Life cycle of the cereal aphid Sitobion avenae F.: polymorphism and comparison of life history traits associated with sexuality

1. Clones of Sitobion avenae from the west of France exhibited four types of responses in growth chambers to short days and low temperatures: in addition to permanently parthenogenetic clones (anholocyclic) and clones producing both males and parthenogenetic females (androcyclic), lineages producing both mating females and males were categorized into holocyclic and intermediate types, the latter investing into both sexual and parthenogenetic reproduction.
2. Holocyclic, intermediate and androcyclic clones were tested outdoors for sexual production in autumn and results were consistent with those obtained in growth chambers. Eggs from holocyclic and intermediate clone selfings were laid and hatched for most crosses.
3. Reciprocal crosses within and between life cycle variants showed no effect of the type of cross on the number of eggs laid per mating female, their hatching success, or the survival and fecundity of the parthenogenetic females born from eggs (fundatrices).
4. Eggs from intermediate × intermediate crosses hatched 20 days earlier than those involving at least one holocyclic parent. It is suggested that this short diapausing time gives a selective advantage to intermediate clones in oceanic climates, which could compensate for their lower sexual production in autumn.
5. Selfed offspring showed inbreeding depression, which seems to be common in non host-alternating aphids.
6. Mating with androcyclic males affects percentage (lower) and time (longer) of egg hatching, but not the other investigated traits.
7. The significance of intragenotypic strategy mixing in androcyclic and intermediate clones is discussed as an overall adaptation to the uncertainty of winter climate in oceanic zones.     

The Effect of Iodoacetate on Phospholipid Levels and Membrane Permeability

Leakage of electrolytes from discs of cucumber cotyledons isenhanced by floating them for 3 d on 10^–3 M iodoacetateinstead of water. The respiration of the discs is severely inhibitedby iodoacetate and the total quantity of phosphatidyl choline,phosphatidyl ethanolamine, and phosphatidyl inositol falls to77 per cent of the control level at 3 d in young cotyledonsand 50 per cent in old cotyledons. ¹⁴C-acetate-labelling experimentsprovide evidence of phospholipid turnover; those phospholipidssubject to the most rapid turnover tend to be the ones thatdisappear most rapidly from discs treated with iodoacetate.     

The effect of diet and live host presence on the growth and reproduction of Terebrasabella heterouncinata (Polychaeta: Sabellidae)

Summary

The effect of diet type and the presence or absence of a live host on the growth and production of eggs and larvae by Terebrasabella heterouncinata were quantified. Diet was shown not to have a significant effect on the time in which the worms on live hosts reached their maximum size. Diet did, however, influence the maximum size and consequently the growth rate of worms, which were larger and grew faster on kelp-fed abalone than on those fed a commercial pellet diet. Despite diet having no effect on fecundity and offspring size, kelp-fed worms matured earlier. The maximum size of kelp-fed worms was unaffected by the absence of a live host, suggesting that the worms do not rely on the host for food. The absence of a live host reduced the growth and sexual maturation rates of worms. There was no difference in the size of offspring in the two treatments, but fewer worms matured sexually and fewer broods were produced on “shells only” than on live hosts. The lower growth rate and reproductive output of worms on “shells only” may be due to the diversion of energy from growth and reproduction to burrow expansion.     

SENSORY MEASUREMENT OF FOOD TEXTURE BY FREE-CHOICE PROFILING

Panelists were trained to measure texture of processed cheese analogues of known composition by free-choice profiling. Panel scores were analyzed by generalized Procrustes (a multivariate method). Plots of the Procrustes scores for the first 2 principal component axes from analysis of separate replicates reflected the experimental design. To compare replicates, scores from Procrustes analysis of the original data were subjected to Procrustes analysis. The results showed that panelists’ assessment of replicates was consistent. Regression of the scores from this second Procrustes analysis showed that they were well explained by the linear effects of either moisture in nonfat solids or fat content. Panelists who performed differently from the rest could be identified. Panelists were more sensitive to changes in moisture in nonfat solids content than fat. It was concluded that the sensory texture of the cheese analogues could be measured satisfactorily by free-choice profiling.     

