Nematode Interactions on Beetle Hosts Indicate a Role of Mouth-Form Plasticity in Resource Competition

Competition is rampant across kingdoms, arising over potential mates, food resources, and space availability. When faced with opponents, phenotypic plasticity proffers organisms indispensable advantageous strategies to outcompete rivals. This tactic is especially crucial on decaying insect hosts as myriad microbes and numerous nematodes struggle to establish thriving populations and ensure resource availability for future generations. Scarab beetles and their associated nematode symbionts on La Réunion Island have provided exceptional systems to study complicated cross-phylum interactions in soil, and recently we have identified a previously unexplored beetle host, Gymnogaster bupthalma, to be reliably co-infested with diplogastrids Pristionchus mayeri and Acrostichus spp. These nematodes maintain the capacity to plastically respond to environmental conditions by developing disparate mouth forms, a strict bacterial-feeding morph or an omnivorous morph that enables predation on other nematodes. In addition, under stressful settings these worms can enter an arrested development stage called dauer, non-feeding dispersal larvae that resume development into reproducing adults when conditions improve. By investigating this beetle-nematode system in a natural context, we uncovered a novel Pristionchus strategy, wherein dauer dispersal from the carcass is gradual and a reproducing population is sustained. Remarkably, usually preferential-bacterial morph P. mayeri develop as predators in populations dense with competitors.

A Revised Description of the Larva of Leptocerina pauliani (Ross 1957 (Trichoptera: Leptoceridae), an Endemic Species of La Réunion Island

Leptocerina is an endemic Afrotropical genus of Trichoptera, with 19 species documented but only five partially described at the larval stage. The first description of Leptocerina pauliani (Ross 1957) larva by Marlier & Marlier (1982) included very few illustrations, making comparisons with other species challenging. I present a revised description of the L. pauliani larval stage, using specimens collected from the River Marsouins in La Réunion Island. I apply a focus stacking approach for emphasizing coloration patterns and providing a detailed description of larval characters. Criteria for distinguishing L. pauliani from the other species of Leptocerina already described or partially described for the larval stage are discussed.

Instability of the NS1 Glycoprotein from La Reunion 2018 Dengue 2 Virus (Cosmopolitan-1 Genotype) in Huh7 Cells Is Due to Lysine Residues on Positions 272 and 324

La Reunion island in the South West Indian Ocean is now endemic for dengue following the introduction of dengue virus serotype 2 (DENV-2) cosmopolitan-I genotype in 2017. DENV-2 infection causes a wide spectrum of clinical manifestations ranging from flu-like disease to severe dengue. The nonstructural glycoprotein 1 (NS1) has been identified as playing a key role in dengue disease severity. The intracellular NS1 exists as a homodimer, whereas a fraction is driven towards the plasma membrane or released as a soluble hexameric protein. Here, we characterized the NS1 glycoproteins from clinical isolates DES-14 and RUN-18 that were collected during the DENV-2 epidemics in Tanzania in 2014 and La Reunion island in 2018, respectively. In relation to hepatotropism of the DENV, expression of recombinant DES-14 NS1 and RUN-18 NS1 glycoproteins was compared in human hepatoma Huh7 cells. We observed that RUN-18 NS1 was poorly stable in Huh7 cells compared to DES-14 NS1. The instability of RUN-18 NS1 leading to a low level of NS1 secretion mostly relates to lysine residues on positions 272 and 324. Our data raise the issue of the consequences of a defect in NS1 stability in human hepatocytes in relation to the major role of NS1 in the pathogenesis of the DENV-2 infection.

First report on the occurrence of Typhlodromus (Anthoseius) transvaalensis (Nesbitt) (Acari: Phytoseiidae) in India with a redescription of the species

This paper reports for the first time the occurrence of Typhlodromus (Anthoseius) transvaalensis (Nesbitt) in India. Morphometric measurements of the Indian specimens collected on an unidentified plant in Ramanagara district of Karnataka are provided along with a redescription of the species, and a comparison with specimens from Japan, Africa, Argentina and La Réunion Island to show similarities and variations in morphological traits of taxonomic importance.

Lava flow hazard map of Piton de la Fournaise volcano

Piton de la Fournaise, situated on La Réunion Island (France), is one of the most active hot spot basaltic shield volcanoes worldwide, experiencing at least two eruptions per year since the establishment of the observatory in 1979. Eruptions are typically fissure-fed and form extensive lava flow fields. About 95 % of some ~250 historical events (since the first confidently dated eruption in 1708) have occurred inside an uninhabited horse-shoe shaped caldera (hereafter referred to as the Enclos) which is open to the ocean on its eastern side. Rarely (12 times since the 18th century), fissures have opened outside of the Enclos where housing units, population centers and infrastructure are at risk. In such a situation, lava flow hazard maps are a useful way of visualizing lava flow inundation probabilities over large areas. Here, we present a lava flow hazard map for Piton de la Fournaise volcano based on: i) vent distribution, ii) statistics of lava flow lengths, iii) lava flow recurrence times, and iv) simulations of lava flow paths across multi-temporal (i.e., regularly updated) topography using the DOWNFLOW stochastic numerical model. A map of the entire volcano highlights that the most probable (up to 12 %) location for future lava flow inundation is within the Enclos, where about 100,000 visitors are present each year. Hazard distribution changes throughout the analysis period due to the high frequency of eruptions that constantly modifies the vent opening distribution as well as the topography and the lava flow dimensional characteristics. Outside of the Enclos, probabilities reach 0.5 % along the well-defined rift zones and, although hazard occurrence in inhabited areas is deemed to be very low (