HOLMQUIST, KARSTEN G.A.^{1}*, JEFFREY D. KARRON^{1}, and RANDALL J. MITCHELL^{2}. ^{1}University of Wisconsin Milwaukee; ^{2}University of Akron. - __The effect of variation in floral morphology on pollen and gene dispersal in __*Mimulus ringens*.

Traditional models of animal-mediated pollen dispersal (Bateman 1947)
assume that the transported pollen available for pollination is
completely mixed and experiences a fixed rate of decay. This model
overestimates initial, and underestimates tail deposition
probabilities. The high skew of empirical pollen dispersal functions
coupled with the poor fit of traditional models may indicate that the
amount of pollen "carried over" from one flower to the next
may not be a constant fraction. The interactions between the
pollinator, floral reproductive organs, and the transported pollen
load may result in portions of the pollen load experiencing
differential transport conditions. This may lead to highly variable
donor and recipient specific deposition patterns. The high skew and
systematic deviations from earlier pollen carryover models common to
empirical pollen deposition data have led to the development of both
modified single-geometric (Morris 1995), and double-geometric models
for changing carryover (Harder & Wilson 1998). The double geometric
form of the Harder & Wilson models directly allows for multiple
pathways of pollen removal from the pollinator's body. This critical
assumption allows for the potential effects of pollen donor
morphology, pollinator identity and pollinator behavior on pollen
dispersal to be tested empirically. As a preliminary step in examining
these relationships in *Mimulus ringens*, pollen deposition was
quantified for linear arrays of *M. ringens* visited by three
sympatric species of *Bombus*. Fluorescent dye was readily
detectable over an average of 17.4 flowers, with an observed maximum
of 27 flowers receiving pollen in a given foraging sequence.
Deposition patterns were highly variable with respect to pollen donor
identity and pollinator species. The amount of initial pollen
deposition is correlated with herkogamy (R=0.774). Also, the mean
transport distance is correlated with initial pollen deposition
(R=0.636). The double exponential regression explains the empirical
pollen deposition function far better than the single geometric
model.
**Key words:** mating systems, *Mimulus ringens*, pollen dispersal, pollination