The mutation rate at fifty-four perfect (uninterrupted) dinucleotide microsatellite loci is estimated by direct genotyping of 96 Arabidopsis thaliana mutation accumulation lines. The estimated rate differs significantly among motif types with the highest rate for AT repeats (2.03 × 10−3 per allele per generation), intermediate for CT (3.31 × 10−4), and lowest for CA (4.96 × 10−5). The average mutation rate per generation for this sample of loci is 8.87 × 10−4 (SE 2.57 × 10−4). There is a strong effect of initial repeat number, particularly for AT repeats, with mutation rate increasing with the length of the microsatellite locus in the progenitor line. Controlling for motif and initial repeat number, chromosome 4 exhibited an elevated mutation rate relative to other chromosomes. A survey of dinucleotide repeats across the entire Arabidopsis genome indicates that AT repeats are most abundant, followed by CT, and CA. The great majority of mutations were gains or losses of a single repeat. Several lines exhibited multiple step changes from the progenitor sequence, although it is unclear whether these are multi-step mutations or multiple single step mutations. Generally, the data are consistent with the stepwise mutation model of microsatellite evolution.

Wetlands are major sources of carbon dioxide, methane, and other greenhouse gases released during microbial degradation. Despite the fact that decomposition is mainly driven by bacteria and fungi, little is known about the taxonomic diversity of bacterial communities in wetlands, particularly Sphagnum bogs. To explore bacterial community composition, 24 bogs in Vermont and Massachusetts were censused for bacterial diversity at the surface (oxic) and 1 m (anoxic) regions. Bacterial diversity was characterized by a terminal restriction fragment length (T-RFLP) fingerprinting technique and a cloning strategy that targeted the 16S rRNA gene. T-RFLP analysis revealed a high level of diversity, and a canonical correspondence analysis demonstrated marked similarity among bogs, but consistent differences between surface and subsurface assemblages. 16S rDNA sequences derived from one of the sites showed high numbers of clones belonging to the Deltaproteobacteria group. Several other phyla were represented, as well as two Candidate Division-level taxonomic groups. These data suggest that bog microbial communities are complex, possibly stratified, and similar among multiple sites.

This article documents the addition of 512 microsatellite marker loci and nine pairs of Single Nucleotide Polymorphism (SNP) sequencing primers to the Molecular Ecology Resources Database. Loci were developed for the following species: Alcippe morrisonia morrisonia, Bashania fangiana, Bashania fargesii, Chaetodon vagabundus, Colletes floralis, Coluber constrictor flaviventris, Coptotermes gestroi, Crotophaga major, Cyprinella lutrensis, Danaus plexippus, Fagus grandifolia, Falco tinnunculus, Fletcherimyia fletcheri, Hydrilla verticillata, Laterallus jamaicensis coturniculus, Leavenworthia alabamica, Marmosops incanus, Miichthys miiuy, Nasua nasua, Noturus exilis, Odontesthes bonariensis, Quadrula fragosa, Pinctada maxima, Pseudaletia separata, Pseudoperonospora cubensis, Podocarpus elatus, Portunus trituberculatus, Rhagoletis cerasi, Rhinella schneideri, Sarracenia alata, Skeletonema marinoi, Sminthurus viridis, Syngnathus abaster, Uroteuthis (Photololigo) chinensis, Verticillium dahliae, Wasmannia auropunctata, and Zygochlamys patagonica. These loci were cross-tested on the following species: Chaetodon baronessa, Falco columbarius, Falco eleonorae, Falco naumanni, Falco peregrinus, Falco subbuteo, Didelphis aurita, Gracilinanus microtarsus, Marmosops paulensis, Monodelphis Americana, Odontesthes hatcheri, Podocarpus grayi, Podocarpus lawrencei, Podocarpus smithii, Portunus pelagicus, Syngnathus acus, Syngnathus typhle,Uroteuthis (Photololigo) edulis, Uroteuthis (Photololigo) duvauceli and Verticillium albo-atrum. This article also documents the addition of nine sequencing primer pairs and sixteen allele specific primers or probes for Oncorhynchus mykiss and Oncorhynchus tshawytscha; these primers and assays were cross-tested in both species.

The population-level effects of landscape heterogeneity in migration corridors are not well understood, especially in aquatic ecosystems. Using 17 microsatellite loci, we assessed the spatial genetic structure of creek chub Semotilus atromaculatus, a headwater stream fish, in eight small tributaries (202 individuals) connected by a river (a lotic corridor) and eight small tributaries (200 individuals) connected by a nearby downstream reservoir (a lentic corridor). Genetic diversity measured in terms of gene diversity and allelic richness was higher in the river tributaries than reservoir tributaries. Both the river and reservoir tributaries exhibited significant population differentiation but differed in their patterns of isolation by distance. Pairs of river tributaries showed increasing genetic differentiation with increasing geographic distance, whereas reservoir tributaries showed no effect of geographic distance on genetic distance. Bayesian estimates of gene flow showed a trend of higher recent migration among river tributaries than reservoir tributaries, but the difference was not statistically significant. Our results may indicate an association between one feature of the aquatic landscape's structure (i.e., whether a connecting water body and migration corridor is riverine or reservoir in type) and population genetic structure in a headwater stream fish. Accordingly, additional genetic studies of populations inhabiting tributaries of river-reservoir networks in other watersheds are needed to further assess this possibility.