Asymmetric intraspecific competition among larvae of the damselfly Ischnura elegans (Zygoptera: Coenagrionidae)

Abstract. 1. A laboratory competition experiment is described in which the growth and development rates of larvae of the damselfly Ischnura elegans (Lind.) were measured over an entire instar.
2. Two larval instars which commonly occur together in the field were used in the experiment; they were maintained with a superabundance of prey and either larvae from the same or the larger/smaller instar.
3. Small larvae suffered increased development times and decreased size increases at the moult in the presence of large larvae but similar interference effects were not evident when these smaller larvae were in the presence of other small larvae.
4. Development time and size increases of large larvae were not significantly affected by the presence of small larvae.
5. Irrespective of the instar combinations investigated, interference effects were reduced when there were more perches available, although in only a few cases was this reduction significant.
6. The consequences of the asymmetric competition reported in the experiment for the study of lifetime reproductive success in damselflies are discussed. Late emerging adults may incur reduced reproductive success.     

Studies in the Principles of Phytotoxicity: IV. THE EFFECTS OF THE DEGREE OF NITRATION ON THE TOXICITY OF PHENOL AND OTHER SUBSTITUTED BENZENES

1. The relative toxicity of phenol, o- and p-nitro, 2:4-dinitro-,and 2:4:6- trinitrophenol was measured by up to five techniques.Determinations were made of the concentrations required to reduceby half (i) the growth rate of Trichoderma viride at pH 3, (ii)the frond multiplication rate of Lemna minor at pH 5·1–5·4,(iii) the respiration rate of yeast at pH, (iv) the respirationrate of infiltrated leaf disks of Brassica alba at pH 3, and(v) the number of B. alba seedlings surviving after sprayingwith buffered solutions of the compounds. Whenever possibletoxicity was measured at a pH level below pK so as to eliminatethe effect of pH on toxicity, but in some of the measurementswith 2:4-dinitro- phenol (pK = 4·0) and with picric acid(pK = 0·8) this was not feasible. It was then necessaryto measure toxicity at a pH at which the compound was much dissociated;from the measured values of toxicity of dinitrophenol the toxicityat a lower pH was estimated from the generalized pH-activityrelationship of Simon and Beevers (5952). 2. The relative toxicity of the nitrophenols is very similarwhichever test procedure is employed. The first two nitrationsare accompanied by large increases in toxicity, but with thethird successive nitration there is a decrease. 3. The toxicity of the corresponding mono, di, and trinitroderivatives of anisole, phenetole, toluene, and nitrobenzenewas determined using T. viride. In each series the first andthird stages of nitration brought about large increases in toxicitybut the intermediate one had little effect. 4. All the p-nitro compounds were more toxic than their o- isomers. 5. On the basis of the concepts put forward by Ferguson (1939)and Albert (1951) it is concluded that the toxic action of thenitroanisoles and nitrotoluenes is ‘structurally non-specific’,i.e. the effect is not dependent on the presence or absenceof a particular chemical group in the molecule. With both thenitrobenzene and the phenol series the results suggest thatthe exact chemical structure is an important factor.     

Nocturnal feeding by Dark-bellied Brent Geese Branta bernicla bernicla

The occurrence and extent of nighttime feeding by Dark-bellied Brent Geese Branta bernicla bernicla on salt marshes adjacent to their tidal roost site were assessed on the north Norfolk coast using position-sensitive radio transmitters. Nine birds were monitored on 143 bird-nights, and feeding was recorded on 87. The frequency of feeding by night varied widely between individuals. The mean proportion of the night spent feeding for one bird was 19.7 ± 8%. Of this, 59% occurred within ± 1.5 h of high tide. Neither the proportion of the whole night spent feeding nor the intensity of feeding around high tide varied with the length of the night or with time after sunset at which high tide occurred. The extent of nocturnal feeding was also independent of the brightness and duration of moonlight. The birds fed for significantly longer on colder nights, and there was a significant positive relationship between the proportion of the night spent feeding and maximum temperature the preceding day. Analysis of daytime activity budgets on inland pastures showed that the proportion of time engaged in nonfeeding, energy-expensive activities was also positively related to maximum daytime temperature. Increases in the proportion of the night spent feeding after warmer days were achieved by increasing the period of time spent feeding on either side of the high tide, not by increasing feeding intensity at high tide. It is concluded that the geese compensate for increased energy expenditure during the day by increasing the extent to which they feed at night. Implications of increasing energy expenditure as a result of disturbance during the day are discussed.     

Incorporating Movement Behavior and Barriers to Improve Kernel Home Range Space Use Estimates

Abstract: Kernel-based utilization distribution (UD) estimates are powerful tools to investigate home range space use and resource selection in many vertebrate species. By ignoring local movement information provided by the serial correlation between successive locations and the constraints to movement imposed by obvious boundaries, the classical kernel method results in loosely estimated UDs that tend to overflow into never-visited areas and eventually in possibly biased estimates of space use and habitat selection. We improved biological relevance of kernel home range space use estimates by incorporating both movement (and activity) information and boundary constraints.