Using hybrid systems to explore the evolution of tolerance to damage

Hybridization is common and important to the adaptive evolution of plants. Hybridization has resulted in the formation of new species and the introgression of traits between species. This paper discusses the advantages of using hybrid systems to explore the evolution of tolerance to herbivore damage (i.e., the ability to diminish the negative effects of damage on fitness). The major consequence of hybridization likely to make it influential for tolerance evolution is that hybridization generates broad variation in traits that can be selected for or against. In addition to generating greater variation in tolerance to damage and its putative traits (e.g., traits associated with allocation patterns and meristem production), hybridization can generate greater independence among tolerance traits and between tolerance and defense traits. Greater independence may provide a greater ability to discern mechanisms of tolerance, give a greater probability of detecting allocation costs of tolerance, and provide an effective means to evaluate tradeoffs between tolerance and defense. Interspecific hybrid systems can also be used to evaluate the importance of co-adaptation of tolerance traits. Moreover, recombinant hybrids can be used in selection studies focusing on tolerance to damage to discern whether parental combinations of tolerance traits are favored over novel combinations. Research in hybrid systems that investigate the selective importance of tolerance, the patterns of inheritance of tolerance traits, and the genetic architecture of plant species involved can be vital to our evaluation of the adaptive role of tolerance to damage. This revised version was published online in July 2006 with corrections to the Cover Date.     

Context-dependent reproductive site choice in a Neotropical frog

In organisms whose offspring develop in discrete habitat patchessuch as pools, studies have frequently shown that adults avoidsites based on a single risk factor facing offspring. However,natural reproductive sites often vary in multiple risk factorsin both space and time. In this study, I used choice tests amongfield mesocosms to determine whether adults of a Neotropicalanuran, Edalorhina perezi, select the safest pools for offspringbased on two biotic risks of different magnitude: insect predatorsand conspecific competitors. I also investigated whether adultsite-choice was context dependent (i.e., whether it varied bysex or by season or whether it was based on local pool quality).I found that both sexes avoided pools containing predatory insects,but only females significantly avoided those containing conspecifictadpoles. When offered two risky options, both sexes favoredpools with competitors over those with predators. Site-choicebehavior also varied depending on the temporal and spatial context.Female sensitivity to insect predators decreased late in theseason. In addition, both sexes exhibited dampened reproductiveactivity when only risky sites were available locally. Thisstudy emphasizes that social and environmental factors simultaneouslyimpact reproductive site choice. Whether a site is acceptedultimately depends not only on the assessment of mortality risksto offspring but also on the sex and spatiotemporal contextof the decision maker.     

Addressing amino acid-derived inhibitory metabolites and enhancing CHO cell culture performance through DOE-guided media modifications

Previously, we identified six inhibitory metabolites (IMs) accumulating in Chinese hamster ovary (CHO) cultures using AMBIC 1.0 community reference medium that negatively impacted culture performance. The goal of the current study was to modify the medium to control IM accumulation through design of experiments (DOE). Initial over-supplementation of precursor amino acids (AAs) by 100% to 200% in the culture medium revealed positive correlations between initial AA concentrations and IM levels. A screening design identified 5 AA targets, Lys, Ile, Trp, Leu, Arg, as key contributors to IMs. Response surface design analysis was used to reduce initial AA levels between 13% and 33%, and these were then evaluated in batch and fed-batch cultures. Lowering AAs in basal and feed medium and reducing feed rate from 10% to 5% reduced inhibitory metabolites HICA and NAP by up to 50%, MSA by 30%, and CMP by 15%. These reductions were accompanied by a 13% to 40% improvement in peak viable cell densities and 7% to 50% enhancement in IgG production in batch and fed-batch processes, respectively. This study demonstrates the value of tuning specific AA levels in reference basal and feed media using statistical design methodologies to lower problematic IMs.     

