Thermal stratification influences maturation and timing of spawning in a local Clupea harengus population

Maturation and timing of spawning in relation to temperature were studied in a local Atlantic herring Clupea harengus population inhabiting a small semi‐enclosed ecosystem (7 km²) separated from the larger outer fjord system by narrow sills on the west coast of Norway. Ambient temperatures varied annually up to 4° C during both the pre‐spawning and spawning periods from February to April, but without affecting the spawning time. Instead, the timing of spawning was found to be related to thermal stratification in response to spring warming, which occurred about the same time every year regardless of initial temperatures.     

Larval and adult nutrition effects on blood/nectar choice of Culex nigripalpus mosquitoes

Abstract. The impact of nutritional variables on the development of host-seeking and biting behaviours after emergence by female Culex nigripalpus mosquitoes were studied using air-flow olfactometer and close-range biting assays, respectively. Unfed females failed to develop resting stage ovarian follicles. When offered a bird host in the absence of competing stimuli, sugar-fed mosquitoes were significantly more responsive in both host-seeking and biting than unfed controls. In a choice olfactometer assay using nectar odours (honey scented with artificial apple-blossom oil) versus host odours (a bird), unfed females preferred honey over bird odours except when honey odour was weak. After sucrose feeding, females switched from honey to bird preference. This change in behaviour was accompanied by significant accumulation of lipid and by follicular growth to the resting stage. Elevation of host responsiveness after sugar feeding was reversible; starvation ultimately resulted in females preferring honey over bird odours. When the larval diet was restricted by crowding, the wing-length and total lipid of resultant adult females were reduced. Although differences were subtle, unfed bird-responding females tended to have longer wings and more lipid than their honey-responding counterparts.     

Effect of Ditylenchus dipsaci on Alfalfa Mortality,Winterkill, and Yield

Ditylenchus dipsaci-infected and noninfected alfalfa plants in a naturally infested field were studied from July 1980 to September 1982. Forty-one percent of the plants died during the study. Ninety-seven percent of the plants that died were infected with D. dipsaci. Sixty-nine percent of the observed mortality occurred during winter. Forage yield of infected plants was significantly lower than yield of noninfected plants at each harvest. Stored carbohydrates in infected plants were significantly lower than in noninfected plants. In a controlled environment test, significantly greater mortality occurred in frozen severely infected plants than in frozen noninfected plants, while no mortality occurred in severely infected or noninfected plants that were not frozen. Both forage yield and stored carbohydrates were significantly lower in severely infected than noninfected, non-frozen plants. Mortality in greenhouse-grown plants that were transplanted to field plots was significantly greater in D. dipsaci-infected plants than in noninfected plants after one winter.     

The regenerated tail of juvenile leopard geckos (Gekkota: Eublepharidae: Eublepharis macularius) preferentially stores more fat than the original

The tail of many species of lizard is used as a site of fat storage, and caudal autotomy is a widespread phenomenon among lizards. This means that caudal fat stores are at risk of being lost if the tail is autotomized. For fat-tailed species, such as the leopard gecko, this may be particularly costly. Previous work has shown that tail regeneration in juveniles of this species is rapid and that it receives priority for energy allocation, even when dietary resources are markedly reduced. We found that the regenerated tails of juvenile leopard geckos are more massive than their original counterparts, regardless of dietary intake, and that they exhibit greater amounts of skeleton, inner fat, muscle and subcutaneous fat than original tails (as assessed through cross-sectional area measurements of positionally equivalent stations along the tail). Autotomy and regeneration result in changes in tail shape, mass and the pattern of tissue distribution within the tail. The regenerated tail exhibits enhanced fat storage capacity, even in the face of a diet that results in significant slowing of body growth. Body growth is thus sacrificed at the expense of rapid tail growth. Fat stores laid down rapidly in the regenerating tail may later be used to fuel body growth or reproductive investment. The regenerated tail thus seems to have adaptive roles of its own, and provides a potential vehicle for studying trade-offs that relate to life history strategy.     

Intraspecific variation in wing colour is related to larval energy reserves in monarch butterflies (Danaus plexippus)

The physiological basis for pigment synthesis in lepidopteran wing scales is well‐studied, although less is known about the reasons why individuals of the same species vary in pigmentation. Monarch butterflies (Danaus plexippus L.) show subtle variations in the shade of orange on their wings and this is known to predict flight ability and mating success. The present study tests the possibility that the shade of orange is associated with the amount of residual energy reserves carried over from the larval stage. Using monarchs reared in captivity under identical conditions (n = 207), the residuals of a regression of wing size and mass at eclosion, which indicate larval energy reserves, are obtained. This measure is positively related to adult longevity without feeding, indicating the importance of this reserve to the monarchs, as well as the value of the measure for this investigation. The shade of orange (i.e. hue) is determined on scanned wings using image analysis. Importantly, orange hue is predicted significantly by residual mass at eclosion (individuals with more mass are redder). The linkage between these traits may explain previous findings whereby redder monarchs fly further and mate more because both behaviours would be enhanced with greater energy stores. The findings of the present study add to a growing body of work showing how intraspecific variation in pigmentation has biological significance to monarchs, and possibly other butterflies. Although much remains to be investigated regarding the physiological underpinnings of this variation, the results of the present study indicate that future efforts should be rewarding.     

