Using multiple traits to estimate the effects of heat shock on the fitness of Aphidius colemani

Extreme temperature events are a great challenge for most ectotherms, particularly for the immature stages of parasitoids, as they do not possess the ability to behaviourally thermoregulate. In this study, we measured the effect of an acute heat shock, combined with desiccation stress (34 °C and 35% r.h. during 10 h) during the mummy stage on several fitness‐related traits of emerging adults of the aphid parasitoid Aphidius colemani Viereck (Hymenoptera: Braconidae: Aphidiinae). Our results showed that the emergence rate was strongly affected by the heat shock (63 ± 2.3 vs. 96.1 ± 0.7% for stress vs. control conditions, respectively), and the resulting population was male biased. Heat stress reduced the lifespan of emerged parasitoids but had no effect on fat reserves and female size. Egg load at emergence and parasitism rate were also reduced by heat treatment. The antennal symmetry was disturbed by the heat treatment, and stressed individuals had reduced mating success compared to control parasitoids. Specifically, time before wing fanning, a typical male courtship behaviour, was significantly longer in parasitoid pairs involving females that had emerged from heat‐treated mummies. Additionally, olfactometry tests on experimental females indicated that their response to host odour was similar to that of control individuals, but they required a longer time for perception. These results highlight that exposure to high temperatures during the mummy stage has cumulative detrimental effects that may strongly impact parasitoid populations under natural conditions and hinder the success of biological control programs.     

The effects of latitude and day length on fattening strategies of wintering coal tits Periparus ater (L.): a field study and aviary experiment

1. Cyclic daily fattening routines are very common in wintering small wild birds, and are thought to be the consequence of a trade-off between different environmental and state-dependent factors. According to theory, these trajectories should range from accelerated (i.e. mass increases exponentially towards dusk) when mass-dependent predation costs are the most important cause of mortality risk, to decelerated (i.e. the rate of mass gain is highest at dawn and decreases afterward) when starvation is the greater risk. 2. We examine if geographically separate populations of coal tits, wintering in Scotland and central Spain under contrasting photoperiods, show differences in their strategies of daily mass regulation. We describe population differences in wild birds under natural conditions, and experimentally search for interpopulation variation in diurnal body mass increase under common, manipulated, photoperiod conditions (LD 9 : 15 h vs. 7 : 17 h), controlling for temperature, food availability, predator pressure and foraging arena. 3. Winter diurnal mass gain of wild coal tits was more delayed towards the latter part of the daylight period in central Spain (i.e. the locality with longer winter days) than in Scotland. In both localities, the pattern was linked to the average mass at dawn, with mass increasing more rapidly in lighter birds. However, under the controlled photoperiod situation the pattern of daily mass gain was similar in both populations. Diurnal body mass gain was more accelerated at the end of the day, and the increase in body mass in the first hour of the day was considerably lower under the long (9 h) than under the short (7 h) photoperiod in both populations. 4. Wintering coal tits show patterns of mass gain through the day that are compatible with current theories of the costs and benefits of fat storage, with birds at lower latitudes (with longer winter days) having a greater tendency to delay mass gain until late in the day. The experimental study revealed that these patterns are plastic, with birds responding directly to the photoperiod that they experience, suggesting that they are continually making fine-scale adjustments to energy reserves on the basis of both inherent (e.g. state-dependent) and extrinsic cues.     

How and why does the areole meristem move in Echinocereus (Cactaceae)?

Background and Aims In Cactaceae, the areole is the organ that forms the leaves, spines and buds. Apparently, the genus Echinocereus develops enclosed buds that break through the epidermis of the stem adjacent to the areole; this trait most likely represents a synapomorphy of Echinocereus. The development of the areole is investigated here in order to understand the anatomical modifications that lead to internal bud development and to supplement anatomical knowledge of plants that do not behave according to classical shoot theory.Methods The external morphology of the areole was documented and the anatomy was studied using tissue clearing, scanning electron microscopy and light microscopy for 50 species that represent the recognized clades and sections of the traditional classification of the genus, including Morangaya pensilis (Echinocereus pensilis).Key Results In Echinocereus, the areole is sealed by the periderm, and the areole meristem is moved and enclosed by the differential growth of the epidermis and surrounding cortex. The enclosed areole meristem is differentiated in a vegetative or floral bud, which develops internally and breaks through the epidermis of the stem. In Morangaya pensilis, the areole is not sealed by the periderm and the areole meristem is not enclosed.Conclusions The enclosed areole meristem and internal bud development are understood to be an adaptation to protect the meristem and the bud from low temperatures. The anatomical evidence supports the hypothesis that the enclosed bud represents one synapomorphy for Echinocereus and also supports the exclusion of Morangaya from Echinocereus.     

Studies on Endosperm Development and Deposition of Storage Reserves in Coix lacryma-jobi

The transition from free nuclear to cellular endosperm of Coix lacryma-jobi was eompleted 2 days after pollination. By 3 days after pollination the central cell was filled with endosperm cells. At first all cells of endosperm underwent division, later cell division was limited mainly in the peripheral region. 10 days after pollination the epidermal layer ceased its periclinal division and became the aleurone layer. Cell division persisted in the subepidermal 'cambium-like layers until the caryopsis nearly matured. Ceils of the inner region of endosperm became enlarged. Several layers of transfer cells were formed at the basal part of the endosperm. Starch grains appeared in endosperm cells on the 9th day after pollination. 10 days after pollination, lipid bodies occurred in the aleurone layer and the underlying layers. 13 and 15 days after pollination, the small vacuoles of aleurone cells contained protein and 20 days after pollenation they became aleurone grains. By 15 days after pollination pro tein bodies were formed in starch endosperm. Storage reserve deposition continued until the grain ripened. A correlation between endosperm and emoryo development was also observed.     

Ripe pollen structure and histochemistry of some gymnosperms

Some aspects of pollen cytology at dispersal were studied in 12 species of gymnosperms. The pollen grains differed in: 1. volume and cell number; 2. polarization of external structure and internal cell components; 3. wall thickness, especially of the intine, and the resulting percentage of cell volume with respect to total pollen grain volume; 4. stratification and chemical nature of the various intine layers; 5. nature and location of polysaccharide reserves; 6. morphological differences between the dry and hydrated states and phenomena related to hydration; 7. presence and site of orbicles. The various characters are compared and discussed in relation to the length of the reproductive cycle and the relations between the male gametophyte and its female counterpart.     

The role of seed reserves in arbuscular mycorrhizal formation and growth of Leucaena leucocephala (Lam.) de Wit. and Zea mays L.

We show here that seed reserves in Leucaena leucocephala (Lam.) de Wit. and Zea mays L. (maize) are important for mycorrhizal formation and seedling growth. Seed reserve removal reduced mycorrhizal formation markedly in Leucaena but not in maize, except at 15 and 45 days after seed reserve removal. Partial or total removal of seed reserves decreased plant growth and tissue nutrient concentrations in both hosts. Nodule number in Leucaena, which was related positively to plant biomass and mycorrhizal infection levels, was reduced when one or both cotyledons were severed. Leucaena seedlings without or with partial seed reserves had higher nutrient use efficiencies throughout seedling growth. But such an effect was observed only initially in maize. Seed reserve removal increased the specific absorption rates of nutrients in both hosts. Phosphorus absorption rate was significantly and positively related to root infection levels in both Leuceana and maize. Though the growth rates of plants without seed reserves were low initially, these plants had higher growth rates during later stages. We conclude that seed reserves are not only important for seedling growth, but also for mycorrhizal formation and nodulation. Received: 15 July 1999 / Accepted: 6 December 1999