Floral synorganization and its influence on mechanical isolation and autogamy in Marantaceae

The flowers of Marantaceae (～ 550 species) exhibit a highly derived pollination mechanism within Zingiberales, with a rapid and irreversible style movement based on a close synorganization of different floral parts. Given the complexity of the structure, we assume that little variation is possible if functionality is to be maintained. To test this, we investigated how much floral diversity exists in the clade and whether this diversity potentially influences the breeding system and placement of pollen on the pollinator. Flowers of 66 species covering the five major phylogenetic clades of the family were analysed. All species are similar in their basic flower construction: the fleshy staminode forms the tunnel‐shaped roof of the flower and narrows the tube with stiff swellings, and the hooded staminode holds the style under tension and narrows the flower entrance with its trigger appendage. Despite morphological diversity of the pollination apparatus, functionality is maintained by coordinated variation of the fleshy and hooded staminodes. Autogamy is usually avoided by herkogamy. However, in a few exceptions, subtle morphological changes alter the breeding system from allogamy to autogamy. Variable floral proportions allow for differential pollen deposition potentially causing mechanical isolation between sister taxa. This study clearly illustrates that structural variation is not only present in the highly synorganized flowers of Marantaceae, but that it also creates potentially new options for evolutionary diversification. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168 , 300–322.     

Extreme climatic events drive mammal irruptions: regression analysis of 100‐year trends in desert rainfall and temperature

Extreme climatic events, such as flooding rains, extended decadal droughts and heat waves have been identified increasingly as important regulators of natural populations. Climate models predict that global warming will drive changes in rainfall and increase the frequency and severity of extreme events. Consequently, to anticipate how organisms will respond we need to document how changes in extremes of temperature and rainfall compare to trends in the mean values of these variables and over what spatial scales the patterns are consistent. Using the longest historical weather records available for central Australia – 100 years – and quantile regression methods, we investigate if extreme climate events have changed at similar rates to median events, if annual rainfall has increased in variability, and if the frequency of large rainfall events has increased over this period. Specifically, we compared local (individual weather stations) and regional (Simpson Desert) spatial scales, and quantified trends in median (50th quantile) and extreme weather values (5th, 10th, 90th, and 95th quantiles). We found that median and extreme annual minimum and maximum temperatures have increased at both spatial scales over the past century. Rainfall changes have been inconsistent across the Simpson Desert; individual weather stations showed increases in annual rainfall, increased frequency of large rainfall events or more prolonged droughts, depending on the location. In contrast to our prediction, we found no evidence that intra‐annual rainfall had become more variable over time. Using long‐term live‐trapping records (22 years) of desert small mammals as a case study, we demonstrate that irruptive events are driven by extreme rainfalls (>95th quantile) and that increases in the magnitude and frequency of extreme rainfall events are likely to drive changes in the populations of these species through direct and indirect changes in predation pressure and wildfires.     

The effect of altered macroclimate on N-fixation by boreal feather mosses

Plant productivity is predicted to increase in boreal forests owing to climate change, but this may depend on whether N inputs from biological N-fixation also increases. We evaluated how alteration of climatic factors affects N input from a widespread boreal N-fixer, i.e. cyanobacteria associated with the feather moss Pleurozium schreberi. In each of 10 forest stands in northern Sweden, we established climate-change plots, including a control (ambient climate) plot and three plots experiencing a +2°C temperature increase, an approximately threefold reduction in precipitation frequency, and either 0.07, 0.29 or 1.16 times normal summer precipitation. We monitored N-fixation in these plots five times between 2007 and 2009, and three times in 2010 after climate treatments ended to assess their recovery. Warmer temperatures combined with less frequent precipitation reduced feather moss moisture content and N-fixation rates regardless of total precipitation. After climate treatments ended, recovery of N-fixation rates occurred on the scale of weeks to months, suggesting resilience of N-fixation to changes in climatic conditions. These results suggest that modelling of biological N-inputs in boreal forests should emphasize precipitation frequency and evaporative water loss in conjunction with elevated temperature rather than absolute changes in mean precipitation.     

Lichen Specific Thallus Mass and Secondary Compounds Change across a Retrogressive Fire-Driven Chronosequence

In the long-term absence of major disturbances ecosystems enter a state of retrogression, which involves declining soil fertility and consequently a reduction in decomposition rates. Recent studies have looked at how plant traits such as specific leaf mass and amounts of secondary compounds respond to declining soil fertility during retrogression, but there are no comparable studies for lichen traits despite increasing recognition of the role that lichens can play in ecosystem processes. We studied a group of 30 forested islands in northern Sweden differing greatly in fire history, and collectively representing a retrogressive chronosequence, spanning 5000 years. We used this system to explore how specific thallus mass (STM) and carbon based secondary compounds (CBSCs) change in three common epiphytic lichen species (Hypogymnia phsyodes, Melanohalea olivacea and Parmelia sulcata) as soil fertility declines during this retrogression. We found that STMs of lichens increased sharply during retrogression, and for all species soil N to P ratio (which increased during retrogression) was a strong predictor of STM. When expressed per unit area, medullary CBSCs in all species and cortical CBSCs in P. sulcata increased during retrogression. Meanwhile, when expressed per unit mass, only cortical CBSCs in H. physodes responded to retrogression, and in the opposite direction. Given that lichen functional traits are likely to be important in driving ecological processes that drive nutrient and carbon cycling in the way that plant functional traits are, the changes that they undergo during retrogression could potentially be significant for the functioning of the ecosystem.     

