Hybridization may endanger the rare North Apennine endemic Cirsium bertolonii

Abstract

AbstractWe examined populations of North Apennine stenoendemicsCirsium bertoloniiin the Apuan Alps and Tuscan-Emilian Apennines and found individuals morphologically shifted to co-occurringC. acaulonorC. erisithales. Hybrid status of these intermediates was confirmed by flow cytometry, morphometrics and amplified fragment length polymorphism (AFLP). We interpreted these hybrids taxonomically asCirsium ×sagrense(C. acaulon × C. bertolonii) andC. ×abetonense(C. bertolonii × C. erisithales). Estimated genome size (2C) was 2244 ± 31 Mbp forC. ×sagrenseand 2152 ± 99 Mbp forC. ×abetonense. Their genomic GC content was 38.95 ± 0.35% and 38.77 ± 0.26%, respectively. Diploid chromosome number 2n = 34 was counted forC.bertolonii, and the previously reported 2n = 12 needs to be considered erroneous. We foundC. bertoloniito be a gynodioecious species (like many otherCirsiumspecies) that is not reproductively isolated by ploidy level or chromosome number from co-occurring congeners. The relatively frequent occurrence ofC. ×sagrensein Monte Sagro (locus classicusofC. bertolonii) and the prevalence ofC. ×abetonensein Alpe Tre Potenze suggest that hybridization occurs repeatedly inC. bertolonii, as also confirmed by older herbarium specimens.C. ×abetonenseproduces ripe achenes and F2 hybrids or backcrosses, as some otherCirsiumhybrids do. Genetic erosion/swamping via interspecific hybridization can therefore pose a risk to the genetic integrity ofC. bertolonii, as it does for some other narrowly endemic high-mountainCirsiumspecies in Europe.