Dispersal Patterns and the Evolution of Distyly in Oxalis alpina

Publisher Website
Google Scholar
Abstract
Individuals from distylous and tristylous populations of O. alpina (Rose) Knuth (section Ionoxalis) from southeastern Arizona [USA] were crossed and the fitness of the resultant F1 hybrids analyzed to provide estimates of genetic divergence among populations. Crossability was highest when tristylous individuals were used as seed parents. Crosses among distylous populations resulted in the lowest seed set. Proportions of flowering F1 progeny were highest for crosses with tristylous individuals as seed parents, and lowest for distylous .times. distylous crosses. Pollen fertility of F1 progeny was higher in the trisylous .times. tristylous crosses than in distylous .times. distylous crosses. Results consistently indicated a higher degree of genetic relationship among tristylous populations than among distylous populations. A likely explanation for the present distribution of trisylous and distylous populations in Arizona is the initial migration of a tristylous race into this region, followed by disjunction into isolated populations due to Pleistocene drying. Following isolation, variation in evolutionary rate has apparently resulted in retention of tristyly in some populations, and the independent evolution of distyly in those populations which have diverged at the greatest rates. Crossability data and analysis of F1 fitness thus suggest a likely dispersal pattern for O. alpina in southeastern Arizona as well as the evolutionary relationship between tristylous and distylous reproductive systems in this species.