Niches and neutral processes contribute to the resource–diversity relationships of stream detritivores

1. Explaining resource–diversity relationships is a long‐standing goal in ecology, and there is currently little consensus as to the relative contributions of neutral versus a variety of proposed niche‐related mechanisms. 2. The resource–diversity relationship of insect detritivores was examined in a survey of 25 small, parallel streams flowing into the Bay of Fundy in eastern Canada, with the objective of determining whether neutral processes (sampling effects) could account for the observed patterns. 3. Detritivore taxonomic richness showed a positive, but decelerating relationship with quantity of detritus. Richness also increased with catchment area and with stream permanence. 4. Species distribution patterns were significantly nested, and low resource streams (little detritus) tended to have species with large ranges (i.e. found in many or most streams). 5. Sampling effects could explain only part of the positive relationship between richness and detrital resources, but accounted for the species richness–area relationship. 6. Two mechanisms that could potentially increase niche space as resource abundance increased were rejected: there was no evidence that riparian forest diversity or beta diversity increased with detrital resources. 7. Two niche‐related mechanisms were consistent with existing data, but will require further testing. First, flood disturbance may decrease species richness by eliminating species that require benign habitat, and lowering detritus retention, producing a positive correlation between detritivore richness and resources. Second, large wood in streams located in older riparian forest may increase habitat heterogeneity (number of niches) and the retention of organic matter, again leading to a positive relationship between detritivore diversity and detrital resources. 8. It was concluded that the positive ‘productivity–diversity’ relationship for stream detritivores was most likely produced in part by sampling effects, but also by ecological processes (disturbance and succession) that simultaneously influence resource level and niche availability.     

Determinate Floral Buds of Plantain (Musa AAB) as a Site of Adventitious Shoot Formation

Floral buds of the ‘False Horn’ plantain clonesMusa (AAB) ‘Harton Verde’, ‘Harton Negra’,and ‘Currare’ terminate in a large single floralstructure. The apices of these floral buds are here designatedas determinate since they have lost the ability to produce additionalfloral initials or buds. Terminal peduncle segments can be culturedin a modified Murashige and Skoog (1962) medium supplementedwith N⁶-benzyl-aminopurine (5 mg I^–1). Under these conditions,this apparent inability to yield buds can be overcome as vegetativeshoot clusters form in the axils of the bracts. Rooted plantletsare obtainable by treating shoots with naphthaleneacetic acid(1 mg I^–1) and activated charcoal (0.025%). The adventitiousorigin of the shoots has been established. Musa cultivars, plantains, floral bud, adventitious buds, tissue culture     

Is the endangered Apium repens (Jacq.) Lag. rare because of a narrow regeneration niche?

The conservation of rare plant species is an important aspect of global biodiversity protection, but in many cases these species and the reasons why they are rare are poorly understood. The perennial umbellifer Apium repens is generally regarded to be a rare species all over its European range. We hypothesized that its rarity might be caused by a restricted regeneration niche, that is, highly specific requirements for sexual regeneration, low seed dispersal potential and low endurance capacity of seeds in the ground. We conducted several experimental investigations on its germination ecology, hydrochorous dispersal potential and soil seed bank properties. Apium repens showed high germination success under a variety of abiotic conditions. Either light or cold-wet stratification was necessary to stimulate germination. Seeds were able to float for more than 50 days when protected from precipitation, and soil seed bank sampling revealed that at least some seeds of A. repens were contained in soil depths of up to 10 cm. Overall, our findings do not support the hypothesis that the rarity of A. repens is caused by highly specific requirements for its sexual regeneration. Nonetheless, its germination ecology should be considered when designing conservation measures for this endangered species.     

Identification of Trypanosoma cruzi Zymodemes by Kinetoplast DNA Probes

Analysis of zymograms of extracts of Trypanosoma cruzi isolated from different hosts in Argentina allowed characterization of 12 zymodemes or "isozymic strains," only six of which were found in human patients. Two of these six zymodemes (Z1 and Z12) were widely distributed and found in more than 80% of human patients. These two "major natural clones" differed significantly in pathogenic activity. Because the groupings obtained by studying enzymes and kinetoplast DNA (kDNA) were similar, it is possible to identify the zymodeme by analyzing kDNA. A 290-bp fragment was amplified by PCR using primers for the sequences flanking the hypervariable regions of kDNA minicircles. Labeled probes for this fragment, prepared from Z1 and Z12 reference stocks, hybridized specifically with PCR-amplified kDNA from parasite stocks, allowing identification of zymodemes.     

A panel of microsatellite markers to detect and monitor demographic bottlenecks in the riverine dragonfly Orthetrum coerulescens F.

Odonates (dragonflies and damselflies) are important indicators for monitoring anthropogenic impacts on freshwater ecosystems. We developed a panel of microsatellite loci for the keeled skimmer Orthetrum coerulescens, a libellulid dragonfly inhabiting small streams. By using two different isolation techniques, nine microsatellite loci have been isolated. Screening of 209 individuals resulted in an overall number of 88 alleles, ranging from three to 19 alleles per locus. The observed heterozygosity ranged from 0.37 to 0.83. One locus showed significant deviation from Hardy–Weinberg equilibrium.     

Polymorphic microsatellite loci to study population dynamics in a dragonfly,the libellulid Trithemis arteriosa (Burmeister, 1839)

One of the most widely distributed dragonfly species in Africa is the red‐veined‐dropwing Trithemis arteriosa. It is an indicator for permanent water bodies, which are freshwater ecosystems of high environmental value especially in arid regions. For studies to determine population structures, assess species viability and monitor environmental changes, a panel of 10 polymorphic microsatellite loci was developed. The number of alleles per locus ranged from four to 12, with an observed heterozygosity ranging from 0.149 to 0.843.     

Development and characterization of seven novel di‐, tri‐, and tetranucleotide microsatellite markers in Atka mackerel (Pleurogrammus monopterygius)

We describe the enrichment for and characterization of seven Pleurogrammus monopterygius microsatellite loci. We used (GACA)₄ as an oligonucleotide enrichment probe and screened 484 clones from the enriched library. The seven microsatellite loci include five tetranucleotide, one dinucleotide, and one trinucleotide motif. These markers can potentially be useful tools for use in population genetics studies, parentage analyses, and examining other life history questions.