Reproductive Biology of Two Sympatric Species of Polyalthia (Annonaceae) in Sri Lanka. II. Breeding Systems and Population Genetic Structure

The breeding systems of two sympatric species, Polyalthia coffeoides and Polyalthia korinti (Annonaceae), are assessed using a range of approaches, including controlled pollination experiments and analysis of intersimple sequence repeat markers within and between populations. Natural (open) pollination resulted in similar levels of fruit formation as artificial cross-pollination, suggesting that pollinator availability is not a limiting factor in reproduction. Both species possess facultatively xenogamous breeding systems, with 33%–36% fruit formation in artificially crossed experiments and 17%–19% fruit formation following geitonogamy. Reduced fruit set following geitonogamy suggests partial self-incompatibility; this is supported by index of selfincompatibility values of ca. 0.5 in both species. Analysis of population genetic structure supports the hypothesis of a mixed but largely xenogamous mating system. Genetic diversity within populations was estimated to be ca. 80% and 66% of total genetic diversity for P. coffeoides and P. korinti, respectively. The levels of gene flow between populations were moderate (Nm ¼ 2:033 for P. coffeoides and 0.970 for P. korinti), and genetic identity (I) values between populations within species were high. This possibly reflects the fragmentation of a previously more extensive population, correlated with the historical deforestation associated with crop cultivation and irrigation in Sri Lanka