Strategic ejaculation and level of polyandry in <Emphasis Type="Italic">Callosobruchus chinensis</Emphasis> (Coleoptera: Bruchidae)

Variation in the level of polyandry of females produces a difference in the risk of sperm competition among males. As a consequence, investment in ejaculate expenditure by males should vary. We compared the number of sperm ejaculated by males into the female reproductive organ of six strains of the adzuki bean beetle, Callosobruchus chinensis (Coleoptera: Bruchidae), when males were reared at different larval densities in a bean. A significant positive correlation was found between the remating frequency of females and the ratio of the ejaculate sizes of high-density and low-density males as a measure of the response to the risk of sperm competition among males. The measure was estimated by dividing the number of sperm ejaculated by males reared at high larval density in a bean with the number of sperm ejaculated by males reared alone. The number of sperm transferred by a male to a female was not correlated with the duration of copulation. The results suggest an evolutionary relationship between ejaculatory expenditure and the level of polyandry in C. chinensis.     

High sucrose consumption promotes obesity whereas its low consumption induces oxidative stress in Drosophila melanogaster

The effects of sucrose in varied concentrations (0.25–20%) with constant amount of yeasts in larval diet on development and metabolic parameters of adult fruit fly Drosophila melanogaster were studied. Larvae consumed more food at low sucrose diet, overeating with yeast. On high sucrose diet, larvae ingested more carbohydrates, despite consuming less food and obtaining less protein derived from yeast. High sucrose diet slowed down pupation and increased pupa mortality, enhanced levels of lipids and glycogen, increased dry body mass, decreased water content, i.e. resulted in obese phenotype. Furthermore, it suppressed reactive oxygen species-induced oxidation of lipids and proteins as well as the activity of superoxide dismutase. The activity of catalase was gender-related. In males, at all sucrose concentrations used catalase activity was higher than at its concentration of 0.25%, whereas in females sucrose concentration virtually did not influence the activity. High sucrose diet increased content of protein thiols and the activity of glucose-6-phosphate dehydrogenase. The increase in sucrose concentration also enhanced uric acid level in females, but caused opposite effects in males. Development on high sucrose diets was accompanied by elevated steady-state insulin-like peptide 3 mRNA level. Finally, carbohydrate starvation at yeast overfeeding on low sucrose diets resulted in oxidative stress reflected by higher levels of oxidized lipids and proteins accompanied by increased superoxide dismutase activity. Potential mechanisms involved in regulation of redox processes by carbohydrates are discussed.     

Rapid evolution of larval development time during mass-rearing in the melon fly, Bactrocera cucurbitae

A quantitative genetic analysis of rapid evolution of a life history trait has been conducted on the first 24 generations of mass-rearing in the melon fly Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae). The phenotypic variance of larval development time in each generation was divided into genetic and residual components. Mean and phenotypic coefficients of variation of larval development time decreased gradually as generations proceeded as a result of artificial selection for shorter larval period in the mass-rearing procedure. There was a trend that additive genetic coefficients of variation in larval development time decreased with generations. These changes are entirely attributed to genetic responses to laboratory selection under the mass-rearing environment because the population was maintained at a very large size so as to exclude random genetic drift and inbreeding depression, which would be other factors responsible for the observed genetic changes. The residual coefficients of variation in larval development time did not change with generations. Realized heritability of larval development time was low. The heritabilities for larval development time estimated from parent–offspring regression at generations 60 and 70, when the evolutionary plateau was asymptotically reached, were not significantly larger than 0. Received: April 22, 1999 / Accepted: September 20, 1999     

On interference among larvae of the greasy cutworm,Agrotis ypsilon rott. (lepidoptera: Noctuidae)

Summary The greasy cut worm,Agrotis ypsilon Rott., has a characteristic habit; the larva feeds on the small seedling of the host plant. Studies in a population in outbreak area suggested that the food shortage temporally took place, causing the reduction of weights of pupae and adults. The fact that this species depends on the small seedling as the host seemed to be responsible for this food shortage. However, it was found that the larval crowding also affected the body weight, even if the food was supplied in excess. It was further suggested that the weight reduction is due to the injury caused by the encounter of larvae. The oviposition habit to lay small egg masses and the aggressive behaviour of the larva was considered to be responsible for the uniform distribution at the later larval stage. Probably, the larval dispersion enabled the larva to forage in the most effective way as well as it protected the larva from the attack of another ones. As a result, this would enable the maximum number of individuals to survive. It seemed that the functions noted above did not work in the population being under outbreak condition, because the larval density was unusually high due to mass-invasion of moths.     

