Insights into the cytotype and reproductive puzzle of Cotoneaster integerrimus in the Western Carpathians

The Western Carpathians are traditionally recognized as one of the hotspots of temperate European biodiversity. The polyploid and apomictic group of Cotoneaster integerrimus s.l. is supposed to be particularly variable there, and this is also mirrored by taxonomy. We therefore examined the ploidal and reproductive pattern of C. integerrimus s.l. and its close relative Cotoneaster tomentosus in the Western Carpathians and compared it to that in the Bohemian Massif. Using flow cytometry, we detected tetraploid (468 individuals, 100 populations) and pentaploid (35 individuals, 11 populations) cytotypes, and eight additional mixed populations. The pentaploid cytotype was found exclusively in C. tomentosus, which only occurs in the Western Carpathians. A further flow cytometric seed screen (1114 seeds) revealed facultative apomixis (10.1% of sexual progeny) of tetraploid C. integerrimus s.l., whereas the pentaploid C. tomentosus was almost obligately apomictic. In addition, 3.8% of sexual progeny was formed with the contribution of an unreduced female gamete. Moreover, apomixis in tetraploids was further structured into distinct subtypes: pseudogamy (77.2%), autonomous apomixis (3.7%) and haploid parthenogenesis (0.3%). There were no significant differences in the proportions of sexual and asexual seeds between both species and geographic regions. Our comparative dataset from the Western Alps also included sexual diploids. For this reason, greater ploidal and reproductive variation may be expected in that region. The Western Carpathians therefore do not represent a centre of cytotype and reproductive variation of C. integerrimus s.l., and facultative apomixis is a reproductive strategy that predominates in both the Western Carpathians and the Bohemian Massif.