Hybridization and polyploidy as drivers of continuing evolution and speciation inSorbus

Abstract

Interspecific hybridization and polyploidy are pivotal processes in plant evolution and speciation. The fate of new hybrid and polyploid taxa is determined by their ability to reproduce either sexually or asexually. Hybrids and allopolyploids with odd chromosome numbers are frequently sterile but some establish themselves through asexual reproduction (vegetative or apomixis). This allows novel genotypes to become established by isolating them from gene flow and leads to complex patterns of variation. The genus Sorbus is a good example of taxonomic complexity arising from the combined effects of hybridization, polyploidy and apomixis. The Avon Gorge in South-west Britain contains the greatest diversity of Sorbus in Europe, with three endemic species and four putative endemic novel hybrids among its 15 native Sorbus taxa. We used a combination of nuclear microsatellite and chloroplast DNA markers to investigate the evolutionary relationships among these Sorbus taxa within the Avon Gorge. We confirm the genetic identity of putative novel taxa and show that hybridization involving sexual diploid species, primarily S. aria and S. torminalis and polyploid facultative apomictic species from subgenus Aria, has been responsible for generating this biodiversity. Importantly our data show that this creative evolutionary process is ongoing within the Avon Gorge. Conservation strategies for the rare endemic Sorbus taxa should therefore consider all Sorbus taxa within the Gorge and must strive to preserve this evolutionary process rather than simply the individual rare taxa that it produces.

Genetic Diversity and Origins of the Homoploid-Type Hybrid Phytophthora ×alni

“…Thus, better knowledge of the processes that give rise to hybrid taxa is an important question in the evolutionary biology of emerging pathogens. Understanding the mechanisms that lead to speciation and to the establishment, spread, and evolution of hybrid taxa requires investigation of the identity and genetic variability of parental species and of the directionality and recurrence of the hybridization events (9,10).…”

Conservation and population genetic diversity of Curcuma wenyujin (Zingiberaceae), a multifunctional medicinal herb

“…Therefore, asexual reproduction dominates the life cycle of C. wenyujin. In practice, farmers often select robust rhizomes to generate new generations of individuals with genetically identical genomes, and new generations of individuals are more likely to accumulate deleterious mutations that reduce genotype diversity (Holsinger, 2000;Robertson et al, 2010;Ludwig et al, 2013). In addition, farmers often remove flowers during their early developmental period for a greater yield.…”

“…Although these phenomena occur at an extremely low frequency in nature, and most variation (or mutation) is harmful, a small number of beneficial mutations probably accumulate even fix simultaneously (Keightley et al, 1998;de Meeus et al, 2007). Polyploidization could be the main driver of diversification (Soltis et al, 2009;Robertson et al, 2010). 2) Artificial treatment could significantly increase variation (or the rate of evolution) by radiation or other methods, consequently increasing population diversity.…”

“…Low population genetic diversity results in a decreased ability to adapt to the environment, and decreases in product quality and yield (Smithson and Lenne, 1996;Holsinger, 2000;Zhu et al, 2000;Robertson et al, 2010;Ludwig et al, 2013). Based on the results of this and previous studies, we recommended the following: 1) The establishment of a germplasm bank.…”

Sorbus dolichofoliolatus (Rosaceae), a new species from Yunnan, China

“…Sorbus sensu stricto is recognized to include 70-80 species, having the pinnate-leaved rowans (McAllister et al 2005). They included a number of sexual and apomictic species in different regions (Robertson et al 2010). The Himalayan region is thought to be one of the origin centers of this greatly diversified genus (Lo & Donoghue 2012).…”