Theoretical studies on the role of food exploitation for the competition of scaamble type

A model was made to clarify the basic processes of competition to occur among larvae by the exploitation as defined byBakker (1969). It was found that this model is applicable to the experimental results on the food exploitation among Droshophila larvae obtained byBakker (1961). In the model the preimaginal stage is divided into two periods;T_f which is the time that a group of larvae spends in exhausting the food after hatching, and T_s which is the duration of the starvation period after T_f.T_f and then W_l (larval body weight) just after the end of T_f are decided by F_s (amount of food supplied per larva at larval hatching) and F_c (amount of food consumed per larva).T_f affects on the onset of T_s as well as R_l (rate of decrease in the individual body weight during T_s).W_a (weight of emerging adults) is gotten by a subtraction of R_l from W_l just after the end of T_f,R_e is affected directly by these components of W_l and R_l. As a result, W_a and R_e are expressed by functions of F_s. This model confirmed that the food exploitation lead to the competition of scramble type. Finally it was suggested that there exist some strategies which prevent ill-effects owing to the food exploitation.     

Larval growth and perimetamorphosis in the echinoid <Emphasis Type="Italic">Echinocardium cordatum</Emphasis> (Echinodermata): the spatangoid way to become a sea urchin

The prejuvenile development of Echinocardium cordatum (Echinoidea) was investigated by means of scanning electron, confocal and light microscopes, aiming to illustrate the early life history of a spatangoid representative and to compare it with the other major echinoid groups. During the larval development of E. cordatum, two periods follow one another. The first one takes 12 days; it ends with the formation of a complete echinopluteus with twelve elongated larval arms. The second lasts from 3 to 12 days; it is entirely devoted to the building of the echinid rudiment and ends with the acquisition of larval competence. No appendage other than arms develops at the larva’s outer surface. Competent larvae are demersal. They settle onto the substratum and test it for suitability using the five rudiment podia that protrude through the vestibule opening. Metamorphosis is a rapid event that lasts less than an hour. The rudiment does not everse and its spines and podia actively tear up the larval epidermis which is progressively covered by the growing vestibular epidermis. The resulting postlarva is short-lived and morphologically similar to both the late rudiment and the early juvenile, which, however, is exotrophic. Late rudiments in E. cordatum show basic spatangoid features being bilaterally symmetric and having clavulae and sphaeridia. More importantly, they already have the convex shape and the appendage cover of early juveniles. Metamorphosis in E. cordatum appears to be less complex, i.e. no rudiment is everted, and more complete, since, in contrast to “regular” echinoids, no transitory appendages are seen. Metamorphosis/development of E. cordatum, thus, is closer to that of clypeasteroids, since the rudiment of the latter already bears juvenile definitive appendages, when everted during metamorphsis.     

Colonisation and bioerosion of experimental substrates by benthic foraminiferans from euphotic to aphotic depths (Kosterfjord, SW Sweden)

In the cold-temperate setting of the Swedish Kosterfjord area, experimental carbonate and PVC substrates were deployed for a 6, 12 and 24-month duration along a transect from euphotic to aphotic depths in order to study bioerosion and carbonate accretion patterns. Among the organisms that contribute to the latter by secreting calcareous skeletons, epibenthic foraminiferans represent a major component, both in terms of diversity (a dozen species) as well as in the number of individuals (exceeding 50,000 individuals per m² at certain depths). The by far dominating species were found to be Cibicides lobatulus and the agglutinating Lituotuba lituiformis, along with smaller numbers of Planorbulina mediterranensis, Tholosina vesicularis and Nubecularia lucifuga. The foraminiferal distribution exhibits a pronounced abundance maximum in shallow waters at 7 and especially 15 m and a maximum in diversity at 15-50 m water depth. Some of the foraminiferans encountered, such as Cibicides lobatulus and the rare Gypsina vesicularis, were found to contribute also to the bioerosion of the calcareous substrates by etching shallow attachment scars. These prominent traces witness the former presence of benthic foraminiferans on fossil to Recent hardgrounds, inferring a potential applicability as an in situ proxy where tests are not preserved. Estimated minimum carbonate production rates for the dominant Cibicides lobatulus reach a maximum of 0.326 g/m²/year with the highest rates occurring at 7 to 30 m water depth. Carbonate production rates are up to two magnitudes higher on the PVC (0-0.326 g/m²/year) than on the carbonate substrates (0-0.010 g/m²/year) and are considerably higher than estimates previously reported from the western Baltic.     

Synthetic peptides inducing metamorphosis in a tropical jellyfish: a quantitative structure-activity relationship study

Synthetic peptides are known to trigger metamorphosis to the polyp stage in larvae and larva-like buds of the jellyfish Cassiopea andromeda. Coupling of a hydrophobic moiety to the amino terminus of such peptides was found to increase their efficiency. Hydrophobicity can thus be considered an important factor in the biological activity of peptidic inducers. By establishing the n-octanol/water partition coefficient in order to characterize the hydrophobicity of bioactive peptides, we demonstrate that this parameter and efficiency are positively correlated in peptides of the same amino acid sequence. Hydrophobicity proved to be of much lesser importance than amino acid sequence when data of structurally disparate inducer peptides were considered.