Interspecific competition between entomopathogenic nematodes (Steinernema) is modified by their bacterial symbionts (Xenorhabdus)

BACKGROUND: Symbioses between invertebrates and prokaryotes are biological systems of particular interest in order to study the evolution of mutualism. The symbioses between the entomopathogenic nematodes Steinernema and their bacterial symbiont Xenorhabdus are very tractable model systems. Previous studies demonstrated (i) a highly specialized relationship between each strain of nematodes and its naturally associated bacterial strain and (ii) that mutualism plays a role in several important life history traits of each partner such as access to insect host resources, dispersal and protection against various biotic and abiotic factors. The goal of the present study was to address the question of the impact of Xenorhabdus symbionts on the progression and outcome of interspecific competition between individuals belonging to different Steinernema species. For this, we monitored experimental interspecific competition between (i) two nematode species: S. carpocapsae and S. scapterisci and (ii) their respective symbionts: X. nematophila and X. innexi within an experimental insect-host (Galleria mellonella). Three conditions of competition between nematodes were tested: (i) infection of insects with aposymbiotic IJs (i.e. without symbiont) of both species (ii) infection of insects with aposymbiotic IJs of both species in presence of variable proportion of their two Xenorhabdus symbionts and (iii) infection of insects with symbiotic IJs (i.e. naturally associated with their symbionts) of both species. RESULTS: We found that both the progression and the outcome of interspecific competition between entomopathogenic nematodes were influenced by their bacterial symbionts. Thus, the results obtained with aposymbiotic nematodes were totally opposite to those obtained with symbiotic nematodes. Moreover, the experimental introduction of different ratios of Xenorhabdus symbionts in the insect-host during competition between Steinernema modified the proportion of each species in the adults and in the global offspring. CONCLUSION: We showed that Xenorhabdus symbionts modified the competition between their Steinernema associates. This suggests that Xenorhabdus not only provides Steinernema with access to food sources but also furnishes new abilities to deal with biotic parameters such as competitors

Facilitation of P acquisition by intercropping cereal and grain legumes in field conditions

Intercropping systems consist in growing two or more species simultaneously in the same field for at least part of their growth cycle. In situations of limiting nutrient availability, acquisition of resources in intercrops (IC) is generally improved compared to sole crops (SC), as a result of positive interactions between the intercropped plant species, i.e. either niche complementarity or facilitation. Evidence has recently accumulated that intercropped cereals and grain legumes promote the use of soil P resources, though few reports derived from field trials. We investigated whether (i) intercropping of durum wheat with pea or faba bean does improve soil P acquisition; (ii) facilitative interactions can be detected, and (iii) soil P availability does influence such effects. We conducted two 1-year experiments in a long term P fertilizer field trial with a gradient of Olsen-P soil content from 1, except in the lower P soil content, where faba bean was outcompeted by wheat in the later stages. P export was increased in IC vs. SC at the legume flowering stage, while it decreased afterwards to similar amounts mainly due to faba bean suppression. Our data suggest positive plant-plant interactions (niche complementarity/facilitation) at earlier growth stages of wheat-legume intercrops that transiently resulted in a more efficient use of soil P resources but then receded until harvest

Is P acquisition facilitated by intercropping of durum wheat and grain legumes in field conditions?

Intercropping systems consist in growing two or more species simultaneously in the same field for at least part of their growth cycle. In situations of limiting nutrient availability, acquisition of resources in intercrops is generally improved compared to sole crops, as a result of positive interactions between the intercropped plant species, i.e. either niche complementarity or facilitation. Evidence has recently accumulated that intercropped cereals and grain legumes promote the use of soil P resources, though few reports derived from field trials. We investigated whether (i) intercropping of durum wheat with pea or faba bean does improve soil P acquisition; (ii)facilitative interactions can be detected, and (iii) soil P availability does influence such effects. We conducted two 1-year experiments in a long term P fertilizer field trial with a gradient of Olsen-P soil content from 1, except in the lower P soil content, where faba bean was outcompeted by wheat in the later stages. P export was increased in intercrops vs. sole crops at the legume flowering stage, while it decreased afterwards to similar amounts mainly due to faba bean suppression. Our data suggest positive plant-plant interactions (niche complementarity/facilitation) at earlier growth stages of wheat-legume intercrops that transiently resulted in a more efficient use of soil P resources but then receded until harvest

Functional repertoire convergence of distantly related eukaryotic plankton lineages revealed by genome-resolved metagenomics

Marine planktonic eukaryotes play a critical role in global biogeochemical cycles and climate. However, their poor representation in culture collections limits our understanding of the evolutionary history and genomic underpinnings of planktonic ecosystems. Here, we used 280 billion Tara Oceans metagenomic reads from polar, temperate, and tropical sunlit oceans to reconstruct and manually curate more than 700 abundant and widespread eukaryotic environmental genomes ranging from 10 Mbp to 1.3 Gbp. This genomic resource covers a wide range of poorly characterized eukaryotic lineages that complement long-standing contributions from culture collections while better representing plankton in the upper layer of the oceans. We performed the first comprehensive genome-wide functional classification of abundant unicellular eukaryotic plankton, revealing four major groups connecting distantly related lineages. Neither trophic modes of plankton nor its vertical evolutionary history could explain the functional repertoire convergence of major eukaryotic lineages that coexisted within oceanic currents for millions of year

Functional repertoire convergence of distantly related eukaryotic plankton lineages abundant in the sunlit ocean

International audienceMarine planktonic eukaryotes play critical roles in global biogeochemical cycles and climate. However, their poor representation in culture collections limits our understanding of the evolutionary history and genomic underpinnings of planktonic ecosystems. Here, we used 280 billion Tara Oceans metagenomic reads from polar, temperate, and tropical sunlit oceans to reconstruct and manually curate more than 700 abundant and widespread eukaryotic environmental genomes ranging from 10 Mbp to 1.3 Gbp. This genomic resource covers a wide range of poorly characterized eukaryotic lineages that complement long-standing contributions from culture collections while better representing plankton in the upper layer of the oceans. We performed the first, to our knowledge, comprehensive genome-wide functional classification of abundant unicellular eukaryotic plankton, revealing four major groups connecting distantly related lineages. Neither trophic modes of plankton nor its vertical evolutionary history could completely explain the functional repertoire convergence of major eukaryotic lineages that coexisted within oceanic currents for millions of years

Functional repertoire convergence of distantly related eukaryotic plankton lineages abundant in the sunlit ocean

International audienc

Functional repertoire convergence of distantly related eukaryotic plankton lineages abundant in the sunlit ocean

International audienc

Functional repertoire convergence of distantly related eukaryotic plankton lineages abundant in the sunlit ocean

International audienc