Resource competition and fire‐regulated nutrient demand in carnivorous plants of wet pine savannas

Question: What are the mechanisms by which fire reduces competition for both a short‐lived and a long‐lived species in old‐growth ground‐cover plant communities of wet pine savannas (originally Pinus palustris, replaced by P. elliottii)? Location: Outer coastal plain of southeastern Mississippi, USA. Methods: I reviewed previous competition experiments and proposed a new hypothesis to explain the relationship between fire, competition, and species co‐existence in wet longleaf pine savannas. The first study is about growth and seedling emergence responses of a short‐lived carnivorous plant, Drosera capillaris, to reduction in below‐ground competition and above‐ plus below‐ground competition. The second study deals with growth and survival responses of a long‐lived perennial carnivorous plant, Sarracenia alata, to neighbour removal and prey‐exclusion to determine if a reduction in nutrient supply increased the intensity of competition in this nutrient‐poor system. Results: Fire increased seedling emergence of the short‐lived species by reducing above‐ground competition through the destruction of above‐ground parts of plants and the combustion of associated litter. Prey exclusion did not increase competitive effects of neighbours on the long‐lived species. However, because the experiment was conducted in a year without fire, shade reduced nutrient demand, which may have obviated competition for soil nutrients between Sarracenia alata and its neighbours. Conclusion: Repeated fires likely interact with interspecific differences in nutrient uptake to simultaneously reduce both above‐ground competition and competition for nutrients in old‐growth ground cover communities in pine savannas. Restoration practitioners should consider the possibility that the composition of the plant community is just as important as fire in ensuring that frequent fires maintain species diversity.     

Variability of cross-tissue X-chromosome inactivation characterizes timing of human embryonic lineage specification events

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Effects of variable water motion on regeneration of Hemipholis elongata (Echinodermata, Ophiuroidea)

Abstract. To determine whether increased water motion affects patterns of regeneration in the subtidal burrowing brittlestar Hemipholis elongata (phylum Echinodermata), individuals were subjected to laboratory-controlled turbulence conditions. Half of each replicate aquarium experienced oscillatory (wave-like) turbulence while the other half had no turbulence. Individual brittlestars from which arm-tips had been removed were allowed to burrow and to regenerate. Regenerated arm-tip length and weight were tested for differences between organisms in calm and turbulent conditions. Regenerated arm-tip length differed significantly between control and treatment, but arm-tip dry weight and skeleton/tissue ratio of regenerated arm-tips did not. To quantify plasticity in the skeleton, 15 morphological measurements made on the proximal face of vertebral ossicles (using scanning electron microscopy) were integrated as an index of overall ossicle size. We found a significant difference in the overall size index of the vertebral ossicles between treatments, but could not determine which of the measurements contributed most to the difference. The results indicate that regeneration in H. elongata is a complex process that can be modified by environmental conditions.     

Genetic differentiation in diapause response along a latitudinal cline in European yellow dung fly populations

Abstract.  1. Seasonality is a prime selective factor expected to result in local adaptation of life cycles and dormancy. Genetic differentiation in diapause response was investigated along a European latitudinal cline in the dung fly Scathophaga stercoraria (Diptera: Scathophagidae). Such differentiation may be mediated by additive or dominance genetic and/or maternal effects, which need to be distinguished.
2. Replicate sibships from five European populations (Lugano, Switzerland: 46.00°N; Zurich, Switzerland: 47.37°N; Oxford, U.K.: 51.75°N; Lund, Sweden: 55.70°N; Reykjavik, Iceland: 64.15°N) were raised in a common laboratory environment known to induce pupal winter diapause (12 °C and 12 h light), revealing a genetic latitudinal cline in both the proportion of individuals entering diapause and diapause duration in response to winter length estimated from weather data.
3. Populations from the extremes of the cline (Lugano and Reykjavik) were further reciprocally crossed to investigate the underlying genetics. This experiment revealed evidence for diapause induction at 12 °C being dominant (i.e. not merely additive) and clearly rejected maternal effects as the primary source of this between-population variation.     

Metabolic plasticity drives development during mammalian embryogenesis

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Phenotypic switch of smooth muscle cells in paediatric chronic intestinal pseudo-obstruction syndrome

Smooth Muscle Cells (SMC) are unique amongst all muscle cells in their capacity to modulate their phenotype. Indeed, SMCs do not terminally differentiate but instead harbour a remarkable capacity to dedifferentiate, switching between a quiescent contractile state and a highly proliferative and migratory phenotype, a quality often associated to SMC dysfunction. However, phenotypic plasticity remains poorly examined in the field of gastroenterology in particular in pathologies in which gut motor activity is impaired. Here, we assessed SMC status in biopsies of infants with chronic intestinal pseudo-obstruction (CIPO) syndrome, a life-threatening intestinal motility disorder. We showed that CIPO-SMCs harbour a decreased level of contractile markers. This phenotype is accompanied by an increase in Platelet-Derived Growth Factor Receptor-alpha (PDGFRA) expression. We showed that this modulation occurs without origin-related differences in CIPO circular and longitudinal-derived SMCs. As we characterized PDGFRA as a marker of digestive mesenchymal progenitors during embryogenesis, our results suggest a phenotypic switch of the CIPO-SMC towards an undifferentiated stage. The development of CIPO-SMC culture and the characterization of SMC phenotypic switch should enable us to design therapeutic approaches to promote SMC differentiation in CIPO.