Reproductive biology of Phillyrea angustifolia L. (Oleaceae) and effect of galling-insects on its reproductive output

Abstract

Abstract The breeding system of Phillyrea angustifolia is examined in several Spanish populations, both in the southeastern Iberian Peninsula and in the Balearic Islands. Hand-pollination experiments performed on one of the mainland and on one of the island populations demonstrated that the plant is functionally androdioecious. Pollen from males was several times more fertile than pollen from hermaphrodite flowers or self-pollen in the island population, but not so in the Iberian Peninsula. The interpretation of such a result is that androdioecy must have an adaptive advantage in an island system, where inbreeding depression is expected to be greater. Male individuals are much less common than hermaphrodites in all populations studied, thus supporting the prediction made by the models for the maintenance of androdioecy. Sex expression in an individual plant differs between populations. The frequency of sexes was purely bimodal in one population, whereas it was not so in another. Pollen from both male and hermaphrodite flowers appears to be morphologically different, although it remains unknown at what stage of the fertilization process the difference becomes functional. Fruitset in the hermaphrodite individuals was always less than 10%. Most fruits abort at an early stage and there is also a great flower abscission. Fruitset does not appear to be influenced by any of the plant traits describing size or fecundity. A high unpredictability of flowering in an individual was also observed in all populations. P. angustifolia is attacked by a cecidomyiid fly that induces the formation of galls in the ovaries (producing 'deformed' fruits which have been confused until recently with parthenocarpic fruits), thus reducing the plant reproductive output. The production of such galls (most of them in the hermaphrodite individuals but a small proportion also in males) is highly variable among plants and among populations, representing from 0 to 97% of the initiated fruits. Such variability in gall incidence does not respond to variability in plant size, fecundity, distance to flowering conspecifics or time that flowers are available for fly oviposition. A high consistency in gall production was found in both the mainland and the island populations. The greater abundance of galls in the islands compared with the mainland populations is interpreted as a result of the higher temperatures in the former which might influence the activity period of the flies.