Beetle pollination and floral thermogenicity in Magnolia tamaulipana (Magnoliaceae)

Abstract

The pollination biology involving floral thermogenicity of Magnolia tamaulipana was conducted at the El Cielo Reserve in Tamaulipas, Mexico, during May 1996. Our results indicate that M. tamaulipana possesses a highly specialized beetle pollination system involving Cyclocephala (Scarabaeidae: Dynastinae) and members of the Staphylinidae, Of the 366 insects visiting 213 flowers of M. tamaulipana, 364 were beetles. Cyclocephala caelestis accounted for 52\% and Myrmecocephalus sp. for 46\% of the visits. Breeding system experiments indicated that the flowers were self-compatible but only 44\% of the open-pollinated stigmas were pollinated, Cyclocephala caelestis was frequently observed to feed on petals but never sepals. As a reward, flowers offered petals high in carbohydrate and low in fiber to Cyclocephala. The protogynous 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 sexual 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-phase flowers and from 0.2 degrees to 5.0 degrees C for male-phase flowers. The two species of beetles showed differential visitation to trees associated with floral thermogenicity. Our data indicate that large-flowered trees dissipate more heat and, therefore, more floral odor from their petals than small-flowered trees, thereby attracting a greater number of Cyclocephala.