Microhabitats and diel downstream migration of young grayling (Thymallus thymallm L.)

SUMMARY. 1, Microhabitats chosen by young grayling ( Thymallus thymallus L.) were investigated by electrofishing. The first feeding habitat was marginal areas where water velocity did not exceed 15 cms⁻¹. Fry fed on drift in the first 10 cm of the water column below the surface. This location was very stable during the first weeks of growth (mid-April to mid-May). When they were 3–3.5 cm long, fry began using benthic areas and gradually moved away from the banks towards the channel.
2. A downstream migration was noted from the beginning of emergence (mid-April) to the end of May. This mainly nocturnal movement involved all fish sizes and caused a complete removal of young-of-the-year by June from the spawning tributary.     

Radiation précoce des coniferes Taxodiaceae et bois affines du Jurassique de France

Three Jurassic fossil-wood taxa from France have been investigated, Taxodioxylon lemoignei n.sp. from the Oxfordian, Prototaxodioxylon romanensis Philippe from the Pliensbachian, and P. sp. from the Hettangian. Wood of this type, prior to the Late Cretaceous, is reviewed. The Oxfordian wood shows a structure characteristic of a Taxodiaceae, previously unknown before the Late Cretaceous. It is well differentiated from contemporaneous woods of Cupressaceae. The systematic position of the Liassic forms, with mixed type of pitting, remains more arguable. These taxodiaceous woods, along with known reproductive structures, reinforce the idea that this family was well separated from Cupressaceae already in the Middle Jurassic. *** Fossil wood, Jurassic, France, Taxodiaceae.     

Four new species of Provanna Dall (Prosobranchia,Cerithiacea?) from East Pacific hydrothermal sites

Four new species of Provanna Dall, 1918 are described from East Pacific hydrothermal sites: Provanna ios sp.n., P. goniata sp.n., P. echinata sp.n. and P. variabilis sp.n. The type species of Provanna, P. Iomana Dall, 1918 and Trichotropis (Cerithioderma) pacifica Dall, 1908. which here is transferred to Provanna , are the only additional species known of the genus. Results of some preliminary anatomical investigations are given and a tentative position in the Cerithiacea is suggested. The four new species were collected by manned submersibles from sites of hydrothermal activity; P. Iomana has been dredged on two occasions only. from an area known for hydrothermal activity and we assume that the type- and only known locality for P. pacifica also is affected by hydrothermal acitivity.     

Modelled effects of precipitation on ecosystem carbon and water dynamics in different climatic zones

The ongoing changes in the global climate expose the world's ecosystems not only to increasing CO₂ concentrations and temperatures but also to altered precipitation (P) regimes. Using four well-established process-based ecosystem models (LPJ, DayCent, ORCHIDEE, TECO), we explored effects of potential P changes on water limitation and net primary production (NPP) in seven terrestrial ecosystems with distinctive vegetation types in different hydroclimatic zones. We found that NPP responses to P changes differed not only among sites but also within a year at a given site. The magnitudes of NPP change were basically determined by the degree of ecosystem water limitation, which was quantified here using the ratio between atmospheric transpirational demand and soil water supply. Humid sites and/or periods were least responsive to any change in P as compared with moderately humid or dry sites/periods. We also found that NPP responded more strongly to doubling or halving of P amount and a seasonal shift in P occurrence than that to altered P frequency and intensity at constant annual amounts. The findings were highly robust across the four models especially in terms of the direction of changes and largely consistent with earlier P manipulation experiments and modelling results. Overall, this study underscores the widespread importance of P as a driver of change in ecosystems, although the ultimate response of a particular site will depend on the detailed nature and seasonal timing of P change.     

Probing behaviour and sporozoite delivery by Anopheles stephensi infected with Plasmodium berghei

We observed that Plasmodium berghei sporozoite-infected Anopheles stephensi was not impaired in its ability to locate blood on a host. When probing rats, infected mosquitoes took as long as non-infected mosquitoes to locate blood. Contrary to previous suggestions, infective mosquitoes delivered sporozoites into mineral oil even after extensively probing a vertebrate host. We observed that, in mosquitoes having probed a host, both the mean number of sporozoites ejected over 3 min into oil (35.9 v. 31.7 sporozoites) and the proportion of mosquitoes delivering sporozoites (60% v. 50%) were similar to mosquitoes not having probed. We then developed a model of sporozoite delivery, taking into account observations that sporozoites are clumped in the lumen of the glands as well as upon delivery, and that output is uneven and inconsistent. We conclude that clumping optimizes transmission, if a threshold of infection exists and the mean number of sporozoites per clump is greater than the threshold.