Hydrologic versus geomorphic limitation on CPOM storage in stream ecosystems

1. Stream ecosystems are the products of interactions between hydrology, geomorphology and ecology, but examining all three components simultaneously is difficult and rarely attempted. Frequently, either geomorphology or hydrology is treated as invariable or static. 2. To examine the validity of treating either hydrology or geomorphology as static, we studied the individual and combined effects of hydrology and channel geomorphology on coarse particulate organic matter (CPOM) storage. Using data from an experimental leaf release in a hydrologically regulated stream we created a simple numerical model. This allowed us to quantify the relative influence of CPOM trapping and CPOM retention on total long‐term CPOM storage under variable regimes of flood frequency and geomorphic structure. 3. CPOM storage is a function of supply, flood frequency and the type and frequency of in‐stream structures. In‐stream structures perform two distinct functions, trapping and retention, whose relative importance in leaf storage changes with stream hydrology. Trapping is more important for CPOM storage in streams with few floods, while retention is more important in streams with frequent floods. Different structures (e.g. boulders, large wood, small wood) perform these functions at different efficiencies. We found that large wood trapped two to three times more leaves than the bank, but that the bank retained leaves two to three times more efficiently. 4. A modelled channel with five times the amount of large wood as the study channel (a ‘wood restoration’) initially stored 14% more leaves than the modelled ‘natural’ channel. After six floods, however, the modelled wood restoration channel stored 50% less CPOM than the natural channel as the large wood had high trapping but poor retention. The modelled natural channel contained structures that could both trap and retain. Thus, as different structures performed different functions, the structural complexity buffered the stream allochthonous energy base against changes in hydrology through its balance of trapping and retention. 5. As the frequency of floods increased, the spatial distribution of CPOM became increasingly patchy as storage was driven entirely by structures with high retention. Thus, the coupling of flood frequency and geomorphic structure influenced CPOM availability, which in turn has ramifications for the entire stream food web.     

Genetic homogeneity among breeding grounds and nursery areas of an exploited Lake Malawi cichlid fish

1. Nursery areas are commonly recognized as important habitats for the management and conservation of fish stocks. Here we report the use of nursery areas by an exploited offshore cichlid in Lake Malawi, Rhamphochromis longiceps .
2. Like all haplochromine cichlids that have been studied, the species is a maternal mouthbrooder that broods eggs for several weeks following spawning. We found evidence that during this brooding period females migrate from open water to release juveniles in three shallow peripheral waterbodies (Chia Lagoon, Unaka Lagoon, Lake Malombe). However, it was unclear whether there is geographical population structuring within the species, which could indicate stock differences in their use of these nursery habitats, or if the lake contains a genetically panmictic population that employs nursery habitats opportunistically.
3. To investigate spatial and temporal population structuring within the lake we genotyped populations at seven microsatellite DNA loci. Overall, we found no significant spatial structuring among juveniles from the peripheral lagoons or among breeding males within the main lake body. Moreover, we found no evidence of temporal structuring among males on the breeding grounds within Lake Malawi or females entering Chia lagoon. Together, these results suggest that Lake Malawi contains a genetically homogeneous population of R. longiceps .
4. At present we know little of the distribution of juvenile R. longiceps elsewhere in the Lake Malawi basin, but their absence from surveyed rocky and sandy littoral habitats makes it possible that the species is dependent upon a small number of nearshore nursery areas, including these lagoons. As such, conservation of lagoon habitats and monitoring of exploited fish stocks within them may be important for effective preservation of biodiversity within the catchment.     

Answer to “Reevaluation of the conclusion that IRES-activity reported within the 5′ leader of the TIF4631 gene is due to promoter activity”

The accuracy of the data we reported in an RNA Letter to the Editor earlier this year on the promoter activity within the 5′ leader of the TIF4631 gene is questioned by V.P. Mauro and others in this issue. We reply here that we see no inaccuracy in our data.     

Polymorphic microsatellite loci for the trematode Diplostomum pseudospathaceum

We present primers for five polymorphic microsatellite loci in the eye fluke Diplostomum pseudospathaceum (Trematoda), a widely distributed parasite with a complex life cycle used as a model for parasitology and fish immunology. The loci were identified using a GA/CT‐enriched genomic library by subtractive hybridization with magnetic particles. All five loci were highly polymorphic, displaying 17 to 61 alleles and heterozygosities ranging from 0.53 to 0.92. We isolated populations of parasites within the first (snail) and second (fish) intermediate host and found small but significant genetic differentiation (F_ST = 0.012) between the two life stages of the parasite.     

Correlates of extinction risk of birds from two Indonesian islands

Size of distributional range, position in the range, body size and diet are some of the ecological traits that may correlate with local abundance. Evolutionary phenomena such as taxon cycles, acting over much greater time periods, may also influence abundance and promote species extinction. This paper assesses which of a wide range of ecological and historic traits best predict the variation in abundance of tropical forest birds on Sumba and Buru islands in Wallacea (Indonesia). In addition we seek to determine which traits predict species' ability to adapt to secondary or logged forest. The most important correlates of both abundance and ability to transfer were those related to the evolutionary history of the species within the Wallacean Archipelago and not the traits that were more directly related to species ecology. These relationships are maintained when allowance is made for phylogenetic relationships. Our interpretation of the results is that recent colonists to an island are initially rare in the indigenous forest habitat but concomitant with an adaptation to local conditions they gradually become more abundant and taxonomically distinct from other populations of the same species. These results apparently contradict the taxon cycle hypothesis but this may be a result of our focus on indigenous forest habitats rather than on a wider range dominated by anthropogenic ones.     

Use of lichen secondary metabolites as antifeedants to protect higher plants from damage caused by slug feeding

Extracts of 15 species of lichen were tested for antifeedant properties against the field slug Deroceras reticulation (Müller) (Mollusca: Pulmonata). All but three showed some activity and two of these were from endolithic species. The most effective extract was from Letharia vulpina. The major active compound from this species, vulpinic acid, was tested for dose response, applied as a foliar spray to turnip plants and as a dressing to wheat seeds in laboratory experiments. It provided effective protection against slug feeding under these conditions.     

A System of Partial Sterility in the Tomato

A partially sterile condition of the tomato Tiny Tim resultsin smaller-than-normal pollen, high pollen abortion, reducedfruit and seed set, and small seeds of low viability. Pollenabortion is initiated after break-up of the tetrads. In crosses.tothe fertile variety Atom, reduced fruit and seed set is partiallydominant, and apparently-multigenically controlled. Seed sizeis influenced by both cytoplasmic and genic factors. Such partialsterility is suspected to be common, and could result in disturbedsegregation ratios of genes.