Hybridization and competition between the endangered sea marigold (Calendula maritimaAsteraceae) and a more common congener

Abstract

Occurrences of hybridization between the rare, endangered Sicilian endemic, Calendula maritima, and other congeners in the wild have been suspected by several authors, but never demonstrated. In San Cusumano (Trapani), one of the only three Sicilian mainland populations, C. maritima occurs in close proximity to the more common congener C. suffruticosa subsp. fulgida, and individuals morphologically intermediate between the two taxa have been observed. In order to determine whether hybridization is occurring at this site, and, if so, begin to assess the impact it could have on C. maritima, two independent tests of hybridity were conducted by studying (1) the pollen morphology and viability and (2) sequence variation in one chloroplast marker (atpI-atpH) and in the nuclear ribosomal internal transcribed spacer region (ITS). Both palynological and molecular data provided evidence of hybridization between C. maritima and C. suffruticosa subsp. fulgida, and suggest that although fertility of hybrids appeared to be reduced, they are likely capable of back-crossing with parents. Thus, hybridization may be putting C. maritima at risk of extinction via introgression. Anthropogenic habitat disturbance and expansion of C. suffruticosa subsp. fulgida into remaining populations of C. maritima could pose a serious threat to its successful conservation.

Keywords::

• atpI–atpH
• Calendula maritima
• Calendula suffruticosa subsp. fulgida
• hybridization
• ITS
• pollen viability

Acknowledgements

The authors acknowledge C. Di Liberto (Dipartimento di Biologia ambientale e Biodiversità, Università di Palermo) for technical assistance with scanning electron microscopy, the USDA-GRIN for donation of seed accessions, and C. Skema and J. J. Doyle for comments on the manuscript. Financial support provided by the Università degli Studi di Palermo (Fondi di Ateneo per la Ricerca), the International Foundation pro Herbario Mediterraneo, the American Society of Plant Taxonomists, the Botanical Society of America, and the Harold E. Moore Fund is gratefully acknowledged.

Notes

^* Present address: Francesco Maria Raimondo, Angelo Troia, Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche, Università degli Studi di Palermo, via Archirafi 38, I-90123 Palermo, Italy.