Beetle pollination and floral thermogenicity in Magnolia tamaulipana (Magnoliaceae)

The pollination biology involving floral thermogenicity of Magnolia tamauli pana was conducted at the El Cielo Reserve in Tamaulipas, Mexico, during Ma y 1996. Our results indicate that M. tamaulipana possesses a highly special ized beetle pollination system involving Cyclocephala (Scarabaeidae: Dynast inae) and members of the Staphylinidae, Of the 366 insects visiting 213 flo wers of M. tamaulipana, 364 were beetles. Cyclocephala caelestis accounted for 52% and Myrmecocephalus sp. for 46% of the visits. Breeding system expe riments indicated that the flowers were self-compatible but only 44% of the open-pollinated stigmas were pollinated, Cyclocephala caelestis was freque ntly observed to feed on petals but never sepals. As a reward, flowers offe red petals high in carbohydrate and low in fiber to Cyclocephala. The proto gynous flowers of M, tamaulipana opened at night, were viable for a maximum of 24 h, and were thermogenic. Flowers were hottest when they first opened and female. Floral temperatures gradually declined with time and hence sex ual phase and, 24 h after anthesis, were not different from ambient. Excess floral temperatures ranged from 1.0 degrees to 9.3 degrees C for female-ph ase flowers and from 0.2 degrees to 5.0 degrees C for male-phase flowers. T he two species of beetles showed differential visitation to trees associate d with floral thermogenicity. Our data indicate that large-flowered trees d issipate more heat and, therefore, more floral odor from their petals than small-flowered trees, thereby attracting a greater number of Cyclocephala.