Charles Gers

Diversity of energy fluxes and interactions between arthropod communities: from Soil to Cave

Abstract The vertical distribution of a species may directly indicate the stage of organic matter decomposition in which it takes part. Observations have so far been limited to superficial layers, but studies on the continuum from the litter to underground biotopes, through the recently discovered superficial underground compartment, open new perspectives in the analyses of matter and energy fluxes. Sampling at different levels, from leaf litter to caves, using pitfall traps and sunken tubes, has revealed the existence of exchanges of organic matter and Arthropoda between different layers. The importation of energy from soil to cave follows two routes: passive and active. For the passive route, I measured dissolved substances in water at five levels. For the active route, I evaluated the migrations of insects and other invertebrates (downwards as well as upwards). For the analysis of arthropod communities, using the notion of functional groups, I showed the existence of links between two components, hypogean species, and endogean-epigean species, defining an ecotone along the vertical gradient ‘soil to cave’. The superficial underground compartment is not isolated, but is rather a whole food web with epigean and endogean organisms penetrating and interlinking with another web of hypogean origin.

Relationships between Collembola, soil chemistry and humus types in forest stands (France)

Soil samples were taken under four tree species in various forest sites located in southern France. For each sampled A horizon of the soil profile, pH, organic matter content, C:N ratio and amounts of exchangeable cations (K, Ca, Mg) were measured, and collembolan fauna was extracted using Berlese-Tullgren funnels. A total of 78 species representing 11 families and 47 genera were identified. The relationships between Collembola and soil parameters were determined by co-inertia analysis which corresponds to the simultaneous Correspondence Analysis of the collembolan data table and the Multiple Correspondence Analysis of the environmental data table. The analysis revealed that the distribution of 10 species was related to pH, organic matter content via C and N and to base cations (K, Ca, Mg). Samples, linking these collembolan species and chemical parameters, were clustered according to humus forms. Collembola seem to be linked closer to the physical structure of humus than to its chemical parameters. Their specific contribution to pedogenetic processes as yet remains to be clarified.

Molecular phylogeny of the Erebia tyndarus (Lepidoptera, Rhopalocera, Nymphalidae, Satyrinae) species group combining CoxII and ND5 mitochondrial genes: A case study of a recent radiation

The genus Erebia is one of the more controversial groups among the Holarctic Lepidoptera. In this genus, composed of around 100 mountain species, the Erebia tyndarus complex has certainly been a major source of debate for more than a century. According to the literature, between 2 and 11 species, and at least 45 subspecies or semi-species have been recognized. For the first time, we provide a complete molecular study, based on the ND5 and CoxII mitochondrial gene sequences, including all the recognized species and 60% of the subspecies of the entire group, with European, Caucasian, Siberian and North-American taxa. Our analyses led us to recognize 11 species even though there was some poor discrimination between Western Europe species. A complete study of the events of speciation is presented in the light of glacial and interglacial cycles during the Pleistocene.

ISSR (Inter Simple Sequence Repeats) as molecular markers to study genetic diversity in tarantulas (Araneae, Mygalomorphae)

Abstract Although all species of the Brachypelma genus are protected under CITES, few studies have been performed on the genetic structure of the populations of these endangered tarantulas. Here we propose, for the first time in spiders, to use ISSR (Inter Simple Sequence Repeat) technique to study the genetic variability of Mexican populations of Brachypelma vagans (Ausserer 1875). We used a nonlethal technique to collect samples from six populations in the Yucatan peninsula and we tested seven ISSR primers. Four of these primers gave fragments (bands) that were sufficiently clear and reproducible to construct a binary matrix and determine genetic variability parameters. We revealed a very high percentage of polymorphism (P  =  98.7%) the highest yet reported for tarantula spiders. Our results show that the ISSR-PCR method is promising for intraspecific variation of tarantula spiders.

