Format: ORAL

Ethan Newman1,2, Allan Ellis1, Bruce Anderson1

1Stellenbosh University, Stellenbosch, South Africa 2Rhodes University, Grahamstown, South Africa

Pollinators are important drivers of floral divergence and speciation in plants. Indeed, Tritoniopsis revoluta populations appear to have diverged in response to different long proboscid fly pollinators, as evidenced by closely matched floral tube lengths and pollinator proboscis lengths. But in addition to long proboscid flies, most populations are also visited by solitary bees with short proboscides. Here we investigate how different functional pollinator groups affect pollen receipt across a wide range of floral tube length phenotypes. We experimentally increased floral tube length variance in two populations by translocating short and long tubed plants from elsewhere. We then counted the number of pollen grains deposited on virgin stigmas after single visits by either bees or long proboscid flies. We demonstrate that these distinct functional groups of pollinators have very different effects on pollen movement. More specifically, although bees may be important pollinators in these systems, they are unlikely to impose strong selection on floral tube length. In contrast, the morphological fit between the proboscides of long tongued flies and the corolla tubes of T. revoluta flowers appears to be a key feature affecting pollen transfer. This study explains why the tube lengths of T. revoluta are apparently adapted to flies rather than bees, even when both are present.