Can species richness be maintained in logged endemic Acacia Heterophylla forests (Reunion Island, Indian Ocean) ?

It is assumed that forests can serve multiple uses, including wood production and maintenance of high biodiversity level. We tested this hypothesis by studying eradication methods of invasive plants currently implemented in exploited endemic Acacia heterophylla forests located in a tropical highland forest region on the island of Réunion. We also compared species richness in logged (over time) and natural forests. Our results show that all individuals of the widespread alien invasive plant Rubus alceifolius were generated from cuttings. We quantifi ed the high growth capability of this species by comparing with those of Acacia heterophylla along with Rubus apetalus var. apetalus, a close non-invasive congener. The substantial multiplicative and vegetative growth ability of R. alceifolius enabled it to form monospecific patches in only 2.5 years. The species richness of the exploited Acacia heterophylla forest was thus very affected. Although the species richness increased over time after logging, the extent of the resulting richness was not as great as that in natural forests which, moreover, included numerous exotic plants. The authors assess the impact of highly disturbing logging operations and, based on the results of the comparisons, are very pessimistic about the possibility of maintaining species richness in logged forests. Nevertheless, the results indicate that the situation is not beyond hope and an eradication program specifi cally tailored to this kind of forest is proposed if exploitation will stop

Liens entre la mise en place d'une filière d'utilisation d'une plante exotique envahissante et la conservation des milieux naturels : cas du goyavier Psidium cattleianum Afzel. ex Sabine à La Réunion (Myrtales : Myrtaceae)

Résumé : Afin de limiter l'impact négatif des plantes exotiques envahissantes sur les milieux naturels, de nombreuses actions de lutte sont entreprises. La mise en place de filières d’exploitation de certaines de ces espèces paraît être une solution intéressante pour la conservation d'une part mais également pour l'acquisition d'une nouvelle ressource économique d'autre part. Toutefois, les avis à ce sujet sont très partagés, et de nombreux auteurs ont montré que la mise en place d'une filière n'a pas d'intérêt pour la conservation des milieux naturels et des espèces autochtones. Le cas de la mise en place récente d'une filière bois autour du goyavier Psidium cattleianum à La Réunion, plante exotique envahissante la plus abondante sur l'île, est donc un sujet d'études approprié afin d'évaluer l'intérêt de sa mise en place. Notre étude, située au niveau d’une forêt tropicale humide de montagne montre que trois ans après des actions de coupes de tiges de P. cattleianum, la richesse spécifique est légèrement plus importante, toutes strates confondues, et ce aussi bien pour les espèces indigènes qu'exotiques. Il existe cependant des différences significatives au niveau du degré d'envahissement et du nombre de rejets de souches de goyavier qui sont plus importants trois ans après les actions de coupe des tiges de P. cattleianum. Nous concluons sur l'effet négatif de la mise en place de la filière sans poursuite dans le temps d'actions de lutte, notamment du fait de la reprise rapide du P. cattleianum et de l'arrivée de nouvelles plantes exotiques profitant de la perturbation engendrée par ces actions. Afin de développer une filière profitable à tous, nous proposons d'une part, de réaliser une cartographie précise du goyavier de manière à évaluer le potentiel et l'intérêt coût/bénéfice, et d'autre part de tenir compte que la ressource est épuisable, en prévoyant d’associer d'autres plantes exotiques envahissantes à cette filière.Summary: Harvesting invasive alien plants and conservation links: the specific case of the strawberry guava, Psidium cattleianum Afzel. exSabine, in La Réunion Island. In order to limit the negative impact of invasive alien plants in native habitats, numerous control actions are being conducted. Harvesting invasive alien species appears to be an interesting solution, firstly, for the conservation, and secondly for the acquisition of a new economic resource. However, opinions on this matter varied, and numerous authors showed that harvesting alien plants has no interest for the native environments and the species conservation. The case of the recent harvesting for the wood industry of the strawberry guava, Psidium cattleianum Afzel. exSabine, in la Reunion Island, the most abundant invasive alien plant on the island, is a suitable subject of studies in order to assess the harvesting interest. Our study, localised within a tropical mountain rainforest, shows that three years after stems cutting, species abundance is slightly more important, all strata taken together, as well for indigenous and exotic plant species. Nevertheless,the authors show significant differences in the degree of invasion and the number of shoots which are more important three years after P. cattleianum stems cutting.The authors conclude on the negative effect of harvesting without control action over time, in particular because of the rapid P. cattleianum regrowth and by the arrival of new alien plants due to the disturbance caused by the treatment. In order to realize a global advantageous harvesting, the authors suggest on one hand to design a precise map in order to value the potential and the cost/profit interest, but also, on the other hand to consider that the used resource is exhaustible, by the association of other invasive alien plants in this harvesting

La richesse spécifique peut-elle être conservée dans des forêts exploitées d’Acacia heterophylla, espèce endémique de l’île de la Réunion (Océan Indien) ?

