Abstract Detail

Hybrids and Hybridization

Folk, Ryan [1].

Phylogenetic relationships in Heuchera (Saxifragaceae) based on ribosomal and low-copy nuclear loci.

Phylogenetic relationships in the North American genus Heuchera (Saxifragaceae) remain little-resolved to date despite interest in this taxon’s hybrid and polyploid evolution and its long history of taxonomic confusion. Previous efforts to estimate phylogeny have been hampered by the slow evolution of standard plant phylogenetic loci so that very little can currently be said as to the relationship of supposed hybrid parents or how natural the current subgeneric taxonomy is. In particular, interpreting the patterns of chloroplast capture I have observed in Heuchera requires a well-resolved species tree based on less capture-prone nuclear loci. Given the morphological diversity and very broad, interrupted distribution of Heuchera, a well-resolved species tree will also be of general evolutionary interest.
I have assembled a multilocus phylogenetic dataset through Sanger sequencing to improve the resolution of phylogenetic relationships, consisting of two rDNA loci (ETS and ITS) and four single-copy nuclear loci (GBSSI-A, GBSSI-B, PepCK, GSII), to contrast against the pattern represented by three plastid loci (TrnL-F, Rpl32-TrnL, Rps16-TrnK, presented previously). These loci were analyzed using parsimony (in TNT) and maximum likelihood (RAxML), both individually and in concatenation.
Preliminary results have shown a tree largely congruent with previous work, but with much greater resolution and bootstrap support. In particular, Heuchera is recovered as monophyletic and sister to Bensoniella of the Pacific Northwest. Within Heuchera, H. glabra, also of the Pacific Northwest, is sister to the rest of the genus. The two Eastern US clades are not at all related to one another and instead are sister to different western clades. These results suggest a Pacific Northwest origin for the genus, with at least two separate colonizations of the Eastern US. Comparison with the chloroplast topology confirms that chloroplast capture events I have observed involved wide hybridizations between distant relatives; in one case the putative parents are no longer sympatric. No well-supported incongruence was observed in nuclear loci, except for H. bracteata and H. hallii, which have been suspected before of undergoing hybridization. Plotting of morphological characters suggests a primitive condition of diffuse, small-flowered inflorescences with exserted sexual parts, with more specialized forms independently acquiring consensed, large-flowered inflorescences with subequal or inserted floral parts, quite congruent with previous Besseyan-influenced hypotheses of flower evolution in Heuchera.

Broader Impacts:

1 - The Ohio State University, 1315 Kinnear Road, Columbus, OH, 43220, USA

Keywords:
Chloroplast capture
hybridization
Saxifragaceae
Phylogenetic incongruence
Low-copy nuclear loci.

Presentation Type: Oral Paper:Papers for Topics
Session: 22
Location: Rosedown/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 9:45 AM
Number: 22004
Abstract ID:632
Candidate for Awards:None