AFLP diversity and spatial structure of Calycophyllum candidissimum (Rubiaceae), a dominant tree species of Nicaragua's critically endangered seasonally dry forest.

The Central American seasonally dry tropical (SDT) forest biome is one of the worlds' most endangered ecosystems, yet little is known about the genetic consequences of its recent fragmentation. A prominent constituent of this biome is Calycophyllum candidissimum, an insect-pollinated and wind-dispersed canopy tree of high socio-economic importance, particularly in Nicaragua. Here, we surveyed amplified fragment length polymorphisms across 13 populations of this species in Nicaragua to elucidate the relative roles of contemporary vs historical factors in shaping its genetic variation. Genetic diversity was low in all investigated populations (mean HE=0.125), and negatively correlated with latitude. Overall population differentiation was moderate (ΦST=0.109, P<0.001), and Bayesian analysis of population structure revealed two major latitudinal clusters (I: 'Pacific North'+'Central Highland'; II: 'Pacific South'), along with a genetic cline between I and II. Population-based cluster analyses indicated a strong pattern of 'isolation by distance' as confirmed by Mantel's test. Our results suggest that (1) the low genetic diversity of these populations reflects biogeographic/population history (colonisation from South America, Pleistocene range contractions) rather than recent human impact; whereas (2) the underlying process of their isolation by distance pattern, which is best explained by 'isolation by dispersal limitation', implies contemporary gene flow between neighbouring populations as likely facilitated by the species' efficient seed dispersal capacity. Overall, these results underscore that even tree species from highly decimated forest regions may be genetically resilient to habitat fragmentation due to species-typical dispersal characteristics, the necessity of broad-scale measures for their conservation notwithstanding.

Cell death upon H(2)O(2) induction in the unicellular green alga Micrasterias.

In the present study, we investigated whether the unicellular green alga Micrasterias denticulata is capable of executing programmed cell death (PCD) upon experimental induction, and which morphological, molecular and physiological hallmarks characterise this. This is particularly interesting as unicellular freshwater green algae growing in shallow bog ponds are exposed to extreme environmental conditions, and the capacity to perform PCD may be an important strategy to guarantee survival of the population. The theoretically 'immortal' alga Micrasterias is an ideal object for such investigations as it has served as a cell biological model system for many years and details on its growth properties, physiology and ultrastructure throughout the cell cycle are well known. Treatments with low concentrations of H(2)O(2) are known to induce PCD in other organisms, resulting in severe ultrastructural changes to organelles, as observed in TEM. These include deformation and part disintegration of mitochondria, abnormal dilatation of cisternal rims of dictyosomes, occurrence of multivesicular bodies, an increase in the number of ER compartments, and slight condensation of chromatin. Additionally, a statistically significant increase in caspase-3-like activity was detected, which was abrogated by a caspase-3 inhibitor. Photosynthetic activity measured by fast chlorophyll fluorescence decreased as a consequence of H(2)O(2) exposure, whereas pigment composition, except for a reduction in carotenoids, was the same as in untreated controls. TUNEL positive staining and ladder-like degradation of DNA, both frequently regarded as a hallmark of PCD in higher plants, could only be detected in dead Micrasterias cells.

Algorithm-based design of synthetic growth media stimulating virulence properties of Metarhizium anisopliae conidia.

AIMS: Synthetic media should be designed for the production of Metarhizium anisopliae conidia with improved virulence properties. METHODS AND RESULTS: A genetic algorithm (GA), demonstrated to be suitable for the design of media for spore mass production (Hutwimmer et al. 2008), was utilized for a multi-objective medium design to improve conidia yield and three proposed virulence properties of conidia: C : N ratio, germination speed and amount of spore-bound Pr1 protease. After five iterative optimizations, 52 media were improved over Sabouraud dextrose agar (SDA). Four media exhibited medium performances (a factor derived from the four single optimization variables) of around 0.7; cf. SDA = 0.532; media with enhanced properties were reached for each single optimization variable; Bioassays against Tenebrio larvae indicated also a slight improvement in virulence of conidia from designed media. A degenerated phenotype of the same strain did not exhibit differences in colony appearance, spore characteristics and virulence if grown on designed media. CONCLUSIONS: The application of a problem-oriented GA is a practical and rapid method to design media for multi-objective purposes. SIGNIFICANCE AND IMPACT OF THE STUDY: The applicability of a GA for multi-objective medium design was demonstrated for the cultivation of anamorphic fungi on solid media.

Algorithm-based design of novel synthetic media for Metarhizium anisopliae simulating its nutritional conditions in the environment.

AIMS: The objective of this study was to develop a novel synthetic growth medium for increased conidium production of the entompathogenic fungus Metarhizium anisopliae. The medium should simulate natural nutritional conditions. METHODS AND RESULTS: Macro- and micronutrients were selected in concentrations found in insects or from sources which are believed to be advantageous for virulence. Medium development was guided by a problem-oriented genetic algorithm (GA) implemented with 'mutation' and 'recombination' operators specific for this optimization problem. Following five optimization steps and a total of 181 medium variations, 19 synthetic media led to increased conidium production as compared with the standard Sabouraud dextrose agar medium: increases in conidia yields of up to 120% and a 17-fold higher conidium production per square centimetre of mycelium were achieved. Rapid germination of conidia, conidial C : N ratio, as well as spore-bound Pr1 protease production were monitored as proposed quality control markers for a virulent inoculum. CONCLUSIONS: It was demonstrated that our problem-oriented GA is a powerful tool for the design of chemically defined cultivation media with special/enhanced properties for anamorphic fungi. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study, which demonstrates the advantage of the use of a GA for the rapid design of solid synthetic media for maximum production of virulent conidia.