Queens defense by workers in the highly polygynous ant Crematogaster pygmaea (Hymenoptera: Myrmicinae)

Some aspects of the biology of Crematogaster pygmaea, a highly polydomous and polygynous ant, are more commonly found in monogynous species. One such characteristic is the high attractiveness of its queens. In this study, this attractiveness was assessed under varying experimental conditions to investigate the factors responsible for its expression and variation, and to identify the nature of queen attractiveness. It was shown (1) that C. pygmaea queens are highly attractive to the workers that cluster on and around them (retinue), (2) that the attractiveness of C. pygmaea queens is context-dependent, i.e., it increases with increasing degree of potential danger to the queen, (3) that the attractiveness signal of C. pygmaea queens is chemically based, and (4) that this signal is persistent and apparently not colony-specific. The proposed hypothesis is that the C. pygmaea queens constantly release an attractiveness signal that is “read” by the workers, in a dependent way linked to the context, and that the main function of this attractiveness is to protect queens. This protection would have a high adaptive value in the context of the social structure and the reproductive strategies in C. pygmaea.     

Examination of the success rate of secondary symbiont manipulation by microinjection methods in the pea aphid system

Insects harbor a wide range of microbial symbionts, but their influence on host phenotypes is described in a limited number of biological models. One experimental approach to gain knowledge on the effects of symbionts to their hosts is to create insect lines with and without symbionts and examine their phenotypes. However, the success rate of symbiont elimination and introduction methods is dependent on several parameters that are scarcely tested or described. The pea aphid, Acyrthosiphon pisum Harris (Hemiptera: Aphididae), is a model insect of symbiosis studies. It harbors a primary symbiont that supplies the host with essential amino acids, and an array of secondary symbionts whose effects have been assessed by manipulating their presence/absence in the insect. Here, we describe the influence of key parameters on the success rate of symbiont manipulation using the pea aphid–secondary symbiont system. We compared two elimination methods differing in antibiotic treatment using several aphid–symbiont combinations. We also created new aphid host–symbiont combinations by secondary symbiont introduction and examined the effects of larval stage of recipient aphids on introduction success. Our study revealed that the aphid–symbiont combination has strong influence on both symbiont introduction and elimination success rates, and that the type of antibiotics and the larval stage of recipient aphids influence the elimination and introduction success rate, respectively.     

Starvation-Induced Multiresistance in Enterococcus faecalis JH2-2

Compared with growing bacteria, carbohydrate-starved cells of Enterococcus faecalis show development of a multiresistance state against heat, H₂O₂, acid, and ethanol, but not against UV irradiation. The kinetics of acquisition of resistance is different according to the stress. Three hours of starvation provide maximal resistance against ethanol, while the tolerance to heat, H₂O₂, and acid increases progressively with the duration of starvation. Chloramphenicol treatment does not abolish the ethanol tolerance. Protein synthesis inhibition during the transitional growth phase and the first hours of starvation partially inhibit the acquisition of heat and oxidative resistances. Antibiotic treatment after 3 h of starvation does not affect the increase of these resistances. We suggest that synthesis of specific proteins revealed by 2-D gel analysis in the first 3 h of starvation, followed by a second mechanism related to protein degradation or alteration, is necessary for acquisition of maximal resistance towards heat and oxidative stresses.     

Ten-year dynamics of vegetation in a Mediterranean temporary pool in western Morocco

The aim of this work was to test the hypotheses that the species composition of the vegetation of one pool in Morocco change continuously along with rainfall fluctuations, that among the vegetation can be recognized Pool species and Opportunistic species with distinct dynamics in time. We expected the Pool species to show lower inter-annual variation than the Opportunistic species. This hypothesis was tested in a 10-year study of the species composition of the vegetation along two permanent transects. The results showed high cumulative species richness (95 species) with large differences between years and a predominance of annual species (77). The proportion of Pool species during these 10 years was low (39%) when compared to opportunists (61%). In dry years the Opportunistic species were dominant and declined during wet years. The number of Pool species was correlated with the amount of rainfall. A large number of these species revealed a preference for wet years. No negative interaction between annuals/perennials and pools/non-pools species was found, suggesting that competition was not a major process during the survey. The intensity of the drought and flood stress, related to climate fluctuations, seems to be the main factors controlling the species composition of the vegetation of this unstable habitat. However, beyond the inter-annual fluctuation of the species composition of the vegetation a directional change was noticed. This directional change could result from a recovery process of the vegetation during the first years of the study after a severe flood which extirpated most of the Opportunistic species of the pool. In the last years this directional change of the species composition of the vegetation is less clear and random recruitment of the Opportunistic species from the surrounding forested habitats could contribute to explain inter-annual changes. The data collected over these 10 years led to the speculation of hypotheses on the consequences of climate change. The expected reduction of humid years and of rainfall regionally may lead to important changes in the species composition of the vegetation of the temporary pools in Morocco. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008     

Evolutionary and functional insights into reproductive strategies of aphids

Aphids are among the few organisms capable of reproducing either sexually or asexually. This plasticity in reproductive mode is viewed as an adaptive response to cope with seasonal changes. Clonal reproduction occurs during the growing season allowing rapid population increase, while sexual reproduction occurs during late summer and leads to frost-resistant eggs that can survive winter conditions. This shift between these two extreme reproductive modes is achieved by using the same genotype, i.e. within the same genetic clone, and is triggered by photoperiodic changes perceived by the aphid brain or visual system. Advances have been made recently to depict genetic programs that relate to the regulation of reproductive modes in aphids. These studies have benefited from the rapid development of genomic and post-genomic resources obtained through the International Aphid Genomics Consortium. Here, we underline the importance of several candidate genes in the switch from clonal to sexual reproduction in aphids and whose roles await full validation. Besides reproductive mode variation expressed at the genotypic level, aphid species also frequently encompass lineages which have lost the sexual phase and hence the alternating clonal and sexual reproductive phases of the life cycle. This coexistence of sex and asexual reproduction within the same species raises questions on its evolutionary and ecological significance. We summarize the knowledge accumulated to date on the maintenance of sex as well as on the origin and evolution of asexuality in aphids. By combining functional genomics, genetic and ecological approaches on reproductive plasticity and polymorphism, we hope to obtain an integrative view of the evolutionary forces shaping aphid reproductive strategies, from gene to population and species levels.