Fragment quality and matrix affect epiphytic performance in a Mediterranean forest landscape

Destruction and fragmentation of habitats represent one of the most important threats for biodiversity. Here, we examined the effects of fragmentation in Mediterranean forests on the epiphytic lichen Lobaria pulmonaria (Lobariaceae). We tested the hypothesis that not only the level of fragmentation affects L. pulmonaria populations, but also the quality of the habitat and the nature of the surrounding matrix affect them. The presence and abundance of the lichen was recorded on 2039 trees in a total of 31 stands. We recorded habitat quality and landscape variables at three hierarchical levels: tree, plot, and patch. We found that L. pulmonaria tends to occur in trees with larger diameters in two types of surveyed forests. In Quercus pyrenaica patches, the mean diameter of colonized trees was smaller, suggesting the importance of bark roughness. Factors affecting the presence and cover of the lichen in each type of forest were different. There was a strong positive influence of distance from a river in beech forests, whereas proximity to forest edge positively affected in oak forests. The influence of the surrounding matrix was also an important factor explaining the epiphytic lichen abundance.     

Survival costs of reproduction in a short-lived perennial plant: Live hard, die young

According to life-history theory, reproductive investments involve costs in terms of growth, future fecundity, and/or survival. However, studies to date have often failed to detect costs of reproduction, with survival costs among the less documented. We investigated the cost of reproduction in Helianthemum squamatum (Cistaceae), a short-lived perennial of semiarid Mediterranean environments. After experimental flower removal, we evaluated next season's growth, reproduction, and survival of the plants. We also monitored an indicator of plant physiological status (F(v)/F(m)) and leaf nutrient concentration at key phenological stages during reproduction. Survival rate in deblossomed plants was significantly higher than in control plants. As far as we know, this is the first experimental evidence of a survival cost of reproduction in a perennial plant. In contrast, no cost to growth or reproduction was found during the next season, and no significant differences in F(v)/F(m) or leaf nutrients were found between control and deblossomed plants. Helianthemum squamatum's success in semiarid Mediterranean ecosystems seems to rely on a persistent seed bank, combined with a sustained high reproductive output at the expense of survival. We conclude that this strategy might be more common than previously thought among short-lived shrubby plants growing in stressful Mediterranean areas.     

Interactive Effects of Three Ecosystem Engineers on Infiltration in a Semi-Arid Mediterranean Grassland

The redistribution of water in semi-arid environments is critical for the maintenance and survival of vegetation patches. We used a systems approach to examine the interactive effects of three engineers—Stipa tenacissima, biological soil crusts, and the European rabbit (Oryctolagus cuniculus)—on infiltration processes in a model gypseous semi-arid Mediterranean grassland. We measured the early (sorptivity) and later (steady-state infiltration) stages of infiltration at two supply potentials using disk permeameters, which allowed us to determine the relative effects of different engineers and soil micropores on water flow through large macropores. We detected few effects under tension when flow was restricted to matrix pores, but under ponding, sorptivity and steady-state infiltration adjacent to Stipa tussocks were 2–3 times higher than in intact or rabbit-disturbed biological soil crusts. Structural Equation Modeling (SEM) showed that both Stipa and biological soil crust cover exerted substantial and equal positive effects on infiltration under ponding, whereas indirectly, rabbit disturbance negatively affected infiltration by reducing crust cover. Under tension, when macropores were prevented from conducting water, Stipa had a direct negative effect and biological soil crust cover was relatively unimportant. More complex SEM models demonstrated that (1) Stipa primarily influenced biological soil crusts by reducing their richness, (2) rabbits exerted a small negative effect on crust richness, and (3) lichens were negatively, and mosses positively, correlated with a derived “infiltration” axis. Our results highlight the importance of biological soil crusts as key players in the maintenance of infiltration processes in Stipa grasslands, and demonstrate the modulating role played by rabbits through their surface disturbances.     

Gene expression following induction of regeneration in <Emphasis Type="Italic">Drosophila</Emphasis> wing imaginal discs. Expression profile of regenerating wing discs

Background  

Regeneration is the ability of an organism to rebuild a body part that has been damaged or amputated, and can be studied at the molecular level using model organisms. Drosophila imaginal discs, which are the larval primordia of adult cuticular structures, are capable of undergoing regenerative growth after transplantation and in vivo culture into the adult abdomen.     

Strategies to restore floodplain vegetation after abandonment of human activities

Restoring the flooding‐related disturbance regime by removing and setting back flood defenses (channel widening) is the most efficient strategy for recovering riparian plant communities in floodplains formerly impacted by human activities such as agriculture, mining, and forestry. Removing flood defenses is generally not socially accepted, and alternative recovery strategies must be explored. We assessed vegetation establishment on 33 sites in the floodplains of the Middle Ebro River and three of its tributaries (NE Spain) where restoration approaches applied in the last 20 years include channel widening, floodplain excavation, and abandonment of agriculture, gravel extraction, and hybrid poplar plantations, with and without plantation of native species. Using analysis of similarity and ordinations, we found that channel widening led to plant communities closely resembling those found on natural gravel bars, including new recruits of keystone tree species. Excavation of the floodplain as the restoration approach resulted in pioneer, non‐strictly riparian communities. Abandonment of agricultural land or clearing of poplar plantations resulted in alternative stable states predominating, regardless of time elapsed since restoration and whether poles of native species were planted. However, forest‐like communities relatively similar to mature, natural riparian references were attainable when hybrid poplars were allowed to resprout after clear‐cutting, or after the human activities were abandoned and trees were not cut. Combining channel widening and assisted revegetation where flood defenses cannot be altered may partially reproduce a mosaic of habitats typical of natural floodplains.     

Recombination correlates with synaptonemal complex length and chromatin loop size in bovids—insights into mammalian meiotic chromosomal organization

Homologous chromosomes exchange genetic information through recombination during meiosis, a process that increases genetic diversity, and is fundamental to sexual reproduction. In an attempt to shed light on the dynamics of mammalian recombination and its implications for genome organization, we have studied the recombination characteristics of 112 individuals belonging to 28 different species in the family Bovidae. In particular, we analyzed the distribution of RAD51 and MLH1 foci during the meiotic prophase I that serve, respectively, as proxies for double-strand breaks (DSBs) which form in early stages of meiosis and for crossovers. In addition, synaptonemal complex length and meiotic DNA loop size were estimated to explore how genome organization determines DSBs and crossover patterns. We show that although the number of meiotic DSBs per cell and recombination rates observed vary between individuals of the same species, these are correlated with diploid number as well as with synaptonemal complex and DNA loop sizes. Our results illustrate that genome packaging, DSB frequencies, and crossover rates tend to be correlated, while meiotic chromosomal axis length and DNA loop size are inversely correlated in mammals. Moreover, axis length, DSB frequency, and crossover frequencies all covary, suggesting that these correlations are established in the early stages of meiosis.