We studied the genetic diversity and structure of the Tillandsia capillaris complex, a morphologically diverse group of highly specialized epiphytes, across the distribution range in arid mountain regions of central Peru, Chile, Bolivia and central Argentina. To elucidate the phylogenetic relationships in the complex and to explore the taxon boundaries among populations, we used three plastid markers (rpoB-trnC-petN, trnK-matK-trnK, ycf1, c. 8100 bp in total) and one single-copy nuclear gene (PHYC, c. 1200 bp) for 69 populations and 96 individuals of the T. capillaris complex plus 16 outgroup taxa. Bayesian inference of plastid DNA data indicates the existence of two evolutionary core lineages, which can be recognized as two distinct species: T. capillaris and T. virescens (as proposed previously on the basis of morphological characters). Tillandsia capillaris is a monophyletic and homogeneous group, widely distributed and less genetically variable, whereas T. virescens (including T. kuehhasii) is genetically more divergent with most of the forms growing at high elevation in arid areas, except for the small clade including T. virescens s.s. (= T. cordobensis), which grows in lower, more humid habitats. The nuclear analysis resulted in a polytomy with some individuals showing incongruent positions between plastid and nuclear topologies. The high haplotype diversity, consisting of 63 plastid DNA haplotypes in 69 populations, was resolved as two core lineages occurring from north to south, allowing us to establish a preliminary view of the genetic variation overlapping between the two taxa. The results suggest that the genetic differentiation into two main clades is consistent with morphological variation in this Andean complex.
Tillandsia capillaris Ruiz & Pav., which belongs to the subgenus Diaphoranthema is distributed in Ecuador, Peru, Bolivia, northern and central Argentina, and Chile, and includes forms that are difficult to circumscribe, thus considered to form a complex. The entities of this complex are predominantly small-sized epiphytes, adapted to xeric environments. The most widely used classification defines 5 forms for this complex based on few morphological reproductive traits: Tillandsia capillaris Ruiz & Pav. f. capillaris, Tillandsia capillaris f. incana (Mez) L.B. Sm., Tillandsia capillaris f. cordobensis (Hieron.) L.B. Sm., Tillandsia capillaris f. hieronymi (Mez) L.B. Sm. and Tillandsia capillaris f. virescens (Ruiz & Pav.) L.B. Sm. In this study, 35 floral and vegetative characters were analyzed with a multivariate approach in order to assess and discuss different proposals for classification of the Tillandsia capillaris complex, which presents morphotypes that co-occur in central and northern Argentina. To accomplish this, data of quantitative and categorical morphological characters of flowers and leaves were collected from herbarium specimens and field collections and were analyzed with statistical multivariate techniques. The results suggest that the last classification for the complex seems more comprehensive and three taxa were delimited: Tillandsia capillaris (=Tillandsia capillaris f. incana-hieronymi), Tillandsia virescens s. str. (=Tillandsia capillaris f. cordobensis) and Tillandsia virescens s. l. (=Tillandsia capillaris f. virescens). While Tillandsia capillaris and Tillandsia virescens s. str. co-occur, Tillandsia virescens s. l. is restricted to altitudes above 2000 m in Argentina. Characters previously used for taxa delimitation showed continuous variation and therefore were not useful. New diagnostic characters are proposed and a key is provided for delimiting these three taxa within the complex.
SummaryWe combined tools of phylogeography, population genetics and biogeographical interpretation to analyse a group of phylogenetically independent lineages (animals and plants) that coexist within the same geographical region, yet under markedly different environments, in order to identify generalized barriers for gene flow. We tested the hypothesis that major geographic features have produced a concordant genetic structure in phylogenetically independent lineages. A rigorous bibliographic search was performed, selecting available molecular information from six taxa occupying distinct southern biomes of South America: Yungas, Prepuna, Puna and northern Monte. We estimated within-population genetic diversity, the genetic structure and haplotype phylogenies to assemble distribution maps of genetic barriers for each species. We found a strong association between genetic variation and latitudinal distribution of populations. We detected a major barrier for six taxa at 27°S latitude and a second one for a group of three species at 25–26°S. Two alternative non-exclusive hypotheses – geology and/or climate – explain concordant genetic barriers in divergent lineages. We suggest that the term ‘biogeographically significant units’ portrays a group of populations of phylogenetically unrelated taxa that inhabit the same geographic region that have been similarly impacted by major physical events, which can be used to identify priority areas in landscape conservation.
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