FISH ASSEMBLAGE RESPONSES TO DIFFERENT SECONDARY CHANNEL DESIGNS IN THE LOWER MISSISSIPPI RIVER,U.S.A.:A TEMPLATE FOR RIVER RESTORATION

The lower Mississippi River(LMR) has been heavily modified for multiple human purposes such as navigation, flood control, and bank stabilization. However, the LMR simultaneously supports a diverse fish fauna that includes recreational and commercial fisheries. Due to river training and diversion structures constructed during the past 80 years, the historic characteristics of the LMR have been drastically altered and have likely influenced fishes and fisheries in the system. One common restoration measure used throughout the LMR has been to "notch" wing-dike structures that close secondary(side) river channels. Dike notching allows year-round flows through secondary channels, which enhances habitat diversity and promotes biological productivity at the ecosystem scale. Although notching is presumed good for LMR fishes and other biota, few studies have examined its effects on fish assemblages. In this study, fish assemblages were sampled at seven LMR secondary channels spanning from river kilometer(rkm) 628(Louisiana-Mississippi, U.S.A.) upstream to rkm 1504(Missouri-Kentucky, U.S.A.). Four secondary channels were termed "permanent"(i.e.,with notched dikes) while three secondary channels were termed "temporary"(i.e., without notched dikes).Fishes were sampled by boat-mounted electrofishing conducted during falling and low stages from1995—1997. Fish assemblages differed between permanent and temporary secondary channels, and varied somewhat between falling and low stages. Gizzard shad(Dorosoma cepedianum), threadfin shad(D. petenense), and white bass(Morone chrysops) demonstrated consistent preferences for low-current conditions associated with temporary secondary channels. Conversely, blue catfish(Ictalurus furcatus), flathead catfish(Pylodictis olivaris), and freshwater drum(Aplodinotus grunniens) were more associated with permanent secondary channels. Future restoration strategies in the LMR should consider dike notching and resultant maintenance of permanent secondary channels in selected river reaches. However, temporary secondary channels also contain unique fish species, and also appear to be important sites of riverine primary production. Restoration strategies should consider a balance of both secondary channel types, which should support the greatest biodiversity for the LMR ecosystem.     

Mechanism of Formation of Novel Covalent Drug·DNA Interstrand Cross-Links and Monoadducts by Enediyne Antitumor Antibiotics

The potent enediyne antitumor antibiotic C1027 has been previously reported to induce novel DNA interstrand cross-links and drug monoadducts under anaerobic conditions [Xu et al. (1997) J. Am. Chem. Soc. 119, 1133-1134]. In the present study, we explored the mechanism of formation of these anaerobic DNA lesions. We found that, similar to the aerobic reaction, the diradical species of the activated drug initiates anaerobic DNA damage by abstracting hydrogen atoms from the C4', C1', and C5' positions of the A1, A2, and A3 nucleotides, respectively, in the most preferred 5'GTTA1T/5'ATA2A3C binding sequence. It is proposed that the newly generated deoxyribosyl radicals, which cannot undergo oxidation, likely add back onto the nearby unsaturated ring system of the postactivated enediyne core, inducing the formation of interstrand cross-links, connecting either A1 to A2 or A1 to A3, or drug monoadducts mainly on A2 or A3. Comparative studies with other enediynes, such as neocarzinostatin and calicheamicin gamma1I under similar reaction conditions indicate that the anaerobic reaction process is a kinetically competitive one, depending on the proximity of the drug unsaturated ring system or dioxygen to the sugar radicals and their quenching by other hydrogen sources such as solvent or thiols. It was found that C1027 mainly generates interstrand cross-links, whereas most of the anaerobic lesions produced by neocarzinostatin are drug monoadducts. Calicheamicin gamma1I was found to be less efficient in producing both lesions. The anaerobic DNA lesions induced by enediyne antitumor antibiotics may have important implications for their potent cytotoxicity in the central regions of large tumors, where relative anaerobic conditions prevail.     

