Odd for an ericad: nocturnal visitors to Lyonia lucida

Background/Question/Methods

It has been hypothesized that every species on the planet is involved in a mutualism to some degree (Bronstein et al. 2006). Animal-mediated pollination is one of the best known and important of these symbioses, with significant ecological, evolutionary and economic impacts. Here I explore pollination of Lyonia lucida, a widespread ericaceous shrub of the Southeastern coastal plain, at Archbold Biological Station (ABS). Despite large floral displays and urceolate, “bumblebee” flowers, L. lucida has been noted by previous observers to have a striking paucity of visitors, while two congeners at ABS attract a host of bees, wasps and other insects. Floral morphology (i.e., corolla length) differs markedly between these other Lyonias and L. lucida, which may be the result of selection against heterospecific pollen transfer. No studies to date have investigated the mating system or pollinator assemblage of this species. To obtain a better understanding of this ubiquitous but understudied shrub, a number of facets of its pollination ecology were explored. Mating system, pollen limitation and diurnal/nocturnal visitation were examined via hand-pollinations, floral observations and temporally-varied floral exclusion treatments. Pollen loads were examined on nocturnal visitors (moths) and the possibility of pollination by thrips was also tested for.

Results/Conclusions

Nocturnal visitation to L. lucida was five times more frequent than diurnal visitation (1.93 visits / 10 min and 0.38 / 10 min, respectively). Diurnal visitors were dominated by one species, Bombus bimaculatus. Nocturnal visitors were more diverse, though all were Noctuid moths. Thrips were not shown to be effective pollinators. Moth proboscides were found to carry substantial pollen loads, averaging 1002 pollen grains. Experimental treatments showed highest fruit initiation rates for open control flowers and those open to diurnal visitors (78.9% and 79.3%), and flowers open to nocturnal visitors showed higher fruit initiation than those bagged during all hours (67.5% and 59.2%). Fruit initiation was high (>90%) for both self- and cross- pollinated flowers in the hand-pollination treatment. Seed set is currently being analyzed and will further illuminate differences between treatments. As far as the author knows, this is the first study to intensively examine nocturnal visitation of an ericad, and preliminary results indicate that these night visitors may be important pollinators for L. lucida. Future work will further investigate the divergence in floral morphology exhibited by L. lucida and test hypotheses regarding heterospecific pollen transfer, floral visitor exclusion and morphological variation across the species' range.