A phylogenetic study of Laeliinae (Orchidaceae) based on combined nuclear and plastid DNA sequences

Abstract

Background and aims: Laeliinae are a neotropical orchid subtribe with approx. 1500 species in 50 genera. In this study, an attempt is made to assess generic alliances based on molecular phylogenetic analysis of DNA sequence data.

Methods: Six DNA datasets were gathered: plastid trnL intron, trnL-F spacer, matK gene and trnK introns upstream and dowstream from matK and nuclear ITS rDNA. Data were analysed with maximum parsimony (MP) and Bayesian analysis with mixed models (BA).

Key results: Although relationships between Laeliinae and outgroups are well supported, within the subtribe sequence variation is low considering the broad taxonomic range covered. Localized incongruence between the ITS and plastid trees was found. A combined tree followed the ITS trees more closely, but the levels of support obtained with MP were low. The Bayesian analysis recovered more well-supported nodes. The trees from combined MP and BA allowed eight generic alliances to be recognized within Laeliinae, all of which show trends in morphological characters but lack unambiguous synapomorphies.

Conclusions: By using combined plastid and nuclear DNA data in conjunction with mixed-models Bayesian inference, it is possible to delimit smaller groups within Laeliinae and discuss general patterns of pollination and hybridization compatibility. Furthermore, these small groups can now be used for further detailed studies to explain morphological evolution and diversification patterns within the subtribe.

Fig. 1.

First part of one of the 360 most-parsimonious trees for the combined analysis of six DNA regions in Laeliinae. L = 5154, CI = 0·49, RI = 0·58. Numbers above the branches are Fitch lengths and numbers below the branches are bootstrap percentages (branches without numbers received <50 % bootstrap support).

Fig. 2.

Second part of the tree in Fig. 1. Numbers above the branches are Fitch lengths and numbers below the branches are bootstrap percentages (branches without numbers received <50 % bootstrap support).

Fig. 3.

Cattleya alliance portion of the combined analysis of six DNA regions in Laeliinae, excluding ITS sequences of four Cattleya species with incongruent placement in individual analyses. Numbers above the branches are Fitch lengths and numbers below the branches are bootstrap percentages (branches without values received <50 % bootstrap support).

Fig. 4.

Bayesian tree of 59 100 trees obtained from two runs 3000 000 chains of MCMC. Numbers above branches represent the posterior probabilities (PP). Nodes with PPs below 50 % have been collapsed.