Breeding System Variability Over Short Geographic Distances in Isolated Populations of a Montane
Species
Teresa Gray
Mentors: Ann Sakai & Stephen Weller
Incompatibility relationships were investigated in a tristylous population of Oxalis alpina located in the Galiuro
Mountains in Arizona. With typical tristylous incompatibility relations, each of the three floral morphs can
donate pollen in equivalent proportions, leading to an equal distribution of short, mid and long-styled morphs
in populations. Varying degrees of modification of incompatibility may occur in populations of O. alpina,
leading to preferential pollination between the short- and long-styled morphs at the expense of the mid-styled
morph. Surveys of morph frequencies in multiple populations of O. alpina have demonstrated that modified
tristylous incompatibility is associated with reduced frequency of the mid-styled morph. Self-compatibility of
the mid-styled morph may favor its retention within a population. A tristylous population of O. alpina from
the Galiuro Mts. in Arizona was expected to have highly modified incompatibility because of its location in an
area dominated by distylous O. alpina. As predicted, the Galiuro population had substantially modified
tristylous incompatibility, based on analysis of mean seed production comparing legitimate and illegitimate
crosses. Also as expected, the mid-styled morph was able to self-fertilize, which may contribute to the
retention of this morph in populations, despite modified tristylous incompatibility.