The reproductive biology and breeding system of Erica andevalensis Cabezudo & Rivera (Ericaceae), an endangered edaphic endemic of southwestern Spain. Implications for its conservation

Abstract

Summary Erica andevalensis C abezudo et R ivera is a strict edaphic endemic of El Andevalo (Huelva province, S Spain), an ancient pyrite mining exploitation area characterized by elevated concentrations of heavy metals and acid sulphates in the local soils and rivers. The reproductive biology of this heather has been studied in terms of flower longevity, nectar secretion, pollinators, and fruit- (flower to fruit) and seed- (ovule to seed) setting under natural, experimental bagging and greenhouse conditions. Additionally, hand-pollination (self- and cross-pollination) has been performed in the greenhouse. Flower longevity was high, close to 24 d in greenhouse conditions; nectar secretion was scarce with a daily mean volume of 0.25 μl and 0.03 mg of sugar. Apis mellifera, Anthidium sp., Andrena sp. and Lysandra sp. have been captured visiting the flowers of E. andevalensis . Mean number of ovules per flower was high, ca. 77, and was statistically independent of population, individual plant and inflorescence. The mean average fertility (74%) also varied at these three levels. Fruit and seed set in natural populations were high, with values ca. 87% for fruiting; in the field the mean number of seeds per fruit was close to 57. The exclusion of insects (i.e. pollinators) in the field lowered very signigicantly fruit- and seed-set, while in the greenhouse absolutely no fruit or seed has occurred spontaneously. Hand-pollination experiments produced significantly lower rates of seeds/fruit compared to plants in the field, but there was no effect of cross- versus self-pollination. Erica andevalensis is therefore a self-compatible not-selfing species. From a conservation point of view, this species is in a “good reproductive health”, it produces high numbers of fruit and seed set under natural conditions. Therefore, no intrinsic reproductive threat is apparent. Nevertheless, the fidelity to its environment appears to be sharply endangering the future of this remarkable heather.