Uracil recognition by replicative DNA polymerases is limited to the archaea, not occurring with bacteria and eukarya

Family B DNA polymerases from archaea such as Pyrococcus furiosus, which live at temperatures ~100°C, specifically recognize uracil in DNA templates and stall replication in response to this base. Here it is demonstrated that interaction with uracil is not restricted to hyperthermophilic archaea and that the polymerase from mesophilic Methanosarcina acetivorans shows identical behaviour. The family B DNA polymerases replicate the genomes of archaea, one of the three fundamental domains of life. This publication further shows that the DNA replicating polymerases from the other two domains, bacteria (polymerase III) and eukaryotes (polymerases δ and ε for nuclear DNA and polymerase γ for mitochondrial) are also unable to recognize uracil. Uracil occurs in DNA as a result of deamination of cytosine, either in G:C base-pairs or, more rapidly, in single stranded regions produced, for example, during replication. The resulting G:U mis-pairs/single stranded uracils are promutagenic and, unless repaired, give rise to G:C to A:T transitions in 50% of the progeny. The confinement of uracil recognition to polymerases of the archaeal domain is discussed in terms of the DNA repair pathways necessary for the elimination of uracil.     

Immunolocalization of MMP-19 in the human intervertebral disc: implications for disc aging and degeneration

Matrix metalloproteinases (MMPs) degrade components of the extracellular matrix of the disc, but the presence of MMP-19 has not been explored. In other tissues, MMP-19 is known to act in proteolysis of the insulin-like growth factor (IGF) binding protein-3, thereby exposing this protein to make it available to influence cell behavior. MMP-19 also has been shown to inhibit capillary-like formation and thus play a role in the avascular nature of the disc. Using immunohistochemistry, normal discs from six subjects aged newborn through 10 years and 20 disc specimens from control donors or surgical patients aged 15-76 (mean age 40.2 years) were examined for immunolocalization of MMP-19; six Thompson grade I discs, five Thompson grade II, eight Thompson grade III, five Thompson grade IV, and one Thompson grade V discs were analyzed. The results indicate that in discs from young subjects, MMP-19 was uniformly localized in the outer annulus. In discs from adult donors and surgical patients, outer and inner annulus cells only occasionally showed MMP-19 localization. The greatest expression of MMP-19 was observed in young discs, and little expression was seen in older or degenerating discs. Because MMP-19 has been shown to regulate IGF-mediated proliferation in other tissues, its decline in the aging/degenerating disc may contribute to the age-related decrease in disc cell numbers.     

Holocene land uplift and its influence on fire history and ecosystem development in boreal Sweden

Lake Uddjaur in northern Sweden was formed as a consequence of non‐uniform glacio‐isostatic uplift in which a forested valley was gradually flooded and high elevation areas became islands. We hypothesized that small islands in Lake Uddjaur burnt through lightning strike more frequently when they were part of a large forested area compared to when they became true islands, and that this reduction in fire impact has enhanced the domination of late successional species and humus accumulation. Fire history and vegetation dynamics were studied by analysis of macroscopic charcoal (> 0.5 mm) and pollen in humus profiles from two islands. According to a model of isostatic uplift, the islands became gradually isolated from the mainland between ca. 2000 to 1000 BP, i.e. during the same time that fire impact declined. Prior to that, both islands were part of a Pinus‐Betula forest landscape affected by fires from ca. 5800 to ca. 1500 BP. Thereafter fire influence ceased and the islands became more strongly characterized by late successional species, e.g. Picea. This change was associated with substantial humus accumulation. The decreased fire influence on these islands contrasts with the regional increase in fire influence during the last 1000 yr. Long‐term influence of wildfire is important in vegetation dynamics and humus accumulation and, thus, post‐glacial isostatic land uplift can indirectly have a substantial influence on ecosystem development. Consequently, this effect should be further considered in long‐time ecosystem studies of areas with large, non‐uniform land uplift such as those found in northern Fennoscandia and eastern Canada.     

The response of a three trophic level soil food web to the identity and diversity of plant species and functional groups

Despite considerable recent interest in how biodiversity may influence ecosystem properties, the issue of how plant diversity and composition may affect multiple trophic levels in soil food webs remains essentially unexplored. We conducted a glasshouse experiment in which three plant species of each of three functional groups (grasses, N‐fixing legumes and forbs) were grown in monoculture and in mixtures of three species (with the three species being in the same or different functional groups) and all nine species. Plant species identity had important effects on the biomasses or population densities of belowground primary consumers (microbial biomass, herbivorous nematodes) and two groups of secondary consumers (microbe‐feeding nematodes and enchytraeids); the third consumer trophic level (predatory nematodes) was marginally not significantly affected at P=0.05. Plant species also influenced the relative importance of the bacterial‐based and fungal‐based energy channels for both the primary and secondary consumer trophic levels. Within‐group diversity of only the soil microflora and herbivorous nematodes (both representing the basal consumer trophic level) were affected by plant species identity. However, community composition within all trophic groupings considered (herbivorous nematodes, microbes, microbe‐feeding nematodes, predatory nematodes) was strongly influenced by what plant species were present. Despite the strong responses of the soil biota to plant species identity, there were few effects of plant species or functional group richness on any of the belowground response variables measured. Further, net primary productivity (NPP) was unaffected by plant diversity. Since some belowground response variables were correlated with NPP across treatments, it is suggested that belowground responses to plant diversity might become more apparent in situations when NPP itself responds to plant diversity. Our results point to plant species identity as having important multitrophic effects on soil food webs, both at the whole trophic group and within‐group levels of resolution, and suggest that differences in plant traits across species may be important in driving the decomposer subsystem.