Chemical characterization of contact semiochemicals for host-recognition and host-acceptance by the specialist parasitoid Cotesia plutellae (Kurdjumov)

Summary.Cotesia plutellae is a specialist parasitoid of Plutella xylostella. This specificity is potentially under the control of several factors before and after oviposition. Thereby, the stimuli that lead female parasitoids to host locations and to oviposition, might be at the basis of the specificity. We explore here the response of C. plutellae females exposed to host cuticular lipids. A total cuticular lipid extract of host caterpillars was fractionated into a hydrocarbon fraction and a non-hydrocarbon fraction. Neither fraction alone had any effect on oviposition behaviour in C. plutellae but the hydrocarbon fraction alone did seem to have a positive effect on the rate of antennal contact by the females. To induce oviposition behaviour, both fractions were necessary and reflect cooperation between at least one compound in each fraction. Identification of cuticular lipids shows that hydrocarbons were dominant (77%). Non-hydrocarbon compounds were mainly represented by 15-nonacosanone (18% of the total lipid extract). This ketone is rare in insect cuticle lipids and is thought to originate from the cabbage epicuticle where it is dominant with n-C29 and 14- and 15-nonacosanol also found among the cuticular lipids of the host caterpillar.

Plant litter mixture partly mitigates the negative effects of extended drought on soil biota and litter decomposition in a Mediterranean oak forest

A major challenge of current ecological research is to determine the responses of plant and animal communities and ecosystem processes to future environmental conditions. Ecosystems respond to climate change in complex ways, and the outcome may significantly depend on biodiversity. We studied the relative effects of enhanced drought and of plant species mixture on soil biota and on litter decomposition in a Mediterranean oak forest. We experimentally reduced precipitation, accounting for seasonal precipitation variability, and created a single-species litter (Quercus pubescens), a two-species litter mixture (Q. pubescens + Acer monspessulanum) and a three-species litter mixture (Q. pubescens + A. monspessulanum + Cotinus coggygria). In general, drier conditions affected decomposers negatively, directly by reducing fungal biomass and detritivorous mesofauna, and also indirectly by increasing the predation pressure on detritivorous mesofauna by predatory mesofauna. This is reflected under drier conditions in that Collembola abundance decreased more strongly than Acari abundance. One Collembola group (i.e. Neelipleona) even disappeared completely. Increased drought strongly decreased litter decomposition rates. Mixed litter with two and three plant species positively affected soil biota communities and led to a more efficient litter decomposition process, probably through a greater litter quality. Faster decomposition in mixed litter can thus compensate slower decomposition rates under drier condition. Synthesis. Our results highlight that, within our study system, drier climate strongly impacts on soil biodiversity and hence litter decomposition. Species-rich litter may mitigate such a decline in decomposition rates. Diverse plant communities should hence be maintained to reduce shifts in ecosystem functioning under climate change.

Analysis of forestry impacts and biodiversity in two Pyrenean forests through a comparison of moth communities (Lepidoptera, Heterocera)

We have compared the biodiversity variations in moth communities between unmanaged forests and commercial forests in a mountainous environment (Pyrenees France). The aim was to evaluate the impact of forestry activities on moth diversity. The data collected from the insects were analysed with a Bayesian specific similarity index (noted SSP index) and by statistical biodiversity indexes comparison. It was seen that diversity and richness were decreased in the plantation compared to the unmanaged forest. Interestingly, the composition of the communities of moths was shown to be not only related to the presence/absence of host plants, but also to be in relation with changes in the differences in forest architecture (i.e. the relative coverage by the different vegetation levels). However, the moth community in the commercial forest still has a high capacity to converge with the moth community present in more natural forests. We report here a list of 177 species of moths, providing information on the distribution of some uncommon species, poorly studied as yet in the Pyrenees.

Pollen morphology and fertility of wild Atlas pistachio (Pistacia atlantica Desf., Anacardiaceae)

Pollen morphology and fertility in different populations of Pistacia atlantica from Algeria have been examined by light and scanning electron microscopy. Characteristics such as the shape and size of the pollen grains, the number of apertures, and the exine surface were recorded for each site for comparison. The pollen grains of Pistacia atlantica are consistently spheroidal to prolate spheroidal and pantoaperturate. The exine ornamentation is reticulate. Significant differences in pollen size and number of apertures were observed between the different sites. The fertility of pollen from different sites was estimated using the acetocarmine staining method and show that mean percentage of fertile pollen is high but varied among the sites with highest value (99.7%) at the Berriane site and lowest value (95.9%) at the Messaad site.