Earthworms Use Odor Cues to Locate and Feed on Microorganisms in Soil

Earthworms are key components of temperate soil ecosystems but key aspects of their ecology remain unexamined. Here we elucidate the role of olfactory cues in earthworm attraction to food sources and document specific chemical cues that attract Eisenia fetida to the soil fungi Geotrichum candidum. Fungi and other microorganisms are major sources of volatile emissions in soil ecosystems as well as primary food sources for earthworms, suggesting the likelihood that earthworms might profitably use olfactory cues to guide foraging behavior. Moreover, previous studies have documented earthworm movement toward microbial food sources. But, the specific olfactory cues responsible for earthworm attraction have not previously been identified. Using olfactometer assays combined with chemical analyses (GC-MS), we documented the attraction of E. fetida individuals to filtrate derived from G. candidum colonies and to two individual compounds tested in isolation: ethyl pentanoate and ethyl hexanoate. Attraction at a distance was observed when barriers prevented the worms from reaching the target stimuli, confirming the role of volatile cues. These findings enhance our understanding of the mechanisms underlying key trophic interactions in soil ecosystems and have potential implications for the extraction and collection of earthworms in vermiculture and other applied activities

Une chaire pour faire face. Introduction

Cet article introduit la problématique générale de l'ouvrage qui retrace la création de la Chaire Mukwege à l'Université de Liège. Il traite surtout des interrogations des chercheurs au sein de cette chaire car rien, dans les cursus universitaires, ne prépare les universitaires à la violence des situations rencontrées.5. Gender equality3. Good health and well-being1. No poverty4. Quality educatio

Hybridization in annual plants: patterns and dynamics during a four-year study in mixed Rhinanthus populations

Hybridization in annual plants is rare, but their short life cycle provides an excellent opportunity to study the dynamics of hybridization. Hybridization occurs between the annual hemiparasites Rhinanthus minor and Rhinanthus angustifolius (Orobanchaceae). Using flower morphology, Kwak (1980) found a prevalence of hybrids close to R. angustifolius in a single population. We aim to find whether this pattern is also found using genetic markers, whether it is generally occurring in mixed populations, and whether these populations are stable over time. We used species-specific genetic markers to determine the number of individuals in a range of hybrid classes in three mixed populations of different ages during four consecutive years. In the young population, F-1 hybrids were found in the first year and mostly hybrids between R. minor and these F(1)s in the second year, but in the years after that, hybrids close to R. angustifolius became more abundant. We also found this in the two older populations, where hybrids close to R. angustifolius always occurred in higher frequencies than hybrids close to R. minor. Over time, R. angustifolius strongly increased in frequency in two populations. Patterns of marker presence and absence suggested that advanced-generation hybrids are mainly formed by backcrossing with one of the parents, predominantly R. angustifolius whenever its frequency in the population is higher than 15%. The dynamics of mixed populations depend on the ecological conditions that regulate the presence of the two parental species, and introgression into R. angustifolius seems prevalent

The roles of pollinators in hybridization between two Rhinanthus species

Biotic pollination is thought to have played an important role in the diversification of the angiosperms, one of the driving factors for speciation. The role of pollinators has often been studied in species pairs with constrasting flower shape and colour, often emphasizing reproductive isolation brought about by the difference in pollinator assemblage. Much less is known about situations where the two hybridizing plant species share the same pollinator guild, and thus have more opportunities for hybridization. The occurrence of hybridization in the genus Rhinanthus (Orobanchaceae), annual hemi-parasitic grassland species pollinated by bumblebees, has been reported since Linnaeus, and we have performed extensive research on hybridization in the species pair Rhinanthus minor – R. angustifolius since 2000. This talk aims to give an overview of the data we have thus far collected on the effects of bumblebee behaviour on the formation of first- and advanced-generation hybrids, look at the expected effects on the long term and discuss the role of differences in selfing rate between the two species

Quantities of ethyl pentanoate and ethyl hexanoate tested and <i>E. fetida</i> responses to each.

<p>- = no attraction, ◊ = earthworm attraction.</p><p>Note: Although p-values at 1 µl for both esters are significant (and in each case earthworms were overrepresented in the treatment arm relative to expectations based on a random distribution) attraction to the treatment arm was not significantly different than to at least one adjacent control arm. Instead earthworms were significantly underrepresented in the most distant control arm. This result is consistent with weak attraction to this low concentration of the target compound.</p

Earthworm behavior in four arm olfactometer.

<p>Observed and theoretical (i.e. random) distributions of earthworms in each arm of the four-arm olfactometer when one arm is treated with (a) <i>G. candidum</i> filtrate, (b) ethyl pentanoate (100% v/v), or (c) ethyl hexanoate (100% v/v). The distributions are compared by a Chi-square Goodness-of-fit test.</p

Treatments employed in the four-arm olfactometer bioassays.

<p>Treatments employed in the four-arm olfactometer bioassays.</p

Earthworm behavior in vertical olfactometer.

<p>Numbers of earthworms (mean ± SD) collected in the top 5 cm of the vertical olfactometer in presence and in absence of G. candidum filtrate for each olfactometer arm length.</p