Impact of superparasitism time intervals on progeny survival and fitness of an egg parasitoid

1.Superparasitism influences the fitness of female parasitoids and their progeny, and increasing time interval between oviposition bouts generally reduces survival probabilities of the second clutch. However, the timing of superparasitism may, under certain conditions, favour the second clutch. 2. This study investigated the effects of superparasitism time intervals on survival and fitness of both clutches, allowing the egg parasitoid Trichogramma euproctidis to parasitise previously parasitised Ephestia kuehniella host eggs at different time intervals. 3. In short intervals (0–1 h), a significant advantage was found for the second clutch over the first clutch (93.1% survival). In contrast, the second clutch was outcompeted by the first clutch in 17–19 h and 27–29 h intervals. Females deposited their eggs into larvae (intraspecific hyperparasitism) in a 39–41 h interval with a probability of survival of 57.1%. Females mostly refused to hyperparasitise pupae (～80% rejection at 124–126 h), and when they did, their progeny never survived. 4. Hyperparasitism significantly increased parasitoid mortality in both clutches from less than 20% (superparasitism only) to over 35%. 5. Except on newly laid eggs (0–1 h), superparasiting females were frequently observed attempting to stab immatures of all stages (from 36.4% to 89.4% of all ovipositions depending on treatment), but infanticide only appeared to succeed on larvae (39–41 h). 6. When the second clutch survived, emerging parasitoids were smaller than control individuals, probably due to resource depletion. 7. These results suggest that T. euproctidis females can detect that a host has been previously parasitised but they cannot perceive superparasitism time intervals.     

Feeding ecology and phylogenetic structure of a complex neotropical termite assemblage,revealed by nitrogen stable isotope ratios

1. In the current ecological classification of termites, four feeding groups (I–IV) are recognised, corresponding to a gradient of decomposition from sound wood to highly mineralised organic matter in the soil. 2. Nitrogen stable isotopes (hereafter δ¹⁵N) were used to place termites from French Guiana rainforests along a wood‐soil decomposition gradient, to test (i) whether feeding group assignation based on morphological characters was accurate and actually represented diet specialisation thresholds, and (ii) to what extent the dietary specialization of species is explained by phylogeny (phylogenetic autocorrelation). 3. δ¹⁵N values vary over a range of 13‰, suggesting that diet diversification contributes to the high species diversity in French Guiana. δ¹⁵N values span a similar interval in all Termitidae subfamilies. Ranges of different subfamilies broadly overlap, although each of them diversified preferentially on one side of the wood‐soil decomposition gradient. Congeneric species share similar feeding habits, whereas distant species tend to feed on distinct substrates. 4. Feeding groups did not completely match stable isotope data: there was no discontinuity between Groups III and IV, and no correlation between anatomical criteria used to distinguish these groups and δ¹⁵N values. Nor was there any consistent difference in δ¹⁵N values between wood feeders of the families Rhinotermitidae (Group I) and Termitidae (Group II). We also suggest that species feeding outside the wood‐soil gradient should be distinguished for their peculiar feeding requirements.     

The Effect of Antihistamines on the Pigments of Green Protista.

SUMMARY. A preliminary survey of the influence of a number of antihistamines on growth of several protozoa indicated that not only growth but also pigment formation in green forms was inhibited. Subsequently, it was demonstrated that molar concentrations of the drugs of less than 1 times 10⁻³ caused chlorosis of cultures of Euglena gracilis var. bacillaris, Chlamydomonas pseudococcum , and Chlorella vulgaris.
With the aid of one of the antihistamines, Pyribenzamine (CIBA), a permanently colorless culture of Euglena was obtained. This culture has been maintained in the chlorotic state in antihistamine-free medium through eighteen serial transfers in constant light. Comparative spectro-photometric studies were made of the pigments extracted from this new euglenid strain with those from normal green, dark-grown and streptomycin-bleached euglenas. Although the dark-etiolated forms retained small amounts of chlorophylls, neither of the drug-bleached cultures showed evidence of these pigments. Quantitatively, the carotenoid picture in dark-bleached and streptomycin-grown organisms was similar, but these pigments were greatly reduced in the Pyribenzamine-treated strain. Further studies on the identity of the carotenoids in the new euglenid are in progress.     

