Evaluating the efficacy of wood shreds for mitigating erosion

An erosion control product made by shredding on-site woody materials was evaluated for mitigating erosion through a series of rainfall simulations. Tests were conducted on bare soil and soil with 30, 50, and 70% cover on a coarse and a fine-grained soil. Results indicated that the wood product known as wood shreds reduced runoff and soil loss from both soil types. Erosion mitigation ranged from 60 to nearly 100% depending on the soil type and amount of concentrated flow and wood shred cover. Wood shreds appear to be a viable alternative to agricultural straw. A wood shred cover of 50% appears optimal, but the appropriate coverage rate will depend on the amount of expected concentrated flow and soil type.     

Genetic population structure of a species' complex of blue mussels (Mytilus spp.)

Blue mussels representing two nominal species (Mytilus trossulus Gould, 1850 and Mytilus galloprovincialis Lamarck, 1819 were collected from 28 intertidal locations along the Pacific coast of the USA in 1990–1991 (total N=1255) and examined for variation at 15 allozyme loci. Twelve samples, mostly from a region of suspected hybridization, were analyzed for variation in seven shell characters. Principal-components analysis of allozyme data revealed three groups based on first principal-component scores, which were identified as M. trossulus, M. galloprovincialis, and hybrids. Canonical discriminant analysis of shell characters was less successful in separating mussels into discrete groups. Each location was characterized for four environmental variables: (1) temperature, (2) salinity, (3) tidal height and (4) degree of exposure to wave action, which were then used as independent variables in a series of multiple-regression analyses, with the proportions of the two species as dependent variables. Temperature and salinity had significant (P<0.05) effects on the macrogeographic distribution of the two species, whereas the effects of height in the tidal zone and degree of wave exposure were not statistically significant. Salinity was found to have a greater influence than temperature on the microgeographic distribution of the two species. M. trossulus was more abundant at locations with lower temperatures and greater salinity variation than M. galloprovincialis. The two species appear to be ecologically distinct, and their genetic integrity is at least partly the result of environmental heterogeneity.     

Sustainability under siege: Transport costs and corruption on West Africa's trade corridors

We use recent data on transport costs in West Africa, including the added burden of bribes and enforced delays, to show how such costs represent a deterrent to investment in — and therefore the sustainability of — agricultural assets. We focus on data for two important tree crops in West Africa, cashew and shea. We also have data for the transport of onions between Niger and the urban market in Accra, Ghana. Our data allow us to predict plausible increases in farm‐gate prices from a reduction in transport costs and bribes. A 10% reduction in the total transport costs (actual costs plus corruption costs) of onions from Niger could result in a 12‐13% price increase to onion farmers. Similar elasticities are 2% for cashew in Ghana and 7% for shea in Mali. These feasible price increases would encourage farmers to improve onion production, and to protect and improve production from cashew and shea trees, thereby enhancing the sustainability of agro‐forestry in West Africa. We call these price increases the “sustainability dividend”.     

Genetic population structure of the southern oyster drillStramonita (=Thais)haemostoma

Nine collections in the southeastern USA of the thaidid molluscStramonita haemastoma, comprising 963 individuals, were made between June 1988 and November 1989, and examined for allozyme variation at 18 electrophoretically-detected loci. Two genetically-differentiated groups were identified and are referred to ascanaliculata-like andfloridana-like snails, based on previously-described subspecies ofS. haemastoma. The two groups were differentiated genetically at a level that is characteristic of congeneric species in other molluscan taxa. The two groups maintained their genetic differences in areas of sympatry, although rare hybrid individuals occurred (about 1.2% of the total set). Shell and radular characters showed little variation within or between the two groups. Within each group, allozyme allele frequencies showed little geographic variation across distances as great as 1 500 km. This result is consistent with the suggestion that species with planktonic larvae (such asS. haemastoma) should have higher rates of gene flow than related brooding species.     

