No abstract

We investigated genetic variation within and among 11 populations of Iris hexagona at its southern limits in the Florida peninsula by using 19 microsatellite loci. All of the populations contain varying numbers of identical multilocus genotypes, indicative of clonal reproduction. Two population samples consist largely of one clonal lineage and two clonal lineages: the first from the Caloosahatchee drainage west of Lake Okeechobee and the other from the Big Cypress Swamp. The populations are predominantly outcrossing, with high levels of heterozygosity, and show a highly significant pattern of isolation by distance that fits a modified stepping-stone model. This pattern breaks down at the local level, however, where metapopulation dynamics or asymmetrical gene flow may exert a stronger effect on patterns of genetic diversity. Though the majority of genetic variation is within populations, 20% occurs between populations. Genetic distance resolves five clusters: four in the Caloosahatchee Valley and one in the Big Cypress Swamp. However, the populations are differentiated strongly enough that frequency-based genetic structure analysis resolves seven effective populations. Assignment tests identify the northernmost population as a likely ancestral point of origin for the others. All of the populations exhibit evidence of a recent bottleneck, which we attribute to founder effects, given the low migration rate of the species and the high degree of population differentiation, as well as the Holocene geological history of the Florida peninsula. We hypothesize that the two predominantly clonal populations may be artifacts of deliberate cultivation by humans.

Ten microsatellite loci isolated from Iris hexagona are described. All these loci are polymorphic, with three to 13 alleles across 24 individuals from a single natural population. Heterozygosity ranged from 0.125 to 0.870. Three loci depart significantly from Hardy–Weinberg equilibrium in our test population. The test population shows significant heterozygote deficiency in these and two other loci. Three loci exhibit significant linkage disequilibrium. These loci will be utilized to investigate patterns of genetic variation in the species throughout the Florida peninsula.

Iris series Hexagonae is a small, monophyletic complex of five species and associated hybrid populations, popularly known as the 'Louisiana irises'. Series Hexagonae has been recognized as a textbook case of introgressive hybridization based on numerous studies in Louisiana. We previously explored patterns of genetic structure and diversity in populations of the complex in Florida. Populations that occupy high, dry habitats have plants with a distinctive floral 'highlands' phenotype. Aquatic populations of I. savannarum also have a consistent floral phenotype ('coastal'). Jacks Branch slough in Glades County harbors the largest population of series Hexagonae sampled in our previous studies. It is an ecologically heterogeneous site, punctuated by sandy uplands that remain above high water and harbor Iris with the highlands floral phenotype as well as coastal types in the wetter areas of the slough. We hypothesized that mesic, but non-inundated, sites in the slough would host hybrids of the two phenotypic groups, and tested these hypotheses with 19 microsatellite loci. All data analyses support our hypothesis of hybridization between the upland and hydric subpopulations. Although two methods of introgression analysis identify some of the individuals from the admixture zone as first-generation hybrids, subsequent admixture was asymmetric with introgression from the 'highland' parent. This is the first report of such assortative processes occurring in the confines of a single population of Iris. We suggest that the evolutionary processes described interspecifically for series Hexagonae commence early at the population level.

Brain abscesses caused by group A Streptococcus (GAS) are infrequently encountered in children. We present two cases of brain abscess (one cerebellar and one located in the temporal lobe) due to GAS infection occurring in close temporal proximity in previously healthy young children living in different geographic areas of southern Israel. The relevant literature since 2000, in the context of recent epidemiological data reporting an increase in the incidence of invasive GAS infections, is reviewed.