Floral and macroecological evolution within Cyrtanthus (Amaryllidaceae) inferences from combined analyses of plastid ndhF and nrDNA ITS sequences

Authors: SNIJMAN, D - SOUTH AFRICAN NATIONAL BIODIVERSITY INSTITUTE; MEEROW, ALAN

Submitted to: South African Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2009
Publication Date: 4/1/2010
Citation: Snijman, D.A., Meerow, A.W. 2010. Floral and macroecological evolution within Cyrtanthus (Amaryllidaceae) inferences from combined analyses of plastid ndhF and nrDNA ITS sequences. South African Journal of Botany. 76:217-238.

Interpretive Summary: Cyrtanthus Aiton is a large, sub-Saharan Africa genus of approximately 55 species found mostly in South Africa. We used DNA sequences from a chlorplast gene, ndhF and nuclear ribosomal DNA to determine the relationships within Cyrtanthus. The genus resolved into three major lineages: a predominantly Afrotemperate lineage, largely restricted to seasonally moist sites in summer rainfall southern Africa, a subtropical lineage found mostly in nonseasonal rainfall regions, often in dry habitats, and a Cape Floristic Region-centered lineage in which most species are concentrated in the summer-dry to nonseasonal rainfall southwest. There is no sequence evidence for hybridization between any of the species. Relationships inferred by the molecular data disagree with those derived from morphological data, but agree with previously published groupings based on chromosome morphology. Mapping floral and ecological characters onto the combined gene tree reveals recurrent patterns of parallel evolution in terms of adapations for bird pollination, but concentration of certain insect pollination syndromes within specific ecological zones.

Technical Abstract: One of the most diverse members of Amaryllidaceae is Cyrtanthus Aiton, a large, sub-Saharan Africa genus of approximately 55 species found mostly in South Africa. To investigate phylogenetic and biogeographic relationships within Cyrtanthus, sequence data from the plastid ndhF gene and the ITS nrDNA region for 41 species were analysed with parsimony, maximum likelihood, and Bayesian-inference approaches. Various recombination detection algorithms were used to test for interspecific hybridization in the ITS alignment. The genus resolved as monophyletic, comprising three poorly to well-supported major lineages: a predominantly Afrotemperate lineage, largely restricted to seasonally moist sites in summer rainfall southern Africa, a subtropical lineage found mostly in nonseasonal rainfall regions, often in dry habitats, and a Cape Floristic Region-centered lineage in which most species are concentrated in the summer-dry to nonseasonal rainfall southwest. The ITS sequence alignment shows no evidence for reticulation between any of the species. Relationships inferred by the molecular data disagree with those derived from morphological data, but agree with previously published groupings based on karyotype morphology. Fitch optimization of selected floral characters on the combined gene tree reveals recurrent patterns of convergence. Ornithophilous floral forms occur in parallel among the three primary clades, putatively sphingophilous species are concentrated in the Afrotemperate lineage in seasonally moist upland grasslands; the brush-type Aeropetes tulbaghia butterfly and inferred long-proboscid fly pollination syndromes are unique in the Cape lineage. Macroecological factors inferred to have influenced the evolution of Cyrtanthus are changes in rainfall seasonality, the advent of fire, and the availability of new habitats at high and low altitudes and in rock-free soils or rock crevices. This study gives greater clarity on relationships within the genus but any new infrageneric classification awaits further sampling.