Respiration and thermogenesis by cones of the Australian cycad Macrozamia machinii

Abstract

1. While cycads are often considered to be wind-pollinated, it is now clear that insects are pollen vectors in many species. This study addresses the role of thermogenesis in pollination biology of the dioecious cycad Macrozamia machinii P.I. Forster & D.L. Jones. 2. The patterns of thermogenesis in intact male and female cones were assessed with thermometry and respirometry throughout the pollination period in the field. 3. Thermogenic episodes in male cones occurred from about 17.00-00.00 h on successive evenings, in association with dehiscence of sporangia and presence of their pollinating weevils (Tranes sp.). 4. Temperatures of the 167 g male cones rose ≈6°C above ambient, and mean rate of oxygen consumption peaked at 7.7 μmol s-1 (3.6 W). Regulation of male cone temperature was not evident, and thermogenesis of female cones was insignificant. 5. Male cones probably heat to augment scent production and enhance weevil activity, including mating and egg-laying, but female cones may benefit from reduced visitation and freedom from damage by weevil larvae. Male cones may be sacrificial in providing the reward to the pollinators while the female cones are safeguarded.