Ev. Franceschinelli et Ks. Bawa, The effect of ecological factors on the mating system of a South American shrub species (Helicteres brevispira), HEREDITY, 84(1), 2000, pp. 116-123
Mating systems are influenced by several ecological factors, including plan
t density, number of flowers per plant, and pollinator movements. In this s
tudy, we investigated the simultaneous effects of these three factors on th
e mating system of a self-compatible Brazilian shrub species: Helicteres br
evispira St. Hil. Outcrossing rate is directly correlated with plant densit
y. Changes in the number of flowers per plant affect outcrossing rate throu
gh their effect on the density of flowers. Variation in foraging behaviour
of hummingbird pollinators is a consequence of the interaction between plan
t density and number of flowers per plant. Territorialist pollinators are c
ommon in high density areas but visit few flowers on each plant, thereby pr
omoting outcrossing. In areas of low plant density, trapliners and rare ter
ritorialists visit several flowers per plant, thus increasing selfing. Our
results indicate that outcrossing rate is a dynamic parameter, with the ext
ent of variation depending on a number of ecological factors. In succession
al species such as those in the genus Helicteres, demographic changes may b
e accompanied by alterations in mating system parameters, with concomitant
effects on the genetic structure of populations.