Pollen fertility of synthetic intra- and interspecific F1 hybrids in Canary Island Tolpis (Asteraceae)

Abstract

Pollen fertility was determined for synthetic F1 hybrids between members of the genus Tolpis endemic to the Canary Islands. Mean fertility varies from 1 to nearly 100%. High hybrid sterility is unusual for island lineages. Surprisingly, the fertility of hybrids between morphologically distinct species was generally higher than some crosses within the morphologically variable group that includes the Tolpis laciniata and T. lagopoda complexes. Within this group, fertility was lower particularly in hybrids involving one recognized segregate species (T. webbii), but none of the four potentially new species had reduced hybrid fertility. Despite the overall fertility differences between groupings within the T. laciniata and T. lagopoda complexes there is variation in fertility within groups; sterility factors have a complex inter-populational distribution. The cause of hybrid sterility is unknown, but preliminary data suggest that both chromosomal and genetic factors are involved.