Determinants of hierarchical genetic structure in Atlantic salmon populations: environmental factors vs. anthropogenic influences

Disentangling the effects of natural environmental features and anthropogenic factors on the genetic structure of endangered populations is an important challenge for conservation biology. Here, we investigated the combined influences of major environmental features and stocking with non‐native fish on the genetic structure and local adaptation of Atlantic salmon (Salmo salar) populations. We used 17 microsatellite loci to genotype 975 individuals originating from 34 French rivers. Bayesian analyses revealed a hierarchical genetic structure into five geographically distinct clusters. Coastal distance, geological substrate and river length were strong predictors of population structure. Gene flow was higher among rivers with similar geologies, suggesting local adaptation to geological substrate. The effect of river length was mainly owing to one highly differentiated population that has the farthest spawning grounds off the river mouth (up to 900 km) and the largest fish, suggesting local adaptation to river length. We detected high levels of admixture in stocked populations but also in neighbouring ones, implying large‐scale impacts of stocking through dispersal of non‐native individuals. However, we found relatively few admixed individuals suggesting a lower fitness of stocked fish and/or some reproductive isolation between wild and stocked individuals. When excluding stocked populations, genetic structure increased as did its correlation with environmental factors. This study overall indicates that geological substrate and river length are major environmental factors influencing gene flow and potential local adaptation among Atlantic salmon populations but that stocking with non‐native individuals may ultimately disrupt these natural patterns of gene flow among locally adapted populations.     

A History of the Study of Phyllotaxis

The study of the patterns formed by similar units in plants(e.g. leaves, scales, florets) is traced from the first primitiveobservations in ancient times to the sophisticated studies oftoday. Mathematics entered into the study early, at first asa way of describing the patterns observed, with Fibonacci numbersand the golden section playing a major role, and later in theconstruction of models designed to explain their origin. Observationand experiment alternated with theory. Explanations offeredalternated between functional and causal. Functional explanationsthat were at first teleological gave way to those based on theidea of natural selection. Causal explanations alternated betweenthe chemical and the mechanical. New light has been cast onthe subject with the realization that phenomena similar to phyllotaxisoccur in realms outside of botany. Phyllotaxis; genes; algae; comparative morphology; evolutionary theory; systems research; optimal design; polypeptide chains; living crystals; allometry     

Delayed setting of the photoperiodic response in recombinant clones of the aphid species Sitobion avenae

1. To explore the possible causes of apparent changes in reproductive mode from obligate to cyclical parthenogenesis over time in recombinant clones of the aphid Sitobion avenae Fabricius, all F1 progenies from various crosses were tested for several consecutive years for sexual morph production, after several weeks' exposure to a short photoperiod. 2. Variable proportions of the F1 progenies from selfing and outcrossing holocyclic clones did not produce mating females when induction was attempted in the year of hatching, but only after further induction, the following year or after. This ‘delayed setting of the photoperiodic response’ (DSPR) was much stronger in recombinants from crosses involving only clones from oceanic regions than in those involving one clone from a region with a continental climate. 3. F1 progenies resulting from crosses between one holocyclic and one intermediate clone did not show DSPR. It appeared again in the F2. 4. DSPR preferentially affected the latest hatched clones in a given progeny. 5. This phenomenon is neither an experimental artefact nor as a result of clone contamination. It appears to be because of a genetically controlled quantitative trait affecting the length of the ‘interval timer’, and may represent an adaptation of holocyclic aphid clones from oceanic regions to unpredictable winter climates.     

Understanding A Snail's Eye at a Snail's Pace

This paper is cast in the form of answers to pertinent (sometimesimpertinent) questions which a reader might ask of persons devotingthe better part of a scientific career to studying the eye ofa snail. Two structures in the eye of Helix aspersa are emphasized:the microvilli and microvesicles of type I photosensory cells.Evidence is presented to support the conclusions that the microvilliare the light-sensitive organelles and that the microvesicles,termed photic vesicles, bring to the microvilli substances neededin photoreception, such as photopigment and perhaps calcium.The evidence consists of: uptake of radioactive vitamin A bythe villi and vesicles, formation of a black precipitate byboth structures upon prolonged staining with osmium tetroxide,the effects of light and dark upon the microvilli and photicvesicles, a comparison between the photic vesicles of a light-tolerantslug and those of a nocturnal slug, and a preliminary findingof a high concentration of calcium in the somatic layer of theretina. The movement of the photic vesicles from the Golgi centers,where they are formed, to the microvilli is attributed to rhythmic,light-dependent pulsations of the eye caused by contractionsof smooth muscle cells embedded in the optic capsule.