Hybridization between ecotypes in a phenotypically and ecologically heterogeneous population ofIris savannarum(Iridaceae) in Florida

Abstract

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.

On biodiversity and conservation of the Iris hexagona complex (Phaeiris, Iridaceae)

“…Our results are also congruent with those of Meerow et al (2007, 2011, 2017) in showing the high genetic dissimilarity among the distinct populations of Phaeiris , even when using different methods and molecular markers (Meerow et al 2007, 2011, 2017). While most apomictic and asexual (clonal) plants have considerable genetic variation (reviewed in Bengtsson 2009), we do not see much evidence for this phenomenon in the non‐hybrid species of Phaeiris .…”

“…Although the genetically peculiar and relatively homogenous populations from the Big Cypress Swamp, Lake Wales Ridge, and Polk Uplands all were assigned to P. savannarum by Meerow et al (2011), they may deserve recognition at the specific rank, especially if the Caloosahatchee population of the same taxon (located close to the type locality of P. savannarum ) also is genetically distinct (e.g., Meerow et al 2011). Moreover, the Highlands and Coastal plants of P. savannarum are phenotypically distinct (Meerow et al 2017). This issue calls for more research.…”

“…Summary of the taxonomic treatments of Phaeiris hexagona and non-extinct related species referred to in this study. Alexander (1931) Viosca (1935); Foster (1937); Hamlin et al (2017) Henderson (2002; Meerow et al (2007Meerow et al ( , 2011Meerow et al ( , 2017 This study Delta Alexander 1931, also see Henderson 1994). Perhaps because of this, the popular name of the genus Phaeiris became the Louisiana irises (e.g., Viosca 1935, among others).…”

“…The taxonomic interpretation of the blue flags of Louisiana and Florida indeed has been partly challenged by Randolf (1966) and especially by Henderson (2002), Ward (2008, 2011), and Meerow et al (2007, 2011, 2017). For example, the studies of Hamlin and Arnold (2014, 2015) that combined the populations of three taxa ( Iris giganticaerulea , I. hexagona , and I. savannarum ) under I. hexagona “… may be more a scenario of species divergence than population level adaptation” (Meerow et al 2017:318, see also Meerow et al 2011).…”

“…The taxonomic interpretation of the blue flags of Louisiana and Florida indeed has been partly challenged by Randolf (1966) and especially by Henderson (2002), Ward (2008Ward ( , 2011, and Meerow et al (2007Meerow et al ( , 2011Meerow et al ( , 2017. For example, the studies of Arnold (2014, 2015) that combined the populations of three taxa (Iris giganticaerulea, I. hexagona, and I. savannarum) under I. hexagona ".…”