Sex ratio variation in gynodioecious species ofEchiumendemic to the Canary Islands

Abstract

Species of Echium from the Canary Islands represent an adaptive radiation of plants involving evolutionary changes in habitat and life form. Alongside these changes, evolutionary transitions of the sexual system have occurred: approximately one quarter of Echium species from the Canary Islands are dimorphic for gender, paralleling other adaptive radiations of plants on oceanic islands, such as Schiedea in Hawaii. Here, I report on the variation in the frequency of female plants among eight gynodioecious populations representing four species of Echium on the island of Tenerife, and provide preliminary estimates of the seed fertility of females and hermaphrodites, which is an important determinant of the sex ratio for gynodioecious species. Across populations, female frequencies ranged between 6% and 54%, a much wider range than had previously been reported for gynodioecious species of Echium on the Canary Islands. Substantial frequencies of female plants occurred, even though no differences in the seed fertility of females and hermaphrodites were detected.