Integrative approaches in genome structure analysis

1. Download : Download high-res image (325KB)
2. Download : Download full-size image

     

Influence of experimental conditions on visco-hyperelastic properties of skeletal muscle tissue using a Box–Behnken design

The Mechanical characterization of skeletal muscles is strongly dependent on numerous experimental design factors. Nevertheless, significant knowledge gaps remain on the characterization of muscle mechanics and a large number of experiments should be implemented to test the influence of a large number of factors. In this study, we propose a design of experiment method (DOE) to study the parameter sensitivity while minimizing the number of tests. A Box-Behnken design was then implemented to study the influence of strain rate, preconditioning and preloading conditions on visco-hyperelastic mechanical parameters of two rat forearm muscles. The results show that the strain rate affects the visco-hyperelastic parameters for both muscles. These results are consistent with previous work demonstrating that stiffness and viscoelastic contributions increase with strain rate. Thus, DOE has been shown to be a valid method to determine the effect of the experimental conditions on the mechanical behaviour of biological tissues such as skeletal muscle. This method considerably reduces the number of experiments. Indeed, the presented study using 3 parameters at 3 levels would have required at least 54 tests per muscle against 14 for the proposed DOE method.     

Detection of hormesis effect in longevity: simulation approach for heterogeneous population.

Manifestation of hormesis in longevity was modelled by modification of the mortality rate during and after the period of a stress factor action. In heterogeneous population this can lead to observation of unchanged mortality during action of the stress and decrease in mortality after stress period. Stochastic simulations were made to investigate the possibility of detecting the hormesis effect on the basis of the stress-control longitudinal data. The goal of the stochastic simulation was to investigate the role in the hormesis detection of control and stressed group size, of population heterogeneity variance value, of stress and hormesis attributable risks as well as the role of a prior information about the survival in the control group. It was demonstrated that if the attributable risks for stress and hormesis effects are approximately equal, then in both 'high' and 'low' heterogeneous populations the hormesis phenomenon is detected with probability higher than 75% even in relatively 'small' groups of 50 subjects. In case of 'weak' effect the hormesis phenomenon is not detected in a 'highly heterogeneous' population even in a group composed of 1000 subjects. In a 'low heterogeneous' population the hormesis phenomenon is detected with probability higher than 70% when the group size is not less than 200 subjects. Information about the survival in control group did not play a critical role in all experiments and exact survival curve may be replaced by the traditional Kaplan-Meier estimate.     

Reduction of the filtration rate of Daphnia galeata by dissolved photosynthetic products of edible phytoplankton

The filtration rate of Daphnia galeata was determined in in situ experiments in Bautzen Reservoir and in laboratory experiments, where daphnids were exposed to filtrates that previously contained either natural phytoplankton or cultured eukaryotic algae (Scenedesmus obliquus or Asterionella formosa), respectively. Individual filtration rate (FR) was measured using fluorescent beads, taking into account ingested beads in the gut only. Compared to heated control treatments (100 °C), dissolved compounds released by the nutritious cultured algae during the preconditioning phase or by the natural phytoplankton assemblages from Bautzen Reservoir strongly reduced the filtration rate of D. galeata (down to 60%). Heating deactivated these dissolved compounds. A significant correlation was found between primary production measured in situ and the reduction of FR in the filtrate of reservoir water, indicating that extra-cellular products released during photosynthesis triggered the reduction of the filtration rate. The ratio of ingested to collected beads was used to quantify the proportion of food, which was not only collected but passed the mouth of D. galeata. The ratio of ingestion to collection was compared between filtered and unfiltered reservoir water both media identical with respect to the concentration of dissolved compounds, whereas other factors (e.g. food concentration, temperature, filtration rate) were different. The changes in this ratio between filtered and unfiltered reservoir water suggest that D. galeata is capable of a chemosensory control of the ingestion behaviour by detecting external metabolites.     

The impact of intralacustrine introductions with regard to space utilization and competition for territories to a cichlid fish community in Lake Malawi,Africa

At Thumbi Island West in Lake Malawi, a number of cichlid species was introduced from elsewhere in the lake some 20 years ago. These are now, in part, well established and could have an effect on the indigenous fish fauna. Repeated removals of the males of the introduced species from their territories were undertaken and artificial miniature reefs were established to find out whether the emptied existing territories or the newly established potential territories would be occupied by indigenous species. The results show that the emptied territories were almost invariably re-occupied by either a male of the introduced species conspecific to the previous territory holder or they remained empty. The newly established miniature reefs were not occupied by territorial males of either introduced or indigenous species but by young fish of a variety of species.