Seasonal pattern in age, sex and body condition of Barn Owls Tyto alba killed on motorways

The Barn Owl Tyto alba was the most common owl killed on motorways in northeastern France. The possible causes of this mortality and the age, sex and body condition of the road-killed birds in 1991–1994 have been investigated. The number of birds killed on roads was highest in the period from early autumn to late winter, i.e. during the non-breeding period, and showed a pattern similar to that of the temporal difference between sunset, which varies with day length, and peak of traffic, the occurrence of which is constant throughout the year. An autumnal mortality peak, concomitant with the post-fledging dispersal, was mainly of immature birds, especially females. A second mortality peak in late winter was composed mainly of mature birds, with an equal proportion of males and females. From autumn to winter, there was no significant change in body mass in the different age and sex categories of birds killed on roads, except for mature males which had a significantly lower body mass in winter. From early autumn to late winter, the mean body mass of immature owls killed on motorways did not differ significantly from that of captive immatures fed ad libitum. This suggests that the immature birds were in good body condition. In contrast, the body mass of road-killed mature females was significantly lower than that of captive mature females over the same time periods. In mature males in late winter, a drop in body mass in both road-killed and captive birds suggests an endogenous seasonal phenomenon. Except for mature females, Barn Owls killed on roads in 1991–1994 were in good body condition. This does not support the idea that only birds in poor body condition were killed. We conclude that the mortality of Barn Owls on motorways in autumn and winter was probably related to the concomitance between the peak of traffic and the onset of hunting activity and the large number and dispersal of immature individuals during the same period.     

Warming increases the proportion of primary production emitted as methane from freshwater mesocosms

Methane (CH₄) and carbon dioxide (CO₂) are the dominant gaseous end products of the remineralization of organic carbon and also the two largest contributors to the anthropogenic greenhouse effect. We investigated whether warming altered the balance of CH₄ efflux relative to gross primary production (GPP) and ecosystem respiration (ER) in a freshwater mesocosm experiment. Whole ecosystem CH₄ efflux was strongly related to temperature with an apparent activation energy of 0.85 eV. Furthermore, CH₄ efflux increased faster than ER or GPP with temperature, with all three processes having sequentially lower activation energies. Warming of 4 °C increased the fraction of GPP effluxing as CH₄ by 20% and the fraction of ER as CH₄ by 9%, in line with the offset in their respective activation energies. Because CH₄ is 21 times more potent as a greenhouse gas, relative to CO₂, these results suggest freshwater ecosystems could drive a previously unknown positive feedback between warming and the carbon cycle.     

Warming alters the size spectrum and shifts the distribution of biomass in freshwater ecosystems

Organism size is one of the key determinants of community structure, and its relationship with abundance can describe how biomass is partitioned among the biota within an ecosystem. An outdoor freshwater mesocosm experiment was used to determine how warming of～4 °C would affect the size, biomass and taxonomic structure of planktonic communities. Warming increased the steepness of the community size spectrum by increasing the prevalence of small organisms, primarily within the phytoplankton assemblage and it also reduced the mean and maximum size of phytoplankton by approximately one order of magnitude. The observed shifts in phytoplankton size structure were reflected in changes in phytoplankton community composition, though zooplankton taxonomic composition was unaffected by warming. Furthermore, warming reduced community biomass and total phytoplankton biomass, although zooplankton biomass was unaffected. This resulted in an increase in the zooplankton to phytoplankton biomass ratio in the warmed mesocosms, which could be explained by faster turnover within the phytoplankton assemblages. Overall, warming shifted the distribution of phytoplankton size towards smaller individuals with rapid turnover and low standing biomass, resulting in a reorganization of the biomass structure of the food webs. These results indicate future environmental warming may have profound effects on the structure and functioning of aquatic communities and ecosystems.     