Mitochondrial DNA polymorphisms reveal additional genetic heterogeneity within the Leptasterias hexactis (Echinodermata: Asteroidea) species complex

Sea stars of the Leptasterias hexactis complex are important members of the rocky intertidal community of the temperate and subarctic North American Pacific coasts. Recent attempts to determine the genetic structure and taxonomic relationships of these sea stars have not been completely successful, due to the combination of extreme morphological variability and relative scarcity of taxonomically-informative genetic (allozyme) polymorphisms. The present study used mitochondrial DNA restriction-site polymorphisms for PCR (polymerase chain-reaction)-amplified products to provide additional information about this complex. Five restriction-site haplotypes were identified in southern Alaska and in the Puget Sound region that were allozymically distinct. Because the allozymic differences (Nei's unbiased genetic differences >0.08) are maintained in sympatry, the haplotypes behave evolutionarily as conventional species. Although most haplotypes show deficiencies of heterozygotes for polymorphic allozyme loci, there is no evidence for the existence of cryptic species within any of the haplotypes. Rather than consisting of a few polytypic and cosmopolitan species, the L. hexactis complex is apparently composed of numerous species with more restricted ranges. Determining the exact ranges and taxonomic relationships of the various species will require additional study.     

Are meiofaunal species cosmopolitan? Morphological and molecular analysis of Xenotrichula intermedia (Gastrotricha: Chaetonotida)

Many meiofaunal species are reported to be cosmopolitan, but due to uncertainties of identification, the affiliation of specimens from geographically distant areas to the same species-taxon is problematic. In this study, we examined morphological and molecular variation in samples of Xenotrichula intermedia Remane (Gastrotricha: Chaetonotida) from the Mediterranean Sea, the northwestern Atlantic and the northern Gulf of Mexico. Univariate analysis of 16 morphological traits was unable to detect differences among populations, except for the length of the pharynx, which was significantly shorter in the Gulf of Mexico specimens. Canonical discriminant analysis separated the Gulf of Mexico specimens from the other two populations, with pharynx length contributing about half of the total discrimination. Molecular analysis based on restriction-fragment length polymorphisms (RFLPs) in a 710-base pair polymerase chain-reaction (PCR) produet representing roughly half of the mitochondrial cytochrome oxidase I (COI) gene detected four haplotypes: one each from the Mediterranean and the Gulf of Mexico populations and two coexisting within the Atlantic population. The estimated nucleotide-sequence divergence calculated for each pairwise combination of haplotypes (based on the proportion of shared fragments) ranged from 5.3 to 11.5%. The high genetic divergence and the inability to clearly separate populations based on morphology suggest that individuals characterized by different haplotypes are genetically isolated sibling species.     

Phylogeography of two squid (Loligo pealei and L. plei) in the Gulf of Mexico and northwestern Atlantic Ocean

The loliginid squids Loligo pealei LeSueur and L. plei Blaineville (both recently proposed for reclassification as Doryteuthis) are commercially important, similar in appearance, and sympatric throughout much of the northwestern Atlantic Ocean, the Gulf of Mexico, and the Caribbean Sea. To investigate possible cryptic speciation and population structure, we examined samples (collected from 1995 to 1997) of both species for restriction fragment length polymorphisms (RFLPs) in PCR products of the mitochondrial gene cytochrome c oxidase (subunit I). RFLP haplotypes were further characterized by direct sequencing. In North American waters, cryptic speciation was rejected by the far greater nucleotide sequence divergence between species (~14%) versus within species (<1%). Each species displayed about a dozen RFLP haplotypes, but only three of their respective haplotypes were found among 90% of L. pealei specimens (n=356) and 97% of L. plei specimens (n=431). For L. pealei, a genetic break existed between the northern Gulf of Mexico and the Atlantic Ocean; among sample units within each population, gene flow was consistent with panmixia. The phylogeography of L. pealei is likely a consequence of the eastward currents of the Florida Straits, the elevated temperatures of those surface waters, and the restriction of this species to the continental shelf. For L. plei, a genetic break existed between longitudes 88°W and 89°W, with the northwestern Gulf of Mexico and the northeastern Gulf-Atlantic Ocean comprising separate populations; among sample units within each population, gene flow fit an isolation-by-distance model. If the genetic break found for L. plei represents resident populations separated by nearshore physical parameters (e.g. effects of the Mississippi River and the sediment boundary at longitude 88°W), the lack of structure within the Gulf for L. pealei might be due to its distribution farther from shore. However, the two populations of L. plei probably represent annual recolonization from the southwestern Gulf of Mexico and from the eastern Caribbean Sea, whereas the populations of L. pealei probably are permanent residents within their respective regions.