It is assumed that forests can serve multiple uses, including wood production and maintenance of high biodiversity level. We tested this hypothesis by studying eradication methods of invasive plants currently implemented in exploited endemic Acacia heterophylla forests located in a tropical highland forest region on the island of Réunion. We also compared species richness in logged (over time) and natural forests. Our results show that all individuals of the widespread alien invasive plant Rubus alceifolius were generated from cuttings. We quantifi ed the high growth capability of this species by comparing with those of Acacia heterophylla along with Rubus apetalus var. apetalus, a close non-invasive congener. The substantial multiplicative and vegetative growth ability of R. alceifolius enabled it to form monospecific patches in only 2.5 years. The species richness of the exploited Acacia heterophylla forest was thus very affected. Although the species richness increased over time after logging, the extent of the resulting richness was not as great as that in natural forests which, moreover, included numerous exotic plants. The authors assess the impact of highly disturbing logging operations and, based on the results of the comparisons, are very pessimistic about the possibility of maintaining species richness in logged forests. Nevertheless, the results indicate that the situation is not beyond hope and an eradication program specifi cally tailored to this kind of forest is proposed if exploitation will stopLa richesse spécifique peut-elle être conservée dans des forêts exploitées d'Acacia heterophylla, espèce endémique de l'île de la Réunion (océan Indien) ? - Il est globalement considéré que les forêts peuvent assurer des usages multiples, incluant la production de bois et le maintien d'un niveau élevé de biodiversité. Dans le but de tester cette hypothèse, nous avons étudié les méthodes d'éradication de Rubus alceifolius actuellement utilisées au sein d'une forêt exploitée d'Acacia heterophylla, espèce endémique de l'île de la Réunion. Nos résultats montrent que tous les individus de l'espèce envahissante la plus répandue dans la zone -Rubus alceifolius-, proviennent de bouturage. Nous avons aussi quantifié la forte capacité de croissance de cette espèce au travers d'une comparaison de croissance avec l'Acacia heterophylla mais aussi avec un congénère indigène - Rubus apetalus var. apetalus. Ces capacités de multiplication et de croissance végétatives importantes permettent à Rubus alceifolius de former des massifs monospécifiques en seulement 2,5 ans. La richesse spécifique de la forêt d'Acacia heterophylla exploitée en est alors largement affectée. En effet, de manière générale, même si la richesse spécifique semble augmenter légèrement au cours du temps, les espèces observées sont généralement des espèces exotiques envahissantes. Comparant l'extraction du bois à un haut niveau de perturbation, les auteurs sont très pessimistes sur la possibilité de maintenir une diversité spécifique élevée au sein d'une forêt exploitée. Néanmoins ces résultats apportent une lueur d'espoir et un programme d'éradication mieux adapté au type de forêt étudié est proposé

High-throughput triggered merging of surfactant-stabilized droplet pairs using traveling surface acoustic waves

We present an acoustofluidic device for fluorescently triggered merging of surfactant-stabilized picoliter droplet pairs at high throughput. Droplets that exceed a preset fluorescence threshold level are selectively merged by a traveling surface acoustic wave (T-SAW) pulse. We characterize the operation of our device by analyzing the merging efficiency as a function of acoustic pulse position, duration, and acoustic pressure amplitude. We probe droplet merging at different droplet rates and find that efficient merging occurs above a critical acoustic power level. Our results indicate that the efficiency of acoustically induced merging of surfactant stabilized droplets is correlated with acoustic streaming velocity. Finally, we discuss how both time-averaged and instantaneous acoustic pressure fields can affect the integrity of surfactant layers. Our technique, by allowing the merging of up to 105 droplets per hour, shows great potential for integration into microfluidic systems for high-throughput and high-content screening applications

Confining Trypanosoma brucei in emulsion droplets reveals population variabilities in division rates and improves in vitro cultivation

Trypanosome parasites are infecting mammals in Sub-Saharan Africa and are transmitted between hosts through bites of the tsetse fly. The transmission from the insect vector to the mammal host causes a number of metabolic and physiological changes. A fraction of the population continuously adapt to the immune system of the host, indicating heterogeneity at the population level. Yet, the cell to cell variability in populations is mostly unknown. We develop here an analytical method for quantitative measurements at the single cell level based on encapsulation and cultivation of single-cell Trypanosoma brucei in emulsion droplets. We first show that mammalian stage trypanosomes survive for several hours to days in droplets, with an influence of droplet size on both survival and growth. We unravel various growth patterns within a population and find that droplet cultivation of trypanosomes results in 10-fold higher cell densities of the highest dividing cell variants compared to standard cultivation techniques. Some variants reach final cell titers in droplets closer to what is observed in nature than standard culture, of practical interest for cell production. Droplet microfluidics is therefore a promising tool for trypanosome cultivation and analysis with further potential for high-throughput single cell trypanosome analysis