Phylogeography sheds light on the central-marginal hypothesis in a Mediterranean narrow endemic plant.

BACKGROUND AND AIMS: Understanding the factors that shape variation in genetic diversity across the geographic ranges of species is an important challenge in the effort to conserve evolutionary processes sustaining biodiversity. The historical influences leading to a central-marginal organization of genetic diversity have been explored for species whose range is known to have expanded from refugia after glacial events. However, this question has rarely been addressed for Mediterranean endemic plants of azonal habitats such as rocky slopes or screes. In this context, this comprehensive study examined molecular and field data from Arenaria provincialis (Caryophyllaceae), a narrow endemic plant of south-eastern France. METHODS: Across the whole geographic range, an investigation was made of whether high levels of abundance and genetic diversity (estimated from amplified fragment length polymorphism markers) are centrally distributed, to evaluate the relevance of the central-marginal hypothesis. Phylogeographic patterns inferred from chloroplast DNA (cpDNA) were used, applying Bayesian methods to test the influence of past biogeographic events. Multivariate analysis combining phylogeographic and ecological data was used to reveal the historical and ecological distinctiveness of populations. KEY RESULTS: Despite the narrow distribution of A. provincialis, a high level of nucleotide variation is found within cpDNA loci, supporting its persistence throughout the Pleistocene period. The area characterized by the highest genetic diversity is centrally located. Structured phylogeography and Bayesian factor analysis supported the hypothesis that the central area of the distribution was the source of both westward and eastward migrations, probably during arid periods of the Pleistocene, and more recently was a crossroads of backward migrations. By contrast, the two areas located today at the range limits are younger, have reduced genetic diversity and are marginal in the ecological gradients. CONCLUSIONS: This study highlights a case of strong population distinctiveness within a narrow range. Phylogeography sheds light on the historical role of the areas centrally situated in the distribution. The current range size and abundance patterns are not sufficient to predict the organization of genetic diversity.

Megarectum after surgery for anorectal malformations.

PURPOSE: Megarectum complicating surgery for anorectal malformation (ARM) has implications for long-term continence. Factors influencing continence and defecation include intact rectal reservoir, innervation/proprioception of the anorectal muscle complex, functioning anorectal inhibitory reflex (AIR), and intact perception at the anal margin. We studied outcomes after surgery for ARM with emphasis on megarectum; particularly as to whether altered rectal proprioception from anatomic sacrococcygeal anomalies affect incidence. We also assessed whether an abnormal AIR could trigger passive rectal dilatation without mechanical obstruction. METHODS: Eighty six infants (53 male) with ARM over 20 years were included. Demographics, surgical history, pathology, defecation patterns, imaging, manometry, and morbidity were analyzed. Incidence of sacrococcygeal malformations in children with and without megarectum was compared using Fisher exact test. Manometry results were evaluated for integrity of AIR and correlated to megarectum occurrence. RESULTS: There were 23 high/intermediate and 63 low ARMs. Fourteen (16%) developed a megarectum: 6 of 23 in high and 8 of 63 in low anomalies (P = .33). Twelve patients underwent megarectum resection at a median of 2.6 years (7 months to 10 years); 2 received bowel management protocols. Fifty-seven percent (8/14) of children with and 7% (5/72) without megarectum had sacrovertebral anomalies (P = .0001). Patients with preoperative manometry (n = 5) demonstrated an intact AIR. Colonic manometry demonstrated hyperactive colons (n = 2). Constipation was the predominant preoperative symptom; 3 patients suffered from incontinence after resection. All the specimens showed normal innervation and thickened muscularis on pathology. CONCLUSIONS: Sacral anomalies, which are more prevalent in children who developed megarectum, may result in abnormal rectal proprioception contributing to this pathology. Innervation anomalies may coexist, although preoperative manometries showed normal AIRs. Rectal dysmotility may lead to stool retention with subsequent dilatation, and patients who underwent colonic manometry had diffuse colonic hypermotility. Further physiologic and cellular studies are needed to elucidate the causes of this significant complication after surgical ARM repair in the absence of obstruction.

Lengthening technique for long gap esophageal atresia and early anastomosis.

BACKGROUND/PURPOSE: The treatment of long gap esophageal atresia remains a major surgical challenge. Whereas many approaches have been used for this problem, none are ideal. The authors used a technique originally described by Dr John E. Foker and accomplished early repair in 3 infants with long gap atresia. METHODS: Three infants with esophageal atresia underwent thoracotomy shortly after birth and had a long gap preventing primary anastomosis. External traction sutures were placed on each esophageal pouch and exteriorized through the thoracic wall. The esophageal ends were approximated 1 to 2 mm daily by traction on the sutures. Anastomosis was performed when the 2 ends came together. RESULTS: Three infants were included (31, 34, 37 weeks gestation, weights 1.38 kg, 1.9 kg, and 2.3 kg, respectively). The esophageal gaps were 3, 5, and 4.5 cm, respectively. Definitive anastomosis was performed at 14, 17, and 10 days, respectively. Two patients had anastomotic leaks that were treated conservatively. One patient had an esophageal stenosis that required dilatation. CONCLUSIONS: This technique allowed rapid esophageal lengthening in these 3 cases and led to early repair of long gap esophageal atresia, avoiding the need for a prolonged hospitalization or eventual replacement as well as long-term swallowing difficulties.