Molecular Evidence for the Compilospecies Model of Reticulate Evolution in Armeria (Plumbaginaceae)

Abstract

Cladistic analyses of the nuclear ribosomal DNA (nrDNA) internal transcribed spacer (ITS) sequences from 55 samples corresponding to 34 taxa in the genus Armeria reveal that ITS sequence diversity among and within species utterly conflicts with patterns of morphological similarity. Three facts are apparent from the results here reported: (1) different samples of a single subspecies, A. villosa subsp. longiaristata, appear in three of the five major clades; (2) samples of at least one of the six subspecies of A. villosa appear in four of the five major clades; and (3) the composition of major clades shows greater congruence with the geographic origin of plants than with the traditional systematic arrangement based primarily on morphology. Specifically, the clades here termed Ia, II, III, and IV each encompass terminals restricted to geographically delimited areas. There are alternative explanations for the ITS pattern, but the most likely one is that nucleotide positions supporting the major clades are due, in some of the samples, to concerted evolution following horizontal transfer (gene flow) rather than to recency of common ancestry. This interpretation is consistent with previous systematic and experimental evidence and implies that reticulation in Armeria may be extensive. Harlan and de Wet (1963, Evolution 17:497-501) proposed the compilospecies concept to account for situations in which a genetically "aggressive" species captures portions of the genome of other sympatric species by means of extensive introgression. Evidence of extensive reticulation, ecological diversification, and geographic pattern indicates that A. villosa may fit the compilospecies concept, which is here supported on molecular grounds for the first time.

A plastid tree can bring order to the chaotic generic taxonomy of Rytidosperma Steud. s.l. (Poaceae)

“…3A). The existence of a geographical structure to the cpDNA data, such that samples show affinity according to geographical area of origin rather than to morphology and thus traditional systematic arrangement, could confuse patterns at morphological and ecological levels (Fuertes Aguilar et al, 1999a;Feliner et al, 2004). Geographical patterning in cpDNA markers has been reported for the Tasmanian eucalypts (McKinnon et al, 2001(McKinnon et al, , 2004, for Iberian species of Phlomis (Albaladejo et al, 2005) and for white oaks in Europe (Dumolin-Lapé-gue et al, 1997;Petit et al, 2002).…”

“…Geographical patterning in cpDNA markers has been reported for the Tasmanian eucalypts (McKinnon et al, 2001(McKinnon et al, , 2004, for Iberian species of Phlomis (Albaladejo et al, 2005) and for white oaks in Europe (Dumolin-Lapé-gue et al, 1997;Petit et al, 2002). In these plant groups there is mounting evidence for the presence of several haplotypes within a single species, shared among species within geographical regions, with introgression and hybridisation being invoked as the most likely cause (Dumolin-Lapégue et al, 1997;Steane et al, 1998;Fuertes Aguilar et al, 1999a;Jackson et al, 1999;McKinnon et al, 2001;Petit et al, 2002). Given that the species in the present analysis hybridise in nature (Brock and Brown, 1961;Spies et al, 1992;Visser and Spies, 1994a, b, c, d;Waters, 2007), the occurrence of several ploidy forms within a single species, haplotype sharing among species from the same area (Waters, 2007;Waters et al, 2008) and continuous variation in morphological characters among several species, geographical patterning could offer an explanation to some of the patterns evident in the plastid tree presented here (Fig.…”

Contrasting nuclear‐plastidial phylogenetic patterns in the recently diverged IberianPhlomis crinitaandP. lychnitislineages (Lamiaceae)

“…Double-strand amplification of the ITS region (ITS1+5.8s+ITS2) was performed with P1A and P4 primers (Fuertes Aguilar & al., 1999b). The PCR profile for the amplification of the ITS region comprised an initial step of 94ºC (5 min), 38 cycles with 94ºC (30 s), 52ºC (30 s), and 72ºC (60 s) and a final extension step of 72ºC (10 min).…”

“…The fact that intraindividual heterogeneity for ITS repeat copies can remain for a given period of time following a hybridization event despite the action of concerted evolution (Zimmer & al., 1980) also makes this marker useful in detecting cases of reticulate evolution among divergent lineages (Sang & al., 1995;Whittall & al., 2000;Fuertes Aguilar & Nieto Feliner, 2003). Even if concerted evolution has been active and different copies are homogenised, ITS sequence data may still provide valuable information on reticulate evolution when showing incongruent patterns with respect to other differently inherited markers (e.g., cpDNA, Rieseberg, 1991) or morphological and biogeographical evidence (Sytsma, 1990;Fuertes Aguilar & al., 1999b;Nieto Feliner & al., 2004). The genus Phlomis L. (Lamiaceae) comprises over Systematic and evolutionary relationships within the diploid Western Mediterranean Phlomis crinita/lychnitis complex remain controversial apparently due to hybridization and introgression.…”

Phylogenetic and phylogeographic analysis of the western Mediterranean Arenaria section Plinthine (Caryophyllaceae) based on nuclear, plastid, and morphological markers

“…The main causes for disagreement between gene phylogeny and taxonomy at this level appear to be horizontal transfer and lineage sorting (deep coalescence; Doyle, 1992). Since comparison with plastid DNA trees is relatively unsuccessful in our study, possible cases of horizontal transfer might be suggested based on the detection of additive polymorphic sites (APS; Rauscher & al., 2002;Wichman & al., 2002) and the concurrence of ITS similarity and geographic sympatry (Fuertes Aguilar & al., 1999b).…”