ABSTRACT
Many marine species have widespread geographic ranges derived from their evolutionary and ecological history particularly their modes of dispersal. Seagrass (marine angiosperm) species have ranges that are unusually widespread, which is not unexpected following recent reviews of reproductive strategies demonstrating the potential for long-distance dispersal combined with longevity through clonality. An exemplar of these dual biological features is turtle grass (Thalassia testudinum) which is an ecologically important species throughout the tropical Atlantic region. Turtle grass has been documented to have long-distance dispersal via floating fruits and also extreme clonality and longevity. We hypothesize that across its range, Thalassia testudinum will have very limited regional population structure due to these characteristics and under typical models of population structure would expect to detect high levels of genetic connectivity. There are very few studies of range-wide genetic connectivity documented for seagrasses or other sessile marine species. This study presents a population genetic dataset that represents a geographic area exceeding 14,000 km2. Population genetic diversity was evaluated from 32 Thalassia testudinum populations sampled across the Caribbean and Gulf of Mexico. Genotypes were based on nine microsatellites, and haplotypes were based on chloroplast DNA sequences. Very limited phylogeographic signal from cpDNA reduced the potential comparative analyses possible. Multiple analytical clustering approaches on population genetic data revealed two significant genetic partitions: (a) the Caribbean and (b) the Gulf of Mexico. Genetic diversity was high (H E = 0.641), and isolation by distance was significant; gene flow and migration estimates across the entire range were however modest, we suggest that the frequency of successful recruitment across the range is uncommon. Thalassia testudinum maintains genetic diversity across its entire distribution range. The genetic split may be explained by genetic drift during recolonization from refugia following relatively recent reduction in available habitat such as the last glacial maxima.
ABSTRACT
Many ecosystems are experiencing rapid transformations due to global environmental change. Understanding how ecological shifts affect species persistence is critical to modern management strategies. The edge of a species range is often where physiological tolerances are in conflict with ability to persist. Extreme examples of clonality over large spatial and temporal scales can occur where the life history of a species allows for it. We examine extreme clonality in an aquatic plant species at the edge if its range. Here we describe an ancient seagrass clone of unprecedented size inhabiting a 47 km stretch of a central Florida estuary, the Indian River Lagoon (IRL). Amongst the largest clones on earth detected, this Thalassia testudinum (turtlegrass) genet had ramets dispersed across 47 km of this water body. Indeed among 382 samples collections along the length of the IRL, 89% were a single shared multilocus genotype. Furthermore, this clone was the only genet detected at 63% of sample sites. The presence of such a large clone demonstrates they can form and persist over long periods. In addition, we must challenge the paradigm that fragmentation is not possible in this species. Reliance on clonality is an expected component of a classic 'bet-hedging' strategy enabling persistence on timescales typically not considered, including millennia. At locations near ocean inlets we did find a few other individuals of T. testudinum supporting the concept that recruitment is dispersal limited. These additional clones indicate there is the potential, albeit limited, for seeds based recruitment to occur when environmental conditions are favorable during a "window of opportunity." Extreme clonality represents a potential strategy for survival such that in the extreme, clonal populations of a species would be the first to decline or disappear if conditions extend beyond the adaptability of the local genotype. This disappearance possibility makes the species a potential sentinel of system decline.
ABSTRACT
OBJECTIVE: Although suboptimal glycemic control is known to be common in diabetic adults, few studies have evaluated factors at the level of the physician-patient encounter. Our objective was to identify novel visit-based factors associated with intensification of oral diabetes medications in diabetic adults. RESEARCH DESIGN AND METHODS: We conducted a nonconcurrent prospective cohort study of 121 patients with type 2 diabetes and hyperglycemia (A1C > or =8%) enrolled in an academically affiliated managed-care program. Over a 24-month interval (1999-2001), we identified 574 hyperglycemic visits. We measured treatment intensification and factors associated with intensification at each visit. RESULTS: Provider-patient dyads intensified oral diabetes treatment in only 128 (22%) of 574 hyperglycemic visits. As expected, worse glycemia was an important predictor of intensification. Treatment was more likely to be intensified for patients with visits that were "routine" (odds ratio [OR] 2.55 [95% CI 1.49-4.38]), for patients taking two or more oral diabetes drugs (2.82 [1.74-4.56]), or for patients with longer intervals between visits (OR per 30 days 1.05 [1.00-1.10]). In contrast, patients with less recent A1C measurements (OR >30 days before the visit 0.53 [0.34-0.85]), patients with a higher number of prior visits (OR per prior visit 0.94 [0.88-1.00]), and African American patients (0.59 [0.35-1.00]) were less likely to have treatment intensified. CONCLUSIONS: Failure to intensify oral diabetes treatment is common in diabetes care. Quality improvement measures in type 2 diabetes should focus on overcoming inertia, improving continuity of care, and reducing racial disparities.