Reproductive biology of island and mainland populations of Primula mistassinica (Primulaceae) on Lake Huron shorelines

To investigate the influence of insularity on plant reproductive biology at a local geographic scale, we examined aspects of reproduction in distylous Primula mistassinica Michx. (Primulaceae) on Lake Huron shorelines of the Bruce Peninsula and adjacent Tobermory Islands in Ontario, Canada. A total of 7 mainland and 13 nearshore island populations were compared. Controlled pollinations demonstrated that P. mistassinica possesses a dimorphic incom patibility system with intermorph crosses setting significantly more seeds than self or intramorph crosses. Floral morphology, population style-morph ratios, and seed fertility were compared in mainland and nearshore island p opulations to determine whether there was evidence for differences in repro ductive traits between these areas. Style-morph ratios did not differ signi ficantly from equilibrium expectations, and there were no consistent differ ences between island and mainland populations in floral morphology or ferti lity. Rather, the generalized pollination system of P. mistassinica and ext ensive historical opportunities for colonization appear to have mitigated i nsular effects so that proximate ecological factors are more relevant to th e current reproductive biology of populations.