Bulbils contra seeds: reproductive investment in two species of Gagea (Liliaceae)

The reproductive biology of the sympatric species Gagea lutea and Gagea spathacea was analyzed morphologically and by resource allocation measurements. Both taxa reproduce vegetatively by bulbils. The hexaploid G. lutea regularly forms seeds, but flowering plants cease to produce bulbils. Seed set was never observed in nonaploid G. spathacea which does not stop vegetative reproduction when flowering. In this species, the pollen contains a high proportion of non-viable grains. Already sterile plants invest more resources (per cent of total nitrogen) into bulbils than G. lutea (10.9 vs. 5.9%). For flowering plants, the respective values are 6.1% (flowers) plus 18.4% (bulbils) for G. spathacea versus 14.8% (flowers only) for G. lutea. G. spathacea lost the ability to reproduce sexually and relies solely on vegetative reproduction. This seems to require the breakdown of the switch mechanism between the bulbil and flower formation (as in G. lutea) and a higher net investment in reproduction, hampering individual growth.