The transmissibility of a potyvirus by an aphid vector: reliability of measurements under controlled conditions

Reproducibility of measurements of the transmission rate of a given potyvirus by a given aphid vector was assessed using a standardised transmission procedure. The plant-virus-vector system studied was: Cucurbita pepo - Papaya ringspot virus - Aphis gossypii. Several elements concerning the rearing and handling of the aphids were analysed. One of these, the climatic conditions under which the aphids were reared, influenced the transmission rate of the virus. Six trials were carried out to measure the rate of transmission of the virus from a defined leaf surface area. The measurements appeared to be reliable. A two year experiment was carried out to compare transmission rates at different dates. Although strong variations were observed in some source plants, the transmission rates obtained for samples of 10 source plants were stable, with a 10% coefficient of variation. The results show that transmissibility of the virus is a stable property which is independent of the trial date. They are discussed in relation to standardised elements of the transmission process.     

Transformation of the Mesonephros into Epididymis in the Cock: Fate of Collecting and Secretory Tubule Antigens

By means of purified rabbit anti-adult chicken kidney antibodies two types of antigens have been identified in the mesonephros: one (PS), localized in the cells of the proximal secretory tubules, the other (CT) characteristic of the collecting segments.
During the conversion of certain mesonephric tubules into epididymal ductules in the male, the CT-antigen disappears, whereas the PS-antigen not only persists but can also be detected in the cells of the parietal layers of Bowman's capsules as they transform before connecting with the rete testis. In the adult cock, the PS-antigen is found at the apical part of the cells of the ductuli efferentes, whereas the ductuli conjugentes and ductus epididymidis are negative.
In the female, the PS-antigen is also found to persist in the cells of the proximal segment and to appear in the cells of the parietal layers of Bowman's capsules. However, between 2 and 3 months after hatching it disappears, although perfectly well preserved tubuli of mesonephric origin can be observed at much later stages.
In the epididymal tubuli of the sexually mature cock, large sheets of the epithelial walls are seen to detach and to fall into the lumina where they disintegrate. The cellular contents thus released mix with the mass of the spermatozoa. Arguments tending to exclude a fixation artifact are presented and the possibility that the observation reflects a cyclic physiological process is discussed.     

Interruption of Water Delivery at Physiological Maturity is Essential for Seed Development, Germination and Seedling Growth in Pea (Pisum sativum L.)

As pea plants (Pisum sativum L.) cv. Finale and Solara developin the field, pods located at the second flowering node, increasein fresh and dry weight until 75 d after planting (DAP); thereafter,dry weight and moisture content decrease rapidly. Seed developmentconsists of three phases, all limited by low moisture content(MQ. The first phase (PI) corresponds to the formation of theembryo and surrounding structure (MC is stable at 85%). Duringthe second phase (P2) the cotyledons are filled (MC decreasesfrom 84% to 55%). The third phase (P3) entails desiccation onthe mother plant. Fresh and dry weight increase until 75 DAP(55% MC or physiological maturity, PM) and rapidly decreaseduring the third phase until 14% MC. Leakage conductivity ofimmature seeds reflects sap arrival in the testa and accumulationin the apoplast it is important during PI and the onset of P2,but during P2 it decreases slowly until physiological maturityand rapidly thereafter. Immature seed germination is noted from62 DAP, increases until 67 DAP, then decreases with a maximumat physiological maturity; some days after physiological maturitygermination is complete (up to 100%). Seedling growth from immatureseeds during P2 is low, but slowly increases until physiologicalmaturity. When germination (up to 100%) is attained seedlinggrowth is normal. Hydration of the immature seed indicates that55% MC is a highly specific value at which a transition in thehydration rate is occurring. Moisture loss from pea seeds duringthe P2 filling stage appears to be necessary for seed adaptationto the abrupt desiccation which occurs at physiological maturity.Physiological maturity is attained when disruption of the vascularconnection between the pod and the mother-plant occurs. Key words: Physiological maturity, germination, growth, pea