Spatial and temporal genetic structure in a hybrid cordgrass invasion.

Invasive hybrids and their spread dynamics pose unique opportunities to study evolutionary processes. Invasive hybrids of native Spartina foliosa and introduced S. alterniflora have expanded throughout San Francisco Bay intertidal habitats within the past 35 years by deliberate plantation and seeds floating on the tide. Our goals were to assess spatial and temporal scales of genetic structure in Spartina hybrid populations within the context of colonization history. We genotyped adult and seedling Spartina using 17 microsatellite loci and mapped their locations in three populations. All sampled seedlings were hybrids. Bayesian ordination analysis distinguished hybrid populations from parent species, clearly separated the population that originated by plantation from populations that originated naturally by seed and aligned most seedlings within each population. Population genetic structure estimated by analysis of molecular variance was substantial (F(ST)=0.21). Temporal genetic structure among age classes varied highly between populations. At one population, the divergence between adults and 2004 seedlings was low (F(ST)=0.02) whereas at another population this divergence was high (F(ST)=0.26). This latter result was consistent with local recruitment of self-fertilized seed produced by only a few parental plants. We found fine-scale spatial genetic structure at distances less than ∼200 m, further supporting local seed and/or pollen dispersal. We posit a few self-fertile plants dominating local recruitment created substantial spatial genetic structure despite initial long-distance, human dispersal of hybrid Spartina through San Francisco Bay. Fine-scale genetic structure may more strongly develop when local recruits are dominated by the offspring of a few self-fertile plants.

Clinical and histopathologic observations concerning hypotony after trabeculectomy with adjunctive mitomycin C.

Prolonged hypotony-induced maculopathy is a serious complication of trabeculectomy with adjunctive mitomycin C. We performed trabeculectomies with intraoperative mitomycin C on 59 eyes of 52 consecutive patients. Exposure time to mitomycin C was five minutes in the first seven patients, two of whom had prolonged hypotony-induced maculopathy. One of these required surgical revision of the filtering procedure. Light and electron microscopic study of the excised, avascular bleb disclosed an irregular epithelium and largely acellular subepithelium of loosely arranged connective tissue. In the remaining 52 eyes, the exposure time to mitomycin C was titrated between two and five minutes according to each patient's risk for failure of filtration from excessive fibrosis. Four additional cases of prolonged hypotony-induced maculopathy occurred among these 52 cases (7.7%), all of which were in the lower risk groups that received two- or three-minute exposure to mitomycin C. Four procedures failed, requiring further glaucoma surgery, and all of the patients were in the higher risk groups, receiving three- to five-minute exposures. Our titration of the exposure time to mitomycin C may have reduced, but did not eliminate, the risk fo prolonged hypotony-induced maculopathy, and further study is needed to establish the optimum protocol for the use of this drug as an adjunct to trabeculectomy.