Strong genetic differentiation and postglacial origin of populations in the marine midge Clunio marinus (Chironomidae,Diptera)

The marine midge Clunio marinus (Chironomidae, Diptera) is characterized by a one‐dimensional distribution along the European Atlantic coast, where its lunar and circadian emergence rhythms are genetically adapted to the local tidal regimes, resulting in a series of ‘temporal races’. Clunio marinus is restricted to rocky coasts and thus the temporal races occur in different rocky patches. We studied 10 populations of Clunio marinus from five different regions, spanning the major rocky mainland coasts from Spain to Norway, using amplified fragment length polymorphisms (AFLP), microsatellites and mitochondrial cytochrome oxidase I (COI) sequences. Star‐like patterns of COI haplotypes within regions indicate postglacial colonization. A high degree of shared polymorphisms in AFLP markers suggests colonization from a single source, implying postglacial evolution of timing adaptations in relation to the local tidal regime. In contrast, no COI haplotypes are shared among regions. We hypothesize that different levels of differentiation of nuclear vs. mitochondrial markers in the source region were carried forward during postglacial expansion. Despite the recent origin of populations, all markers reveal distinct genetic differentiation between rocky coasts on a scale of 650–1150 km. Differentiation between rocky coasts is not correlated to timing adaptations, suggesting that geographic isolation is prevalent between rocky coasts and that this facilitated the evolution of local timing adaptations. At the same time there is little genetic differentiation within rocky coasts on a scale of 2–6 km; leaving open the possibility that within rocky coasts with large variation in tidal regimes, temporal adaptations evolved in the face of gene flow.     

Root based approaches to improving nitrogen use efficiency in plants

In the majority of agricultural growing regions, crop production is highly dependent on the supply of exogenous nitrogen (N) fertilizers. Traditionally, this dependency and the use of N-fertilizers to restore N depleted soils has been rewarded with increased plant health and yields. In recent years, increased competition for non-renewable fossil fuel reserves has directly elevated prices of N-fertilizers and the cost of agricultural production worldwide. Furthermore, N-fertilizer based pollution is becoming a serious issue for many regions where agriculture is highly concentrated. To help minimize the N footprint associated with agricultural production there is significant interest at the plant level to develop technologies which can allow economically viable production while using less applied N. To complement recent reviews examining N utilization efficiency in agricultural plants, this review will explore those strategies operating specifically at the root level, which may directly contribute to improved N use efficiencies in agricultural crops such as cereals, where the majority of N-fertilizers are used and lost to the environment. Root specific phenotypes that will be addressed in the context of improvements to N acquisition and assimilation efficiencies include: root morphology; root to shoot ratios; root vigour, root length density; and root N transport and metabolism.     

Differentiation of innate but not learnt responses to host‐habitat odours contributes to rapid host finding in a parasitoid genotype

Abstract In parasitoids, host‐habitat odour can influence host searching within the habitat. This is the case in Leptopilina sp. (Hymenoptera, Figitidae), a Drosophila parasitoid searching for larvae by ovipositor probes. This a behaviour can be conditioned to fruit odours. In a previous study, the latency of probing to a fruit odour is reported to have a genetic variability within a laboratory strain. This suggests a link between rapidity of host discovery and fitness. In the present study, this hypothesis is tested by comparing responses to host‐habitat odours between two genotypes of Leptopilina heterotoma Thomson, from the Mediterranean coast (Antibes) and from Burgundy (Tailly). The two genotypes present contrasting rhythms and levels of locomotor activity linked to contrasting interspecific competition in their area of origin. The high activity observed in the Mediterranean genotype is interpreted as an adaptive response to a limited time‐window to win against a competitor species absent in Burgundy. The present study finds differentiation in innate but not learnt responses to host‐habitat odours. The more active genotype (Antibes) has a higher probability and a shorter latency of innate probing to the odours than the less active genotype (Tailly); Antibes females also find larvae and complete infestations more rapidly. Learning equalizes the probability and the latency of probing to the odours in both strains, and increases the probing duration. Innate responses to host‐habitat odours would allow time‐limited insects to increase their reproductive rate, when host predictability is high in the habitat. Selection of faster innate responses to host and habitat cues without evolution of learnt responses indicates that the initial host discovery is more crucial to fitness than subsequent ones.