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Open all hours---Daphne maximises chances of reproduction
In natural selection as in human life, we are familiar with the idea of cost-benefit analysis. This is beautifully illustrated by the reproductive ecology of the shrub, Daphne laureola, described by Conchita Alonso (Sevilla, Spain, pp. 61-66). In its Mediterranean upland habitat, D. laureola flowers very early (late January to early April), thus minimising competition for pollinators. However, pollinators are themselves relatively scarce at this time of the year and during periods of poorer weather their foraging may be very limited. Against this background, the evolved strategies for breeding in D. laureola include a long flowering season, long-lived flowers that last for up to a month, availability to pollinators for 24 h per day and two different breeding systems: female plants are obligately out-breeding while hermaphrodite plants may be out- or in-breeding. The author has carried out experiments to determine the importance of these features, firstly by assaying pollinator choice---there was no evidence of preference for hermaphrodite versus female flowers---and secondly by exclusion of pollinators. When pollinators were excluded for half the flowering season, fruit set dropped from ca 30 % to ca 15 %, i.e. in proportion to the period of pollinator exclusion. In hermaphrodite plants, which were in any case more fecund, the drop was only from ca 43 % to ca 31 %, indicating the role of self-pollination in these plants. However, when pollinators were excluded from the flowers at night but not in the day, there was no effect on fruit set in female plants and even a slight increase in hermaphrodite plants. The author concludes that, in this population of D. laureola, nocturnal pollinators are not important, despite the flowers being visited by night-flying moths. We do not know whether this holds for other populations of this shrub but nevertheless, the paper provides some fascinating insights into what the author calls 'early blooming's challenges.'
Professor J. A. BryantUniversity of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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