Morphometric, AFLP and plastid microsatellite variation in populations of Scalesia divisa and S. incisa (Asteraceae) from the Galápagos Islands

Abstract

Scalesia divisa and S. incisa (Asteraceae), both endemic to the Galápagos Islands, are found only on San Cristóbal, where S. divisa grows in the north‐west of the island while S. incisa occurs in the north‐east. At localities in between, populations with deviating individuals occur. Here we analyse the population structure of S. divisa, S. incisa and two deviating populations based on morphology, AFLP markers and two plastid microsatellite loci. The deviating populations were collected from either side of the island. In a principal components analysis based on morphological characters they appeared to be intermediate between the presumed pure species. When using a discriminant analysis, the two populations that were geographically furthest apart were best discriminated. A Mantel test showed that there was a significant correlation between morphological differentiation and geographical distance, which was also indicated in a distance tree. A second distance tree based on AFLP characters revealed the same topology, but the branches were longer. This was explained by high within‐population variation, as demonstrated by AMOVA. Although only a small proportion of the total variance was explained by the between‐population component, the populations were distinct enough to be separated by a discriminant analysis. A high level of misclassification was only found between one of the S. incisa populations and one of the deviating populations. The plastid markers supported the results obtained from AFLP. We hypothesize that the pattern of variation is the result of hybridization between two formerly isolated species. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 143, 243−254.

Molecular, Morphological, and Experimental Evidence for Hybridization between Threatened Species of the Galapagos Endemic GenusScalesia(Asteraceae)

“…The method was modified in accordance with Nielsen et al (2003) to use fluorescent EcoRI primers from TAG Copenhagen A/S rather than radioactive primers. PCR amplifications were carried out in a PTC 200 Peltier Thermal Cycler (MJ Research).…”

“…From this the genus of 15 known species, which are all tetraploid, has evolved (Eliasson 1974). Nielsen et al (2003) suggested that Scalesia incisa Hook. f. and Scalesia divisa Andersson on San Cristó bal hybridize, and on Santa Cruz, Eliasson (1974) reported intermediate specimens between Scalesia pedunculata Hook.…”

“…f. and Scalesia aspera Andersson, as well as between S. aspera and Scalesia crockeri J. T. Howell. Thus, hybridization might be an important evolutionary process in the genus (Nielsen et al 2003). We used morphological and molecular approaches and artificial hybridization experiments to clarify whether hybridization among S. crockeri, S. aspera, and S. pedunculata has been the mechanism that has produced morphologically intermediate populations between them.…”

Multivariate analysis in a genetic divergence study of Psidium guajava

“…In wild (Nielsen et al, 2003) as well as in cultivated (Roldán-Ruiz et al, 2001) plants, low concordance has been reported between molecular and phenotypic genetic divergence. This scenario is commonly reported, except when the molecular markers used are closely linked to the genes controlling the morphological characteristics analyzed.…”

“…This scenario is commonly reported, except when the molecular markers used are closely linked to the genes controlling the morphological characteristics analyzed. Nielsen et al (2003) applied discriminant analysis to 6 natural populations from the genus Scalesia and found an increase in the discrimination of individuals in 5 of these populations using AFLP markers compared with using morphometric data.…”