Homoploid hybrid origin of Yucca gloriosa: intersectional hybrid speciation in Yucca (Agavoideae, Asparagaceae)

Abstract

There is a growing appreciation for the importance of hybrid speciation in angiosperm evolution. Here, we show that Yucca gloriosa (Asparagaceae: Agavoideae) is the product of intersectional hybridization between Y. aloifolia and Y. filamentosa. These species, all named by Carl Linnaeus, exist in sympatry along the southeastern Atlantic coast of the United States. Yucca gloriosa was found to share a chloroplast haplotype with Y. aloifolia in all populations sampled. In contrast, nuclear gene-based microsatellite markers in Y. gloriosa are shared with both parents. The hybrid origin of Y. gloriosa is supported by multilocus analyses of the nuclear microsatellite markers including principal coordinates analysis (PCO), maximum-likelihood hybrid index scoring (HINDEX), and Bayesian cluster analysis (STRUCTURE). The putative parental species share only one allele at a single locus, suggesting there is little to no introgressive gene flow occurring between these species and Y. gloriosa. At the same time, diagnostic markers are segregating in Y. gloriosa populations. Lack of variation in the chloroplast of Y. aloifolia, the putative maternal parent, makes it difficult to rule out multiple hybrid origins of Y. gloriosa, but allelic variation at nuclear loci can be explained by a single hybrid origin of Y. gloriosa. Overall, these data provide strong support for the homoploid hybrid origin of Y. gloriosa.

Timing of rapid diversification and convergent origins of active pollination within Agavoideae (Asparagaceae)

“…queretaroensis clade is not clear. Low ML BSV and BI PP for these relationships demonstrate a lack of variation in the plastid genomes of these taxa, which can be attributed to rapid diversification of the clade or hybridization as seen in studies using nuclear genes (Leebens‐Mack et al, 1998; Heyduk et al, 2016; Rentsch and Leebens‐Mack, 2012).…”

The geography of hybrid speciation in plants

“…Of these, allopatric distribution of the hybrid species is the result of human activity in the case of Senecio squalidus L. (see Table 1 (Baldwin & al., 2011), and in Dubautia scabra (Friar & al., 2008). Yucca gloriosa represents a system strongly influenced by human activity, as one of the parental species (Y. aloifolia L.) probably was introduced by humans to the area where Y. gloriosa originated (Rentsch & Leebens-Mack, 2012).…”

“…"These three diploid species occur sympatrically along the southeastern Atlantic coast of the United States… " "Yucca aloifolia is thought to be a relatively recent addition to the flora of the south-eastern United States possibly as a consequence of both human-mediated dispersal … and natural dispersal …" Rentsch & Leebens-Mack, 2012 may allow us "to test the hypothesis that ecological divergence arises during homoploid hybrid speciation and is an essential feature of the process". Reviewing work on Helianthus paradoxus Heiser and H. deserticola Heiser (Lexer & al., 2003a(Lexer & al., , b, 2004Gross & al., 2004), Abbott & al.…”

Interspecies gene flow is a key evolutionary process for the adaptation of long-lived species to new environmental conditions

“…(Leong Pock Tsy et al, 2013). A change in flowering phenology compared to the parental species was observed in Quercus afares Pomel (Mir et al, 2006) and Yucca gloriosa L. (Rentsch & Leebens-Mack, 2012), whereas ethological isolation was suggested for Stenella clymene Cray (the clymene dolphin) (Amaral et al, 2014) (Table 1). As reported by Mavárez & Linares (2008), detecting hybrid species still remains a challenge despite the numerous genetic resources available for testing their occurrence, including the possibility of analysing DNA from fossils, and in spite of the effective statistical methods developed recently to distinguish hybridization from incomplete lineage sorting (Wen et al, 2016).…”