Trade-off between flight and reproduction in the African armyworm moth, Spodoptera exempta

ABSTRACT. The existence of a trade-off between flight and reproduction in the migratory noctuid, Spodoptera exempta (Wlk.), was examined in experiments in which female moths were flown on flight balances and then provided with distilled water or sucrose solution. For individuals flight-tested from the night of eclosion (night 0) through night 1 and fed only distilled water, there was a linear, negative relationship between weight-related fecundity and flight duration. When flight was recorded through night 2, a curvilinear relationship was obtained suggesting that highly active moths suffer a smaller decrease in fecundity than predicted from its rate of decline with increasing flight duration in less persistent fliers. The hypothesis that this reflects an energetically expensive, initial phase of each flight, followed by a less costly, cruising phase is examined. Fecundity was independent of flight duration in females provided with sucrose after flight but was related to moth weight, as it was in all unflown moths. Effects of flight and feeding on longevity and mating frequency are also reported.
There is a clear trade-off between flight and fecundity in S.exempta which is only evident in moths denied access to a source of carbohydrate after flight. The results indicate the importance of nectar sources in the field in allowing restoration of lipid reserves depleted during migratory flight. An important implication of this conclusion is that lipid is the resource limiting to fecundity in this species and not protein as is generally supposed for leaf-feeding insects. This might be expected in highly active species as lipid is the resource for which the energetically expensive functions of flight and reproduction must compete.     

Mobilization of lipid and carbohydrate reserves in the migratory grasshopper Melanoplus sanguinipes

Abstract. The North American migratory grasshopper Melanoplus sanguinipes Fabricius (Orthoptera: Acrididae) exhibits heritable variation in predisposition to make long-duration flights, and performance of long-duration flight enhances reproductive output. As a first step in understanding the physiological basis of these phenomena, we examined the mobilization of lipid and carbohydrate reserves during flight and in response to injection of extracts of the corpora cardiaca. Extract of conspecific corpora cardiaca elevates the concentration of haemolymph lipid. Both synthetic locust adipokinetic hormone I (AKH I) and synthetic Locusta migratoria AKH II raise the concentration of lipid in the haemolymph. However, although AKH I is more active than AKH II in locusts, dose-response curves for the two peptides are similar in M.sanguinipes. Neither extract of conspecific corpora cardiaca nor locust AKH I affects haemolymph carbohydrate in this species. Haemolymph carbohydrate and total glycogen reserves are Diminished by tethered flight; in contrast, haemolymph lipid is elevated by flight. Grasshoppers identified as presumptive migrants or non-migrants do not differ significantly in body composition. Total lipid reserves did not decrease measurably after extended flight, even though total reserves of carbohydrate do not appear to be sufficient to maintain the durations of flight performed.     

The establishment of stem nutrient distribution zones of European larch and tamarack using principal component analysis

Some parts of the xylem can act as a nutrient reserve (or source) to satisfy the plant needs during spring flush or when uptake is insufficient. The distribution patterns have been used to delimit different distribution zones of nutrients in the stem but establishing the limits of the zones can be subjective when a single element is used. In this study, we provide a new methodology for analyzing stem nutrients, taking into consideration the common underlying of nutrients in the different distribution zones. The distribution of P, K, Ca, Mg, Mn and Zn was evaluated on an annual basis, using disks from 8 trees, sampled every 20 cm along the stem, in two 18-year-old plantations of European larch [Larix decidua (Mill.)] and tamarack {Larix laricina [K. Koch (Du Roi)]}. Using principal component analysis, more than 90% of the total variance was explained by the first three components. Based on these components, three groups of nutrients were identified: P and K (mobile), Ca and Mn (immobile), and Mg and Zn (intermediately mobile). Five distribution zones were delimited using factorial scores: bark, apical region, external xylem, transition xylem, and internal xylem. The apical and external xylem zones were characterized by mobile nutrients while the internal zone of the xylem was characterized by immobile and intermediately mobile nutrients. As well as establishing common zones of each nutrient, principal component analysis enabled us to characterize zones based on a group of nutrients. If the different distribution zones are considered, the estimation of the internal reserve contribution to plant's nutritional status and the evaluation of the changes in the distribution patterns of elements following natural or artificial perturbations could be improved. Discriminant functions are provided to classify new observations in the different distribution zones.