Abstract
Gene flow between closely related species is a frequent phenomenon that is known to play important roles in organismal evolution. Less clear, however, is the importance of hybridization between distant relatives. We present molecular and morphological evidence that support origin of the plant genus Physacanthus via “wide hybridization” between members of two distantly related lineages in the large family Acanthaceae. These two lineages are well characterized by very different morphologies yet, remarkably, Physacanthus shares features of both. Chloroplast sequences from six loci indicate that all three species of Physacanthus contain haplotypes from both lineages, suggesting that heteroplasmy likely predated speciation in the genus. Although heteroplasmy is thought to be unstable and thus transient, multiple haplotypes have been maintained through time in Physacanthus. The most likely scenario to explain these data is that Physacanthus originated via an ancient hybridization event that involved phylogenetically distant parents. This wide hybridization has resulted in the establishment of an independently evolving clade of flowering plants.
Highlights
Opinions regarding the importance of hybridization in biology have varied through time [1,2], modern consensus leaves little doubt about its importance in evolutionary processes
There is a handful of examples of natural wide hybrids in plants [17,18] and even fewer in animals [19], the vast majority of known wide hybrids are derived from artificial crosses, often for purposes of agronomic or horticultural improvement [20,21]
Sequence data are consistent with a hypothesis of wide hybridization for the origin of Physacanthus accompanied by the establishment and long-term maintenance of heteroplasmy
Summary
Opinions regarding the importance of hybridization in biology have varied through time [1,2], modern consensus leaves little doubt about its importance in evolutionary processes. There is a handful of examples of natural wide hybrids in plants [17,18] and even fewer in animals [19], the vast majority of known wide hybrids are derived from artificial crosses, often for purposes of agronomic or horticultural improvement [20,21]. Progeny of both artificial and natural wide hybridization are usually sterile; in consequence, advanced generations are few and their long-term evolutionary significance is limited
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