteristics and decomposability does not follow the same trend as the direct effect of climate. This finding has important implications in the prediction of the effects of climate change on semiarid ecosystems.     

The ‘truck‐driver’ effect in leaf‐cutting ants: how individual load influences the walking speed of nest‐mates

The foraging behaviour of social insects is highly flexible because it depends on the interplay between individual and collective decisions. In ants that use foraging trails, high ant flow may entail traffic problems if different workers vary widely in their walking speed. Slow ants carrying extra‐large loads in the leaf‐cutting ant Atta cephalotes L. (Hymenoptera: Formicidae) are characterized as ‘highly‐laden’ ants, and their effect on delaying other laden ants is analyzed. Highly‐laden ants carry loads that are 100% larger and show a 50% greater load‐carrying capacity (i.e. load size/body size) than ‘ordinary‐laden’ ants. Field manipulations reveal that these slow ants carrying extra‐large loads can reduce the walking speed of the laden ants behind them by up to 50%. Moreover, the percentage of highly‐laden ants decreases at high ant flow. Because the delaying effect of highly‐laden ants on nest‐mates is enhanced at high traffic levels, these results suggest that load size might be adjusted to reduce the negative effect on the rate of foraging input to the colony. Several causes have been proposed to explain why leaf‐cutting ants cut and carry leaf fragments of sizes below their individual capacities. The avoidance of delay in laden nest‐mates is suggested as another novel factor related to traffic flow that also might affect load size selection The results of the presennt study illustrate how leaf‐cutting ants are able to reduce their individual carrying performance to maximize the overall colony performance.     

Morphology agrees with molecular data: phylogenetic affinities of Euptychiina butterflies (Nymphalidae: Satyrinae)

Euptychiina is the most species‐rich subtribe of Neotropical Satyrinae, with over 450 known species in 47 genera (14 monotypic). Here, we use morphological characters to examine the phylogenetic relationships within Euptychiina. Taxonomic sampling included 105 species representing the majority of the genera, as well as five outgroups. A total of 103 characters were obtained: 45 from wing pattern, 48 from genitalia and 10 from wing venation. The data matrix was analysed using maximum parsimony under both equal and extended implied weights. Euptychiina was recovered as monophyletic with ten monophyletic genera, contrasting previous DNA sequence‐based phylogenies that did not recover the monophyly of the group. In agreement with sequence‐based hypotheses, however, three main clades were recognized: the ‘Megisto clade’ with six monophyletic and three polyphyletic genera, the ‘Taygetis clade’ with nine genera of which three were monophyletic, and the ‘Pareuptyhia clade’ with four monophyletic and two polyphyletic genera. This is the first morphology‐based phylogenetic hypothesis for Euptychiina and the results will be used to complement molecular data in a combined analysis and to provide critical synapomorphies for clades and genera in this taxonomically confused group.     

The Effect of Long and Short Day Length upon the Growth of Whole Plants and the Level of Soluble Proteins, Sugars, and Stevioside in Leaves of Stevia rebaudiana Bert.

Long-day conditions increase internode length, leaf area, anddry weight and reduce the interval between the appearance ofsuccessive leaf pairs in S. rebaudiana as compared with shortdays. Total soluble leaf sugars, protein, and stevioside contentare also augmented in both absolute and relative terms and thebiosynthesis of steviol, the aglucone present in stevioside,is increased by 45%. The interaction between dry matter, steviosidecontent, and day length is discussed and a theory for the biologicalrole of stevioside as a possible defence mechanism against insectherbivory is proposed: as such this is the first known caseof a tetracyclic diterpene glycoside assuming this function.     

Borate promotes the formation of a complex between legume AGP‐extensin and Rhamnogalacturonan II and enhances production of Rhizobium capsular polysaccharide during infection thread development in Pisum sativum symbiotic root nodules

The capacity to bind to biomolecules is considered to be the basis for any physiological role of boron (B). Legume arabinogalactan protein‐extensin (AGPE), a major component of the infection thread matrix of legume nodules is a potential B‐ligand. Therefore, its role in infection threads development was investigated in Pisum sativum grown under B deficiency. Using the AGPE‐specific antibody MAC265, immunochemical analysis revealed that a 175 kDa MAC265 antigen was abundant in +B but much weaker in –B nodule extracts. A B‐dependent complex involving AGPE and rhamnogalacturonan II (RGII) could be co‐purified using anti‐RGII antiserum. Following fractionation of –B nodules, MAC265 antigens were mostly associated with the bacterial pellet. Immunogold staining confirmed that AGPE was closely associated with the surface of rhizobia in the lumen of threads in ?B nodules whereas in +B nodules, AGPE was separated from the bacterial surface by a sheath of capsular polysaccharide. Interestingly, colonies of rhizobia grown in free‐living culture without B developed low capsule production. Therefore, we propose that B could be important for apical growth of infection threads by strengthening thread wall through a B‐dependent AGPE‐RGII interaction and by promoting bacterial advance through a B‐dependent production of a stable rhizobial capsule that prevents AGPE attachment.