Abstract
Polyploidization plays an important role in species formation as chromosome doubling results in strong reproductive isolation between derivative and parental taxa. In this note I describe a new species, Mimulus peregrinus (Phrymaceae), which represents the first recorded instance of a new British polyploid species of Mimulus (2n = 6x = 92) that has arisen since the introduction of this genus into the United Kingdom in the 1800’s. Mimulus peregrinus presents floral and vegetative characteristics intermediate between Mimulus guttatus and Mimulus luteus, but can be distinguished from all naturalized British Mimulus species and hybrids based on a combination of reproductive and vegetative traits. Mimulus peregrinus displays high pollen and seed fertility as well as traits usually associated with genome doubling such as increased pollen and stomata size. The intermediate characteristics of Mimulus peregrinus between Mimulus guttatus (2n = 2x = 28)and Mimulus luteus (2n = 4x = 60-62), and its close affinity with the highly sterile, triploid (2n = 3x = 44-45) hybrid taxon Mimulus × robertsii (Mimulus guttatus × Mimulus luteus), suggests that Mimulus peregrinus mayconstitute an example of recent allopolyploid speciation.
Highlights
The genus Mimulus (Phrymaceae) comprises more than 120 species, the majority (75%) of which occur in western North America, and the remaining having a world-wide distribution including Eastern North America, South America, Australia, the Himalayas, Japan and Madagascar (Grant 1924, Beardsley and Olmstead 2002, Wu et al 2007).Copyright Mario Vallejo-Marín
I speculate that M. peregrinus may represent the hexaploid derivative of a hybrid between M. guttatus and M. luteus, a careful examination of additional populations of both parental and hybrid taxa is required to elucidate the genetic origin, extent and distribution of this new polyploid species
Known only from a single collection outside of a protected area, M. peregrinus is provisionally assessed as Critically Endangered (CR D; population size estimated to number less than 50 mature individuals) (IUCN 2011)
Summary
The genus Mimulus (Phrymaceae) comprises more than 120 species, the majority (75%) of which occur in western North America, and the remaining having a world-wide distribution including Eastern North America, South America, Australia, the Himalayas, Japan and Madagascar (Grant 1924, Beardsley and Olmstead 2002, Wu et al 2007). Despite the importance of hybridization and polyploidization for plants in general, the opportunity to study early events in speciation via this route is limited by the small number of angiosperm species known to have originated via allopolyploidization in the last 150 years (e.g. Spartina anglica (Ayres and Strong 2001), Tragopogon mirus, T. miscellus (Soltis et al 2004, 2012), Senecio cambrensis and S. eboracensis (Abbott and Lowe 2004)). A comparison of vegetative and reproductive morphology, DNA content, and chromosome number of this new polyploid species against other British Mimulus, strongly suggests a hybrid origin for M. peregrinus and a close affinity with the sterile triploid hybrid M. I speculate that M. peregrinus may represent the hexaploid derivative of a hybrid between M. guttatus and M. luteus, a careful examination of additional populations of both parental and hybrid taxa is required to elucidate the genetic origin, extent and distribution of this new polyploid species. If an allopolyploid origin is demonstrated, M. peregrinus has the potential to serve as a study system to understand the evolutionary processes associated with the origin of species through hybridization and polyploidization following the breakdown of geographic barriers caused by human-assisted dispersal
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