Marielle Renucci

Temporal variations of hemolymph esterase activity and juvenile hormone titers during ovocyte maturation in Acheta domesticus (Orthoptera)

Using in vitro methods, juvenile hormone (JH) esterase activity and alpha-naphthylacetate esterase activity were determined in the hemolymph during the first reproductive cycle of the house cricket, Acheta domesticus. Biochemical properties of the hemolymph JH esterase were studied. alpha-Naphthylacetate esterases increased during the first gonotrophic cycle: peaks of their activity could be observed concomitant with peaks of JH esterase activity. The fluctuations in JH esterase activity correlated with those of hemolymph JH titers. The results are discussed.

Ovaries and regulation of juvenile hormone titer in Acheta domesticus L. (Orthoptera)

A study was performed on females Acheta domesticus to examine the effects of various experimental conditions on the ovarian physiology. Using a radioimmunoassay to determine juvenile hormone (JH) titers as well as in vitro JH biosynthesis, we observed that retention of mature follicles in egg-retaining females, i.e., virgins or mated females not provided an egg-laying substrate, inhibits JH production and consequently oocyte development. Mating in intact as well as ovariectomized females does not affect corpora allata activity. It is only when mating is associated with egg laying that JH biosynthesis and hemolymph titers increased and oocyte development and fecundity are stimulated. Despite lower JH biosynthesis, ovariectomized females present enlarged corpora allata and the levels of JH observed in their hemolymph were intermediate between those of intact egg-laying and virgin females. In intact females, the hemolymph JH titers as well as the JH esterase activities were related to ovarian development. JH esterase activity was very high in ovariectomized animals. Several factors involved in ovarian development of A. domesticus are discussed.

Colony structure in a plant-ant: behavioural, chemical and genetic study of polydomy in Cataulacus mckeyi (Myrmicinae)

Social organisation of colonies of obligate plant-ants can affect their interaction with myrmecophyte hosts and with other ants competing for the resources they offer. An important parameter of social organisation is whether nest sites of a colony include one or several host individuals. We determined colony boundaries in a plant-ant associated with the rainforest understorey tree Leonardoxa africana subsp. africana, found in coastal forests of Cameroon (Central Africa). This myrmecophyte is strictly associated with two ants, Petalomyrmex phylax and Cataulacus mckeyi. Plants provide food and nesting sites for P. phylax, which protects young leaves against insect herbivores. This mutualism is often parasitised by C. mckeyi, which uses but does not protect the host. The presence of C. mckeyi on a tree excludes the mutualistic ant. Because Petalomyrmex -occupied trees are better protected, their growth and survival are superior to those of Cataulacus -occupied trees, giving P. phylax an advantage in occupation of nest sites. C. mckeyi often colonises trees that have lost their initial associate P. phylax, as a result of injury to the tree caused by disturbance. Polydomy may allow C. mckeyi to occupy small clumps of trees, without the necessity of claustral colony foundation in each tree. Investigating both the proximate (behavioural repertoire, colony odour) and the ultimate factors (genetic structure) that may influence colony closure, we precisely defined colony boundaries. We show that colonies of C. mckeyi are monogynous and facultatively polydomous, i.e. a colony occupies one to several Leonardoxa trees. Workers do not produce males. Thus, the hypothesis that polydomy allows workers in queenless nests to evade queen control for their reproduction is not supported in this instance. This particular colony structure may confer on C. mckeyi an advantage in short-distance dispersal, and this could help explain its persistence within the dynamic Leonardoxa system.

Inhibition of polyamine biosynthesis alters oviposition behavior in female crickets

The role of polyamines in the expression of cricket oviposition, a juvenile hormone-dependent behavior, was investigated using a specific inhibitor of ornithine decarboxylase, alpha-difluoromethylornithine (alpha-DFMO). The fat body of treated female house crickets (Acheta domesticus) did not show any putrescine and presented reduced levels of spermidine, whereas spermine titres were significantly enhanced. In nervous tissue, alpha-DFMO did not affect spermine titres but induced a severe drop in spermidine levels. In polyamine depleted females, the expression of egg-laying behavior was delayed and was expressed less frequently compared with controls. As drug treatment did not seem to affect juvenile hormone titres, the data suggest that juvenile hormone might act on behavior by way of polyamine metabolism. These results support the view that, in insects, as in vertebrates, the ornithine decarboxylase-polyamine system is involved in the maturation of complex behaviors.

Juvenile hormone degradation in nerve tissues and fat body of female Acheta domesticus (Insecta, Orthoptera)

Abstract 1. 1. Experiments aimed at determining the pathways of juvenile hormone (JH) degradation were carried out on tissue samples from adult female Acheta domesticus. 2. 2. Enzymes degrading juvenile hormone (JH esterases and epoxide hydrases) were present in the fat body, brain and nerve cord homogenates. 3. 3. On the other hand, no degradation activity was measured in the suboesophageal ganglion. 4. 4. Considered separately, in brain or nerve cord homogenates, JH esterases and epoxide hydrases displayed parallel variations. 5. 5. However, total JH degradation in these tissues showed opposite variations, meaning that degradation was highest in the brain when it was lowest in the nerve cord. 6. 6. Concomitant with these high and low readings (64–72 hr), a dramatic increase in JH titre was recorded in the hemolymph.

