Summary: Ecology, 88(3), 2007, pp. 706­715
Ó 2007 by the Ecological Society of America
ECOLOGICAL AND EVOLUTIONARY MECHANISMS FOR LOW
SEED : OVULE RATIOS: NEED FOR A PLURALISTIC APPROACH?
J. NATHANIEL HOLLAND
1
AND SCOTT A. CHAMBERLAIN
Department of Ecology and Evolutionary Biology, Rice University, MS-170, 6100 South Main Street, Houston, Texas 77005 USA
Abstract. Central to the ecology and evolution of a broad range of plants is
understanding why they routinely have submaximal reproduction manifested as low
seed : ovule and fruit : flower ratios. We know much less about the processes responsible for
low seed : ovule ratios than we do for fruit : flower ratios. Current hypotheses for low
seed : ovule ratios are largely drawn from those for fruit : flower ratios, including proximate
(ecological) causes of pollen limitation, resource limitation, and pollen quality, as well as the
ultimate (evolutionary) hypothesis of ``bet hedging'' on stochastic pollination. Yet, such
mechanisms operating on fruit : flower ratios at the whole-plant level may not best explain low
seed : ovule ratios at the individual-flower level. We tested each of these proximate and
ultimate causes for low seed : ovule ratios using the specialized pollination mutualism between
senita cacti (Pachycereus schottii) and senita moths (Upiga virescens). Seed : ovule ratios were
consistently low (;0.61). Such excess ovule production by senita likely has a strong genetic

Source: Azevedo, Ricardo - Department of Biology and Biochemistry, University of Houston
Holland, J. Nathaniel - Department of Ecology and Evolutionary Biology, Rice University

Collections: Biology and Medicine; Environmental Sciences and Ecology