Beetle pollination and floral thermogenicity in Magnolia tamaulipana (Magnoliaceae)

• Published in: International journal of plant sciences Vol. 160; no. 1; pp. 64 - 71
• Main Authors: Dieringer, G, Cabrera R, L, Lara, M, Loya, L, Reyes-Castillo, P
• Format: Journal Article
• Language: English
• Published: Chicago The University of Chicago Press 1999; University of Chicago, acting through its Press
• Subjects: Biology; calyx; carbohydrates; chemical constituents of plants; corolla; Cyclocephala; dietary fiber; diurnal variation; flowering; flowers; Flowers & plants; heat production; heat sums; Insects; Magnolia; open pollination; pollination; pollinators; self compatibility; sexual reproduction; Staphylinidae; temperature; Mexico; Cyclocephala; reproductive biology; cloud forest; floral thermogenicity; pollination; Mexico; Magnolia
• ISSN: 1058-5893; 1537-5315
• DOI: 10.1086/314099

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° to 9.3°C for
female-phase flowers and from 0.2° to 5.0°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.