Effects of juvenile hormone on polyamines of the fat body and neural tissue of the cricket Acheta domesticus

Abstract The levels of polyamines and the activity of two of the rate limiting enzymes of their biosynthesis were studied in neural tissue and in the fat body of adult females of Acheta domesticus , submitted to different physiological experiments. Allatectomy, performed during the last larval instar, suppressed juvenile hormone production, resulted in the absence of the peak of hormone occurring in 3-day-old adult females and affected the normal pattern of polyamine distribution. As early as day 4 post-emergence, putrescine titres markedly decreased in the fat body, and spermidine levels dropped in the neural tissue. In the fat body, allatectomy depressed ornithine decarboxylase activity, but increased S -adenosylmethionine decarboxylase activity. In the neural tissue, lack of juvenile hormone depressed both ornithine decarboxylase and S -adenosylmethionine decarboxylase activities, resulting in a significant reduction of polyamine titres. Juvenile hormone injections into allatectomized females enhanced enzyme activities and increased polyamine titres. These findings suggest that the neural tissue, like the fat body, may be a target organ for juvenile hormone action. The present data reveal tissue-specific patterns of polyamine metabolism and demonstrate the action of juvenile hormone on polyamine metabolism.

Ecdysone deprivation affects polyamine metabolism in the house cricket Acheta domesticus

Abstract The basic importance of polyamines, which are involved in the regulation of DNA, RNA and protein synthesis, are underlined in numerous works. Using HPLC analysis, we determined polyamine levels in several tissues of 10-day old adult crickets subjected to different hormonal conditions. Ovariectomy performed during the last larval instar suppressed haemolymph ecdysteroids and significantly increased the spermidine titres in nervous tissue whereas it decreased the overall polyamine levels in the fat body. Ecdysone injections into ovariectomized females reduced the spermidine content in nervous tissue and markedly increased the overall fat body polyamine levels, an effect which was mimicked by saline injections in this last tissue. As compared to control values, the activity of ornithine decarboxylase (ODC), the first key enzyme in polyamine biosynthesis was significantly reduced by ovariectomy either in nervous tissue or in fat body. In ovariectomized females, ecdysone injections significantly stimulated only the fat body ODC activity. The effects of polyamines on protein phosphorylation was examined. The phosphorylation of two proteins (207 and 128 kDa respectively) present in the fat body and the nervous tissue of control and ovariectomized females decreased in the presence of polyamines. The phosphorylation of a 53.5 kDa phosphoprotein only present in the nervous tissue differed according to the hormonal status of the female and was strongly enhanced by polyamines. Polyamines also stimulated the phosphorylation of a 37.5 kDa phosphoprotein present in both nervous tissue and fat body. In this last tissue, the phosphorylation of a 20 kDa phosphoprotein present in ovariectomized females was inhibited by the addition of polyamines. This work demonstrates an action of ecdysone on polyamine levels in nervous tissue and underlines the ability of polyamines to modulate the phosphorylation of specific phosphoproteins which are under hormonal control. These data emphasize the importance of polyamines in the regulation of cell functions.

Changes in composition of cuticular biochemicals of the facultatively polygynous ant Petalomyrmex phylax during range expansion in Cameroon with respect to social, spatial and genetic variation

In social insects, biochemicals found at the surface of the cuticle are involved in the recognition process and in protection against desiccation and pathogens. However, the relative contribution of evolutionary forces in shaping diversity of these biochemicals remains largely unresolved in ants. We determined the composition of epicuticular biochemicals for workers sampled in 12 populations of the ant Petalomyrmex phylax from Cameroon. Genetic variation at 12 microsatellite markers was used to infer population history and to provide null expectations under the neutrality hypothesis. Genetic data suggest a recent southward range expansion of this ant species. Furthermore, there is a decline southward in the numbers of queens present in mature colonies. Here, we contrast the pattern of biochemical variation against genetic, social and spatial parameters. We thus provide the first estimates of the relative contribution of neutral and selective processes on variation of ant cuticular profile. Populations in migration–drift disequilibrium showed reduction of within‐population variation for genetic markers as well as for cuticular profiles. In these populations, the cuticular profile became biased towards a limited number of high molecular weight molecules. Within‐ and among‐population biochemical variation was explained by both genetic and social variation and by the spatial distribution of populations. We therefore propose that during range expansion of P. phylax, the composition of epicuticular compounds has been affected by a combination of neutral processes — genetic drift and spatially limited dispersal — and spatially varying selection, social organization and environmental effects.

Physiological approach to the onset of receptivity in female Acheta domesticus: I. Role of the corpora allata and ovaries

During the 32 hr following the imaginal moult, all female Acheta domesticus actively or passively refuse male courtship; they are unreceptive. As of 32 hr, the most precocious females become receptive and accept mating. At this time, juvenile hormone (JH III) synthesized by corpora allata (CA) is already detectable in hemolymph, while ecdysteroids (synthesized by ovaries) begin increasing at 48 hr. JH III and ecdysteroid levels in hemolymph were measured by RIA. After allatectomy and/or ovariectomy, all females became receptive, thus showing that CA and/or ovaries are not essential to the onset of receptivity. However, male courtship is longer for allatectomized females; in ovariectomized females, mating is delayed.

Isolation of putative olfactory receptor sequences from pig nasal epithelium

Binding to olfactory receptors is the first step in odorant and pheromonal recognition and discrimination. These receptors constitute one of the most important, although poorly known, families of neuronal receptors. In this study we used degenerated oligonucleotides and a RT-PCR approach to selectively amplify olfactory receptors in the nasal epithelium of the domestic pig Sus scrofa. Several combinations of oligonucleotide were tested and allowed the isolation of eleven different partial sequences belonging to the seven transmembrane olfactory receptor family. These receptors formed a separate family within the seven transmembrane receptor superfamily in pigs. Using the criteria of Ben Arie et al. [Ben-Arie N., Lancet D., Taylor C., Khen M., Walker N., Ledbetter DH., Carrozzo R., Patel K., Sheer D., Lehrah H. and North M., Hum. Mol. Genet., 3 (1994) 229-235], the 11 receptors described here can be classified into three known families and seven subfamilies (one known and six new).