Format: ORAL

Andrea Case1, Svea Hall1, Eli Graber2, Cooper Murphy2, Lynda Delph2, Grant Godden3, Nico Cellinese3, Chris Blackwood1,4

1. Department of Plant Biology, Michigan State University, East Lansing, Michigan, USA 2. Department of Biology, Indiana University, Bloomington, Indiana, USA 3. Florida Natural History Museum, University of Florida, Gainesville, Florida, USA 4. Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, Michigan, USA

Tight integration of floral traits may constrain floral diversity among closely related species and influence mechanisms of pre-mating reproductive isolation as well as the potential for reproductive interference when close relatives co-occur. Here, we present a detailed analysis of floral morphology inLobeliasect.Lobelia(Campanulaceae). This monophyletic clade comprises 25 eastern North American species with a diversity of breeding systems, from obligate inbreeding to bee and hummingbird pollination to gynodioecy. Even thoughLobeliasect.Lobeliaspecies are phenotypically and ecologically similar, largely cross-compatible in the greenhouse, and frequently sympatric, hybrids are rarely observed in the wild. We measured 40+ morphometric characters on preserved flowers from across the ranges of 19 species, including samples from allopatric and sympatric populations and greenhouse-grown hybrids. A single principal component explained more than half of the variation in overall flower size and showed strong phylogenetic compared to geographic structure. Species exhibit distinct floral forms that fall along three continuous axes of floral shape: shorter, wide corolla tubes accommodating bumblebee access; long, narrow tubes associated with hummingbird pollination; continuous length variation with medium-sized tubes, with the smallest borne on selfing species and larger flowers associated with visits by small bees and butterflies. While the sex organs of all species show the form typical of the Lobelia “pollen pump,” their lengths and angles within the flower differ in ways that should affect the likelihood of interspecific pollen transfer. Individual metrics of size and shape show different patterns of inheritance in hybrids, with most matching one of the parents and only some traits showing intermediate values. We interpret these patterns in light of effects on reproductive dynamics, isolation and interference where these congeners occur in sympatry.