Phenotypic plasticity and “cultural transmission” of alternative social organizations in the fire ant Solenopsis invicta

Summary We investigated the process of sexual maturation in winged queens of the fire ant Solenopsis invicta, a species with two distinct forms of social organization. We found that queens of the monogynous social form (single reproductive queen per colony) differ little or not at all from queens of the polygynous form (multiple reproductive queens per colony) in weight and fat content when these are pupae or newly-eclosed adults. Furthermore, the size of a sclerotized region of the adult thorax, which is set during larval growth, does not differ between queens of the two forms. In contrast, winged queens of the two social forms differ dramatically in their physiological phenotypes once they have matured, with monogynous queens weighing more and having greater fat reserves than polygynous queens. A crossfostering experiment revealed that the different maturation processes of queens of the two forms are induced largely by the type of colony in which a queen matures (monogynous or polygynous) rather than being due to intrinsic genetic differences between the forms. However, genetic variation at a single locus does appear to play some role in determining physiological phenotype in queens of the polygynous form, providing an example of genotype-environment interaction in the expression of these physiological traits. Differences between the social forms in the mature phenotypes that are produced constrain the reproductive options of queens, so that the characteristic social organization of a colony is perpetuated by virtue of the social environment in which new queens are reared. Correspondence to: L. Keller     

Distribution quantitative de la méiofaune dans l'aire d'épandage de l'égout de Marseille

A quantitative analysis of meiofauna was carried out at ten sample stations distributed along a transect off Marseilles' (France) sewage outfall in November, 1981. The meiofauna was counted and average and total biomass of nematodes and copepods were calculated for each station. Comparison of data between stations or groups of stations was made using statistical tests. The results revealed three sectors in which effects of pollution on meiofauna differed: (1) A heavily polluted coastal zone (at a distance of 30 to 150 m from the outfall), relatively poor in meiofauna, which, however, was not completely absent-as were macrobenthic organisms; the meiofauna was composed mainly of nematodes and copepods, but acarians and naupliar larvae (probably copepods) were also numerous; the copepods were uncommonly large in size, and alone consituted most of the total benthic biomass in this zone. (2) An intermediate zone (400 to 1 150 m away from the coast), also polluted and much richer in meiofauna than the coastal zone; the meiofauna groups were more diversified, annelids (mainly polychaetes) increasing in number, while acarians became scarce and copepods decreased in size; at 400 m away from the outfall, where the sediment is strongly polluted, the nematode population consisted of large individuals which contributed greatly to the biomass; at 400 and 800 m, the distribution of both meiofauna and macrobenthos was heterogeneous; at 1 150 m away from the outfall, maximal meiofaunal densities were recorded, due primarily to an increase in nematode numbers; here, unlike all the stations nearer to the coast, total nematode biomass was greater than copepod biomass. (3) An off-shore zone (1.8 to 4 km distant from the coast), slightly polluted, where meiofauna densities were reduced and individuals decreased in size with increasing depth. Generally, an enrichment in the meiofauna was evident from the coastal to the intermediate zone. Enrichments induced by urban pollution have been recorded previously, but not, as in the present study, at a distance of 1 km away from the outfall, succeeding to a highly impoverished coastal zone. Thus, by supplying organic matter and nutrients, Marseilles' sewage can enrich sediments, but only to a certain distance away from the outfall, where the deleterious effects of pollutants are attenuated.     

Alginate modifies the physiological impact of CeO2 nanoparticles in corn seedlings cultivated in soil

Alginates are naturally occurring components of organic matter in natural soil whose effects on nanoparticle （NP） toxicity to plants is not well understood. In the present study, corn plants were grown for one month in soil spiked with 400 mg/kg CeO2 NPs with various alginate concentrations. After one month of growth in the NPs impacted soil, plants were harvested and analyzed for Ce and mineral element concentrations. Chlorophyll concentration and heat shock protein 70, used as biomarkers for oxidative stress, were also evaluated. Results showed that, compared to CeO2 NPs treatment, alginate at 10, 50, and 100 mg/kg increased Ce concentration in roots by approximately 46%, 38%, and 29% and by 115%, 45%, and 56% in shoots, respectively. CeO 2 NPs without alginate increased Mn accumulation in roots by 34% compared to control. CeO2 NPs with low and medium alginate increased Mn by ca. 92% respect to NPs without alginate and by ca. 155% respect to control. CeO2 NPs without/with alginate significantly increased accumulation of Fe and Al in roots. In addition, alginate at 50 mg/kg increased Zn accumulation in roots by 52% compared to control. In shoots, K increased at all NP treatments but the accumulation of other elements was not affected. Alginate enlarged the impact of CeO2 NPs to corn plants by reducing chlorophyll a content and triggering overexpression of heat shock protein 70.     

The Influence of Temperature on Norovirus Inactivation by Monochloramine in Potable Waters: Testing with Murine Norovirus as a Surrogate for Human Norovirus

Human noroviral infections are generally more common during winters in temperate regions. This study used a murine norovirus (MNV) as a human norovirus surrogate to test the effect of water temperature (4 and 25°C) on virus survival and its susceptibility to the levels of monochloramine (~1.89 ppm) to terminally disinfect municipally treated potable waters. The titre of MNV remained essentially unchanged for at least 24 h in raw river water at both temperatures. The virus became undetectable in <2 h in monochloramine-containing samples held at 25°C, but its titre remained virtually unaltered at 4°C (P < 0.05) under the same conditions. These findings strongly suggest that water temperature can influence the norovirucidal activity of monochloramine and its possible impact on the seasonality of outbreaks of noroviral infections.     

Exposure to pyriproxyfen (juvenile hormone agonist) does not alter maternal care and reproduction in the European earwig

Sublethal exposure to pesticides can alter the survival and reproduction of a wide range of non-target organisms. However, it remains unclear whether this exposure can alter behaviours that are often essential for long-term population dynamics and maintenance, such as parental care. In this study, we tested the effect of pyriproxyfen exposure (an insect growth regulator) on maternal care in the European earwig, an insect that is both used in pest control in pip-fruit orchards and considered a pest in stone fruit orchards. We exposed 424 females at doses either 10 times lower, equivalent or 10 times higher than normal application rates in French orchards. As maternal care can change over the weeks of family life, we exposed the earwig mothers at five different days before and after egg hatching. We then measured the expression of ten forms of maternal care towards eggs and juveniles, six non-caring behaviours, eggs and juvenile development, metabolic reserves in mothers at egg hatching and females’ production of a terminal clutch. First, our results revealed that the three tested doses of pyriproxyfen were non-lethal and confirmed that maternal care decreased throughout both pre- and post-hatching family life. However, we did not detect any effect of pyriproxyfen on maternal care and non-care behaviours, eggs and juvenile development, quantities of lipids, proteins and glycogen in mothers at egg hatching, and on the production of a future clutch. Overall, these findings suggest that the maximal doses of pyriproxyfen authorized in French orchards is likely to have limited effects on the short- and long-term maintenance of populations of the European earwig and raises fundamental questions about the nature of the link between juvenile hormone and parental care in insects.