The geographic covariation of functional traits of flowers and pollinators in Delphinium caeruleum

A crucial question regarding plant-pollinator interactions is how can plants single out the efficient pollinators when plants cannot directly assess the quality of their visitors? Some floral traits can be interpreted as an entry barrier that plants impose on floral visitors, incorporating a strategic cost, such as mechanical obstacles or physical barriers. We posit that these “mechanical fit” traits may vary within a species across different pollinator landscapes in populations, leading to a matching of traits between plants and local pollinator insects. Here, we observed the pollinator species, visitation rate and pollination efficiency, and measured the pollinator and floral traits in three populations of Delphinium caeruleum. Additionally, we made a comparison between the operative strength of staminodes and the strength that insects were able to exert on opening the staminodes. We also compared the length of the nectar spur and the proboscis of insects, for the purpose of verifying whether there was a match between these traits. Our results indicated that the floral traits, visitor species, visitation frequency, and pollination efficiency of visitors differed among populations. The operative strength of staminodes and length of the nectar spur matched the strength and proboscis length of the local visitors respectively, and those visitors who could successfully enter the flower boasted a high pollination efficiency. Our results demonstrate that pollinator shifts have resulted in geographically divergent operative strength of staminodes across the populations, which might be a consequence of plants’ adaptation to local pollinator landscapes.