Identifying multiple origins of polyploid taxa: a multilocus study of the hybrid cloak fern (Astrolepis integerrima; Pteridaceae).

Abstract

PREMISE OF THE STUDY: Molecular studies have shown that multiple origins of polyploid taxa are the rule rather than the exception. To understand the distribution and ecology of polyploid species and the evolutionary significance of polyploidy in general, it is important to delineate these independently derived lineages as accurately as possible. Although gene flow among polyploid lineages and backcrossing to their diploid parents often confound this process, such post origin gene flow is very infrequent in asexual polyploids. In this study, we estimate the number of independent origins of the apomictic allopolyploid fern Astrolepis integerrima, a morphologically heterogeneous species most common in the southwestern United States and Mexico, with outlying populations in the southeastern United States and the Caribbean. METHODS: Plastid DNA sequence and AFLP data were obtained from 33 A. integerrima individuals. Phylogenetic analysis of the sequence data and multidimensional clustering of the AFLP data were used to identify independently derived lineages. KEY RESULTS: Analysis of the two datasets identified 10 genetic groups within the 33 analyzed samples. These groups suggest a minimum of 10 origins of A. integerrima in the northern portion of its range, with both putative parents functioning as maternal donors, both supplying unreduced gametes, and both contributing a significant portion of their genetic diversity to the hybrids. CONCLUSIONS: Our results highlight the extreme cryptic genetic diversity and systematic complexity that can underlie a single polyploid taxon.