Does hybridization with a widespread congener threaten the long‐term persistence of the Eastern Alpine rare local endemic Knautia carinthiaca?

Abstract

Interspecific hybridization, especially when regularly followed by backcrossing (i.e., introgressive hybridization), conveys a substantial risk for many endangered organisms. This is particularly true for narrow endemics occurring within distributional ranges of widespread congeners. An excellent example is provided by the plant genus Knautia (Caprifoliaceae): Locally endemic K. carinthiaca is reported from two isolated populations in southern Austria situated within an area predominantly occupied by widespread K. arvensis. While K. carinthiaca usually inhabits low‐competition communities on rocky outcrops, K. arvensis occurs mainly in dry to mesic managed grasslands, yet both species can coexist in marginal environments and were suspected to hybridize. Flow cytometry revealed that diploid K. carinthiaca only occurs at its locus classicus, whereas the second locality is inhabited by the morphologically similar but tetraploid K. norica. In the, therefore, single population of K. carinthiaca, flow cytometry and AFLP fingerprinting showed signs of introgressive hybridization with diploid K. arvensis. Hybridization patterns were also reflected in intermediate habitat preferences and morphology of the hybrids. Environmental barriers to gene flow seem to prevent genetic erosion of K. carinthiaca individuals from the core ecological niches, restricting most introgressed individuals to peripheral habitats. Efficient conservation of K. carinthiaca will require strict protection of its habitat and ban on forest clear cuts in a buffer zone to prevent invasion of K. arvensis. We demonstrate the large potential of multidisciplinary approaches combining molecular, cytometric, and ecological tools for a reliable inventory and threat assessment of rare species.

Heteroploid Knautia drymeia includes K. gussonei and cannot be separated into diagnosable subspecies

“…Moreover, nonhierarchical K ‐means clustering of AFLP data covering the taxonomic diversity of both diploid and polyploid Knautia species (B. Frajman et al, unpublished manuscript) groups K. drymeia in the same cluster with K. dinarica and K. sarajevensis , making them likely candidates for occasional hybridization. In general, hybridization between Knautia species is common (Rešetnik et al, 2014; Čertner et al, 2015).…”

Patterns of rapid diversification in heteroploid Knautia sect. Trichera (Caprifoliaceae, Dipsacoideae), one of the most intricate taxa of the European flora

“…Subsequently, the climatic oscillations of the Pleistocene likely stimulated the alternation of phases of allopatric divergence with periods of secondary contacts of previously isolated lineages [ 88 – 90 ], thereby reshuffling species distributions and triggering reticulation and polyploidisation (see below). Finally, the spread of grasslands in the course of Holocene anthropogenic deforestation certainly contributed to the range expansion of the nowadays most widespread species, K. arvensis , and triggered secondary contacts with other, previously isolated lineages [ 24 , 91 ].…”

Crop‐to‐wild hybridization in cherries—Empirical evidence from Prunus fruticosa

“…Some rare (i.e., low abundance) species can hybridize with their widespread congeners (e.g., introgression of Morus L., Burgess, Morgan, Deverno, & Husband, ; Rumex L., Ruhsam, Jacobs, Watson, & Hollingsworth, ), which in extreme cases may lead to local extinction as a result of demographic or genetic swamping (Ellstrand & Elam, ; Todesco et al., ). Introgressive hybrid swarms typically occur in transitional or peripheral habitats (e.g., Čertner, Kolář, Schönswetter, & Frajman, ; Raudnitschka, Hensen, & Oberprieler, ). In addition, anthropogenic activities may promote the formation of hybrid swarms by enhancing secondary contact between species (e.g., Hanušová, Ekrt, Vít, Kolář, & Urfus, ) or by creating open habitats suitable for the survival and expansion of hybrids (Wójcicki, ).…”